Re: [electricboats] AGM or LiFePo4

The distributor is General Electronics. I found them on Alibaba.com. I have attached the spec sheet. My batteries are due in to Toronto in the next day or so and when I get them I will post something about them.

Phil

On Thursday, April 30, 2020, 05:15:32 p.m. EDT, georgeh3ci <george@hommeonline.net> wrote:

Hey Phil,

Can you share your China source of LifePo4?  That looks like a great price! If I'm doing my math right that's over 800 AH at 12v?  Or am I missing something?

Thanks,

 

g

 

 

From: electricboats@groups.io <electricboats@groups.io> On Behalf Of Phil Boyer via groups.io
Sent: Monday, April 27, 2020 12:15 PM
To: electricboats@groups.io
Subject: Re: [electricboats] AGM or LiFePo4

 

I have 10KW of LifePo4 batteries on order from China and are due to land in Toronto first week of May. My cost so far was $2600 Canadian or $1900 US. I have not cleared customs yet so not sure what the duty and taxes will be.
My question is why do you need a different charger as mentioned below? The LifePo4 cells can be charged to 3.65 volts max so is there another factor I am not thinking of?

Phil

 

On Monday, April 27, 2020, 11:49:32 a.m. EDT, L Schmitz via groups.io <terminalift=yahoo.com@groups.io> wrote:

 

 

Hello Pat,  I did the upgrade last year. I went from 4  12v 220 ah agm to   lifepo4    I put together 4 battery boxes with  3.2v 90ah cylinder cells. 4P4S for each box. Then in series for 48v system. You will need a bms and a different  charger  This is a cool upgrade and not too difficult.. I am able to monitor the batteries in charge and discharge mode at any given time with my I phone.  I have great continuous run time and overnite charging with  my dock power. I can suggest a couple sources depending on east or west coast usa.;  I hope this helps.  thank you  best regards Larry Schmitz

 

​Terminalift LLC

9444 Mission Park Place

Santee, CA 92071

Ph: (619) 562-0355

F: (619) 562-2060

 

 

On Monday, April 27, 2020, 08:03:54 AM PDT, sw via groups.io <v1opps=yahoo.com@groups.io> wrote:

 

 

Is that 24v or 48v?

Can buy surpluses Tesla , leaf or other packs too

On Monday, April 27, 2020, 07:43, greenpjs04 <forums@greensdomain.com> wrote:

Hello everyone,

Over 10 years ago, you guys helped me to convert my 24' pontoon to
electric.  I ended up with a Torqeedo Cruise 4, four group 31 AGM
batteries and a 4 channel DualPro charger.  I've had ten great summers
using this configuration on some inland lakes in Ohio. Last summer, I
started noticing the battery capacity wasn't what it was when the
batteries were new.  The Torqeedo would shut down due to "depleted
batteries", but I was always able to turn it off and then back on where
upon I could return home at a slower pace. That is one of the things I
like about electric vs gasoline.  I have never been stranded.

Anyway, I suppose it is time to replace the batteries.  I can't complain
about getting 10 years out of them.  As I see it, I have two options:

1. Buy another set of AGMs - a little under $1000

2. Buy LiFePo4's - at least double the cost, but less weight and more
usable range.

As an engineer, I like using new technologies so I lean toward the
LiFePo4's.  However, many of the posters I follow on this forum bought
them directly from Chinese suppliers.  With all the COVID 19 disruptions
to business and our government threatening to raise tariffs, I worry
about placing an order that never gets filled.

I would appreciate any opinions on which way to go and any
recommendations for low risk suppliers for batteries.

Thanks,

Pat

Re: [electricboats] AGM or LiFePo4

Hey Phil,

Can you share your China source of LifePo4?  That looks like a great price! If I'm doing my math right that's over 800 AH at 12v?  Or am I missing something?

Thanks,

 

g

 

 

From: electricboats@groups.io <electricboats@groups.io> On Behalf Of Phil Boyer via groups.io
Sent: Monday, April 27, 2020 12:15 PM
To: electricboats@groups.io
Subject: Re: [electricboats] AGM or LiFePo4

 

I have 10KW of LifePo4 batteries on order from China and are due to land in Toronto first week of May. My cost so far was $2600 Canadian or $1900 US. I have not cleared customs yet so not sure what the duty and taxes will be.
My question is why do you need a different charger as mentioned below? The LifePo4 cells can be charged to 3.65 volts max so is there another factor I am not thinking of?

Phil

 

On Monday, April 27, 2020, 11:49:32 a.m. EDT, L Schmitz via groups.io <terminalift=yahoo.com@groups.io> wrote:

 

 

Hello Pat,  I did the upgrade last year. I went from 4  12v 220 ah agm to   lifepo4    I put together 4 battery boxes with  3.2v 90ah cylinder cells. 4P4S for each box. Then in series for 48v system. You will need a bms and a different  charger  This is a cool upgrade and not too difficult.. I am able to monitor the batteries in charge and discharge mode at any given time with my I phone.  I have great continuous run time and overnite charging with  my dock power. I can suggest a couple sources depending on east or west coast usa.;  I hope this helps.  thank you  best regards Larry Schmitz

 

​Terminalift LLC

9444 Mission Park Place

Santee, CA 92071

Ph: (619) 562-0355

F: (619) 562-2060

 

 

On Monday, April 27, 2020, 08:03:54 AM PDT, sw via groups.io <v1opps=yahoo.com@groups.io> wrote:

 

 

Is that 24v or 48v?

Can buy surpluses Tesla , leaf or other packs too

On Monday, April 27, 2020, 07:43, greenpjs04 <forums@greensdomain.com> wrote:

Hello everyone,

Over 10 years ago, you guys helped me to convert my 24' pontoon to
electric.  I ended up with a Torqeedo Cruise 4, four group 31 AGM
batteries and a 4 channel DualPro charger.  I've had ten great summers
using this configuration on some inland lakes in Ohio. Last summer, I
started noticing the battery capacity wasn't what it was when the
batteries were new.  The Torqeedo would shut down due to "depleted
batteries", but I was always able to turn it off and then back on where
upon I could return home at a slower pace. That is one of the things I
like about electric vs gasoline.  I have never been stranded.

Anyway, I suppose it is time to replace the batteries.  I can't complain
about getting 10 years out of them.  As I see it, I have two options:

1. Buy another set of AGMs - a little under $1000

2. Buy LiFePo4's - at least double the cost, but less weight and more
usable range.

As an engineer, I like using new technologies so I lean toward the
LiFePo4's.  However, many of the posters I follow on this forum bought
them directly from Chinese suppliers.  With all the COVID 19 disruptions
to business and our government threatening to raise tariffs, I worry
about placing an order that never gets filled.

I would appreciate any opinions on which way to go and any
recommendations for low risk suppliers for batteries.

Thanks,

Pat

[electricboats] Health Benefits Of Sailing

 

Do you have to justify days spent on the water – to your family? your boss? yourself? Is it not just egotistical hedonism, an escape from responsibilities? Maybe, but now researchers have discovered scientifically (which we privately knew all along) that sailing is actually the same as going to a health farm (and cheaper, probably. Here are the results, brought to you by Dr Gillian McKeith

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Re: [electricboats] AGM or LiFePo4

Interesting discussion.

I hadn't considered the current draw of a balancing BMS on a LiFePO4 pack. I had thought about the (slight) risk of a balancing MOSFET failing and bringing down the pack, so I bought a simple battery monitoring system, which only provides high/low voltage and high temperature cutoff. It's always powered, and draws a few microamps. My little 4s pack loses maybe 10mV sitting in the boat over the winter with no charging at all. I'm a fan of bottom balancing, which makes sense for a traction pack, whose main purpose is to be drained by a motor and then recharged. I'm going into my third season, and the cell voltages have drifted very little.

I wanted to know the cell voltages at a glance, but  didn't want powered volt meters draining them. I found little voltage display modules on eBay for two dollars each, and wired one across each cell with a push-button switch. It takes 3 seconds for a module to boot and display the cell voltage.

I also wired the solar charger to the pack through a double throw switch so I could charge the pack through the BMS (normal setting), or directly to the cells, in case I ever need to recover from a low voltage shutdown. The switch also lets me disconnect the charger completely for all those sunny days when the boat just sits there and the battery is already at a good state of charge.

My thought about commercial batteries that are bricked by their BMSs: if the warranty is expired, cut open the case and clip on a charger. Commercial failure? DIY recovery opportunity.

Re: [electricboats] AGM or LiFePo4

Thank you for the info

Everybody was telling me to just keep the bms powered all the time

I wasn't sure so I added switches to the bms power so I can switch them off

Since I'm usually gone a lot

But since home a lot now I leave it on and can see it every few days

Once Was gone for a few month and came back and saw pack was near zero

All that I know was on was a volt meter

( could be a pre charge on too since I didn't see a separate pre charge switch,unless built in relay via the key)

Lost at least one battery (6 cells) from that ....

As I mentioned I just use the bms to balance the cells since I draw too much power to run it through the bms

Don't want to burn up the bms

Cheers

On Tuesday, April 28, 2020, 09:47:21 AM PDT, Myles Twete <matwete@comcast.net> wrote:

I'm not so sure that "the BMS should only be used in case the charger fails"---if the charger fails ON, even a BMS will probably be useless to stop it.  Same story for a charger that fails by allowing pack to discharge into the charger after shutting down.  Ignoring the charger failure scenarios, a BMS is useful during charging in 2 or 3 ways:

·       Identifying that a cell has reached a maximum voltage and informing the charger so it can shut charge current OFF

·       Cell balancing (typically by bypassing current around full cells)

·       Allowing charging to restart after cell imbalance corrected

 

The basic CV/CI charger is blind to what is happening at the individual cell level, while a BMS cell monitor/manager is cognizant at that level.  And while it is important that the BMS is commonly referred to as being used to "balance" all the cells, they often can and should provide critical information, data or control to the charging system to ensure against overcharging a single cell.  Yes, wildly out-of-balance cells should not be expected if a BMS has been managing cells regularly or at least occasionally.  But they can happen.  Fortunately, the outliers are usually "leaky" or perhaps most common, self-discharging or discharging thru leaky BMS mosfets.  And so a single or a few low cells won't cause much of an increase in charged cell voltage for the rest of the majority of cells at the final charge voltage.  If, however there were widespread self-discharging but a small number that did not, then those few cells are at risk if a blind charger does not respond to cell voltage reaching a maximum first.  And so, a BMS sending out a stop command to the charger can be useful, and not because the charger itself has failed.

 

In my case, I have some 240 cell pairs, all with BMS connections but only maybe once every 12-18months do I ever power these BMS circuits.  I also have not generally been using the BMS to control and limit charging.  Mostly I charge with a CV/CI power supply, start it charging and come back the next day to shut it off.  I do make sure ahead of time that there are no outlier cells that are significantly higher voltage than the rest or that there are too many low outliers which would add up to allow the high cells to get overcharged.  And I stop charging at 46-48v while the pack is rated for over 49v.

 

While this may sound crazy, I also only am charging the pack about once per 2-3months, so we're only talking 4-9 charge cycles.  I trust the cells themselves more than I trust the leakiness risk of the BMS mosfets (and standby power).  The downside is that I do see 6 out of 240 cell pairs that significantly drift (again, either self-discharging or discharging thru an unpowered mosfet/load resistor).  And 3 of these are significant---between 100 and 350mv decay in voltage over a year.  It's important (given I am not powering the BMS circuits always) to consider these decay magnitudes when letting my pack voltage drop to its lower levels.  Yes, I could just trust the BMS cards, and I do, but I do not want to stress them for no reason and risk my pack life due to failed BMS self-discharge.  I personally think it's more risky to power these BMS cards 365+ days when I really only need to power them before or after the few times I'm going to charge the pack.

 

I recently found myself speaking on the phone with a sales engineer for a noted lithium battery manufacturer.  I thought it was an engineer working for my company so I was frank in my opinion about the batteries in question.  I was quite vocal about my opinion that "no self-respecting engineer would design a built-in BMS that is always powered and will self-discharge a battery before the box was ever opened, sitting on the shelf".  The sales engineer for the battery manufacturer appreciated my frankness.  I said, it's fine to have a BMS that monitors cells when there are no loads on the battery, however it's not fine to design a system that continues such loading to the point that the low cell voltage is reached.  Worse, these common 12v lithium batteries will at that point, either blow a fuse or open a mosfet internally that denies ever being able to recharge the cells or use them again.  I.E. the BMS itself "bricks" the lithium battery.  I pointed out that even the cheapest of kids toys where "batteries are included" include a plastic tab that the user has to pull out before use.  This is to ensure the battery doesn't self-discharge thru the toy/lamp/whatever.  I also pointed out that this was a "design choice" and that a responsible design would instead open up a mosfet that disallowed any further discharge (even internally), but would allow charging.  Laptop computer batteries at least do this somewhat.

 

Many or most modern sealed 12v lithium batteries w/self-contained BMS have this same design flaw.  And they internally draw enough current that within 1-2years on the shelf, they become bricks.  So much for long life of lithium.

Our BMS circuits will similarly draw power and one needs to consider this.  Mine draw about 1watt each.  If I kept all BMS cards powered continuously, a full pack in my boat would discharge thru the BMS cards in 1500 hours (not to mention the DCDC losses to make the 12v for the BMS cards).  While this sounds like a lot of time, it's only 2 months!  So it's important to understand when your BMS is powered, what power it takes, how often you really need it powered and can you sensibly power it only when it's needed.

 

-MT

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of Matt Foley
Sent: Tuesday, April 28, 2020 8:00 AM
To: electricboats@groups.io
Subject: Re: [electricboats] AGM or LiFePo4

 

To piggy back on what Tom said, 

 

Its best practice to have two means of protecting batteries. On the charge side, the charger have the correct charge profile and the BMS is secondary and should only be used as back up in case the charger fails. On the discharge side, the motor controller/inverter should be programmed with the correct voltage settings and the BMS is the failsafe. 

 

Unless you are charging at a high C rate (most of us in DIY electric boats are not) you do not need to worry about CVCC. You can just charge with CV and stop. Unlike lead acid, which prefer to be fully charged and even over charged occasionally, lithium prefers to be less than fully charged. They would be perfectly happy sitting at 50% SOC for years.  If using a lead acid charger, turn off the float charge or make it as low as possible. Be certain it does not have an equalization charge. Overcharging lithium just once can and most likely will ruin them, sometimes in a dramatic way. 

 

For lifepo4 I stop charging at 3.5 VPC. There is almost no capacity above that voltage.  If you look at a discharge chart you will see what I mean. Lifpo4 voltages should not be confused with lithium chemistries with a 4.2 VPC cutoff 

 

I typically use  90% as upper limit and 10% on the low end. 

 

 

 

Matt Foley 

Sunlight Conversions

Perpetual Energy, LLC

201-914-0466

sunlightconversions.com

instagram.com/sunlightconversions/

youtube/sunlightconversions

 

 

 

On Tuesday, April 28, 2020, 09:40:12 AM EDT, THOMAS VANDERMEULEN <tvinypsi@gmail.com> wrote:

 

 

MARTIN: Since you have expertise, I hope you'll agree that the acronym 'BMS' stands for battery management system, but that what some people are referring to as a BMS is actually a battery protection system.
A BMS that's suitable for a 16 cell, LiFePO4 prismatic pack, such as might be found aboard a sailboat -- such as the Orion Jr. or the Dilithium BMSC from Thunderstruck -- would provide for measuring and reporting individual cell voltages; balancing the cell voltages within the pack; and also often the ability to measure cell or pack temperature.  The Orion Jr even implements charger control in a single unit, while the Dilithium units from Thunderstruck separate the two functions -- BMS & charge control -- into two different units, but enables using two different modes of communication between the two devices, including CAN.
in contrast, the typical "BMS" that's embedded in 48v battery packs used for electric bicycles, for instance, provides only for the overcharge protection to shut off charging when voltage reaches the safe operating limit, and low voltage protection to shut off discharging to load when voltage drops to the safe operating level for that battery pack.
In the case of battery protection circuits, it's possible for individual cells to get out of balance relative to one another, such that one cell will reach full charge voltage before the others in a pack.  The protection circuit cuts off charging due to the high cell voltage cut-off, and the remaining cells will be less than fully charged.
Many of the ElectricBoat members are familiar with everything I've just mentioned, but it may be useful to repeat the information as new members come aboard.
Fair Winds to all!
[-tv]
Tom VanderMeulen
"Grace O'Malley"
Cape Dory 27
Monroe, Michi.

Re: [electricboats] AGM or LiFePo4

To clarify, I meant you should always use the correct charger with the correct settings and not solely rely on a BMS as your only means of not overcharging on at the pack level. Individual cell monitoring is a whole other discussion. 

Matt Foley

Sunlight Conversions 

1-201-914-0466

Sunlightconversions.com

WeChat: Mattymoonshine

Sent from mobile device 

On Apr 28, 2020, at 12:47 PM, Myles Twete <matwete@comcast.net> wrote:



I'm not so sure that "the BMS should only be used in case the charger fails"---if the charger fails ON, even a BMS will probably be useless to stop it.  Same story for a charger that fails by allowing pack to discharge into the charger after shutting down.  Ignoring the charger failure scenarios, a BMS is useful during charging in 2 or 3 ways:

·       Identifying that a cell has reached a maximum voltage and informing the charger so it can shut charge current OFF

·       Cell balancing (typically by bypassing current around full cells)

·       Allowing charging to restart after cell imbalance corrected

 

The basic CV/CI charger is blind to what is happening at the individual cell level, while a BMS cell monitor/manager is cognizant at that level.  And while it is important that the BMS is commonly referred to as being used to "balance" all the cells, they often can and should provide critical information, data or control to the charging system to ensure against overcharging a single cell.  Yes, wildly out-of-balance cells should not be expected if a BMS has been managing cells regularly or at least occasionally.  But they can happen.  Fortunately, the outliers are usually "leaky" or perhaps most common, self-discharging or discharging thru leaky BMS mosfets.  And so a single or a few low cells won't cause much of an increase in charged cell voltage for the rest of the majority of cells at the final charge voltage.  If, however there were widespread self-discharging but a small number that did not, then those few cells are at risk if a blind charger does not respond to cell voltage reaching a maximum first.  And so, a BMS sending out a stop command to the charger can be useful, and not because the charger itself has failed.

 

In my case, I have some 240 cell pairs, all with BMS connections but only maybe once every 12-18months do I ever power these BMS circuits.  I also have not generally been using the BMS to control and limit charging.  Mostly I charge with a CV/CI power supply, start it charging and come back the next day to shut it off.  I do make sure ahead of time that there are no outlier cells that are significantly higher voltage than the rest or that there are too many low outliers which would add up to allow the high cells to get overcharged.  And I stop charging at 46-48v while the pack is rated for over 49v.

 

While this may sound crazy, I also only am charging the pack about once per 2-3months, so we're only talking 4-9 charge cycles.  I trust the cells themselves more than I trust the leakiness risk of the BMS mosfets (and standby power).  The downside is that I do see 6 out of 240 cell pairs that significantly drift (again, either self-discharging or discharging thru an unpowered mosfet/load resistor).  And 3 of these are significant---between 100 and 350mv decay in voltage over a year.  It's important (given I am not powering the BMS circuits always) to consider these decay magnitudes when letting my pack voltage drop to its lower levels.  Yes, I could just trust the BMS cards, and I do, but I do not want to stress them for no reason and risk my pack life due to failed BMS self-discharge.  I personally think it's more risky to power these BMS cards 365+ days when I really only need to power them before or after the few times I'm going to charge the pack.

 

I recently found myself speaking on the phone with a sales engineer for a noted lithium battery manufacturer.  I thought it was an engineer working for my company so I was frank in my opinion about the batteries in question.  I was quite vocal about my opinion that "no self-respecting engineer would design a built-in BMS that is always powered and will self-discharge a battery before the box was ever opened, sitting on the shelf".  The sales engineer for the battery manufacturer appreciated my frankness.  I said, it's fine to have a BMS that monitors cells when there are no loads on the battery, however it's not fine to design a system that continues such loading to the point that the low cell voltage is reached.  Worse, these common 12v lithium batteries will at that point, either blow a fuse or open a mosfet internally that denies ever being able to recharge the cells or use them again.  I.E. the BMS itself "bricks" the lithium battery.  I pointed out that even the cheapest of kids toys where "batteries are included" include a plastic tab that the user has to pull out before use.  This is to ensure the battery doesn't self-discharge thru the toy/lamp/whatever.  I also pointed out that this was a "design choice" and that a responsible design would instead open up a mosfet that disallowed any further discharge (even internally), but would allow charging.  Laptop computer batteries at least do this somewhat.

 

Many or most modern sealed 12v lithium batteries w/self-contained BMS have this same design flaw.  And they internally draw enough current that within 1-2years on the shelf, they become bricks.  So much for long life of lithium.

Our BMS circuits will similarly draw power and one needs to consider this.  Mine draw about 1watt each.  If I kept all BMS cards powered continuously, a full pack in my boat would discharge thru the BMS cards in 1500 hours (not to mention the DCDC losses to make the 12v for the BMS cards).  While this sounds like a lot of time, it's only 2 months!  So it's important to understand when your BMS is powered, what power it takes, how often you really need it powered and can you sensibly power it only when it's needed.

 

-MT

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of Matt Foley
Sent: Tuesday, April 28, 2020 8:00 AM
To: electricboats@groups.io
Subject: Re: [electricboats] AGM or LiFePo4

 

To piggy back on what Tom said, 

 

Its best practice to have two means of protecting batteries. On the charge side, the charger have the correct charge profile and the BMS is secondary and should only be used as back up in case the charger fails. On the discharge side, the motor controller/inverter should be programmed with the correct voltage settings and the BMS is the failsafe. 

 

Unless you are charging at a high C rate (most of us in DIY electric boats are not) you do not need to worry about CVCC. You can just charge with CV and stop. Unlike lead acid, which prefer to be fully charged and even over charged occasionally, lithium prefers to be less than fully charged. They would be perfectly happy sitting at 50% SOC for years.  If using a lead acid charger, turn off the float charge or make it as low as possible. Be certain it does not have an equalization charge. Overcharging lithium just once can and most likely will ruin them, sometimes in a dramatic way. 

 

For lifepo4 I stop charging at 3.5 VPC. There is almost no capacity above that voltage.  If you look at a discharge chart you will see what I mean. Lifpo4 voltages should not be confused with lithium chemistries with a 4.2 VPC cutoff 

 

I typically use  90% as upper limit and 10% on the low end. 

 

 

 

Matt Foley 

Sunlight Conversions

Perpetual Energy, LLC

201-914-0466

sunlightconversions.com

instagram.com/sunlightconversions/

youtube/sunlightconversions

 

 

 

On Tuesday, April 28, 2020, 09:40:12 AM EDT, THOMAS VANDERMEULEN <tvinypsi@gmail.com> wrote:

 

 

MARTIN: Since you have expertise, I hope you'll agree that the acronym 'BMS' stands for battery management system, but that what some people are referring to as a BMS is actually a battery protection system.
A BMS that's suitable for a 16 cell, LiFePO4 prismatic pack, such as might be found aboard a sailboat -- such as the Orion Jr. or the Dilithium BMSC from Thunderstruck -- would provide for measuring and reporting individual cell voltages; balancing the cell voltages within the pack; and also often the ability to measure cell or pack temperature.  The Orion Jr even implements charger control in a single unit, while the Dilithium units from Thunderstruck separate the two functions -- BMS & charge control -- into two different units, but enables using two different modes of communication between the two devices, including CAN.
in contrast, the typical "BMS" that's embedded in 48v battery packs used for electric bicycles, for instance, provides only for the overcharge protection to shut off charging when voltage reaches the safe operating limit, and low voltage protection to shut off discharging to load when voltage drops to the safe operating level for that battery pack.
In the case of battery protection circuits, it's possible for individual cells to get out of balance relative to one another, such that one cell will reach full charge voltage before the others in a pack.  The protection circuit cuts off charging due to the high cell voltage cut-off, and the remaining cells will be less than fully charged.
Many of the ElectricBoat members are familiar with everything I've just mentioned, but it may be useful to repeat the information as new members come aboard.
Fair Winds to all!
[-tv]
Tom VanderMeulen
"Grace O'Malley"
Cape Dory 27
Monroe, Michi.

Re: [electricboats] AGM or LiFePo4

I'm not so sure that "the BMS should only be used in case the charger fails"---if the charger fails ON, even a BMS will probably be useless to stop it.  Same story for a charger that fails by allowing pack to discharge into the charger after shutting down.  Ignoring the charger failure scenarios, a BMS is useful during charging in 2 or 3 ways:

·       Identifying that a cell has reached a maximum voltage and informing the charger so it can shut charge current OFF

·       Cell balancing (typically by bypassing current around full cells)

·       Allowing charging to restart after cell imbalance corrected

 

The basic CV/CI charger is blind to what is happening at the individual cell level, while a BMS cell monitor/manager is cognizant at that level.  And while it is important that the BMS is commonly referred to as being used to "balance" all the cells, they often can and should provide critical information, data or control to the charging system to ensure against overcharging a single cell.  Yes, wildly out-of-balance cells should not be expected if a BMS has been managing cells regularly or at least occasionally.  But they can happen.  Fortunately, the outliers are usually "leaky" or perhaps most common, self-discharging or discharging thru leaky BMS mosfets.  And so a single or a few low cells won't cause much of an increase in charged cell voltage for the rest of the majority of cells at the final charge voltage.  If, however there were widespread self-discharging but a small number that did not, then those few cells are at risk if a blind charger does not respond to cell voltage reaching a maximum first.  And so, a BMS sending out a stop command to the charger can be useful, and not because the charger itself has failed.

 

In my case, I have some 240 cell pairs, all with BMS connections but only maybe once every 12-18months do I ever power these BMS circuits.  I also have not generally been using the BMS to control and limit charging.  Mostly I charge with a CV/CI power supply, start it charging and come back the next day to shut it off.  I do make sure ahead of time that there are no outlier cells that are significantly higher voltage than the rest or that there are too many low outliers which would add up to allow the high cells to get overcharged.  And I stop charging at 46-48v while the pack is rated for over 49v.

 

While this may sound crazy, I also only am charging the pack about once per 2-3months, so we're only talking 4-9 charge cycles.  I trust the cells themselves more than I trust the leakiness risk of the BMS mosfets (and standby power).  The downside is that I do see 6 out of 240 cell pairs that significantly drift (again, either self-discharging or discharging thru an unpowered mosfet/load resistor).  And 3 of these are significant---between 100 and 350mv decay in voltage over a year.  It's important (given I am not powering the BMS circuits always) to consider these decay magnitudes when letting my pack voltage drop to its lower levels.  Yes, I could just trust the BMS cards, and I do, but I do not want to stress them for no reason and risk my pack life due to failed BMS self-discharge.  I personally think it's more risky to power these BMS cards 365+ days when I really only need to power them before or after the few times I'm going to charge the pack.

 

I recently found myself speaking on the phone with a sales engineer for a noted lithium battery manufacturer.  I thought it was an engineer working for my company so I was frank in my opinion about the batteries in question.  I was quite vocal about my opinion that "no self-respecting engineer would design a built-in BMS that is always powered and will self-discharge a battery before the box was ever opened, sitting on the shelf".  The sales engineer for the battery manufacturer appreciated my frankness.  I said, it's fine to have a BMS that monitors cells when there are no loads on the battery, however it's not fine to design a system that continues such loading to the point that the low cell voltage is reached.  Worse, these common 12v lithium batteries will at that point, either blow a fuse or open a mosfet internally that denies ever being able to recharge the cells or use them again.  I.E. the BMS itself "bricks" the lithium battery.  I pointed out that even the cheapest of kids toys where "batteries are included" include a plastic tab that the user has to pull out before use.  This is to ensure the battery doesn't self-discharge thru the toy/lamp/whatever.  I also pointed out that this was a "design choice" and that a responsible design would instead open up a mosfet that disallowed any further discharge (even internally), but would allow charging.  Laptop computer batteries at least do this somewhat.

 

Many or most modern sealed 12v lithium batteries w/self-contained BMS have this same design flaw.  And they internally draw enough current that within 1-2years on the shelf, they become bricks.  So much for long life of lithium.

Our BMS circuits will similarly draw power and one needs to consider this.  Mine draw about 1watt each.  If I kept all BMS cards powered continuously, a full pack in my boat would discharge thru the BMS cards in 1500 hours (not to mention the DCDC losses to make the 12v for the BMS cards).  While this sounds like a lot of time, it's only 2 months!  So it's important to understand when your BMS is powered, what power it takes, how often you really need it powered and can you sensibly power it only when it's needed.

 

-MT

 

From: electricboats@groups.io [mailto:electricboats@groups.io] On Behalf Of Matt Foley
Sent: Tuesday, April 28, 2020 8:00 AM
To: electricboats@groups.io
Subject: Re: [electricboats] AGM or LiFePo4

 

To piggy back on what Tom said, 

 

Its best practice to have two means of protecting batteries. On the charge side, the charger have the correct charge profile and the BMS is secondary and should only be used as back up in case the charger fails. On the discharge side, the motor controller/inverter should be programmed with the correct voltage settings and the BMS is the failsafe. 

 

Unless you are charging at a high C rate (most of us in DIY electric boats are not) you do not need to worry about CVCC. You can just charge with CV and stop. Unlike lead acid, which prefer to be fully charged and even over charged occasionally, lithium prefers to be less than fully charged. They would be perfectly happy sitting at 50% SOC for years.  If using a lead acid charger, turn off the float charge or make it as low as possible. Be certain it does not have an equalization charge. Overcharging lithium just once can and most likely will ruin them, sometimes in a dramatic way. 

 

For lifepo4 I stop charging at 3.5 VPC. There is almost no capacity above that voltage.  If you look at a discharge chart you will see what I mean. Lifpo4 voltages should not be confused with lithium chemistries with a 4.2 VPC cutoff 

 

I typically use  90% as upper limit and 10% on the low end. 

 

 

 

Matt Foley 

Sunlight Conversions

Perpetual Energy, LLC

201-914-0466

sunlightconversions.com

instagram.com/sunlightconversions/

youtube/sunlightconversions

 

 

 

On Tuesday, April 28, 2020, 09:40:12 AM EDT, THOMAS VANDERMEULEN <tvinypsi@gmail.com> wrote:

 

 

MARTIN: Since you have expertise, I hope you'll agree that the acronym 'BMS' stands for battery management system, but that what some people are referring to as a BMS is actually a battery protection system.
A BMS that's suitable for a 16 cell, LiFePO4 prismatic pack, such as might be found aboard a sailboat -- such as the Orion Jr. or the Dilithium BMSC from Thunderstruck -- would provide for measuring and reporting individual cell voltages; balancing the cell voltages within the pack; and also often the ability to measure cell or pack temperature.  The Orion Jr even implements charger control in a single unit, while the Dilithium units from Thunderstruck separate the two functions -- BMS & charge control -- into two different units, but enables using two different modes of communication between the two devices, including CAN.
in contrast, the typical "BMS" that's embedded in 48v battery packs used for electric bicycles, for instance, provides only for the overcharge protection to shut off charging when voltage reaches the safe operating limit, and low voltage protection to shut off discharging to load when voltage drops to the safe operating level for that battery pack.
In the case of battery protection circuits, it's possible for individual cells to get out of balance relative to one another, such that one cell will reach full charge voltage before the others in a pack.  The protection circuit cuts off charging due to the high cell voltage cut-off, and the remaining cells will be less than fully charged.
Many of the ElectricBoat members are familiar with everything I've just mentioned, but it may be useful to repeat the information as new members come aboard.
Fair Winds to all!
[-tv]
Tom VanderMeulen
"Grace O'Malley"
Cape Dory 27
Monroe, Michi.

Re: [electricboats] AGM or LiFePo4

To piggy back on what Tom said, 

Its best practice to have two means of protecting batteries. On the charge side, the charger have the correct charge profile and the BMS is secondary and should only be used as back up in case the charger fails. On the discharge side, the motor controller/inverter should be programmed with the correct voltage settings and the BMS is the failsafe. 

Unless you are charging at a high C rate (most of us in DIY electric boats are not) you do not need to worry about CVCC. You can just charge with CV and stop. Unlike lead acid, which prefer to be fully charged and even over charged occasionally, lithium prefers to be less than fully charged. They would be perfectly happy sitting at 50% SOC for years.  If using a lead acid charger, turn off the float charge or make it as low as possible. Be certain it does not have an equalization charge. Overcharging lithium just once can and most likely will ruin them, sometimes in a dramatic way. 

For lifepo4 I stop charging at 3.5 VPC. There is almost no capacity above that voltage.  If you look at a discharge chart you will see what I mean. Lifpo4 voltages should not be confused with lithium chemistries with a 4.2 VPC cutoff 

I typically use  90% as upper limit and 10% on the low end. 

Matt Foley 

Sunlight Conversions

Perpetual Energy, LLC

201-914-0466

sunlightconversions.com

instagram.com/sunlightconversions/

youtube/sunlightconversions

On Tuesday, April 28, 2020, 09:40:12 AM EDT, THOMAS VANDERMEULEN <tvinypsi@gmail.com> wrote:

MARTIN: Since you have expertise, I hope you'll agree that the acronym 'BMS' stands for battery management system, but that what some people are referring to as a BMS is actually a battery protection system.
A BMS that's suitable for a 16 cell, LiFePO4 prismatic pack, such as might be found aboard a sailboat -- such as the Orion Jr. or the Dilithium BMSC from Thunderstruck -- would provide for measuring and reporting individual cell voltages; balancing the cell voltages within the pack; and also often the ability to measure cell or pack temperature.  The Orion Jr even implements charger control in a single unit, while the Dilithium units from Thunderstruck separate the two functions -- BMS & charge control -- into two different units, but enables using two different modes of communication between the two devices, including CAN.
in contrast, the typical "BMS" that's embedded in 48v battery packs used for electric bicycles, for instance, provides only for the overcharge protection to shut off charging when voltage reaches the safe operating limit, and low voltage protection to shut off discharging to load when voltage drops to the safe operating level for that battery pack.
In the case of battery protection circuits, it's possible for individual cells to get out of balance relative to one another, such that one cell will reach full charge voltage before the others in a pack.  The protection circuit cuts off charging due to the high cell voltage cut-off, and the remaining cells will be less than fully charged.
Many of the ElectricBoat members are familiar with everything I've just mentioned, but it may be useful to repeat the information as new members come aboard.
Fair Winds to all!
[-tv]
Tom VanderMeulen
"Grace O'Malley"
Cape Dory 27
Monroe, Michi.

Re: [electricboats] AGM or LiFePo4

MARTIN: Since you have expertise, I hope you'll agree that the acronym 'BMS' stands for battery management system, but that what some people are referring to as a BMS is actually a battery protection system.
A BMS that's suitable for a 16 cell, LiFePO4 prismatic pack, such as might be found aboard a sailboat -- such as the Orion Jr. or the Dilithium BMSC from Thunderstruck -- would provide for measuring and reporting individual cell voltages; balancing the cell voltages within the pack; and also often the ability to measure cell or pack temperature.  The Orion Jr even implements charger control in a single unit, while the Dilithium units from Thunderstruck separate the two functions -- BMS & charge control -- into two different units, but enables using two different modes of communication between the two devices, including CAN.
in contrast, the typical "BMS" that's embedded in 48v battery packs used for electric bicycles, for instance, provides only for the overcharge protection to shut off charging when voltage reaches the safe operating limit, and low voltage protection to shut off discharging to load when voltage drops to the safe operating level for that battery pack.
In the case of battery protection circuits, it's possible for individual cells to get out of balance relative to one another, such that one cell will reach full charge voltage before the others in a pack.  The protection circuit cuts off charging due to the high cell voltage cut-off, and the remaining cells will be less than fully charged.
Many of the ElectricBoat members are familiar with everything I've just mentioned, but it may be useful to repeat the information as new members come aboard.
Fair Winds to all!
[-tv]
Tom VanderMeulen
"Grace O'Malley"
Cape Dory 27
Monroe, Michi.

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Re: [electricboats] AGM or LiFePo4

Some bms can be customized to have a high and low bms cut offs like the ant bms I use

But since I draw too many amps I cannot use it unless I add an external contactor (maybe one day...)

So I just use it for balance

From the little I know u need cc-cv charger (I think even lead acid chargers use cc-cv but different bulk charging?)

I had a old lead acid charger that the manufacture changed to lithium charger, so it can be done 

Not sure how it was done..

If your happy with like 5-10 ? amps charging there are solar buck/boost green chargers u can buy off eBay for 30-40$ that can use variable dc input like old computer power supply and give you variable dc cc-cv output 

Ant bms..I use 32s but don't need to use all of them.   https://www.ebay.com/itm/8S-20S-Smart-lithium-Lipo-Lifepo4-LTO-Battery-BMS-Protection-Board-Bluetooth-APP/312949237002?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D225074%26meid%3D3478c6f3ad0b40b987f509bb5731dd6b%26pid%3D100005%26rk%3D6%26rkt%3D12%26mehot%3Dpf%26sd%3D192687500566%26itm%3D312949237002%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWebWithBBEV2aDemotion%26brand%3DUnbranded&_trksid=p2047675.c100005.m1851

Charger.  https://www.ebay.com/itm/LCD-MPPT-Solar-Regulator-Charge-Controller-24-36-48-60-72V-10A-60V-DC-DC-Boost-/232106050473?hash=item360a9943a9

https://www.ebay.com/itm/Power-Supply-CNC-Module-DC10V-75V-to-0-60V-12A-720W-Buck-Controller-Converter/352121040565?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D225074%26meid%3D485df95e9c7548dfb4853cba7f2d783e%26pid%3D100005%26rk%3D1%26rkt%3D12%26mehot%3Dco%26sd%3D184264237590%26itm%3D352121040565%26pmt%3D1%26noa%3D0%26pg%3D2047675%26algv%3DSimplAMLv5PairwiseWebWithBBEV2aDemotion%26brand%3DDrok&_trksid=p2047675.c100005.m1851

I'm no expert but these have worked for me and my budget 

On Tuesday, April 28, 2020, 03:32:01 AM PDT, greenpjs04 <forums@greensdomain.com> wrote:

Wow!  Thank you for all the responses.  I will investigate all your
suggestions further.  One topic that came up but has me confused is the
BMS needed for LiFePo4 batteries.  From past research, I know that some
cells offered for sale are just that - cells without any BMS.  To use
those, I would have to add a BMS designed for LiFePo4 chemistry. 
DualPro's website says their chargers "can" be programmed for LiFePo4
but I doubt that applies to my 10 year old AGM charger.

So, moving on to the LiFePo4 battery packs with built in BMS's, how does
one charge those?  I found very little detail mentioned. Just things
like "Includes BMS!" and similar claims.  Can any charger with a voltage
above the battery voltage be used to charge these batteries?  In other
words, does the internal BMS fully protect the batteries by handling
charge rate and monitoring state of charge to avoid over-charging?

Pat