T-Pain Is On A Boat: Re: [Electric Boats] Re: Batteries wired in series

My bank is 16x lithium cells in series.

I am using a BMS for individual cell monitoring which can interrupt charging if one cell goes over max voltage and cutback on throttle at a low threshold and kills throttle completely at a lower threshold.

While the BMS isn't smart enough to provide individual cell voltages, I have wired my battery boxes for remote BMS and voltage monitoring. So each battery box has a waterproof 5-pin connector on it which is lead to a panel at my Nav-station. From there, I wired up each of the 16 BMS cell modules and the volt meters. This lets me easily see the blinking lights of the cell-modules to see which are in error or shunting as well as the voltages of each cell on the meters.

As a safety measure, I have used small 1A self-resetting fuses (really not expensive and often sold in packs of 5, 10, 25) at the pos and neg of each 4-cell pack. This should prevent any cable connection mix ups from frying anything.

/Jason

Jason Taylor

v:514-815-8204

e:j@jtaylor.ca

On Apr 28, 2016, at 11:43, James Lambden james@electroprop.com [electricboats] <electricboats@yahoogroups.com> wrote:

I have worked on 48, 72 and 96 VDC systems for 10 years.

The only time I have ever felt DC electricity was on a 48 volt boat. My arm was sweaty and I came in contact with the shunt and felt a tingle. I don't know of any cases of anyone ever being shocked by 48 volt DC and having any serious consequences.

I have studied these systems for years and I think the biggest hazard with low voltage DC systems is when the batteries fail at the end of their life while connected to a string (48 volt ) charger. One battery will fail before all the rest and this battery will steal the voltage from the other batteries as the resistance of the failed battery goes high. I consider a 48 volt battery charger on a 48 volt battery to be an unregulated charger and very dangerous. It is very likely that at the end of the batteries life, when charged by a string charger, that one of the batteries will experience a thermal event, start boiling its electolyte, put Hydrogen gas into the boat which we know is very explosive, and more problematic that that, potentially go thermal and catch the boat on fire. This is even more of a problem on batteries connected in parallel.

The other big issue that I have with these unregulated charging setups is the batteries go out of balance. This happens incrementally every time you charge with a string charger. As soon as the battery is out of balance by .1 of a volt, the battery life gets shortened. There is a definite knee in the life of the battery that starts when balance is out. Most batteries last 4 years with one of these string chargers when they could last 8 to 10 years with a balancing setup. With battery banks costing $2,000 and a days work in changing and disposing of them, I have to ask myself why are people going this route. Overall its expensive, time intensive and dangerous.

The other issue is as soon as the batteries start going out of balance, improper charging causes the batteries to lose amp hour capacity and that is usually a straight line event with time. It takes 3 to 6 months to destroy a battery pack, half way into that unbalanced cycle, the batteries will have half their power. Batteries suffer greatly from imbalance because now they are not receiving their proper charge voltage. The weakest battery gets too high a voltage and all the rest of the batteries get undercharged, and the whole battery bank fails prematurely.

We have moved to one charger with dedicated temp sensor per battery. The cost of perfect battery management costs $2,500. With shunt and screen its close to $3,000. Each battery charger can affect a charge enable relay for any string charger on the system including solar. In most applications the system pays for itself in 4 years by avoiding costly premature battery replacement

Part of my job is to bring this technology to as many people as possible by reducing the price. I have started on a project that will monitor each of the 12 volt batteries and when one of those goes over 15 volts the system de-activates a charge enable relay and turns off the string charger, and provides a warning. This is the bare bones essential that should be in every system. We think we can accomplish this for under $200 including a screen where you can see all 4 battery voltages. After we build the minimum safety system, we will be turning our attention to a system that balances as well. I know the vast majority of new boat motor sales are going for an inexpensive system but if you look at the cost of ownership, you might be surprised what you are getting yourself into when you choose an unregulated string charger for your charging setup.

If you have an unregulated 48 volt battery charger, the responsibility is yours to make sure your batteries are remaining in balance. Don't wait for a thermal event or a gas off event. As time goes by, check your batteries more often. When you see an imbalance of more than .1 of a volt, you need to balance your bank.

You want to keep your boat safe, your crew safe, and avoid costly, unnecessary battery replacement. The best way at this time to charge a battery is with a dedicated battery charger with dedicated temperature sensor. If you want to charge at the string level (48, 72 96 ) then you need to monitor each individual battery if you want an inherently safe system. The key to safely charging batteries is to monitor all batteries in a system, and affect a charge enable relay based on individual battery health.

You want to know the condition of your batteries before you leave the dock. Amp hour counting battery meters do not compensate for less capacity of the bank over time. If you don't know the strength of your battery bank, you could be leaving the dock with an empty battery and never even know it.

A simple way of knowing the health of your battery bank is look at the resting voltage with no charger or load on the battery. If you batteries are resting at 12.4, there is most likely only half the remaining capacity left in them. If your batteries are going out of balance, it will also show up in the resting voltages.

Look after your batteries, and your batteries will look after you!

James
James Lambden
The Electric Propeller Company
625C East Haley Street,
Santa Barbara, CA
93103

805 455 8444
jlambden: Skype

www.electroprop.com

james@electroprop.com
On Apr 28, 2016, at 7:48 AM, Hannu Venermo gcode.fi@gmail.com [electricboats] <electricboats@yahoogroups.com> wrote:
Most welders and plasma systems work around 30-40 volts.
The EU low voltage directive is set at 80V DC for a reason.
And I´m somewhat conversant with electrical stuff, as I build and design (industrial type) CNC systems.
No argument that 62 V is unpleasant.
Just that neither 48, nor 80V, is really dangerous, nor 220V single phase (with RCD and or GFI).
380V 3-phase is not particularly dangerous, unless its high power.
But, 400V DC is dangerous and needs to be tested to make sure its off.
Moral:
High voltage DC is very dangerous.
The commonly accepted and legal limit is 80V DC.

And most especially on these high power devices where power is tens to hundred kW plus, such as boats and cars.

Anecdote:
We connected 380V, 100 amps, live wires, on our extension cords.
With a running 50 kW diesel generator.
It ran upto 4 industrial cnc machines at a time (on lowered accelerations, due to limited total power).
We ran the genset 10 hours a day 3 months straight, and needed to fill the tank once (1000 l iirc).

But yes, we had industrial engineers and technicians, with experience (about 14 of 18 were engineers).
Its not amateur stuff.
I would not connect live 50 kW stuff, myself.

We could not get the power company to turn on the power for 3+ months.
T.I.S. wins, again..

On 28/04/2016 15:43, Chris Hudson clh5_98@yahoo.com [electricboats] wrote:
I work in the electrical field. We have 125 volt battery banks with the center of the bank grounded. Accidentally coming in contact with the +62.5 or the -62.5 volt side to ground gives a wicked shock. A hit across the heart at that voltage could be deadly. Don't underestimate our "low" voltage systems.

Sent from myPhone
--   -hanermo (cnc designs)  