T-Pain Is On A Boat: Re: [Electric Boats] AGM Batteries? >> LiIon usage rate?? [3 Attachments]

[Attachment(s) from Robert Lemke included below]

I'm still confused as to your experience with LiFePO4 cells. The 12 volt 60 a-hr cell from Balqon using (4) 60 a-hr single cells in one package is without a BMS and since it is a sealed container you would have to break the case open to install a BMS. The reason that they run without a BMS is the cells have been balanced before assembly and they spec 1C instead of a 3C rating. Also they derate cycle life from 2000 to 1750 cycles. Lead acid battery's cells get out of balance but since they only can be cycled 400~500 times you are tossing them before the cells get too far apart. When you build your own voltage pack, it is so easy to balance, why even trust some after market BMS that could fail and kill a cell.

Pictures are of the 8 cells, balancing with jumper leads (I banded my cells and didn't want to un-band for parallel balancing) and both the 50 amp 12 volt charger and the Variable PS used for the balancing.

Bob

From: Kirk McLoren <kirkmcloren@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Monday, August 26, 2013 8:54 PM
Subject: Re: [Electric Boats] AGM Batteries? >> LiIon usage rate??

none at the moment.

Looked and thought it didn't pencil well. Hoped for the usual decline with time.

Inflation is trumping that it seems.

As for battery management units. If you look around you will find groups that built various designs and some offer a printed circuit board.

You need to be a bit of a geek or know one.

Otherwise you are asking for trouble. Li cells can be broken.

"The further a society drifts from truth the more it will hate those who speak it."
George Orwell

From: Robert Lemke <robert-lemke@att.net>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Monday, August 26, 2013 8:08 PM
Subject: Re: [Electric Boats] AGM Batteries? >> LiIon usage rate??

Kirk,

Which cells are you using?

From: Kirk McLoren <kirkmcloren@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Monday, August 26, 2013 5:42 PM
Subject: Re: [Electric Boats] AGM Batteries? >> LiIon usage rate??

I would use a BMS

From: oak <oak_box@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Monday, August 26, 2013 1:25 PM
Subject: Re: [Electric Boats] AGM Batteries? >> LiIon usage rate??

Yes, on their "show all batteries" page, they have a 12V battery listed for $300, 11.2 - 16V, 60AH, max current < 1CA.

From your note, it sounds like the "CA" is the "battery capacity" - that makes a lot more sense than "continuous amps" - just trying to get my terminology straight here!

So... This is MUCH more reasonable. If I can buy a 24V 60AH lithium battery combination for $600 instead of $2500, that's a MUCH more viable option!!!! And if I can drain that battery at a continuous 25A rate for 2 hours, for 2000 cycles, I'd be thrilled!

Final question - as long as I monitor the voltage reasonably closely with a voltmeter, and charge with a trickle charger of 2A for a very long time, then I don't *have* to spend an amount equal to the battery cost on a BMS and high power charger, right???

From: Robert Lemke <robert-lemke@att.net>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Monday, August 26, 2013 2:32 PM
Subject: Re: [Electric Boats] AGM Batteries? >> LiIon usage rate??

You must have looked at a 12 volt battery instead of 3.2 volt cells. The cells are 3C for both charge and discharge so a 60 a-hr battery that you assemble with (4) cells can be discharged/charged at 180 amps.

Bob

From: oak <oak_box@yahoo.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Monday, August 26, 2013 12:09 PM
Subject: Re: [Electric Boats] AGM Batteries? >> LiIon usage rate??

Ok, so I took a quick look at the balqon web site, and see that they offer a 12V, 60Ah Li battery for $300.

HOWEVER, the web page lists "max discharge current" at "<1CA" - does this mean less than 1 continuous Amp???

I understand if that means I'll only get 60Ah at least than 1A continuous.

But what is the limit to how much current I can pull out of the battery for a continuous period of 1-4 hours?

From: Steve Dolan <sdolan@scannersllc.com>
To: "electricboats@yahoogroups.com" <electricboats@yahoogroups.com>
Sent: Monday, August 26, 2013 11:28 AM
Subject: RE: [Electric Boats] AGM Batteries?

John, John, John,

I'm running a bank of 12 AGM's for the last 8 years and they seem to be still going strong. I have noticed the last year some degradation thoug so I'm getting close and Yes I will go to LiFePo4's when it's time so will save for that day

Only $2500??

Replacing my 200AH 144V bank with LiFePo4's will run around $12000. The good news is Bob's post got me thinking about what size I really need.

Unlike cars and forklifts we are more interested in run time at a set speed in boats. Often I've found when talking to Car Guys they haven't a clue what we are up against when figuring out pack size since we normally maintain a set speed for hours running from point to point in adverse conditions, typically using 1C. I couldn't figure out why all of them where going with smaller packs. Bob has me thinking, I didn't consider the difference in Ah rates. Since I would only pull .5C (about 50A max at 6 knots) on a set of 100 AH LiFePo's I can get away with ½ the cost I was considering (200Ah)

I might owe Bob a commission… 8O)

Steve in solomons MD

I quit using flooded cells and went to AGM about 15 years ago for everything on the farm and in the boats as well. All the cars, tractors, and trucks. Much better batteries.

Roger L.

----- Original Message -----

From: oak

To: electricboats@yahoogroups.com

Sent: Monday, August 26, 2013 9:32 AM

Subject: Re: [Electric Boats] AGM Batteries?

John,

Maybe you aren't taking into account the major difference between usable a-hr capacity between AGM and LiFePO4. Since you quoted $200 per AGM, I'm assuming these are no bigger than 100 a-hr. When you calculate for usable a-hr, the AGM shouldn't be pulled down more than 50% DOD, the lithium can be pulled down to 80% DOD for 2000 cycles vs 400 for AGM. How they get their a-hr rating is also different, an AGM is pulled to 100% DOD at a 20 hour rate vs a lithium being pulled to 80% DOD at a 1 hour rate. If the AGM was pulled at a 1 hour rate, the the a-hr rating would be 1/2 of what it is at the 20 hour rate due to Peukert effect. An easy rule of thumb, what ever a-hr worked for your needs with lead, you can size the LiFePO4 bank at 1/2 the size for the same usable a-hr. 200 a-hr lead bank could be replaced by a 100 a-hr lithium bank. I have (2) 12 volt 100 a-hr Winston banks and each ran $440, so again, much cheaper than lead.

Bob

Bob,

If I did the full lifetime analysis, I'd probably agree with you the Li batteries were (long term) a better deal.

The issue is that for me to fund a single 24V bank, I'm looking at around $2500.

For my larger boat, it's $5000 for the 48V bank.

Even assuming $200 per 12V battery for AGM, it's sooo much more affordable on the budget, even if I know I will most likely have to replace the AGM bank a couple of times over the next 10 years. If I spend $1000 on AGM batteries every 2 years, I'd break even on a Li purchase after 10 years. Given that I typically don't keep boats for more than 2 years, certainly not as long as 10 years, it's just too long of a period for ROI. And there's no way I'd begin to expect to get much on resale of used batteries of any type.

If I end up sticking with my C-22 LONG term, and sticking with the electric motor LONG term, I might eventually try a Li pack as the primary battery for that boat, and keep a AGM or possibly even FLA as backup, just because it's soooo much cheaper. But it'll be a while before I can afford another $2500 of hobby bucks.

Again, I'm not disagreeing with you technically. I'd LOVE to try out a LI bank and see how well it really works. It's just the initial investment plunge that's holding me back.

John

From: Robert Lemke <robert-lemke@att.net>
To: " electricboats@yahoogroups.com " < electricboats@yahoogroups.com >
Sent: Monday, August 26, 2013 10:15 AM
Subject: Re: [Electric Boats] AGM Batteries?

John,

I used to use Odyssey AGM for my electric kayak for a 16~18 mile range. Last year I switched to LiFePO4 and the same weight in batteries, now have a 80 mile range. When you consider cycle life, these Winston lithium cells give the best bang for the buck.

http://www.balqon.com/store.php#!/~/category/id=0&offset=0&sort=priceAsc

Bob

From: oak <oak_box@yahoo.com>
To: " electricboats@yahoogroups.com " < electricboats@yahoogroups.com >
Sent: Monday, August 26, 2013 6:06 AM
Subject: [Electric Boats] AGM Batteries?

I recently noticed that a number of my deep cycle marine flooded lead acid batteries had been pretty much cooked dry from the Texas sun and the relatively moderate discharge cycles of the Torqeedo motors.

The batteries are Exide batteries, group 27, 160 reserve minutes. After re-filling the batteries, they would charge, but certainly won't take a load for very long. The batteries came with a 2 year replacement warranty - and at this point are less than a year old.

I went by the place where I bought them, and noticed they had Exide Vortex AGM batteries (group 24, 100 reserve minutes) on sale for $119.

I pulled two of the most problematic FLA batteries (would take a charge, but at less than 25A were dead in 5-10 minutes), and returned them. The store gave me a full refund, which I turned around and put toward purchasing two of the AGM batteries to give a try.

I have discovered that "maint. free" deep cycle batteries aren't. And they can't begin to take the heat of a Texas summer. However, the power density was ok for my needs. When they were new, and performing well, I could get over an hour run time out of them at moderate power (though this was still far below the rated 160 minutes at 25A rating!)

Will I get better results from the AGM batteries??

Is it realistic to expect with AGM batteries rated for 100 Reserve Minutes (which I understand means I can run them for 100 minutes at 25A load) that I can actually pull 10-20 amps for over an hour, and then charge them back up on a fairly regular basis?

John