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

This is another reason I use the single cells at the capacity (a-hr) that I want and assemble a series string for the desired voltage. If you have a regulated variable power supply you can get that first balance dead on and probably never need a BMS for balancing. I would though, hook up to each cell a voltage monitor with alarm (for your 8 cell 24 volt pack you want to monitor each cell's voltage. These are available for <$30 at hobby stores). Set a low alarm for 2.8 volts and the high alarm for 3.7 volts, this will keep every cell happy.

But back to the regulated power supply for balancing your pack before use. Run all cells down to about 2.8 volts then hook them all in parallel (when you order your series buss bars just buy twice as many for this parallel connection) and then connect the PS set at 3.8 volts and whatever amps it can put out. This will bottom to top balance your cells, making a BMS not needed. I did this 18 months ago, still balanced +/- 0.03 volts. Depending on your cell's capacity and the output of the power supply, this could take 20~40 hours. I balanced (8) 100 a-hr cells, so all those cells in parallel equaled 3.2 volts @ 800 a-hr. I think my PS can put out 10 amps, so balancing of all the cells took about 3 days if memory serves.

Bob

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