# Need Help: Pouch Vs. Prismatic



## rainmaking (Jan 15, 2013)

First Post!!
My application is not for a car but it may lead to that as I have sworn my next car will be electric...
My brother and I are trying to engineer a battery storage system for our boat. The loads will be things like electronics, microwave, possibly hot water, and air conditioning. We plan to have two identical 12V banks that can be charged by the engine alternators (twin outboards with 40A alternators), a small PV system (~20A), and two Li-compatible inverter-chargers (looking at Victron and Mastervolt). We plan to maintain the two banks in isolation unless one is so dead we must parallel it to start an engine.

We have proposals from a couple of advertisers on this forum for the following batteries:
(A) pouch cell system--(2) banks of (4) each 12V packs comprised of 80 10A cells (640 cells total, 1600Ah) with a BMS system that connects to each cell
(B) prismatic cell system--(2) banks of (4) each 3.2V prismatic cells, either 700Ah or 1000Ah. If we can fit the 1000's we will choose these. No BMS, we would monitor voltage of each cell and perhaps attempt to balance them before cranking the main charger when back at the dock.

You guys have lots of experience in this forum that could help us choose. The salesman in the pouch cell case is adamant that it is a better solution but we are concerned about all those connections shaking around on a boat in a marine environment, even though they would be located in the climate controlled cabin. Even with the 1000Ah cells the prismatic solution is significantly less costly.

Advice??


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## Elithion (Oct 6, 2009)

Prismatic. 

Or maybe large cylindrical.

Pouch cells are a bear to install, protect and connect together.

The main reason to use pouch cells is if you need high power cells (discharging in 15 minutes or so). For a boat, you're discharging in hours, not minutes.

> we must parallel it to start an engine

Ouch! Li-ion batteries are not very forgiving of connection in parallel if they are at different state of charge. Avoid that at all cost. But, if you're going to do it regardless, do not use high power pouch cells, for your safety and the integrity of the boat. (I have seen a beautiful catamaran totaled when the captain connected two Li-ion battery banks in parallel.) If you connect high power pouch cells in parallel (different SOC) an immense current will flow between them, and a lot of heat is generated.


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## rainmaking (Jan 15, 2013)

Thanks Elithion!

Yes, hours of discharge...perhaps <0.1C on average, and 0.2C peak. Can we get away with the series charging arrangement with occasional balancing like I described or will the cells drift too much?

I realize we would need some kind of protection to prevent a current flow above the rated charge in the paralleling case. The trick is to isolate the battery from the motor while starting it so your 'jumping' current source isn't sucked away from the starter. Worst case I guess we could use some kind of DC/DC converter to charge the dead bank, or even supply the charger on the dead bank with the inverter on the bank with capacity. In essence couple them on the AC side. I think we will figure something out.


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## Elithion (Oct 6, 2009)

I suggest you connect cells directly in parallel, and then 4 of these sets in series.

I also suggest you get the MiniBMS (from CleanPower): it's easy to understand, and the limitations of an analog BMS are pretty moot when all you have is 4 cells in series. All you need is 4 cell boards and a master (about ~ 82 $). But you must make sure that it is wired so that it can stop charging, and that you can hear its buzzer when any set of cells is empty, else you'll damage cells.

If you top balance the cells, and with only 4 cells in series, and if the charging voltage is regulated, you probably can get away with not controlling charging. On the contrary, preventing over-discharge is what will matter more in your case. So, mind that buzzer!


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## rainmaking (Jan 15, 2013)

Elithion said:


> I suggest you connect cells directly in parallel, and then 4 of these sets in series.


Sorry, I don't understand which cells would be in parallel? With the prismatics (700 or 1000Ah) we would only have 4 cells per bank.


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## Elithion (Oct 6, 2009)

rainmaking said:


> Sorry, I don't understand which cells would be in parallel? With the prismatics (700 or 1000Ah) we would only have 4 cells per bank.


You're right. Please disregard. (I was confused because usually people get 100 Ah cells, or so, and then connect them in parallel.)


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## wessss77 (Jan 4, 2013)

what if they were pouch modules with BMS included and installed? I have seen these with greater than 4000 cycles and still at 90% which is like twice what the prismatics are providing. Won't the discharge only occur on an as needed basis?


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## rainmaking (Jan 15, 2013)

wessss77 said:


> what if they were pouch modules with BMS included and installed? I have seen these with greater than 4000 cycles and still at 90% which is like twice what the prismatics are providing. Won't the discharge only occur on an as needed basis?


Wes,
That is one of the options we are comparing as outlined in my original post. I am not clear what your question means, but system reliability trumps theoretical cell cycle capacity in our application, by a long shot. We will be lucky to be able to put 200 cycles per year on the system and most of those will not be deep cycles. At our low charge/discharge rates we would likely have pretty extended life anyway.


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## wessss77 (Jan 4, 2013)

Ahhhh okay my bad


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## Ziggythewiz (May 16, 2010)

wessss77 said:


> I have seen these with greater than 4000 cycles and still at 90% which is like twice what the prismatics are providing.


Where did you see those?


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## wessss77 (Jan 4, 2013)

Ziggythewiz said:


> Where did you see those?


check these out Ziggy...http://www.electriccarpartscompany.com/Bestgo-Pouch-Cells-Overview_p_265.html


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## Ziggythewiz (May 16, 2010)

Interesting...but they say "a cell randomly picked" while the spec says the same as everyone else using LiFePO4, so how many did they need to randomly pick to get that good of a result?


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## Electric Forklift Guy (Dec 13, 2012)

Elithion said:


> Prismatic.
> 
> Or maybe large cylindrical.
> 
> ...



Just use isolation diodes

Two of these on each positive post (Vishay 150k10va) and you can parallel a dead battery to a fully charged one of you want .

Just remember all the loads go AFTER the diodes but the charger goes directly to the positive terminal on the battery.


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## rainmaking (Jan 15, 2013)

Electric Forklift Guy said:


> Just use isolation diodes
> 
> Two of these on each positive post (Vishay 150k10va) and you can parallel a dead battery to a fully charged one of you want .
> 
> Just remember all the loads go AFTER the diodes but the charger goes directly to the positive terminal on the battery.


Sounds good, but if the alternator and starter wires are combined out of the engines, how could we hook the diodes so the alternators could still supply charging current, or if we were just temporarily paralleling, to provide a load for the alternators?


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