What kind of pouch cells are these?

[amberwolf]

Can someone explain how the battery Ah is calculated. I see cells that claim to be 25Ah but my whole pack was supposedly 45Ah and it has 20 cells.

If you have a pack that is more than 1P (like 14S2P, 13S6P, 20S8P, etc) then the Ah is calculated by multiplying the P number by the individual cell Ah. 14S2P made of 20Ah cells is 2P x 20Ah = 40Ah.

If the pack is only 1P, then the pack Ah is the cell Ah. 14S1P made of 20Ah cells is 1P x 20Ah = 20Ah.

If you don't know the P number and/or don't know the individual cell Ah, you can't calculate the Ah.

In that event, you can first fully charge the pack, then install a common RC Wattmeter, Cycle Analyst, etc., between the battery and the controller, then go ride until the pack is empty and shuts off, and note down the Ah (and Wh) readings the meter gives.

Note that most common wattmeters do not store the data so if it actually powers off it loses all the info, unless you follow the directions for it to install a tiny separate backup battery or aux battery that just powers the meter (and not your system). The Cycle Analyst remembers the data when powered off so it doesn't need this.

If you can't use a meter that stores the data and can't separately power it, then you will need to do the opposite test---ride around and discharge the battery till it shuts off, then install the wattmeter between the charger and the battery, and fully charge it. The Ah / Wh readings you get this way will be higher than the actual battery capacity because charging isn't 100% efficient, *and* because the system may take time to balance the battery, which uses extra power in the process, that will be counted in the Ah / Wh reading but isn't actually part of the available pack capacity. (this is why I recommend doing the first test instead).

 

[wice.lt]

Thank you for explanation. I didn't know about the parallel and Ah. So my cells are all in series making it just 1p20s battery. Honestly I don't even care if I lose capacity just as long as the cells are of better quality and I do want to stick with LiFePO4 just to be more stable. Now the problem is where to get said cells.

 

[999zip999]

Be careful those cells still hold a lot of volatile energy in them. And can catch fire no matter what chemistry they are. They're not just pieces of paper

 

[wice.lt]

Has anyone built a battery out of LTO cells yet? Reading about it and it seems it would be pretty good fit except maybe size.

 

[amberwolf]

They're a lot lower voltage, something like 2.5v full IIRC, and around 2v empty. So you need more series cells to get the same voltage. If your space for a pack is limited to the original size, you would have to reduce the capacity of the pack to fit the extra cells, and use physically smaller cells to do this.

I am not certain as it's been a while but I think LTO is also less energy dense, so you get less capacity for the same size cell (but I could just be thinking of the need for more series cells above).

Here's a few threads in the archived version of the forum discussing LTO packs; there are also discussions in other threads that don't have LTO in the title:

ES 1.0 Graveyard - Search

 

[wice.lt]

Reviving this thread. Looks like I need to get this whole thing rebuilt. I went through the trouble of 3D printing the pouch holders in hopes to protect the pouches but after installing the battery I realized that yet another cell is now dead... My question is, what would you guys recommend in terms of cells and where to procure them. At this point I only want to deal with "known" quality even if it's of a lesser Ah. I see that batteryhookup has the SPIM08HP and I like how they are screwed together and protected, but not sure if 8Ah would really be enough. I think I would like to have LFP for safety but maybe there is something else that you guys use for e-bikes. My battery compartment is 10.25x7.5x8.5 (LxWxH) and I would like to stick with 72V setup. Thanks for any suggestions.

 

[amberwolf]

How much current does your system require? (I might've missed it but didn't see it in this thread).

How many Wh/mile does your ride take under your conditions?



As long as you don't need more than 200A peak, and don't need more than 68Ah, then If you could fit it on there, I'd actually go with something like the ones I just posted in a different thread that I'll copy/paste here:


For large-format cell-modules, one of these

Samsung 24s Lithium Ion 6kWh Module - 3x 8s Modules

This is the best deal on never cycled, large lithium ion battery modules. For more accurate freight calculations we have packages of 1, 4, 8, and 16 modules. All will fit on 1 pallet. These modules were in storage and never cycled. Every battery we tested was right around full capacity. You can...

batteryhookup.com

gets you three 2kwh 8s (30v nominal, 33.6v full) "bricks". So you could have a 16s or 24s 4kwh or 6kwh pack with two or three of them. I'd leave them in their individual 8s bricks as-is, for the protective casings and physical pack support.

You could probably even use them without a BMS with a low enough load on them (whatever is well within the cell capabilities so they're not stressed), and not quite fully charging or discharging them. Just periodically check them for balance.

If it didn't cost as much for shipping to me as the 3 modules themselves, I'd get one of these to build a new 16s pack for the SB Cruiser trike (and have one module as a spare) (and I'd be using them without BMS, since the trike wouldn't put much more than 60-80A peak load on them for a few seconds at each acceleration, less than half their capability, and even less than that for most of the ride.
View attachment 342734
View attachment 342735

 

[wice.lt]

Thanks for reply. My controller is 150A so 200 would be more than enough. I am trying to understand what the dimensions of these are. You are saying to just buy one of the modules and use all 3 cells inside it?

 

[harrisonpatm]

How much current does your system require? (I might've missed it but didn't see it in this thread).

How many Wh/mile does your ride take under your conditions?



As long as you don't need more than 200A peak, and don't need more than 68Ah, then If you could fit it on there, I'd actually go with something like the ones I just posted in a different thread that I'll copy/paste here:


For large-format cell-modules, one of these

Samsung 24s Lithium Ion 6kWh Module - 3x 8s Modules

This is the best deal on never cycled, large lithium ion battery modules. For more accurate freight calculations we have packages of 1, 4, 8, and 16 modules. All will fit on 1 pallet. These modules were in storage and never cycled. Every battery we tested was right around full capacity. You can...

batteryhookup.com

gets you three 2kwh 8s (30v nominal, 33.6v full) "bricks". So you could have a 16s or 24s 4kwh or 6kwh pack with two or three of them. I'd leave them in their individual 8s bricks as-is, for the protective casings and physical pack support.

You could probably even use them without a BMS with a low enough load on them (whatever is well within the cell capabilities so they're not stressed), and not quite fully charging or discharging them. Just periodically check them for balance.

If it didn't cost as much for shipping to me as the 3 modules themselves, I'd get one of these to build a new 16s pack for the SB Cruiser trike (and have one module as a spare) (and I'd be using them without BMS, since the trike wouldn't put much more than 60-80A peak load on them for a few seconds at each acceleration, less than half their capability, and even less than that for most of the ride.
View attachment 342734
View attachment 342735

You know, I was looking at those awhile ago, and it seems like they're way too heavy. The datasheet shows the 24s 6kwh module as 70kg, or just over 150 pounds. Seems pretty heavy for Li-Ion, that's like LFP weight. Is all that extra weight in the steel enclosure?

 

[amberwolf]

You know, I was looking at those awhile ago, and it seems like they're way too heavy. The datasheet shows the 24s 6kwh module as 70kg, or just over 150 pounds. Seems pretty heavy for Li-Ion, that's like LFP weight. Is all that extra weight in the steel enclosure?

If you look at the images on the site you'll see there's a big rackmount enclosure everything is in, along with electronics and heavy cabling, etc. I don't know the weight on each part, but if it's not listed on the page you could ask them, and I bet they could tell you.

You might even be able to convince them to sell you just the 3 internal modules with the cells, and skip the enclosure they come in (but then you have to come up with your own connections, isntead of repurposing the ones that come in the rack as they suggest).

Thanks for reply. My controller is 150A so 200 would be more than enough. I am trying to understand what the dimensions of these are. You are saying to just buy one of the modules and use all 3 cells inside it?

Yeah, just use the the three modules inside the enclosure for 24s, or two for 16s, depending on the voltage you need. 24s is is "88v" nominal, and 100v full. If your controller, DC-DC, etc., can handle that, then you can direclty use the 3 in series. If you can only use 72v (20s), you can disconnect half the cells inside one of the modules and use just the other half (leaving all the cells physically in place).


There are plenty of other options, too--I just recommend using something already pre-built made from EV-grade cells if you can, because the cells will amost certainly be better quality and better matched to each other than those you can buy separately, and they'll be in a (usually) well-designed enclosure to keep them compressed (for pouch or prismatic cells) and protected.