Connect 48v 40ah lifepo4 to 4 3.2v 10ah lifepo4 (38120s) in

I own a 48v 40ah lifepo4 and I was wondering if I can connect in series a 3.2v 10ah (38120s) to my pack. and also can i connect 4 of them together to have a 12.8v 10ah pack and connect it in series to my 48v 40ah pack or do i need to make sure that i make the 12.8v pack has 40ah.
thank you

batteries used in series should have the same capacity. if you use a smaller one in series with a larger one then the smaller one is discharged before the larger one. if you continue beyond the LVC for the cells it will ruin them.

Yes, if you connect 40 ah in series with 10 ah, you will have a 10 ah usable capacity.

This could work for you, but you'd be connecting up the additional battery for just the hard part of the ride, then disconnecting again later before you used up the 10 ah.

I just bought a 48v 40ah lifepo4 and its hooked up to my 18 fet infineon controller. It keeps plowing my 40amp fuses. The battery is 120a instantaneous 80amp continuous. Should I just install a bigger fuse block? What size should I install? Thanks. I also am using a cycle analyst v3 and a 48v 1000watt hub from hallomotor.com

Well, if you want to put out 120A, use a 120A fuse. Although something smaller than that will probably work. Just match the Amp draw of the controller and you should be ok. I'd guess it's max is 80A or less. If it's blowing the 40A fuse by just connecting the battery to the controller, there's a problem with the controller or you're reversing polarity.

Yes, but he still needs to parallel enough of them to have 40 ah, before he connects in series.

40 ah in series with 10 ah = 10 ah.

8 of my lifepo4 packs were dropped when shipped and they have small dents in the corners. I was wondering if these cells are ok to still use. I have a 64v 40ah lifepo4 pack that I am making. There were 8 other damaged cells along with these, but I am replacing those ones. I wanted to use these cells because my pack started out a 48v 40ah pack but I am having replacements sent and I was hoping I could add these 8 cells to make 64v.
Thank you

This is a picture of the really bad ones that I am definitely removing and replacing. Or do you think I can use these ones too?

They aren't unsafe to use. But if they stink they are leaking and will die early. If no stink, they may still not last as long as the others or have the same capacity.

If you have lots of cells, use the best ones, but those dingers are still usable for something else, like lights or whatever. If no other cells to use, then use them.

I'm in two minds about this as usually you're not supposed to use damaged cells, but on the other hand LiFePo4 are not explosive even if damaged. Our LiFePo4 cells were tested (crushed, pierced, etc) and they smoked and had a quiet death. I would test them in a well ventilated area with an extinguisher close by because there's a good chance they're good

Well, I wouldn't go so far as to say they are good. But they should still function for a time, at less than the capacity and c rate of the undamaged cells. How much less depends on the extent of the damage. They might work "good enough" for quite some time.

I see no particular danger in using them, even if leaking. They just won't last long at all if the electrolyte vents from a hole in the crushed area.

most of the ping batteries were beat up like that on the sides. they should work.

Exactly, they'll work fine, just a bit less capacity. They will likely puff first, or leak, but till they do, use em. My best guess is you still get 2 years out of them.

But now that you know, take note if capacity suddenly drops.

at least they are on the end so not too hard to remove later. biggest problem is that when one of them fails because it begins to drain down faster than the others because of a short inside or something like that, then all of the pouches are soldered together in parallel first.

this makes it impossible to determine which one is bad so you have to unsolder all of them and the n test each of them separately to find the bad one. this is part of the reason i keep telling people to NOT combine the pouches in parallel first but to build a pack with the pouches connected serially, then combined in parallel through the sense wires.

you can monitor the voltage and when that one starts dropping below the average of the others, say down to 3.30V and the others stay at 3.38v then you will know one of them is shorted. that is when you can take it apart.

I found cells with the corner damaged as far into the cell as an inch. Surprisingly, if the cell wasn't puffed it seemed to hold normal capacity and had normal resistance.

If the corner is bent and the cell feels a bit puffy (The wrap isn't tight) than you most likely will notice capacity loss.

What you're going to have to do is use a lipo charger to check resistance and capacity vs the other cells. You can charge each individual cell by attaching to the + and - of the cell or the balance leads if they are connected to the pack. But that is the only way to tell how far gone they are and if they are worth using.

Take a look at this bent up lipo pack. I didn't support it well in my battery compartment and saw the huge bulge when I removed the pack. I threw the pack on the side because I thought for sure it needed a cell replacement.

I ran the pack through my charger and it help capacity just fine. I put it back in my bike for a over a month and pulled all my batteries recently. This pack had normal capacity as the others. The bent up cell showed ever so slightly weaker cell output, it would hit 3.7 volts when the others were around say 3.71, but would quickly return to normal cell output. Resistance was surprisingly the lowest of all the cells in the back at around 2 ohms, while others were between 2.2 & 2.8.

This proves that highly bent up packs like this one may not be a problem at all and hold full capacity. The main key seems to be air under the wrap, if you feel a loose wrapper and air under the cell pouch it usually needs replacement. If it is still tight, it doesn't matter that much how mashed the cell is.

You would be surprised just how bent this cell is and it still seems to hold full capacity with no increase in internal resistance.