Lithium ion battery bank advice. Series/parallel combo.

Hello folks. I been reading and reading on this topic here and there is tons of info. I'm not new to fundamentals of electricity by any means, but I'm just smart enough to be dangerous. I have a currie E-zip 400 I got for free and it was missing the batteries. It has the xk-022a controller - 30amp 24vdc. 400w motor . Old brush type I guess. I already took an old battery out of a hoverboard. It's 36vdc and 4AH. I rigged up part of the the hoverboards circuit board to plug the charger and battery into. So the battery is being charged separately from the bike. It worked pretty well but I found that if the boy keeps on the throttle it will shut off. Long story short I found out that it wasn't the battery being totally dead and the controller stopping it for undervoltsge or over current, it was the actual BMS in the battery pack. Dropped to 20v under heavy load and stopped output. So I started to play around. I made a 60 volt battery with 2 hoverboard batteries. That a big NO. I had a od razer junk controller around and tests it out on that. You can guess what happened. Cap blew. Motor started running wide open. Anyways. I researched better and have made a battery cluster- F$#? Out of 4 snap on cordless tool batteries. And also connected to the lithium ion 36v 4ah hoverboard battery. Part numbers of HB battery is jetech JT-BC200-09. 36v 4 ah 244wh. Thesnap on batteries are part numbers CTB8172. Okay I'll try to explain this as best I can. There are 4 cells in each snap on batt. 2 sets of cells in series 7.42 v each. The tools connect the 2 series cells together again in series when the battery is plugged in. So pretty much I have 8 7.42vdc batteries to connect. I parallel the 2 sets of 7.42 volts in each battery together. And then connected in series to a second one. So now I have 2 banks of batteries that are about 16 volts and 4 ah each. (I hope) I connected them in series. Now I have 1 big battery that is 32 VDC and 8 ah. Is this right? My main question is I'm not quite sure that the c rating is or how to tell for sure if this will be enough juice to do any good or if it's just gonna go dead. I need a little help with the math and ohm's law. I also have that other 36v battery from hover board I can connect to the one I made in parallel. That would keep it at around 36volts or so. The hoverboard battery charges to 40 volts with it's charger. Is it safe to use that charger with this new cluster of batteries? I haven't blown one up yet. Don't really wanna. Ohhh. Yeah I know. I'm a tight ass. 5hsts why I don't just buy new batteries. I know the controller wi take the 40 volts. I took it apart to look at the cap voltage but is filled with glue shit and you can't get in it. Lemme know what you smart fellers think. Thanks.

Snayke62 said:

Thesnap on batteries are part numbers CTB8172. Okay I'll try to explain this as best I can. There are 4 cells in each snap on batt. 2 sets of cells in series 7.42 v each. The tools connect the 2 series cells together again in series when the battery is plugged in. So pretty much I have 8 7.42vdc batteries to connect.

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Is 7.42V a spec or based on a voltmeter reading? 2 fully charged batteries (assuming lithium ion), will be 8.4V fully charged, 7.2V nominal. 7.42 is sort of an odd figure. Snap On appears to be using 3.6V as the nominal rating per cell (others use 3.7V as nominal, but for this case I'm assuming 3.6V throughout). Using 3.6V, the pairs you described would be 7.2V nominal.

Snayke62 said:

I parallel the 2 sets of 7.42 volts in each battery together. And then connected in series to a second one. So now I have 2 banks of batteries that are about 16 volts and 4 ah each. (I hope) I connected them in series. Now I have 1 big battery that is 32 VDC and 8 ah. Is this right?

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Based on the battery with the part number your included, it's 14.4V 2 Ah. So 4 - 2Ah cells in series. Note that connecting cells in series does not multiply the Ah, like your math indicates. 8 cells in series (8S) would be 28.8V nominal, not 32V (not sure how you got to 32V, even using your numbers, which would be 7.42 x 4 = 29.68V). Your configuration would be 28.8V 4Ah.

Snayke62 said:

My main question is I'm not quite sure that the c rating is or how to tell for sure if this will be enough juice to do any good or if it's just gonna go dead. I need a little help with the math and ohm's law. I also have that other 36v battery from hover board I can connect to the one I made in parallel. That would keep it at around 36volts or so. The hoverboard battery charges to 40 volts with it's charger. Is it safe to use that charger with this new cluster of batteries?

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If your hoverboard batteries are 36V nominal and lithium ion, that's 10 cells in series. If you use a charger made for 10S on an 8S battery pack, sit back and watch the fireworks. The fully charged 8S comes to 33.6V while the 36V charger puts out 42V.

Be cautious when paralleling any lithium batteries. They need to be within a tenth of a volt of each other before paralleling them.

I apologize my math figures were just what the meter read and what the battery said. Inside these batteries are 4 INR18650 green flat tops. 2 were connected in series hardwired inside the battery pack. So there were 2 sets of 2 18650 in each battery. And I connected them in parallel. I did this to 4 battery packs. So I had 4 batteries that were reading approximately 14volts or so. I connected 2 sets of 2 together in series. So then there were 2 battery packs reading about 28-32 volts. I'm just using a fluke meter at this point. Then I connected the 2 battery packs together in parallel. It was an experiment and I took it back apart so I didn't destroy my batteries. This is the first time I've ever attempted anything like this. I wanna build a battery that will run this thing at 32 or 36 volts. One that will last a while riding around town for my son. Right now he has to baby it and go east or the battery shuts down. And you have to cycle the power switch. I'm trying to revive the 2 12volt 7ah sealed lead acid the other razor took but they are so old and sulfated I don't know if I can get them out of it. They were at .06v when I got them. And wouldn't take anything. I got them up to 10 volts now but I doubt they will ever hold it or have much capacity

]I know it's confusing. Lemme see if I can get a photo of it on here. There are 4 18650 inside the pack. 2 on each side of this pinout. I'm not going to use these. I don't have the correct testers and equipment to build a lion battery pack from what I see on the YouTube university. I just need a bigger damn battery pack I guess.

What I do have is these 2 battery packs. Both from old hoverboards. One is 36v 4ah. Other is 24v 2.6ah. I know I cannot parallel these together. And the voltage created in series would be too much. Is there a safe way to use these together to run the ezip? I don't wanna bypass the controller and do all that crazy stuff either. Use 2 controllers tied into the 1 throttle? It's variable speed throttle. I also have the good motor off a razor mx350

The 36V pack contains 20 cells. The 24V pack contains 7 cells. You have 27 mismatched cells. If you fully deconstruct the packs, you could theoretically configure them as 9S3P, or 33.4V. But the cells will be mismatched, since 7 are 2.4Ah, and 20 are 2Ah, so there's no combination that will get you to 32V or 36V. The only configuration that might work is 7S3P, using 7 cells from the 24V pack and 14 cells from the 36V pack; with 1 - 2.4Ah and 2 - 2Ah cells for each parallel group, with 7 of those groups in series. That would be a 24V 6.4Ah, if the cells were new. It's not advisable to use mismatched cells to build a pack, so I wouldn't do it myself. If you decide to do this, make sure you charge the pack outside.

Better off picking up another 36v and painting them.

Make sure your controller is rated for 36v also.