Lipo Battery Packs in Parallel Noob Question...

bakaneko

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Okay, I think I am going to make an experimental 36V e-bike system and want a cheap battery to test as a start. I've seen these 36V 4.4aH scooter/hover board batteries for about $40-50. I would like to just combine the two in parallel to get a 36V 8.8aH battery. The battery packs seem to have a BMS built in. So, can I just hook two of these guys up in parallel and then charge with a 42-43V charger? Thx :confused:

https://www.ebay.com/itm/36V-4-4Ah-Lithium-Battery-For-6-5-7-8-Board-2-Wheels-Balancing-smart-board/112747210673?hash=item1a4041e7b1:g:D6wAAOSwVqlaJfIe
 


Frankenstein

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With on board bms you can parallel them no problem and charge at the same time, I don't know if a 42v charger is what you want unless that's the max voltage out the pack when charged.
 

bakaneko

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Thx Frankenstein. The last time I had an electric bike I was using 60lbs of SLA batteries so its been a while, LOL. The battery has a peak voltage of 42V and a charging voltage of 43.2V. But, I heard if you charge it less than peak voltage you get better battery life and more cycles. So, I was thinking maybe 95% to 40V or a little lower... I dunno LOL :p
 

GreenMantis

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With on board bms you can parallel them no problem and charge at the same time, I don't know if a 42v charger is what you want unless that's the max voltage out the pack when charged.
That's exactly how that works. With lithium batteries, the stated voltage is kind of a funny issue. Lithium cells are stated to be 3.6 or 3.7v, but what that really means is they are considered fully charged at 4.2v, and fully discharged at 3.0v, and can't EVER go outside that range, or the battery will be damaged, which is why they have to have that protection circuit. S0 a 42 or 43v charger is fine for a 10S pack.
 

Alice

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Thx Frankenstein. The last time I had an electric bike I was using 60lbs of SLA batteries so its been a while, LOL. The battery has a peak voltage of 42V and a charging voltage of 43.2V. But, I heard if you charge it less than peak voltage you get better battery life and more cycles. So, I was thinking maybe 95% to 40V or a little lower... I dunno LOL :p
Yes, you are right that, instead of 100% full cycles, light cycles are better to the battery cycling performance. But normally, 40V is too low voltage to charge a 36V battery pack, 42V need to be the charging voltage, and the battery pack can be recharged timely before being fully dis-charged.
 

Alice

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This 36V 4.4Ah battery pack showed in the above eBay link looks great, made of Samsung 18650-22p and smart balancing protection PCB, which should be suitable for 2pcs connected in parallel and charge with a 42V-43V charger.
 

bakaneko

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i bought two of them over the weekend to make a 36v 8.8ah pack. i will report back when i can. rated discharge is 15A, max continuous 20A, max 30A. supposedly made from samsung 2200mah 18650... we will see i guess
 

bakaneko

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Just an initial update, I got the two battery packs today (2X 36V 4.4aH) and put them in parallel to make one 36V 8.8aH pack. I did a quick test at 1 mile at half to full throttle and voltage drop was like 0.1-0.2V. I think professionals measures the health of a battery pack by voltage drop, aH draw, and resistance (ohms)? I don't have one of the battery capacity draw tools (or whatever its called) but I do have a multimeter.

Any ideas how to get an accurate measure of this battery pack. I think the estimate is 1-2 miles per aH at full throttle. Peak voltage is 42V and 26V is the low voltage cutoff of the battery. I can't seem to find the cutoff voltage for the motor controller? Is it slightly below 36V?

Also, this bike is going to be a working prototype for a new ebike concept I want to build and in addition I want to have a real assisted bike. On my 4-stroke HS-142F, I basically use it like a moped with minimal pedaling. For the ebike, I actually want to use the gears and pedal most of the time...

Also, the point of this post is finding a good source for low cost batteries. This 36V 8.8ah pack cost me about $100 ($90 batteries + $10 charger). Looking at some other ebay comments, one guy made a 22 aH pack for $225. If I were to buy one of the 36V 10aH battery packs on eBay it would be $200-220. This is about a 40-50% discount from retail eBay battery packs and probably a 60%+ from branded retail battery packs. The battery pack uses Samsung 18650s.

So, I guess I will charge to full ~42V and then half pedal/throttle and maintain about 20 mph and see how many miles I can go until the voltage falls to ????. Any one know...
 

greenjon

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If it were me, I think I'd hook the battery packs up to three 12 volt lights in series and put an ammeter in series with that also. Then I'd stick a video camera in front of it and walk away. Sometime after the light went out I'd check the video to see when the light went out. That would tell me I could draw X amps for T amount of time. In other words, it'd measure the actual aH at that particular current draw.

For even more info, I'd put a voltmeter in parallel with the load and make sure the camera could see it. Then by reviewing the video I could plot the voltage drop over time.
 
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