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high and low current lithium cells
#1
can you tell me can you have high current, (from power tools) and low current (from laptop batteries) in the same pack. thanks
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#2
Yes you can as long as you design your usage and system based on the lowest denominator.
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#3
(05-05-2019, 06:19 PM)daromer Wrote: Yes you can as long as you design your usage and system based on the lowest denominator.

Thanks But I am new to all of this, I am trying to build a 7s 10p battery pack for an ebike I have 60 old laptop batteries which I have tested the same way HB does, The last 10 came out of power drill battery packs the mah are not as high which is correct if I am reading things right, Is this still ok to mix
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#4
Laptop cells in a battery for an ebike is generally bad decision because i guess you want some power out of it?
Above setup with laptop cells is recommended to have a continues lower than 270w and max 500W. Thats my preffered numbers.

If we talk about 1kW or even more go with high current cells or choose wisely from laptop packs that you know will take a beating...
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#5
laptop cells in an ebike is fine, as long as you plan creeping up to speed and going very slowly. The amp draw required for an electric motor is higher than what the laptop cells can deliver safely. Or, to keep the pack small and light weight.

Figuring for 200A load:
If you use high amp cells, you could do something like 14s80p (as an example) which could deliver 160-200A without a problem which comes to about 2 - 2.5A per cell
If you use low amp cells, you would need to triple the numbers of cells at least, so a 14s240p (0.8A per cell) or even quadruple to 14s320p (0.6A per cell)

As you can see, the size of the pack drastically increases when using low amp cells. Mixing these two types together for an ebike application still wouldn't be really feasible.
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#6
Korishan: Its not about the speed as such its about the concurrent and max current. The motor current do not "have" to be higher.. It can be a normal 250W ebike that is the most common and then above is fine
Secondly you state mixing is not feasible? In what sense? If you build based on lowest denomination its not an issue. If you fail to follow those rules you will hit a snag...
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#7
daromer: I agree it's not about speed. But, a 25% throttle motor will draw far less current than a 100% throttled motor. Hence, the reason why I said creeping up to speed, aka acceleration
Secondly I refer to feasible as in the size of the pack, nothing more. Using lower amp cells will require far more cells to accomplish the same task as high amp cells. Depending on fast and how far one wants to travel will determine the overall size of the pack. However, if it's only for testing a few 100 meters/ft, then the size doesn't really matter. But if they want to go 30 miles/km's at a decent speed, then pack size is very important.

That's why I said mixing them is fine, and is possible, but not really feasible for long usage, light weight, and high acceleration/speed. In the e-Vehicle arena, I'd want a battery pack that can deliver the highest amps possible with the smallest pack possible.
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Knowledge is Power; Absolute Knowledge is Absolutely Shocking!
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#8
wow I think I need to do more home work,
Both of your replies have revealed to me just how little I know.
A big thanks to both of you.
The ebike is 28v 500w that I was given to ride in the woods.
The original battery is totally dead and a new one will cost £200+, I have looked at this old battery all the cells have leaked can see corrosion under battery wrap and some are very rough, Think the battery has been frozen and thawed a couple of times, Battery was in a shed for over 3yrs 

Cheers 
Dan
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#9
I think someone had something in another thread I had commented on, that normal laptop batteries are not right for e-bikes. You need those from cordless drill power packs where they are rated for high continuous drain.

But what if you can get some high drain lifepo4 batteries, like those that can handle 50A, then pair it up with some normal laptop batteries? Will that work? The theory is that during high drain (ie. full throttle) the laptop batteries will drop in voltage faster than the lifepo4 so the lifepo4 will take more of the high current draw. In case it draws too much from the lifepo4, the normal packs can then supplement and/or start charging the lifepo4 when it's no longer in full throttle and the voltage bounces back up? Just a thought!
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#10
Could work but you most likely push the laptop cells a tad to much during the process. But someone could probably simulate it
The Ultimate DIY Solar and build place
YouTube / Forum system setup / My webpage  Diy Tech & Repairs

Current: 10kW Mpp Hybrid | 4kW PIP4048 | 2x PCM60x | 83kWh LiFePo4 | 10kWh 14s 18650 |  66*260W Poly
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