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I have a scooter with 48v/1000w motor, now I am trying desperately to find a lighter lithium battery but I'm constantly told it will be an impossibly expensive endeavour since lithium is very costly, and for my needs I would be looking at nearly £300-400. Recently though I have being directed to some cheaper possible choices in RC batteries, but I need some advice please.

I can either buy 4 Turnigy 14.8v 5000mAh and wire 2-series 2-parallel for 59v/10Ah, a higher voltage is fine as my controller can handle it.

Or I can buy 6 of these zippy 7.4v 5000mAh and wire 3-series 2-parallel for 44.2v/15Ah.

There are also some Turnigy with 22.2v 5000mAh.

Apologies if I have repeated some questions, but I am told this will work if I balance batteries properly, please can this work?.

Battery 1 http://www.hobbyking.com/mobile/viewproduct.asp?idproduct=15521

Battery 2 http://www.hobbyking.co.uk/mobile/viewproduct.asp?idproduct=8578

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closed as off-topic by uint128_t, PeterJ, Daniel Grillo, Ricardo, W5VO Apr 14 '16 at 6:26

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    \$\begingroup\$ Your math is horribly wrong somewhere. For the 14.8V with 2 in series, you only get 29.6V. For the 7.4V with 3 in series, you only get 22.2V. \$\endgroup\$ – JRE Apr 12 '16 at 12:06
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    \$\begingroup\$ However you slice the stacking, you need to figure out your kWh. I haven't seen your other questions, but it seems like you're looking for about 1kWh of energy. Even Tesla isn't going to be able to get that for less than a few hundred dollars. \$\endgroup\$ – scld Apr 12 '16 at 13:59
  • \$\begingroup\$ You appear to ask essentially the same question repeatedly. You can edit this question and fix it; don't ask a new one. You know the motor is 48V, 1000W, so it needs batteries able to supply 20A continuously. Further, you say (in earlier questions) the existing battery is battery 12Ah. Do you want the new supply to be 12Ah? The Physics: aim for 48V, continuous supply of 20A, and capacity of 12Ah. What is the obstacle to proposing an arrangement of batteries which satisfy that in your questions? EE.SE and the web answer LiPo battery questions; maybe read them first, then clarify your problem? \$\endgroup\$ – gbulmer Apr 12 '16 at 14:56
  • \$\begingroup\$ Do not use Lithium batteries for Rc models! they are designed for the discharge rate of Model Car Motors! not the discharge rate of a scooter motor, you will most likely kill them, this is from experience as a racer of electric touring cars. \$\endgroup\$ – Alex Apr 12 '16 at 16:21
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    \$\begingroup\$ @Alex: You need to account for the battery's C rating. If he's buying 5000mAh batteries to run a motor with current draw of 21A (1000W/48V) then he needs batteries with C ratings of at least 21/5 (4.2). Batteries that size are rated at least 20C so he can pull up to 100A. Note that if he does pull 100A the batteries will run hot. The 20C simply means that the battery will not be destroyed (solder melt or battery explode). I'd personally limit it to around 80% of rated draw. \$\endgroup\$ – slebetman Apr 13 '16 at 6:35
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It can be done with proper batteries, but the ones your looking at are for toy cars and planes etc and just don't have the capacity etc that you require.

I replaced the lead acid batteries in my lawn mower with used lithium batteries from a Nissan Leaf electric car.

I had to disassemble the battery and rebuild it to a 24 volt, 30 Ah battery. It is actually more like a 22.2 volts nominal and 25.2 fully charged, but it works to replace the former 24 volt, 18Ah battery. The lithium battery can supply 120 amps sustained so easily meets your needs. MY motor is 24volt, 1200 watt. So you would just need two of what I built, Which is a 6S1P battery.

With that battery you could tow a trailer full of rocks behind your scooter!

By the way, the battery cost $150.00 US and weigh 1/3 the old lead acid battery.

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As Brian Drummond and JRE have already explained, your calculations seem to be wrong. Maybe you should read some more about battery circuits and how to calculate voltage capacity?

Further, you can edit your question, and update it, rather than asking it again.

I apologise for using some 'shopping' information in my answer, but it seems to be a direct and simple way to deal with part of the underlying motivation for the question. By using ball-park costs, I think this answer can be more helpful.

The motor requires 48V, 1000W, and hence about 21A.

Assuming a LiPo voltage of 3.7V is okay, though it can be 4.2V when fully charged, so be aware of this.

It needs about 48V, and so
48v/3.7V = 12.97, i.e. 13 cells, or 13S
48V/4.2V = 11.43, i.e. 11 cells, or 11S

So 12S is near. It is divisible in several ways, and so it is a reasonable voltage and cell count basis.

Be aware, that would be a peak of 12 x 4.2V = 50.4V, so check your bike's capability.

12V SLA batteries can exceed 12V when fully charged, so it may be okay, but check the spec of the motor-control on your bike. A quick check with a multi-meter to measure the existing voltage across the fully charged SLAs would be a sensible precaution too.

If there is any concern, use no more than 11S, though that is less convenient to build from multiple batteries.

A LiPo able to supply approximately 12Ah, is likely to be able to discharge at significantly more than 21A, but also bear this discharge current in mind when selecting the batteries.

There are lots of web sites selling LiPo batteries. As an example I looked at HobbyKing which has a battery selector.

I haven't found a 12S with anything close to 12Ah. YMMV on other purchasing sites.

So I tried 6S (22.2V) with a capacity over 6Ah. This would need two in series to reach, approximately, 48V. That battery selector found about 8 candidate batteries, over 10Ah, with a high enough discharge rate. For example, I found a 6S 12Ah LiPo for about £90 inc VAT. Again, YMMV.

So, I think it is straightforward for you to find candidate batteries.

However, it is very important that LiPo batteries are never over discharged.

You will need to check that your bike can protect the batteries. If it comes with SLA, then it might not have that capability. Then you will need to build or purchase a LiPo battery-discharge protection system, capable of handling 12S voltage and, at least, 1kW.

You will also need a good battery charger able to recharge 6S 12Ah LiPo batteries. The batteries are likely capable of being charged at over 1kW. I couldn't see such a beast at HobbyKing. The best I saw was 300W, and that was about £100.

Summary: I agree with Brian Drummond. Batteries with comparable capacity to the existing SLA's, plus discharge protection, plus battery charger, is likely to be in the £300+ area. Looking at the cost of batteries alone ignores significant costs, and hence is not realistic.

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Six of those 7.4V batteries in series will give you 44V, but still only 5 Ah.

Which will supply your 48V/1000W motor with 44V and 20A for ... about 15 minutes.

If that's adequate for your needs, go ahead and try it.

To match or exceed the original 12Ah SLA battery you need 3 of these stacks, either in parallel, or switching between them, and that's 18 batteries at £11 each. By the time you've sorted out charging arrangements for this mess, you're back to the estimates you were given before.

This is the third time you have asked essentially the same question and got essentially the same answer.

If it could be done cheaper, it already would be.

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  • \$\begingroup\$ Ok, so it's really not as easy as I thought. \$\endgroup\$ – Stefan Gill Apr 12 '16 at 15:35
  • \$\begingroup\$ It's still potentially a worthwhile exercise. If you're willing to spend time and - yes, money - you'll learn a lot. The gains will be small - a couple of kg weight saving, a few % efficiency - and there's some risk - you'll probably kill a battery pack or two, but if you do it right you'll end up with experience that could be valuable or marketable. But if you just want a working scooter - forget it. \$\endgroup\$ – Brian Drummond Apr 12 '16 at 16:48

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