continuous discharge current and peak discharge current

[adrianlit]

hi im looking at getting a lifepo4 battery custom built in china for a future e bike im developing im looking at 48v with very high ah (whats the highest best ah for 48v) and a 96v with the same high ah capacity...can anyone give me advice on what specs to set for the best performance and range? the motor my bike will be based on is a gng 60v650watt mid motor the companies in china who have got in touch have asked me the continuous discharge current and peak discharge current for the battery? and I keep seeing the C rating for batteries is it the higher the no the better the battery,i know some people on here will ridicule me over my lack of battery understanding this is why im doing this posting so I can put a sample order in for the right spec, can anyone tell me the specs I need to send them? as i wish to place a order asap so I can start testing the prototype ive built asap

 

[CellBalance]

Ask for the specifications sheet on any battery you're dealing with. It should give "standard" and "peak" charge and discharge (standard "C" and peak "C") values.
And for what it's worth:

C value = max amps/ ah Capacity of cell
"20c" simply means that the battery's discharge current is 20 times the amp-hour rating.
If your battery's amp hour rating is 12.5 then 12.5 x 20 = 250 amps.
A battery discharged at a 20C rate will be discharged completely in 1/20 of an hour or 3 minutes.

or max amps = Ah x C ; C = Amps/Ah

Note that there are different C values for Charge and DIScharge and it's not commonly mentioned in any tutorials I've seen. Don't charge with too many amps or you'll cook your batts.
John

 

[dnmun]

who is asking you these questions about the battery discharge rate? have you evaluated the current you will need to make your bike perform as you want it to? or the voltage you will use for the controller?

 

[adrianlit]

its the e battery company who are asking me figures I shall e mail them for the spec sheet

 

[dnmun]

i have never heard of e battery. do you have a link?

 

[wesnewell]

To know the minimum discharge rate needed from the battery pack, you need to know the max amp rate of the controller. The motor has nothing to do with it. A 10ah 1C battery pack is good for 10A (10x1). A 10ah 20C battery pack is good for 200A (10x20). If your pack is going to have a BMS, then it should give its max discharge capability, and the battery pack should be able to provide that many amps too. IOW's, if you have a 30A controller, both the battery pack and BMS should be capable of a 30A output.

 

[dogman dan]

To figure this out, the basic thing you need is to know the amps rating of your controller.

Say it's 20 amps, then if you get a 2c battery, 20 ah should be plenty. My rule of thumb has been to cut whatever discharge they claim the battery will do in half.

So a 2c battery is capable of 40 amps max, assuming it's bms allows it. If you ride 30 mph, that tends to take at least 1000w. 1000w is 20 amps of 48v. So you'd cruise at 30 mph using 1c. That should work fine. If you ride above 30 mph, the amps it takes really increases, and then you require a much bigger battery to handle your amps draw at cruise speed. 40 mph will take about double the amps that 30 took. Or more.

But if you have a 40 amps controller, you'd need at least 30-40 ah of the same type of cells. FWIW, the largest battery that is easy to carry on a bike is 36v 20 ah, 48v 15 ah, or 72v 10 ah. Any more is a royal pain in the ass, and will affect the way the bike rides way too much, unless it's a cargo bike or trike.

Once you get into 40 amps controller, you really need to look into batteries with much better than 2c discharge rating. And if you will ride fast, ( like at 96v) you just can't carry enough to go very far at that speed without it being awkward in some way. You can carry enough to have that speed briefly, and then still do most of your longer ride slower though.