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Old 06-19-2009, 03:30 PM   #5 (permalink)
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Originally Posted by wjdennis View Post
The pack that will be supplying the constant 70A comprises 34 200Ah ThunderSky LCP cells. The back that will be receiving the 70Ah comprises 40 60Ah ThunderSky LFP cells.
If I understand this right, the 1st smaller high power pack essentially acts as a very large capacitor to supply power during the variations in required driving power. The 2nd larger pack would essentially then provide an quasi-average power over the whole drive.

Something to consider is that the current configuration of the controller as a buck converter will only allow you to charge a battery that is of lower voltage than the supply battery. Current flows from high potential to low potential and the controller only makes the supply voltage lower.

I forget the vpc difference of LCP vs LFP, but you show different cell quantities. To use a buck type converter, your LCP pack must have a higher voltage than the LFP pack.

If this isn't the case, there are other more complicated options such as a boost-buck converter. This'll have a boost circuit that'll boost the voltage higher than the supply voltage. Then, you'd have a buck stage to reduce the high voltage to the desired range.

Another thing to consider is that most buck converters require inductance in the output loop to keep the current from rising too fast. For a motor controller like Paul's, the motor has inductance (though, there's the problem with large motors not having enough inductance and only certain controllers can handle them. From what I've read, a curtis 1231c will blow within minutes when connected to a warp 11).

Anyway, if a battery is your load, you'd likely have to add inductance in order to control the charging current. It might be tough to find large inductors capable of handling 70A, but maybe you can make your own from thick wire and some iron laminates.

It's an interesting setup to think about and I'm sure you could get it to work with some engineering.
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