Capacitor in battery pack

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rad
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Capacitor in battery pack

I have a 24 volt EV Global bike, 12 amp SLA batteries. The battery pack has a capacitor in it, next to the electrical outlet.

Question: What is the purpose? Does it even out current spikes or give the motor a surge when turned on?

Also, I was planning on putting a second battery pack on the rear rack and wiring them together for 48 volts. I would also use a new motor and controller, probably Crys 400 series.

Question #2: Someone suggested that I run the two capacitors in parallel to get the same resistance. Should I do this? Do I need them at all?

Thanks in advance,

Rad

rad
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Re: Capacitor in battery pack

Gotta be some electrical geniuses out there.

Anyway, I checked the wiring diagram in the download library and the capacitor is wired in parallel with the battery. That being said, it seems that it would not affect charging of the batteries, but would discharge when the power is turned on. I'm guessing the system needs a jolt to start up.

The Crystalyte system doesn't use a capacitor or it is part of the controller. I am leaning to take them out when I go 48 volt.

Any thoughts?

rad

antiscab
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Re: Capacitor in battery pack

The Crystalyte system doesn't use a capacitor or it is part of the controller. I am leaning to take them out when I go 48 volt.

Dont remove the caps.
the input caps to the controler serve two purposes:
1) limting voltage spike on gate turn offs caused by trace inductance
2) reducing battery side current ripple

the removal of the caps will at best increase the RMS current on the battery side, at worst result in failure of the powerstage due to voltage punch through of the FETs.

if you have to replace the caps, you want at least the same capacitance, with at least the same ESR measured at the controller switching frequency (usually around 15khz).
most (good) capacitor data sheets will give this information, but it wont be listed in catalogues.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

rad
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Last seen: 9 years 7 months ago
Joined: Friday, April 24, 2009 - 07:30
Points: 9
Re: Capacitor in battery pack

Thanks Matt,

The wiring diagram lists the capacitor as C22, 4700uF.

Can I just leave them alone, one per battery pack or do I need to buy one specifically made for 48 volts? I would be running the two battery packs in series to get 48 volts.

rad

antiscab
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Last seen: 2 months 2 weeks ago
Joined: Saturday, July 7, 2007 - 23:55
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Re: Capacitor in battery pack

two in series (one for each 24v pack) would work ok.
battery side ripple will increase as the capacitance will be half, and ESR will be double, but it should still work.

ideally you would replace with either a single 63v 9400uF cap of the same ESR, or 2x 30v 9400uF caps of half the ESR to keep the ripple the same.

Matt

Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah
Vectrix 60Ah Lithium Tyres Fuel Registration Insurance cycle analyst 2 x TC Charger & MC
conversion

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