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Old 07-18-2012, 06:51 PM
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Cool Controller - Super Capacitor - Lipo Pack?

Doing some research on super capacitors. Almost all battery packs sag when the controller pulls the amps, so for example:

Two Shiva Controllers
270v 4000amp Lipo pack

When the Shiva's start requesting the amps, say 2000BA each, the voltage might drop down to 150v, will adding super capacitors stop this huge sag in the pack?
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Old 07-19-2012, 07:34 AM
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Default Re: Controller - Super Capacitor - Lipo Pack?

Maybe for a second or two. Adding more lithium will help for longer.
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Old 07-19-2012, 02:43 PM
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Default Re: Controller - Super Capacitor - Lipo Pack?

I don't know if you do this, but one of the "secrets" that the EV drag guys do to help with voltage sage on the motor side, which is important, is to run a very high input battery voltage and then reduce motor voltage to like 1.5 times of battery pack voltage. The reasoning behind this is that the DC motor motor controller will act like a DC-DC buck convertor in that it will pull less battery amps, but give you more motor amps at reduced voltage and little voltage sag.

Maybe you should run a 400 volt DC input with 110 Lithium battery parallel banks wired in series. Have the motor voltage set to 250 volts and motor current at 3000 amps. The input current will then be 1,875 battery amps at 400 volts input DC.

Try to build this pack such that it does not sage more than 15% from the nominal voltage value when pulling 1,875 amps. Set the battery amps to the current value that the batteries needs to provide at this voltage sag which is about 2200 amps.

Enjoy!!!
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Old 07-19-2012, 03:14 PM
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Default Re: Controller - Super Capacitor - Lipo Pack?

Quote:
Originally Posted by LithiumaniacsEVRacing View Post
Doing some research on super capacitors. Almost all battery packs sag when the controller pulls the amps, so for example:

Two Shiva Controllers
270v 4000amp Lipo pack

When the Shiva's start requesting the amps, say 2000BA each, the voltage might drop down to 150v, will adding super capacitors stop this huge sag in the pack?
Yes they will but it isn't really practical. At least not for drag racing. By the time you have enough capacitance you would be better off just adding more Lithium batteries. Part of the reason for this is the charge in a cap is proportional to its voltage. To make effective use of them you need a high power boost circuit that can accept voltages down to near zero and boost that to motor voltage. This boost device would be larger and heavier than a Shiva. If you just try to parallel the caps with the main battery pack you need a much larger cap because you will be using a very tiny portion of the stored energy. You are talking about several hundred pounds of extra stuff. If you add several hundred pounds of batteries you will eliminate the sag anyway.
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