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Old 09-29-2017, 01:05 AM   #1 (permalink)
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Capacitors in EV to change power-energy balance of a battery?

Say I was building an EV that required performance over range. Eg 80km range when driving nicely but the capacity for several hundred horsepower for no more than about 10-12 seconds.

Is it feasible to install cheap batteries to get the voltage up, in parallel with capacitors to provide huge short term current draw capacity?

Would it be any better than equivalent cost and weight in more batteries?

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Old 09-29-2017, 01:21 AM   #2 (permalink)
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No good. You'd be lucky to get a second worth of power out of your capacitors. They're there for instantaneous power...measured in thousandths of a second, not tens of seconds.

Either buy bigger batteries that can output more all the time, or look for "performance" batteries that can handle sudden, intense rush of power.
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Old 09-29-2017, 08:47 AM   #3 (permalink)
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Capacitors don't hold enough power.
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Old 09-29-2017, 09:08 AM   #4 (permalink)
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Two hundred or so of these ultracapacitors would do the job.
If you have the right electronics to convert the voltages at high currents, and a lot of excess capacity in your wallet.
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Old 09-29-2017, 11:11 AM   #5 (permalink)
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Quote:
Originally Posted by RedDevil View Post
Two hundred or so of these ultracapacitors would do the job.
If you have the right electronics to convert the voltages at high currents, and a lot of excess capacity in your wallet.
Supercaps have enough capacity now to build a (EXPENSIVE) pack to supply the currents you are likely to need (2000-ish amps) for 10-ish seconds.

The packs that racers use appear to lean toward pouch cells instead, that have insane discharge rates. Like 30 a-h cells with 50C discharge rates.

I would add that the Supercaps are still capacitors, so they leak, and they don't leak at the same rate. They get unbalanced quickly without a management system to balance the charge. And when you exceed the rated voltage per capacitor, even a little bit, they fail.

So add some more cash for a balancing system as well. High current balancing is not required, but balancing is required.

Jack over at EVTV had a bank of supercaps wired up that would run his car for about 5 minutes. It was not all that heavy but it certainly took up a bunch of room. This was a few years ago so things have gotten smaller, and the max currents are higher.
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Old 09-29-2017, 04:00 PM   #6 (permalink)
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I have seen ultra capacitors that literally leak out what ever dielectric liquid is used in side them too. It kind of makes a mess and compromises the capacitors.
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Old 09-29-2017, 06:18 PM   #7 (permalink)
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Start by going back to your electrical engineering text books. Use materials that are inexpensive. Concentrate on current flow over time as motor torque is a function of current. Make the units part of your structure. This will let you figure if the cost vs performance meets your needs. Have fun with some sheet aluminum and some pieces of window glass or waxed paper.
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Old 09-29-2017, 09:44 PM   #8 (permalink)
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Quote:
Originally Posted by thingstodo View Post
The packs that racers use appear to lean toward pouch cells instead, that have insane discharge rates. Like 30 a-h cells with 50C discharge rates.
That's the way to do it. Those a123 20ah cells were good for that...too bad they're not around any more. (I think)

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