Hi Voltage Battery/Capacitor design wanted...please

[Jasie]

I have an inkling of electrical knowledge, but I really need a lot of help
here.

I have 10x12v high current Batteries in serial. I want to add some ultra
capacitors (only 2.5v / 450F / 180A) say, 20 to the circuit.
I then want to be able to limit the speed of charge to the capacitors from
the batteries variably, (slow drain from bats results in more overall
power).

These are all powering a motor. The initial start surge to be taken up by
the caps followed by a constant drain on the batteries. The motor also has
regen braking, so how do I dump the brake power back into the caps (up to
max capacity) and then use the remainder for recharging the batteries?
We're talking high amps here of around 40 kw to 150kw burst (accelerating)
max.

I guess this is easy for a knowledgeable person in D.C.

Thanks a lot in advance.

Jason.

 

[Jeroen Vriesman]

I would need some more specifications to come up with a diagram, like some
datasheeds of the batteries and the motor. Like what kind of
current/voltage to expect from the motor when regen breaking is used.

You say you have the batteries in serial, 10x12= 120V, but 20 ultracaps can
only handle 50V, do you mean you have the bats parrallel? If so, you would
have 4x ( 5 caps in series) parrallel.

Thats (450/5)*4 = 360F, max series resistance of 3 milliohm, and 720A max
peak current.

To draw a constand current from the bats, make a coil and normal (but high
current low resistance) in series connected to the bats. With a very heavy
MOSFET between this cap and the ultracaps, you can switch the FET on and
off, while the coil and the capacitor make sure the current from the
batteries is steady.

Then you need to regulate this this current, so that the voltage acros your
ultracaps is the value you need. Maybe you need more than one MOSFET in
parrallel to get a low resistance during ON, PWM regulation would keep the
frequency constant.

The FET could be a VMM650-01F from IXYS, has a 2.2 milliohm resistance max,
and can handle 680A

I would need more about your motor to see how to feed back the beaking
current into the caps.

Cheers,
Jeroen.

 

[N. Thornton]

I have an inkling of electrical knowledge, but I really need a lot of help
here.

I have 10x12v high current Batteries in serial.

I would advise against adding milk.

Regards, NT

 

[Jasie]

I apologise for my bad description. I don't have any of the components yet,
but it's all for an electric vehicle. The batteries power an dc inverter
which then powers the ac motor. I guess that the regen is created as back
emf., back through the inverter. The caps are expensive (95 euros each).
They are to be used as a buffer to charge when braking, then use as power
for acceleration (~10secs). Unfortunately, the caps only come in 2.5v.
Would 20 caps be enough and how do you use them when the battery voltage is
120v and the caps = 50v? Another 30 caps is too expensive and takes up
too much space. Its so I can reduce the main drain on the batteries when
accelerating, and not waste the regen by trying to charge the batteries
which is less efficient that the caps. Can I step down the voltage for the
caps then multiply it when it comes out? Is this possible?

Regen is -200 dc max and drive current is 580 dc max.

How do you charge the batteries using a standard charger? Does it just
connect to the first one then 'flows' into them all?

Thanks.

 

[Jeroen Vriesman]

It's quite some work to deisign a step dwon/ step up/recharge circuit, you
would loose power at such high currents.

isn't it possible to use a 12V motor? That would simplify your design
enormously.