Tank circuits???

**zzsprade** · 03-28-2002, 04:15 AM

Guys I have to appologise about being very new to the whole power supply side of this hobby. I tried doing a search but I still cant quite grasp what a tank circuit is and does? As I said I am very vague when it comes to the power supply and what to do... so any ideas on the whole process would be very much appeciated. Ta!

-Alex

**Mastero** · 03-28-2002, 05:13 AM

Tank circuits are nothing but the power circuits used in Military tanks to produce power it in dessert condition.

They were first devoloped in Germany by Hitler... during the II world war. and so on ...!

We have adapted this technology to produce power to keep are Carputer alive during cranking the engine!

Its nothing but just a 22000uf /30v cap and a MBR6045 diode ..!
attached to the +12 line of the carputer.!

so when you crank the car carputer stays alive with the help of the caps. and the diode prevents the current been pulled back during crank

Well i hope it the above information helps you.

Mastero

**etrik** · 03-28-2002, 09:32 AM

i am havign difficulty finding a 22000uf/30v cap. could i relpace it with a 22000uf/ 25v cap? the one i am looking at is at digikey.com part number P10073-ND or P6423-ND. would these work? thanks,
Etrik

**Dimitris1976** · 03-28-2002, 11:15 AM

Yes a 22000uF/25V will work and will work even better than a 30V one.

**Rob** · 03-28-2002, 11:26 AM

The lightning car audio ones are only 16v normal, 20v peak, so you'll be fine.

Rob

**alexchannell** · 04-01-2002, 01:18 PM

I believe it will work the same as the 30V one, not better. Capacitance has nothing to do with the voltage. A 10uF 20V and a 10uF 1000V cap will have the same ammount of energy if they are brought to the same voltage (as long as the voltage is below the cap's limit). Correct me if I'm wrong.

**Dimitris1976** · 04-01-2002, 05:17 PM

Alexchannel,

I think you are wrong.
For example, a 1000pf/30V capacitor charged at 30V has a charge of 1000pF. Charged at 15V it has 500pF. A 1000pF/15V capacitor charged at 15V has 1000pF of charge.
I don't know if the charge is proportional to the voltage (the way I described in the above example), but I know out of experience (trial and error) that capacitors rated for voltages closer to the max supplied voltage of the system perform better (bigger capacity) than capacitors with the same Farad value but rated for higher voltage.
Of course you can't supply a capacitor with highter voltage than the voltage it is rated for. Ie if you supply 15V to a 1000pF/6V it's going to heat up and melt/leak.

**Rob Withey** · 04-01-2002, 06:21 PM

Dimitris1976, I think you are wrong.

Capacitance is measured in Farads, but charge is measured in Coulombs. The voltage rating on capacitors is the voltage at which the dielectric will start to break down, destroying the capacitor. A pair of capacitors of a particular capacitance (measured in Farads) charged to a particular voltage will have exactly the same charge, regardless of their rating working voltage.

Rob

**Dimitris1976** · 04-01-2002, 06:25 PM

Alexchannell/Rob,

I THINK YOU R RIGHT :-) !

**zootjeff** · 04-02-2002, 05:00 PM

Originally posted by Rob Withey
Dimitris1976, I think you are wrong.
A pair of capacitors of a particular capacitance (measured in Farads) charged to a particular voltage will have exactly the same charge, regardless of their rating working voltage.
Rob

I agree with Rob.
Capacitors with a higher voltage rating will actually work better than ones with a low voltage rating because there is more capacitor area creating a a lower ESR. In this application, the ESR could make the difference between the car computer restarting or not. A cap in the most simple form is two plates. The farther the plates are apart the less capacitance you have and the higher the voltage rating. More area means more conductor carying the current meaning less ESR. You have to make the trade off because for a given uF, the size of the cap goes up with the voltage rating. But the ESR is inversly proportional to the Size and Voltage. (low ESR is good) I think a 20-50 volt cap would probably be the best choice for this application. I wouldn't use a 15 volt cap because it might fail.

I don't understand why you think a 20 volt cap would work better than a 25 volt one. It would be smaller, but functionally I think it would be worse. If the 20 volt cap was made of better materials I could believe it. Tell me some more about your experiment.

I guess it is like saying, My Honda is faster than your Ford. All Hondas are faster than all Fords. The Horsepower is an important factor just like ESR is.

Jeff

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