Help with my tank circuit.

ddt · 05-02-2003, 05:05 PM

I built a tank circuit using this diagram:

I actually used (2) 2200MFD 50V caps wired in paralell.

I used an MBR3045 and went and hooked it up.

The computer wouldn't boot so I broke out the multimeter and while it was getting over 12V coming in it was only registering 3.18V going out (and into the PSU). So I decided to hook up a 1/2W resistor to it and charge the caps.

Well they get to about 10.5V and then go back down to 3 or so volts. And do so repeatedly. What's going on here? Help me!

RobM · 05-02-2003, 05:13 PM

The diode is reversed? (Your diagram is right, BTW.)

ddt · 05-02-2003, 07:10 PM

Well it was a short and I fixed it. After that my computer powered up beautifully and then for the test...

I started the engine... and the computer rebooted

. What now?

ddt · 05-02-2003, 07:12 PM

Quote:

Originally posted by RobM
The diode is reversed? (Your diagram is right, BTW.)

What do you mean? How could it be reversed? A and A go to the battery and K goes to the cap(s), right?

zootjeff · 05-02-2003, 08:50 PM

Quote:

Originally posted by ddt
What do you mean? How could it be reversed? A and A go to the battery and K goes to the cap(s), right?

Nope, your diode it connected right. You could try a few things. Replace the CAP with a small gel cell 12 volt battery, or replace the CAP with a 1 farad cap. Or, replace the Diode with one with less forward voltage drop.

Hey, where did you get that diagram?

-Jeff

ddt · 05-02-2003, 09:22 PM

Quote:

Originally posted by zootjeff

Hey, where did you get that diagram?

-Jeff

Here:

http://www.mp3car.com/vbulletin/show...5&pagenumber=1

but you probably already know that now.

Also, I just remove the caps and replace them with a small 12V gel cell wired the same way?

Also, you made mention of other diodes. I'm using a 250W Top Micro DC-DC Converter. Which diode would you reccomend?

I'm trying to get away from using a big assed cap due to space where I need to mount it. Would a .5 Farad cap work?

ddt · 05-02-2003, 09:26 PM

On this page:

http://www.batterystuff.com/battery/batteries.htm

Would the ES 1.2-12 or the ES 1.9-12 be ideal for this?

Or what about this one?

http://cgi.ebay.com/ws/eBayISAPI.dll...&category=1200

zootjeff · 05-02-2003, 10:21 PM

Quote:

Originally posted by ddt
On this page:

http://www.batterystuff.com/battery/batteries.htm

Would the ES 1.2-12 or the ES 1.9-12 be ideal for this?

Or what about this one?

http://cgi.ebay.com/ws/eBayISAPI.dll...&category=1200

Yes, just replace the Cap by the battery. I would go with the 4-12 but there is a chance the smaller ones would work..

ddt · 05-03-2003, 12:57 AM

So I keep the diode? Is it really necessary with the 4-12 (which I just bought)?

zootjeff · 05-03-2003, 01:39 AM

Quote:

Originally posted by ddt
So I keep the diode? Is it really necessary with the 4-12 (which I just bought)?

Yes you keep the diode. It is still important. Car cranking could still bring down the voltage at your spare battery if you don't have the diode.

ddt · 05-03-2003, 01:45 AM

thanks man! You have been most helpful.

ODYSSEY · 05-03-2003, 02:11 AM

Would there be a problem of overcharging the gel cell?

I came across this site. It talks about adding a limiting resistor to safely charge the gel cell.

zootjeff · 05-03-2003, 04:30 AM

You don't need the resistor or the extra diode. That is being anal and isn't really nessessary. plus the "float" voltage the car puts out is well within the range of the Gel cell.

DodgeCummins · 05-03-2003, 10:11 PM

I don't know about this setup, but if you have two batteries hooked directly to each other and the alternator (like in my diesel truck) you need two batteries of the same capacity, or else one may get overcharged/fail/worse.

Perhaps having your battery on its own circuit and isolated might be different.

zootjeff · 05-04-2003, 04:37 AM

Quote:

Originally posted by DodgeCummins
(like in my diesel truck) you need two batteries of the same capacity, or else one may get overcharged/fail/worse.

How can you overcharge a wetcell battery that charges by having a constant voltage? I can see the argument about having too much inrush current if one is depleted (a smaller battery). If the two batteries are in parallel and they are of different capacities, one runs out faster, but the voltage at the terminals are the same for both, so all the current just comes out of the one with more capacity.

NiCads are trickle charged with a constant current, IE if you hooked a 1.2 volt nicad to a current limited 25 volt source, and set the max current to 50 milliamps, it could charge forever and not get hurt. Where as if you put a wet cell battery in this situation it would kill it after a while because it would try to charge to 25 volts.

So if I'm understanding it correctly, to charge it, you take a wetcell battery (like in a car) and you just hook it directly up to 13.8 volts, if the battery is low, it sucks a lot of current, it is the regulators job to not exceed initial current rating. So if you have two batteries, the regulator cuts out sooner, if they are different capacity, one will take more current, but they will both charge to the same voltage.

Can someone help me understand why you need Isolation? And why this is even a problem?