Power Supply Help Please

[dottney]

I picked up a 12V 4A power supply off Ebay. When it arrived I heard something rattling inside. Opening it up I found the capacitor, with the resistor attached to it, hanging loose.
The resistor is connected to the positive output of the bridge rectifier. I replaced the wire on the capacitor and soldered it to the DC + output lug.
There is solder on another lug of capacitor but I haven't soldered it to anything.

When I turn it on it shows just about 12v. But when I connect a Triton charger to it the charger doesn't light up and the voltage at the DC output lugs shows something like 3.7x V.
Running it with the capacitor & resistor bypassed outputs around 17.3xV which is too high for the Triton. Running it with just the 500ohm resistor connected doesn't put out enough voltage to turn the Triton on.

I'm attaching a pic of the guts with labeled arrows pointing to the various wires and components. Have I incorrectly connected the capacitor? Should the capacitor lug with the solder on it be attached to the DC- output lug?

Any help will be greatly appreciated.
Dave

[Gary Warner]

I haven't see that kind of capacitor since I was fixing tube-type TV's. That lug is the negative connection for the capacitor. Most likely, it was soldered to the "-" solder lug you indicated in the picture. It was common to just "hang" (or mount) the capacitors off of solder lugs. In shipping, the mass of the capacitor caused it to break off the "-" line when the package was dropped a bit.

[dottney]

Thanks Gary, I'm going to put a piece of wire from the lug that has solder on it to the DC- output lug.
Dave

[dottney]

Blast, it didn't work. When I connect the Triton to it the voltage drops to 3.xx V. Anybody have any suggestions, I'm lost.
Dave

[peterv]

Dave, the neg lug may go to the chassis/case ground. I don't see any regulator components. Just a transformer, cap, fuse and bridge rectifier plus a power resistor. Can't believe that will hold any kind of regulated 12v!

Pete

[dottney]

Thanks Pete,
I've gone out and done some reading (ah a dangerous thing). I was thinking about putting in an LM7812 regulator. My only question is about amperage. The LM7812 is rated at 1.5A. Does that mean the I can't charge higher than that with the Triton?
Man I'm glad I didn't pay too much for this thing.
Dave

[ebill3]

See my post in your batteries and chargers thread.

[rick.benjamin]

"I picked up a 12V 4A power supply off Ebay"
The good news: Your power supply is supplying 12 volts.

The bad news:
Your Triton appears to require at least 7 amps and 12 volts,
and to be fully completely operational, needs 10 amps at 12 volts.
The manual implies that if volts sags to 11 volts or below, the charger faults.

Your power supply is not strong (amp wise) enough.

[peterv]

Well said Rick. I use a 4 amp supply for a small Lipo charger. Less than 1000ma batts. Works OK, but would not handle the Triton.
Tha prob is your charger is loading down the power supply and faulting as Rick says.

Pete

[sfsjkid]

The Triton only needs 7A in order to operate at the full stated capability. More current is needed as the cell voltage approaches 12V in order to supply the set charge current. I sometimes use my 12V 2A power supply without problem, but within reason.

Pictures of the power supply in questions from other angles might help.

[ebill3]

Your Triton appears to require at least 7 amps and 12 volts,
and to be fully completely operational, needs 10 amps at 12 volts.But surely, the triton does not require 7 Amps just to "turn on".

From post #1, it appears that just connecting the charger to the power supply drops the voltage from ~12 to ~4. Looks like that 500 Ohm resistor is in series and doing the dastardly deed.

Bill

[dottney]

Thanks guys. Bill gave me some advice over in the other thread. I'm going to try pulling the resistor and putting in an regulator. If that doesn't work I'll punt and go out and get another power supply with a higher amp rating.
Dave

[winged1]

If you can, check your transformer for any identification, it may likely have a secondary output rating in volts and amps. It's physical size would suggest however that it falls short of your needs.

Heres a picture of a transx with a 12vac / 12 amp secondary, just for size comparision -

http://www.sunlesssystems.com/images/trans.jpg

If your feeding a charger, you likely do not need any regulation. Watch the size of the capacitor though. Large is better for ripple, but then your rectifier must be able to handle the inrush current.

[Rodney]

You definitely need pretty good regulation for most of the chargers on the market today. Surely there is someone in your acquaintance that could give you a little help on deciphering the problems with your power supply. They are really a pretty simple item unless it is a switching power supply which, considering the size of the transformer, it might be. Switching power supplys are much more efficient and use smaller transformers than the older full wave rectified one do.