Need help with a battery charger

I bought a battery charger at a flea market a while back. It was only a buck fifty since it"s missing it"s input and output leads.

Would someone be kind enough to take the cover off of their unit and send me a clear picture or two of the wiring?
Your charger should be dual voltage (6 and 12v), with fixed amps.

Thanks!

The heavier wiring is the low voltage output side of the transformer. This looks like a center tapped output winding, which would only use two diodes instead of the four found in a full wave bridge, hence only having three connections to the diodes.

Assuming this is a center trapped transformer, and (CAUTION - assumption) assuming someone hasn"t messed with the connections, the (-) output would be the unused terminal at the top of the transformer & the (+) output would be the unused terminal on the ammeter.

The small glass tubes are fuses. The fact that they"re black indicates they"ve blown, which probably indicates there are bigger problems with the unit than simply missing wires. The transformer should self-limit its output current to a safe value if the output is shorted, as it has to be able to accomodate discharged batteries without damaging itself or the battery. If there"s been enough current through the transformer secondary to blow the fuse, there"s a good chance the diodes and/or the ammeter are also toast.

You"d be very wise to find someone with a good low-range ohmmeter & have them check the transformer windings for shorts before applying power.

The switch selects one of two taps on the primary (AC input) side of the transformer to give the proper output voltage. One side of the AC line most likely connects to the unused terminal on the bottom of the transformer, and the other AC line connects through a fuse to the unused center terminal on the switch. I can"t see enough detail to see how the second fuse is wired.

My suggestion, unless you"re just looking for a project, is to throw it out & go buy a new one. If you insist on playing with this one, the fuses can be replaced with type 3AG using in-line holders that you can buy at any auto parts store. Just make sure you use a fuse rated for 250 volts (most 3AG are) on the AC input side - don"t use the flat blade type automotive fuses. The flat blade type should be OK for the low voltage, high current side. The output fuse should be a little bigger than the maximum reading on the ammeter. A couple amps is probably enough for the input fuse.

BE CAREFUL! Its easy to get zapped from an exposed terminal, or get the transformer hot enough to burn if there has been a short somewhere.

Keith

Thanks for the great reply! I"m a cheapskate and dumpster-diver, so I think I"ll see how far I get with this charger. :-)

If you find some time, would you be able to elaborate on the low-range ohm meter test? I do have access to an electronics mfg. co.

I"m no expert, but I can"t find any sign of heat on the transformer or anywhere else. Hopefully the unit is still good.

Here"s some additional info if anyone needs it:
The rated amp output of this battery charger is 6 amps, and the gauge reads up to 8.

The input amps is said to be 1.2.

The voltage selector switch connects it"s center terminal with one of the outer ones depending on where the switch is. The black wire is 12 volt, and the white is 6. Sorry I didn"t put this info out before, let me know if this changes any one"s ides on how this should be wired.

Lastly Keith, you wrote you couldn"t see enough detail of the second fuse. I can post a better photo if you want, or tell you where it goes. Just let me know what fuses you mean.

Thanks all!

I've been working almost every weekend for the past six weeks, & never seem to have any time to do things like draw schematics. Hopefully, tomorrow will be the last weekend workday for a while. Will try to draw up a wiring diagram this weekend & post it here.

There are three failure modes for a transformer; 1) an open winding, 2) a winding to winding short, and 3) a winding to frame short. A winding-to-winding short will generally result in an overheated transformer due to high current in the shorted windings. An open results in the transformer simply not working. A winding to frame short produces a safety hazard, since the frame can be at 120 volts without drawing enough current to trip a breaker.

A resistance check with a good ohmeter that can accuratly read down into the 10ths of an ohm range, and someone who knows how to use it, can tell whether the resistance on both sides of the center tap is equal, which would indicate no shorted windings, and verify which terminal is the center tap. In the higher resistance range, an ohmmeter can do a quick check for winding to frame short, although a megger (high voltage ohmmeter) is required to do an actual leakage check. An open winding will be obvious.

Diodes can also be checked with an ohmmeter. Most digital ones have a range designated by a diode symbol, and will show lower resistance with the leads connected in one direction than in the other. In your case, the measurements on the diodes should be made between the common point (the center wire) and each of the wires going to fuses. Checking from one fused wire to the other won't tell you anything unless one of them is open, as you're measuring two diodes in series pointing in opposite directions, and you'll get the same readings both ways.

Keith

No hurry with the schematics. You are right about the fuses between the transformer and rectifier. By the way, I'm getting continuity through the fuses.

My multimeter's 0.1 ohm resolution is plus or minus 0.8 percent plus 3 digits. I'm guessing this is too high?
On the transformer, I was getting continuity between all the top terminals with just barely 0.1 ohm. Likewise, I get continuity on all the bottom terminals. I'm reading 10.8 ohms between the two outer terminals, 7.5 between the left and center, and 3.5 on the center and right. I'm not reading continuity between any of the terminals and the frame, or between the top and bottom sets of terminals. Does all this make sense?

As for the diodes, I can't get a steady ohm reading on them in diode mode. Every once in a while the auto-ranger will blip but that's it. I'm getting continuity between all three rectifier leads. This means they're shot, right?

So, when someone has time, would they be able to tell me what my readings mean? I'm sort of suspecting the transformer is bad. This thing only cost me a $1.50, so it's no great loss.

Thanks.

Keith

Don't take this to the bank!

The light bulbs are used to regulate the current since there in mo other form of regulation built in. The green device is a bridge rectifier whose function is to convert AC voltage to pulsating DC. The 6/12 volt switch just changes which transformer secandary winding is used to get the proper charging voltage. After all this I hope it works!

There are no fixed amp chargers as I know them. The current is depends on the state of the battery.

If you take a picture of yours, I would be willing to draw in the connections as needed.

John

I live in Pennsylvania, probably nowhere near close to you. I did show the charger to my grandfather who is an electrical engineer, and he and his co-workers thought they knew how to wire it, but they weren't sure. I promptly forgot how they told me to wire it, and I'd rather know I have it wired right before plugging it in.

I'm going to attempt to post two photos. If they don't work I'll send them right to you. One thing that might not show in the photos is the coarse wire in the upper transformer, and the thinner wire in the bottom half.

The bigger terminals on the front of the unit is the amp gauge, and the smaller terminals belong to the volt switch.

I'm also not sure what those light-bulb type components are. Is the black junk on the inside a bad thing?

Feel free to ask for further info if you need it.

Thanks!

What you say makes sense to me, but when I look at the charger I only see one unused terminal after the rectifier. At least, I think it is the rectifier. I looking at the green thing in the photos I posted.
I did look at a straight 12v charger, but I'm not smart enough to translate to the dual voltage.

Thanks.