Can I fix my battery charger?

[heminate]

My friend had installed a new battery about 2 weeks ago. His battery died. I put my multimeter on it, and it had zero volts. I disconnected the battery and checked the ohms across the cables, it was 0 ohms (a short).

With the battery cables disconnected, I measured the voltage again, and noticed the voltage was recovering on it's own, so I figured perhaps the battery will recover with a good charge.

I got my battery charger which is one of those 70/12/2 or something like that, red battery chargers. (it is just like the century brand battery chargers, but it has a different name) I connected it to the battery. The battery wasn't taking much of a charge, which I thought was strange, since the battery was very new and very discharged. I have not worked with a battery that was this heavily discharged before, but usually a "good" battery that has been discharged, will charge at a high rate.

So I decided to try to help it along, I cranked my battery charger to full blast (70 amps), it made quite a loud humming sound then it got very loud and the amps went down to zero. It sounded like I ruined it. Now when I turn on the battery charger, even at the low rate setting with the cables not connected to anything, it just makes a very loud humming sound. I try quickly tapping the cables together, I don't get any spark.

The battery charger is riveted together, so I cannot easily take it apart to see what got fried. I am guessing there are no fuses in these types of chargers?

Does anyone have any experience repairing one of these battery chargers?

[440roadrunner]

The answer is "maybe." Some general incoherent ramblings on the subject.
First, your ohmeter test may not have meant much, because even a small load like a dome light(s) will be very low resistance. If the car has something like a solenoid operated clock that is trying to "fire", then ditto. Also, most cars have as many as 5, and as few as 3 capacitors (condensers) for radio noise suppression. If a system is completely dead, these caps will measure low resistance for a few seconds while they charge back up
If the battery was not LEFT DISCHARGED for any length of time, and if it wasn't frozen, you may be lucky. The battery may not be hurt
Now, can you post the brand name and maybe some pictures of your charger?
If it is NOT under warrantee, I'd go ahead and drill out the rivets. After all, you have nothing to lose
(However, I've always followed my lifelong philosophy, which is:
You cannot break it if it's broken, but...
You can fix it so it can't be fixed.
I HAVE fixed a few things so that they cannot be fixed)
There are several possibilities.
The fact that it still hums is a good sign.
Did it smoke or smell?
One possibility is that you've heated up the transformer, and it shorted a turn or two inside. If so, it's probably junk
Second, and more likely, is that the rectifier(s) is bad. This is pretty easy to troubleshoot.
First, pull it apart and find out if it has an internal regulator. Most of these type do NOT. Most have a switch, possibly a fuse or breaker, a transformer, and either two diodes or a rectifier "stack."
The easy way to tell if the rectifier is shorted is simply disconnect the two transformer wires feeding it.
Normally, there should be only three of the largest gauge wires coming from the transformer. One goes to one charge lead.
The other two normally go to the rectifier. Disconnect AT LEAST one of these, and make sure nothing else is shorted internally, like, maybe, a wire touching, or plastic sleeving burned off, etc, and see if it quiets down.
I would---WHILE WATCHING IT--run it at no load this way for a minute or two, then unplug and feel the transformer for heat. If you can run it this way for 10 min. or so, without the thing getting hot, the transformer is probably OK
You should be able to measure AC voltage from these heavy leads. The two going to the rectifier should read MORE THAN 24V AC, and EITHER of these should measure 1/2 voltage to the "center tap"--the one going directly to the battery charge lead.
Also, visit the Century site. It appears that they make chargers under a "whole bunch" of brand labels
http://www.centurytool.net/Battery_C...arts_s/225.htm

Here's just a general, simplified circuit. The amperage switch will be on the left, activating different taps on the primary. This circuit shows a filter capacitor, which normal chargers do not have. If your charger is not regulated, and I doubt it, there isn't much in there other than this
http://zedomax.com/image/200609/batterycharger.JPG

[heminate]

Thank you 440roadrunner - very good ideas.
Here are some pictures:

[heminate]

There wasn't any smoke, and it still hums. I will have to try out some of your ideas. Since there was no smoke and it all seemed to happen almost instantaneously, I am thinking a electronic component must have blown, like a rectifier like you were saying. I will have to tear it apart and see what I can find.

[440roadrunner]

Post a pic when you get it opened up. I did a little searching, and cannot find a diagram. I would doubt that one is regulated, which makes things simpler.

That is NOT a very heavy charger. This nonsense of "70A boost" is a big lie. Notice on the label that it says something about "3 seconds on 400 sec off"

What they are telling you there, is that the boost function is VERY lightweight

[heminate]

Looks like it is VERY basic indeed. I'm not a electronics expert, but this looks like a transformer and two rectifier diodes on a "cooling" plate. A switch, and a meter. I realized it was held together with simple bendable tabs, not riveted like I originally thought. The rivets hold the transformer in place.
I plugged it in again just to see what it would do. It draws a lot of current, hums very deep and loud compared to normal operation. No smoke. The current gauge does not move. I know it is drawing alot of current because my lights go a little dimmer and when I unplug it, there is alot of sparking at the plug.
I am confused at why it would be acting this way. It acts as though the transformer windings have melted, or there is a short somewhere? Everything looked "as new" inside.

[heminate]

I almost missed these pics - these are from the other side, basically the switch.

[heminate]

OK, 440roadrunner, I went back and read your original post - you are quite wise. I will go out and try disconnecting those leads to the diodes and some of the other things you suggested.

I'm sorry I can't get a better picture of the diodes, they are sort of hidden in there.

If it does turn out to be a diode, I have no idea where to buy a diode like that. Could I use any diode as long as it could handle the current and voltage?

[440roadrunner]

OK, I don't know where you're located or your skill level
You must be fairly mechanically inclined, can you perform electrical soldering?
Here's the approach I'd take.
First, review the diagram I found:
http://zedomax.com/image/200609/batterycharger.JPG
On the low voltage side of the transformer (the secondary) your's is very similar. The only real difference is that the "I don't know what's in here" is a circuit breaker. It would not cause the loud hum. Also, your charger will not have the capacitor that's shown as a filter (says 2200uf, 25v) That will simply not be there.
You have two possibilities for your trouble:
1: One or both of the diodes is shorted
2: The transformer is shorted.
You need to figure out how to get that diode plate/mess apart, and get AT LEAST one diode out of the circuit.
If your remove or disconnect one diode (does not matter which) and the hum goes away--the transformer runs quietly,--then obviously one of the diodes is shorted.
1: If the transformer is shorted, junk it
2: If a diode is shorted, here's the approach I'd take
Call Century from the webpage I posted, and see what the cost situation is on replacement diode/ rectifiers. It may be ridiculous
If that doesn't pan out, here's what I'd do:
Buy a Radio shack bridge--because that's the closest useable thing they have:
http://www.radioshack.com/family/ind...d=2032269&pg=1
Part no. 276-1185
Now, you WILL NOT BE USING the bridge as designed. Here's a pic of the circuit.



The lead from the transformer to the meter is unchanged. What you want to do is
Disconnect and remove the old diodes from the plate
Unhook the transformer leads from the plate/mess/ diode assy
Crimp or solder extension leads to the transformer so you can hook up the new rectifier and hook to your breaker "(I don't know what's in here)" you said
You can use the old aluminum rectifier plate to mount the new bridge with a small screw. If you have some thermal compound like used for your computer processor, put a small amount between the bridge and the plate
Get the thing mounted, and just hook it up according to the diagram. Notice the layout of the "cut corner" of the bridge, and the markings around the outside edge. Two connections are AC (transformer) and two connections are plus/ minus. Leave the minus terminal on the bridge UNconnected
Leave the wiring hooked from the meter to the transformer unmolested, that is shown as the "center tap" in the diagram
These bridges are so cheap, you might by another for a spare!! Just use "quick connect" flat spade connectors--like used elsewhere in the charger to hook it up.


You CAN of course use individual diodes. If you happen to have an old alternator laying about, it's possible that you could salvage a couple out of it. Many alternators would be difficult to use this way.

[richinny]

have you tried using the charger on a different battery? you need to buy an ammeter and learn how to use it.

[heminate]

Originally Posted by richinny

have you tried using the charger on a different battery? you need to buy an ammeter and learn how to use it.

Usually this charger would spark if you were to very briefly touch the leads together, at the same time, the built in ammeter would jump as the corresponding electrons would travel.

I appreciate your suggestion to buy an ammeter and learn how to use it. I would think the ammeter in the charger would be sufficient.

The load hum this charger makes is clearly telling me it is shorting out and 440roadrunner has given me very good and clear instructions on how to troubleshoot and fix it.

[heminate]

Thank you 440roadrunner, I will tear it apart and see if I can isolate it to the diodes or the transformer. I bought a new "computer" battery charger. I thought I would like it, but it turns out to be pretty disposable junk. It has a computer fan to cool off the electronics inside and the fan bearings are already wearing out. I also miss the analog gauge my old century has. I'd really like to fix this.

Originally Posted by 440roadrunner

OK, I don't know where you're located or your skill level
You must be fairly mechanically inclined, can you perform electrical soldering?
Here's the approach I'd take.
First, review the diagram I found:
http://zedomax.com/image/200609/batterycharger.JPG
On the low voltage side of the transformer (the secondary) your's is very similar. The only real difference is that the "I don't know what's in here" is a circuit breaker. It would not cause the loud hum. Also, your charger will not have the capacitor that's shown as a filter (says 2200uf, 25v) That will simply not be there.
You have two possibilities for your trouble:
1: One or both of the diodes is shorted
2: The transformer is shorted.
You need to figure out how to get that diode plate/mess apart, and get AT LEAST one diode out of the circuit.
If your remove or disconnect one diode (does not matter which) and the hum goes away--the transformer runs quietly,--then obviously one of the diodes is shorted.
1: If the transformer is shorted, junk it
2: If a diode is shorted, here's the approach I'd take
Call Century from the webpage I posted, and see what the cost situation is on replacement diode/ rectifiers. It may be ridiculous
If that doesn't pan out, here's what I'd do:
Buy a Radio shack bridge--because that's the closest useable thing they have:
http://www.radioshack.com/family/ind...d=2032269&pg=1
Part no. 276-1185
Now, you WILL NOT BE USING the bridge as designed. Here's a pic of the circuit.



The lead from the transformer to the meter is unchanged. What you want to do is
Disconnect and remove the old diodes from the plate
Unhook the transformer leads from the plate/mess/ diode assy
Crimp or solder extension leads to the transformer so you can hook up the new rectifier and hook to your breaker "(I don't know what's in here)" you said
You can use the old aluminum rectifier plate to mount the new bridge with a small screw. If you have some thermal compound like used for your computer processor, put a small amount between the bridge and the plate
Get the thing mounted, and just hook it up according to the diagram. Notice the layout of the "cut corner" of the bridge, and the markings around the outside edge. Two connections are AC (transformer) and two connections are plus/ minus. Leave the minus terminal on the bridge UNconnected
Leave the wiring hooked from the meter to the transformer unmolested, that is shown as the "center tap" in the diagram
These bridges are so cheap, you might by another for a spare!! Just use "quick connect" flat spade connectors--like used elsewhere in the charger to hook it up.


You CAN of course use individual diodes. If you happen to have an old alternator laying about, it's possible that you could salvage a couple out of it. Many alternators would be difficult to use this way.

[heminate]

I just now tore apart the charger, and in less than 1 minute, my Fluke 87 confirmed that one of the diodes is fried. As a 2nd confirmation, I plugged in the charger to check the transformer with the diodes disconnected. It sounds normal! So now I just need to find a diode or two that will work for this.

I don't have an old alternator, so I guess I can check out the resources listed above in 440roadrunner's post.

My next question would be how many amp diodes should I get?

P.S. I do know how to solder, no biggie. Thanks for your help 440roadrunner.

[heminate]