220VAC - 12VDC battery charger/booster diagnosis

Thread Starter

HolyHarp

Joined Jun 23, 2018
11
For 26 years the villagers at our rural vocational training center have used a 220VAC - 12VDC battery charger/booster that uses 2 Otter controls (bimetallic automatically resetting circuit breakers). A couple weeks ago the villagers used it and it emitted some smoke and the primary coil became hot. The rectifier bridge was cracked so I replaced it.

The secondary circuit uses an Otter V1 series bimetallic switch (The code by the terminals on the V1 is: 1603781.). But the secondary circuit does not become hot; I don't think there is a problem there. Even with no load, turning on the charger to Normal or Boost creates smoke within a minute and heats up the primary windings. I measured a/c amps when I turned it on: I got a transient starting about 3.5 amps going down to .9 or 1.1 amps (normal/boost). The primary circuit has a G-series Otter Control (marked with the code: 18G4744).

I contacted Otter to see how to check the switches. They said,
"The G & V series are very simple, reliable & robust safety cut-outs. They are there to prevent a fire in a fault condition. They carry the current, but do not control the current. The bimetals are set to operate at a certain temperature. The operating temperature will be reached in a fault condition via the temperature feedback from the winding & the heating caused within the bimetal by the carry current."​
This does not sound correct to me. What do you think? Otter makes both types of devices. It seems very strange to me for a battery charger circuit to have a fire protection device. If it is a thermostat then if the primary coil heats up enough to smoke I would expect it to cut out. I tried cleaning the contacts with fine sand paper with no change in symptoms. I tried to use a lighter to heat both the primary and secondary circuit Otter controls for some seconds. Neither opened their contacts. Perhaps I didn't heat them long enough.

With it disconnected and on the bench; the 2 primary circuits measure resistance of 12.8 and 13.3 Ohms. The secondary windings measure 2.5 Ohms. How can I know if the windings are still good?

Can you give me a pointer as to how to diagnose and bring our handy battery charger back to life? The villagers here use it to power a vibrating table with which they make concrete ornamental paving slabs. Sales of these slabs keeps them fed and puts their children through school. Thank you for any help you can render.
 
For 26 years the villagers at our rural vocational training center have used a 220VAC - 12VDC battery charger/booster that uses 2 Otter controls (bimetallic automatically resetting circuit breakers). A couple weeks ago the villagers used it and it emitted some smoke and the primary coil became hot. The rectifier bridge was cracked so I replaced it.

The secondary circuit uses an Otter V1 series bimetallic switch (The code by the terminals on the V1 is: 1603781.). But the secondary circuit does not become hot; I don't think there is a problem there. Even with no load, turning on the charger to Normal or Boost creates smoke within a minute and heats up the primary windings. I measured a/c amps when I turned it on: I got a transient starting about 3.5 amps going down to .9 or 1.1 amps (normal/boost). The primary circuit has a G-series Otter Control (marked with the code: 18G4744).

I contacted Otter to see how to check the switches. They said,
"The G & V series are very simple, reliable & robust safety cut-outs. They are there to prevent a fire in a fault condition. They carry the current, but do not control the current. The bimetals are set to operate at a certain temperature. The operating temperature will be reached in a fault condition via the temperature feedback from the winding & the heating caused within the bimetal by the carry current."​
This does not sound correct to me. What do you think? Otter makes both types of devices. It seems very strange to me for a battery charger circuit to have a fire protection device. If it is a thermostat then if the primary coil heats up enough to smoke I would expect it to cut out. I tried cleaning the contacts with fine sand paper with no change in symptoms. I tried to use a lighter to heat both the primary and secondary circuit Otter controls for some seconds. Neither opened their contacts. Perhaps I didn't heat them long enough.

With it disconnected and on the bench; the 2 primary circuits measure resistance of 12.8 and 13.3 Ohms. The secondary windings measure 2.5 Ohms. How can I know if the windings are still good?

Can you give me a pointer as to how to diagnose and bring our handy battery charger back to life? The villagers here use it to power a vibrating table with which they make concrete ornamental paving slabs. Sales of these slabs keeps them fed and puts their children through school. Thank you for any help you can render.
If you could post a schematic that would help us to follow your (very detailed and good) description better. There are terms you and everybody else uses but they mean different things to different people so a schematic helps clear up those questions. Anything, even hand scribbled is good.

If you disconnect the secondary completely, so only the primary has power on it and current flowing, what then? (It sounds like a transformer issue to me but...)

The DC resistance of transformer windings can be useful but they do not indicate anything about the current drawn from an AC supply. If you had another transformer that you could compare the DC resistance readings of would be great but it would have to be an identical transformer.
 

Thread Starter

HolyHarp

Joined Jun 23, 2018
11
2018-06-25 10.42.47.jpg

If you disconnect the secondary completely, so only the primary has power on it and current flowing, what then? (It sounds like a transformer issue to me but...)
Even with no load, turning on the charger to Normal or Boost creates smoke within a minute and heats up the primary windings. I measured a/c amps when I turned it on: I got a transient starting about 3.5 amps going down to .9 or 1.1 amps (normal/boost).
By "no load" I mean that the secondary is disconnected from the vibrator or battery or anything.

Thank you for your kind help. I apologize for not including a schematic from the beginning.
 
Last edited:
View attachment 155028

If you disconnect the secondary completely, so only the primary has power on it and current flowing, what then? (It sounds like a transformer issue to me but...)
By "no load" I mean that the secondary is disconnected from the vibrator or battery or anything.

Thank you for your kind help. I apologize for not including a schematic from the beginning.
Ok. Now I get you. I didn't understand the switch was on the primary side.
First up, are the indicators actually bulbs or neons? If neons that's fine but if bulbs can you remove them from their sockets or otherwise isolate them from the circuit please? Then put a resistance meter on the power lead pins and compare the resistance of boost and normal modes. Are they the same or different? I'm trying to check here for a short circuit in the switch.
To test the transformer itself: If the transformer terminations are easy to deal with could you bypass all of the primary connections, isolate all of the transformer connections, primary and secondary, and connect the mains directly to the transformer primary. So the transformer should have five terminals but only two connected to anything, being the mains connections you make. Is that possible? I only ask this so we can eliminate the transformer as being the faulty part because if it is then I'm afraid your charger is now a boat anchor. If the charger were not so old I'd say the chances of a faulty transformer were very slim but since it is older then they can eventually fail. Rare but not impossible.
 

Thread Starter

HolyHarp

Joined Jun 23, 2018
11
Thanks,
  • I don't know what the lights are yet but I can disconnect them.
  • It is a 3 position rocker switch: normal - off - boost. I can bench test the switch. I'll see what I can do.
  • I've taken the primary/secondary/core out of the transformer completely. For the transformer test, what should I measure? Amperage?
 

Thread Starter

HolyHarp

Joined Jun 23, 2018
11
I'm sorry, my previous post should read:

The rocker switch has no unwanted continuities (no short circuits). It has one open circuit which should have continuity.
 

Thread Starter

HolyHarp

Joined Jun 23, 2018
11
I disassembled the rocker switch and cleaned the contacts with an eraser. They weren't burnt. The switch tests out completely now; continuities only where they should be.
 

dendad

Joined Feb 20, 2016
4,467
I agree with the above suggestion, try measuring the primary current to the transformer with nothing at all connected to the secondary. If the current is high or the transformer starts to smoke, then it is probably shorted turns and a new transformer (or complete new charger) would be the best fix.
 

Thread Starter

HolyHarp

Joined Jun 23, 2018
11
Thanks @dendad. Based on my testing in my first post,
Even with no load, turning on the charger to Normal or Boost creates smoke within a minute and heats up the primary windings. I measured a/c amps when I turned it on: I got a transient starting about 3.5 amps going down to .9 or 1.1 amps (normal/boost). The primary circuit has a G-series Otter Control (marked with the code: 18G4744).
it seems that there is probably a short in the primary windings. I wonder about the cause. It seems that the primary circuit Otter control did not do its job. Would you concur? I wonder if there is anyone on the forum that has experience using Otter controls. It seems that the secondary circuit Otter control also did not do its job - the rectifier bridge was cracked.
 

dendad

Joined Feb 20, 2016
4,467
If a winding is a bit loose, it can vibrate and wear the varnish off the wire and then short to the next turn. Once that starts, it just gets worse.
The short could be on the secondary too. But it does sound like a new transformer is the cure.
 
Top