OT battery charger issue

moonlight machine · Aug 8, 2019

Went to charge a car battery, nobody home in charger land. 10.8 volts at the leads. 120v at the transformer, the coil is warm, I unplugged the power to the transformer and scratched the power lead on the terminal, sparks, clear signs of a load on power lead, no power at any combination of the 3 terminals on the load side of the transformer, but is shows 10.8v at the battery leads. wtf?

JST · Aug 8, 2019

What sort of charger is it?

Plain "dumb" transformer/rectifier? Regular older type? More recent ?

Dumb transformer/rectifier types ought to just work, nit much to go wrong except the rectifiers, the transformer is pretty reliable.

The older standard types have SCR and some voltage circuitry to control the charge, obviously any of that may go bad, hard to say what.

Newer ones have more complex contriols, and may refuse to charge unless the battery is at a reasonable state of charge to begin with. If too low it will just sit there and not do anything. The 10.8VDC is still "within range" if that is battery voltage, as I suspect. Most newer chargers ought to charge that,

Your sparks might be either from current going OUT to the battery, OR from a load put on the battery ny a dead charger. No idea which. Is there a meter for current? if so, does it show ANY wiggle at all?

EDIT: One failure mode for batteries is to go open, or nearly open. At that point, they may not accept a charge, and will have very low capacity, if any. In such a case, they may provide "sparks" as you noted, nut have no real ability to really power anything or to accept a charge. Before giving up on the charger, try another battery that is known ok.

Chargers are cheap, it's hardly worth fiddling with them these days, unless it is a special one that cannot easily be replaced.

moonlight machine · Aug 8, 2019

JST said:
What sort of charger is it?

Plain "dumb" transformer/rectifier? Regular older type? More recent ?

Dumb transformer/rectifier types ought to just work, nit much to go wrong except the rectifiers, the transformer is pretty reliable.

The older standard types have SCR and some voltage circuitry to control the charge, obviously any of that may go bad, hard to say what.

Newer ones have more complex contriols, and may refuse to charge unless the battery is at a reasonable state of charge to begin with. If too low it will just sit there and not do anything. The 10.8VDC is still "within range" if that is battery voltage, as I suspect. Most newer chargers ought to charge that,

Your sparks might be either from current going OUT to the battery, OR from a load put on the battery ny a dead charger. No idea which. Is there a meter for current? if so, does it show ANY wiggle at all?

EDIT: One failure mode for batteries is to go open, or nearly open. At that point, they may not accept a charge, and will have very low capacity, if any. In such a case, they may provide "sparks" as you noted, nut have no real ability to really power anything or to accept a charge. Before giving up on the charger, try another battery that is known ok.

Chargers are cheap, it's hardly worth fiddling with them these days, unless it is a special one that cannot easily be replaced.

It's an old transformer type. The only place you can get a spark is when you unplug one of the 110v wires from the transformer. Just touch the terminal with the power cord plugged in, you get a spark from the transformer load as you touch the terminal. short the charge wires, nothing no sparks no meter movement. No power at the low voltage connection to the transformer but it shows 10.8 volts at the battery clamps.

SAG 180 · Aug 8, 2019

10.8 Volts is what you'd expect if one cell of your 12V battery went short circuit and died and you had a good charge in the remaining 5 cells: 2.2V x 5 = 11V.

moonlight machine · Aug 8, 2019

SAG 180 said:
10.8 Volts is what you'd expect if one cell of your 12V battery went short circuit and died and you had a good charge in the remaining 5 cells: 2.2V x 5 = 11V.

Well for sure there is no 5/10 dead battery hiding in my charger.

Tony Quiring · Aug 8, 2019

Description is confusing.

So let me see...

Charger basic transformer and leads..

Plug into power and no voltage out.

Measure A.C. voltage on transformer, 120 or line voltage on input and nothing on output?

These sometimes have a fuse wrapped in the winding.

Unplug from wall and check coils with ohm meter.

Sent from my SAMSUNG-SM-G930A using Tapatalk

JST · Aug 8, 2019

moonlight machine said:
It's an old transformer type. The only place you can get a spark is when you unplug one of the 110v wires from the transformer. Just touch the terminal with the power cord plugged in, you get a spark from the transformer load as you touch the terminal. short the charge wires, nothing no sparks no meter movement. No power at the low voltage connection to the transformer but it shows 10.8 volts at the battery clamps.

Well, I'm not 100% getting the spark deal. But it sounds like the charger is not putting out anything

"Old transformer type" suggests one with an old rectifier, selenium or similar. They go bad, and unlike more modern types, often fail open. Not always..... I HAVE replaced the rectifier in such a unit, but modern rectifiers have a somewhat different characteristic, and may not work the same (power Schottky are closer).

Unless this thing is needed specifically as what it is, it may not be worth it. You have not said what it is for, but unless it is special, I'd go get another charger and never look back. Any newer charger will almost certainly do a better job, and it is not worth your time to dick around with it unless it is super special. .

The 10.8V is yes, about right for a dead cell/weak cell. A specific gravity check on the battery will tell you that answer pretty well, if you can get into the battery. Even many "sealed" batteries are not sealed, they are just made with venting that does not look as if it is removable. But that is "flooded" lead acid types, with actual electrolyte sloshing around in them.

An AGM type is really sealed, with no sloshing pool of acid in it, and those you have to assess based on how they behave.

SAG 180 · Aug 8, 2019

moonlight machine said:
Well for sure there is no 5/10 dead battery hiding in my charger.

If it's a bog stock bridge rectified transformer based charger, then the output has significant ripple, dropping to zero at twice the mains frequency. This gives a false reading on your digital multimeter, hook a small electrolytic cap across the lead (correct polarity of course) and measure the filtered voltage, should be around 14V.

JST · Aug 8, 2019

The meter would read the average value, or 0.66 of the peak. That would make the peak around 16.4 V, which is perfectly credible.

But if it is working, even a bad battery, so long as it has any capacity at all, would hold the voltage constant enough to give a decent reading. And the leads should spark if struck together (a common test, but not one I can recommend for all chargers....).

SAG 180 · Aug 9, 2019

JST said:
The meter would read the average value, or 0.66 of the peak. That would make the peak around 16.4 V, which is perfectly credible.

But if it is working, even a bad battery, so long as it has any capacity at all, would hold the voltage constant enough to give a decent reading. And the leads should spark if struck together (a common test, but not one I can recommend for all chargers....).

Averaging would be the case for an analogue style multimeter with a needle, with a digital meter it would be a random set of readings between zero and peak voltage.

JST · Aug 9, 2019

SAG 180 said:
Averaging would be the case for an analogue style multimeter with a needle, with a digital meter it would be a random set of readings between zero and peak voltage.

Depends on the meter. many do have an averaging setup for DC, and may read a steady number. Of course, that can be overwhelmed by large pulses at low frequency..

Yje OP seems to be getting a steady voltage, so either that is the battery alone, or an average reading.

In the end it doesn't matter much, we know very little about the setup so far. If he wants to go further, some more info might be good.... pics etc. to see what the parts are. And a specificgravity on the battery would show if there is an issue there. Plus, we do not know if thre is enough in the battery to run anything... Nor what the meter is, how it was set, etc, etc.
D

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