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  #1  
Old 07-27-2014, 09:44 PM
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Possible Overvoltage - Diagnostic help?

Had to recharge the battery this AM - was expected, as I had drained the battery - using lights, radio, etc. over the last few weeks while working on car...

At some point in the process, I turned on headlights - to determine if battery was charging at all. Big mistake, apparently! Flash of headlights on, then both dead. Haven't yet disassembled my (euro) headlights, but I'm guessing the bulbs are toast.

When the battery was not taking the charge, I tested it, and realized it was completely dead. No voltage - and absolutely zero continuity across the terminals. (Have never seen a battery sink to this state before). OK, so I replaced the battery...

Now, with the new - and fully charged battery - the car has become very hard to start. Did I cook the glow relay, too? (Glow indicator light now stays on while running.)

Important: That all the fuses for the headlights and the the glow relay's internal fuse are intact.

Assuming that the battery was already shot, and the car's harness was taking the full load of the charger, is it possible I've cooked headlights and the relay without burning the corresponding fuses? Any of this sound familiar to any of you? Too weird?

UPDATE: Turns out all the (remaining good) glow plugs had been blown by the overvoltage. Glow Relay is in good shape, with its 80A fuse looking pristine. That the dashboard glow indicator light was staying on constantly is consistent with what I've learned here, from you guys: That this indicator stays on when 3(?) or more glow plugs are dead.

Replaced glow plugs (headlamps, too) and car starts like a champ!

Thanks for the ThinkTanking here.

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Last edited by DrLou; 07-31-2014 at 08:58 AM. Reason: Update/Resolution
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  #2  
Old 07-27-2014, 10:06 PM
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Answer

The battery charger should not have blown the bulbs.
What setting was the charger at, when this happened??

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  #3  
Old 07-27-2014, 11:04 PM
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I was trying to quick charge it, at a 40 amp setting. Worrying: is that I may have done this damage while switched - intermittently - to the 200 amp 'Start' setting. Thinking that's probably way too much amperage without the buffer of that huge battery to soak it up.

I'll have more findings tomorrow. Frankly, though, the headlamp bulbs are of little concern to me. If I've roasted the glow relay, I'll be unhappy.

What are you thinking?
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'83 300 SD
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr

Last edited by DrLou; 07-27-2014 at 11:17 PM.
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  #4  
Old 07-27-2014, 11:49 PM
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With a completely dead battery accepting no charge at all, the 40 Amp setting on the charger would be supplying at least 16 Volts (if not 18 or 20) to the car, which would look like an open circuit to the charger. That position might or might not blow the lamps—I've never experimented. The starting position of the switch would raise the voltage even higher and definitely would blow the headlamps as they tried to soak up all that wattage.
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Old 07-28-2014, 01:39 AM
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overvoltage will not in itself burn out a fuse. check the voltage anywhere, while the car is running, with a voltmeter. the voltage regulator at the alternator may be shot.
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Old 07-28-2014, 03:19 AM
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Hmm

Quote:
Originally Posted by DrLou View Post
I was trying to quick charge it, at a 40 amp setting. Worrying: is that I may have done this damage while switched - intermittently - to the 200 amp 'Start' setting. Thinking that's probably way too much amperage without the buffer of that huge battery to soak it up.

I'll have more findings tomorrow. Frankly, though, the headlamp bulbs are of little concern to me. If I've roasted the glow relay, I'll be unhappy.

What are you thinking?
One of my main chargers (bought in 1975) has both settings 40 amp, 200 amp, and has been used on more dead battery cars than I can count.

I can't recall any glow relays or headlight bulbs failing.

I suspect you may have poor quality bulbs and/or an electrical wiring issue.

.
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  #7  
Old 07-28-2014, 07:44 AM
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Gents - I appreciate the ThinkTank-ing on this. It's a weird one...

whunter - Yes, I've been using my almost ancient charger for many years now; on many cars with no issues. What's different this time is that the battery was discovered to have no continuity at all. Beyond 'dead' - fully discharged - it was completely nonexistent, essentially, in the circuit. This is the bit which worries me. Have never seen a battery in this state before.

Jeremy5848, bricktron: I'm gonna start testing voltages today on the circuits. The possibility of having fried the voltage regulator is yet another spectre.

Q: Is it diagnostic of a bad Glow Relay that the dashboard glow indicator stays on all the time now? Damn, this was recently replaced. Current behavior: Is that the indicator comes on, as expected, in Ignition Position 2, then shuts off as expected. But the car doesn't start as if the plugs have been heated...
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'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr
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  #8  
Old 07-28-2014, 09:19 AM
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Quote:
Originally Posted by DrLou View Post
..................................
When the battery was not taking the charge, I tested it, and realized it was completely dead. No voltage - and absolutely zero continuity across the terminals. (Have never seen a battery sink to this state before). OK, so I replaced the battery...

Now, with the new - and fully charged battery - the car has become very hard to start. Did I cook the glow relay, too? (Glow indicator light now stays on while running.)

Important: That all the fuses for the headlights and the the glow relay's internal fuse are intact.

Assuming that the battery was already shot, and the car's harness was taking the full load of the charger, is it possible I've cooked headlights and the relay without burning the corresponding fuses? Any of this sound familiar to any of you? Too weird?
Normally you cannot test continuity of a live battery with an ohm meter. The battery is a low impedence (low resistance) device and acts as a very good voltage regulator keeping charging voltage across it to below 14 volts even thought he actual charging voltage is much higher. If the battery had "zero continuity", which I think you meant "open circuit", then it was not regulating at all and the headlights and other electrical components can be damaged by the high voltage.
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Old 07-28-2014, 10:09 AM
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Quote:
Originally Posted by funola View Post
Normally you cannot test continuity of a live battery with an ohm meter. The battery is a low impedence (low resistance) device and acts as a very good voltage regulator keeping charging voltage across it to below 14 volts even thought he actual charging voltage is much higher. If the battery had "zero continuity", which I think you meant "open circuit", then it was not regulating at all and the headlights and other electrical components can be damaged by the high voltage.
funola - Yes, as I mentioned above, old battery showed zero continuity. And I've since confirmed that, yes; the headlamps are blown, as were the radio fuse and one of the low-amperage (white) fuses in the master fusebox. Neither of the headlight fuses were blown, fwiw.

New battery does seem to be charging when running - as much as I can tell from several starts, and only a small amount of driving since replacing the battery yesterday. So I'm guessing the voltage regulator was not cooked...

Glow system remains a worry, though. Car starts as if plugs are not heating at all. Have not yet had a chance to start testing voltages/amperages to plugs, but...

Does it seem even plausible that the Glow Relay could be fried without any damage to its big internal fuse? (As I think about it, perhaps. Because that fuse protects the outbound circuit, I'd imagine, not the inbound one). Thoughts?

I'm just hating the thought of replacing the Glow Relay (again); it's only about 2yrs old, having gotten great, reliable service from the original one for 30 years!
__________________
'83 300 SD
'68 Triumph TR 250 - The only car I ever loved more than the Mercedes; who needs electricity, anyway? - Damn, why did I sell it?!
'59 Jaguar 3.4 'Le Chat Noir' - Damn, why did I sell it?!

It's difficult to make predictions, especially about the future.
- Niels Bohr
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  #10  
Old 07-28-2014, 10:22 AM
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Fuses care about amperage, not voltage. It is very possible for the glow plug relay or any other electrical /electronic device to be damaged by over voltage. Whether it does or not depends on whether it is designed for over voltage protection, i.e. whether it has zener didoes or electronic voltage regulators or not. Good luck.
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  #11  
Old 07-28-2014, 04:27 PM
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How cold does it have to be for the glow circuit to come on? You can measure voltage at the glow plug to know whether the glow is on. You can measure continuity of the wires also. Plug numbers are on the relay. Remove the cover and examine. There is also a cues inside the relay box.

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