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Old 10-06-2015, 20:29   #1
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Alternator output cable sparkles...

I'm putting things back together to get the engine running again (I'm in middle of redoing electrical/plumbing, etc...), but need to run the engine periodically.

When I touch the alternator output cable to the positive bus, it sparkles a little bit, barely noticable. It also sparkles when I touch it to the pos battery terminal.

Is that sparkling normal or is something drawing power through the alternator?

Attached is the current diagram.

Also, with the alt. output cable not connected to pos bus, when I put the pos probe of my digital multimeter on the pos terminal of battery or pos. bus bar and the neg probe on the end of the cable coming from the alternator, I get 13.34 volts (which is the same reading when I touch pos and neg terminals with multimeter).

All black lines are negative, all red lines are pos wires
Alternator is grounded via its bracket to the engine.
Negative bus bar conects to engine block, which connects to strut bolts

The on/off switch is in off position, so no power to ignition bus.

The sparkles occur even when I disconnect the two bilge pumps, battery charger, and echo charge from pos. bus
Does not matter if ignition bus is on or off.
Not shown on diagram is a single engine start battery, but it's not connected to anything except the neg. bus bar and the pos lead from the echo charge.

Thanks for the help.
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Old 10-06-2015, 21:49   #2
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Re: Alternator output cable sparkles...

Quote:
Originally Posted by scherzoja View Post
I'm putting things back together to get the engine running again (I'm in middle of redoing electrical/plumbing, etc...), but need to run the engine periodically.

When I touch the alternator output cable to the positive bus, it sparkles a little bit, barely noticable. It also sparkles when I touch it to the pos battery terminal.

Is that sparkling normal or is something drawing power through the alternator?

Attached is the current diagram.

Also, with the alt. output cable not connected to pos bus, when I put the pos probe of my digital multimeter on the pos terminal of battery or pos. bus bar and the neg probe on the end of the cable coming from the alternator, I get 13.34 volts (which is the same reading when I touch pos and neg terminals with multimeter).

All black lines are negative, all red lines are pos wires
Alternator is grounded via its bracket to the engine.
Negative bus bar conects to engine block, which connects to strut bolts

The on/off switch is in off position, so no power to ignition bus.

The sparkles occur even when I disconnect the two bilge pumps, battery charger, and echo charge from pos. bus
Does not matter if ignition bus is on or off.
Not shown on diagram is a single engine start battery, but it's not connected to anything except the neg. bus bar and the pos lead from the echo charge.

Thanks for the help.
Try disconnecting the voltmeter wire from alternator big + (output/bat) terminal.Voltmeter is only load I can see that would draw a tiny current.
If you still get sparking,remove big + wire from alternator bat+ terminal,set tester to it's highest amp setting. Connect red test lead to bat+/bussbar & neg test lead to alternator bat terminal. If you get a continuous amp reading,you may have an alt. problem. It would drain the battery.
A small spark & zero current is probably OK-just a brief surge charging the alt/regulator up-takes milliseconds.
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Old 10-06-2015, 22:09   #3
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Re: Alternator output cable sparkles...

Thanks for the advice on how to test. I've already tested with voltmeter wire off, but still get arcing. Tomorrow after work I'll test your recommendation with testing amps.

Thanks again.
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Old 10-06-2015, 22:48   #4
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Re: Alternator output cable sparkles...

Disconnecting an alternator while it is running can be a bad idea... Inside is a coil, coils dont like the current through them being changed and will fight the change, the faster the change, the harder they fight. The result is that a live disconnection will produce a large voltage, enough to spark.
Batteries will absorb the spike, so your electronics will be safe, but certainly disconnecting battery in a running car is a good way to kill the car.
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Old 11-06-2015, 04:54   #5
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Re: Alternator output cable sparkles...

Dougal,

Thanks for the caution about disconnecting while running. I presumed Deblen meant with engine off.
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Old 11-06-2015, 08:25   #6
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Re: Alternator output cable sparkles...

Hello scherzoja, while watching this sparkling, you may probably destroy Your alternator. When the alternator is rotating, and the controllight is switched on, the alternator is producing power. When without load, because You disconnected B+, the output voltage can raise very high, to several hundred Volts. This is causing the sparkling. Same time the diodes inside the alternator burn up, shortcutting the output windings.
Never let the alternator rotate without B+ connection!
Greetings
nw
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Old 11-06-2015, 08:45   #7
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Re: Alternator output cable sparkles...

Mariner,

Thanks for the info about possibly destroying the alternator.. I should have mentioned in initial post that the alternator is not spinning. In fact the engine isn't even tunning, it has no oil, coolant, or fuel yet.

Also, the arcing is very subtle, almost imperceptible when contacting the copper part of pod bus bar. Arcing is more noticeable when contacting the stainless steel but on the pos bus bar. I guess that is expected because of higher resistance of stainless.

Thanks again for the help.
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Old 11-06-2015, 09:24   #8
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Re: Alternator output cable sparkles...

It could be that one of the diodes in the alternator is bad. It also could be that you are charging up a capacitor. Do you have any noise suppression capacitors on the alternator?

Try touching the wire multiple times in a few seconds--if the sparks stop, its probably a capacitor. If they continue it is more likely a bad diode.
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Old 11-06-2015, 09:40   #9
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Re: Alternator output cable sparkles...

Quote:
Originally Posted by deblen View Post
Try disconnecting the voltmeter wire from alternator big + (output/bat) terminal.Voltmeter is only load I can see that would draw a tiny current.
If you still get sparking,remove big + wire from alternator bat+ terminal,set tester to it's highest amp setting. Connect red test lead to bat+/bussbar & neg test lead to alternator bat terminal. If you get a continuous amp reading,you may have an alt. problem. It would drain the battery.
A small spark & zero current is probably OK-just a brief surge charging the alt/regulator up-takes milliseconds.
Hi

the above is good advice. Looking at the schematic you provided I see that the field and sensing wires aren't connected. it may not be a problem with some alternators, but what kind of alternator do you have? some times those connections aren't used as they are for other accessories.
If, when you get the engine started and the alt doesn't work try connecting the "s" terminal (red) to the pos bus and the "f" terminal (brown) to the Ign. switch. the field circuit excites the alt. and the sensing circuit controls the load or charging volts/amps.
If you have a continuos current draw it could be a bad diode in the bridge or trio, depending on what alt you have.
Good luck.
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Old 11-06-2015, 10:01   #10
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Re: Alternator output cable sparkles...

Thanks for the direction on where to connect those other wires. I have tested the touch-many-times-in-a-few-seconds and sparking persists. No idea what kind of alternator. There are no markings on it, no serial/model numbers. Tonight when I get home I'll try the tests ya'll have mentioned and upload a pic of the alt.

It'll be another week or do before I get engine running.

Thanks again for your help.
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Old 11-06-2015, 11:31   #11
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Re: Alternator output cable sparkles...

"is something drawing power through the alternator?"
Apparently your battery charger is supplying power and confusing the picture. Proven by the "battery" voltage being well over 13 volts, when a fully charged battery, after the float charge has been drained off, will never exceed 12.8 volts.
I'd get the charger out of the picture until you figured out the rest of it.


You can do alternator diagnostics with just a multimeter, but if there's an auto chain handy, most of them will bench test an alternator for free (and about half the time they get it right) if you bring it in. If they guy doing the testing seems unsure of what he's doing...take it elsewhere.
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Old 11-06-2015, 12:27   #12
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Re: Alternator output cable sparkles...

Quote:
Originally Posted by donradcliffe View Post
It could be that one of the diodes in the alternator is bad. It also could be that you are charging up a capacitor. Do you have any noise suppression capacitors on the alternator?

Try touching the wire multiple times in a few seconds--if the sparks stop, its probably a capacitor. If they continue it is more likely a bad diode.
I agree...likely you have a capacitor somewhere in the works. It has some saved up power which is causing the sparks.

As an example on my boat, with the battery switch moved to OFF (no power) I can turn on an LED light, which runs for a few seconds. This boggled me. Until I realized the light was on the same circuit as the VHF radio. The VHF was providing a wee bit of power back into the circuit. Battery chargers would also be suspect...since they sometimes use large capacitors to "smooth" the output voltage.
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Old 11-06-2015, 15:20   #13
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Re: Alternator output cable sparkles...

OK,

I got home and disconnected all the extra junk, including the four 6v series/parallel batteries. Now all I have is one start battery, no charger connected.
Multimeter on pos and neg posts with nothing connected shows 13.31 volts.

Ground cable goes from neg terminal on the one battery to engine block.
There is no pos cable connected to the battery. The I removed the cabel from the BAT terminal of the alternator and there are no other wired connected to alternator.

Now, with the neg cable going from batt neg post to block and I put pos lead on MM on pos post, then touch neg lead of MM on alternator I get 13.0x volts.

Also, when I connect cable back to BAT terminal of alterntor and touch the pos post of the batter, I get subtle arching.

Deblen, I tried your test with MM set for 10amps, but go reading of zero.

Engine is not running, so can't do any tests with engine running.
I guess I'll take it out and get it tested.
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Old 11-06-2015, 15:39   #14
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Re: Alternator output cable sparkles...

"Now all I have is one start battery, no charger connected.
Multimeter on pos and neg posts with nothing connected shows 13.31 volts. "
Either you're seeing a float charge, or a meter error. Probably a float charge which will go away after 8-12 hours of just sitting there. If you want to knock off the float charge in a few minutes, hook up a load like an old car headlight, anything that will draw some power for five minutes. Then disconnect it and re-measure.

"Now, with the neg cable going from batt neg post to block and I put pos lead on MM on pos post, then touch neg lead of MM on alternator I get 13.0x volts."
Not unusual, you are seeing a "cable loss" of 0.31 volts in your wiring, which includes the cables and the engine block acting as a ground conductor to the alternator. Less would be better, cleaning and tightening connections might help that, or that might just be as good as it gets.

"Also, when I connect cable back to BAT terminal of alterntor and touch the pos post of the batter, I get subtle arching. " When you say the BAT terminal, you do mean the alternator's battery OUTPUT charging terminal, yes? Not the B+ terminal in the alternator's wiring harness, which usually has 2-3 smaller wires in it? I'm not at all certain but think that would mean a bad (leaking or shorted) diode in the alternator, if that's the only connection to the alternator other than ground.

"Deblen, I tried your test with MM set for 10amps, but go reading of zero. "
Not making any assumptions, but are you familiar with using the amp function of your multimeter? With some, you must plug the + test lead into an "amp" socket, not the usual one used for voltage reading. And, there is also a separate internal fuse for the amp functions, which is easily blown if the meter is used incorrectly. That could also cause a "0" reading. You can also get some erroneous readings if the meter is set to AC amps and you're trying to read DC. If you are in doubt--at all--use the amp meter function to test the amperage pulled by a small cabin light, or a small radio, etc. And if that internal fuse is blown, you may need to mail-order a replacement pack, they're almost always rather special and hard to find. And should be replaced with the exact same type.
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Old 11-06-2015, 16:38   #15
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Re: Alternator output cable sparkles...

Thanks for all your replies and advice.

It looks like I'm in the market for a new alternator.
I didn't get the alt. tested, but the local mechanic identified the alternator, which has no markings, as a GM alternator, like one would find in a pickup truck or down at the chevy dealer. Also, the terminal on the alternator labeled BAT is lose; wen I tighten the nut to hold the pos cable on , the stud begins to spin.
Third, after examining the engine rotation (didn't actually look at rotation because engine is not running, no oil, no coolant, no fuel, but I know it rotates CW), I realized that the alternator is being rotated backwards! Not sure for how long the PO ran with that alternator rotating backwards, but I'll guess it might have been pushed to or over it's thermal limits because the cooling fins are directional!

I'm not one to take too many chances and, since the boat's pretty much torn apart for remodel anyway, I'm going to toss this POS and get one that is appropriate for my engine's rotation, appropriate or the 464AH house bank capacity, and one that actually has a manual!.

Again, thanks or all your help and time.
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