New alternator, still not enough voltage

[colo525i]

.3 ohm resistance between the body and the lift hook on the front of the cylinder head. That is pretty low in my book. I'm charging the batt again, but a charged battery seemed to have no effect.

[etcetera]

.3 ohm resistance between the body and the lift hook on the front of the cylinder head. That is pretty low in my book. I'm charging the batt again, but a charged battery seemed to have no effect.

.3 ohms is high. Should be very close to zero.

Measure from - terminal of battery to alternator housing. Also measure from the + terminal of alternator to + terminal of battery. High resistance between either point won't allow your battery to charge.

E = I x R

E Voltage drop
I current in amps
R resistance in ohms

E=40 amps x .3ohms
E=12 volts drop
With this load there is no charging taking place

E=4amps x .3ohms
E=1.2 volts
assuming 14.4volts output from the alt that leaves 13.2 to charge the battery. Not adequate but at least the car will run.

When I measure mine it's practically zero on an analog meter, unfortunately my digital meter was stolen.

http://epg.modot.org/index.php?title...cal_Components

[colo525i]

I'll test some other wires to make sure it isn't this multimeter as well.. I had no idea that such a small reading of resistance would stop charging...more you know i guess. edit--- looks like the multimeter is to blame for that reading. even touching to 2 ends of a copper wire it still shows .3 ohms...

[Karl]

On my car I added a jumper from the alternator case to the engine block, so the alternator is not grounded through its mounting bracket only, and then another heavy wire from that point on the block to the body connection for the battery grounding strap. That cleared up some charging problems. Cars with their battery under the rear seat have to be even more careful of ground connections, just because of the extra distance and more joints between the alternator and battery.

[etcetera]

I'll test some other wires to make sure it isn't this multimeter as well.. I had no idea that such a small reading of resistance would stop charging...more you know i guess. edit--- looks like the multimeter is to blame for that reading. even touching to 2 ends of a copper wire it still shows .3 ohms...

There might be an adjustment to zero the resistance when touching the leads.

[bill g]

A common fallacy has raised its head here. Resistance readings are often misleading in this type of situation - for example a single strand of wire the thickness of a hair will read zero ohms but will not be thick enough to carry the current. Karls post has given a clue here - you could try installing temporary jumper leads between the components to ensure you have good connections.

Bill G

[colo525i]

Thanks for all the ideas, but nothing has helped as of yet. I have tried jumping the ground from the battery to the lift hook on the engine and to the body. Also have tried jumping the B+ post in the engine bay to the + on the battery. No change from either of those. I am thinking it may be the alternator not grounding to the frame somehow. Are there any relays/diodes etc that could not close properly and cause a bad ground as well?

[bsell]

Thanks for all the ideas, but nothing has helped as of yet. I have tried jumping the ground from the battery to the lift hook on the engine and to the body. Also have tried jumping the B+ post in the engine bay to the + on the battery. No change from either of those. I am thinking it may be the alternator not grounding to the frame somehow. Are there any relays/diodes etc that could not close properly and cause a bad ground as well?

So you did not touch the jumper to the case of the alternator itself during the negative circuit check? That would remove the bracket as a suspect. You might have to break the bracket bolts loose and retighten to get clean electrical contact.

The last jumper check I can suggest is to bypass the car's wiring and frame by using two jumpers, one from the case to neg bat post and the other from the B+ on the alternator to the pos bat post. Of course good quality jumper cables (meaning fat boys!) are in order for this test. If the reading is still low at the battery with above idle engine speed, you have a ghost in the machine! or bad jumpers too.

You already cleaned the connections at the battery to remove any old skin effect problems, right? Cleaning all of the ground connections between the block and the car and the battery to car may be the only other recourse. I have found the source of similarly frustrating situations after checking every wire/connection in the circuit. Tedious but necessary.

I take it you got your 141 amps output with the engine revved above idle...

Brian

[colo525i]

I'll give the alt shell to negative battery route a try. When they did the load test on the alternator it managed to put out 141 amps at 2000 rpm but 13 v. It was hooked up to the B+ post and the lift hook. So it would seem the resistance/bad connection is between the B+ and alternator or the bracket and the engine itself. Does that seem correct?

[632 Regal]

after all this anything seems correct, I have thrown cars away with similar electrical nonsence.

I'll give the alt shell to negative battery route a try. When they did the load test on the alternator it managed to put out 141 amps at 2000 rpm but 13 v. It was hooked up to the B+ post and the lift hook. So it would seem the resistance/bad connection is between the B+ and alternator or the bracket and the engine itself. Does that seem correct?