Charging System Issue

[elemgee]

I have a 94 SVX and have have a charging system issue which I think I've unknowingly had for quite some time. Many times over the past few months the engine turns over slowly before starting.

Let me start by saying that I have the alternator wiring upgrade. About a week ago all of my dash lights came on when I was stopped at a light. And occasionally my semi-high output stereo (500 watt amp) will cut out. The next morning I charged the battery, attached a voltmeter to the battery and it read about 12.2 volts with the engine off. When I turned on the engine, the voltmeter read 11.5 volts at the battery. With the engine still running, I moved the positive line of the voltmeter from the positive battery terminal to the top of the alternator - where the cable from the positive terminal of the battery screws in - and it read 15.7 volts.

So it seems that my battery isn't charging (due to the low reading at the battery when the engine is running) but that the alternator is putting out current. Any idea what the problem can be? I should also mention the battery is about 4 years old.

Thanks.

Larry

[aurikai]

Sounds like you might have two problems here. Battery and alternator.

First if your alternator is putting out 15.7 volts you might have a problem with your voltage regulator. Should be putting out about 14 volts +/- 0.5

Overvolting can cause weird things to happen like you experienced (random/all dash lights coming on) and can damage components and even the battery. I had the dash lights issue too with the alternator that was in my SVX when i got it, had a high reading (18 volts!) so i knew the voltage regulator was toast. It cost just as much to get a new/refurbished alternator from Napa or autozone etc... as it would have cost to get a replacement regulator (svx alternator has internal regulator which tends to be more expensive I found) so i got a new alternator and the problem went right away.

12.2v at the battery with engine off is on the low side. 11.5v running is definitely worrying (should be reading similar to what the alternator is putting out which means its getting a charge). Check the wires for damage/correct hook up and have an auto store that offers free battery checks hook their reader up to it to get a definitive answer on battery condition.


It was about 6 months or so that I dealt with this on my svx so I might have remembered the voltage specs a little wrong, but should be pretty close. if someone more experienced has any corrections please do.

hope this helps man!

[Blacky]

I agree with aurikai. 15.7 is too high. 4 years is often the lifespan for a battery depending on your location, driving habits etc. Overcharging or other electrical issues can shorten a battery's life considerably.

[elemgee]

I ran the car in the garage for an hour, at idle, with the headlights on. If it was going to stall out I'd rather it happen in the garage. But it ran the entire hour without stalling. After an hour I rechecked the voltmeter readings. They read 12.7 volts across the battery (engine at idle with headlights on) and 13.7 at the alternator. With the headlights off they read about 13.0. But when I revved the engine up, the reading didn't change from the 13.0.

I read on this website that my original low reading at the battery after startup (around 11.5 volts) may be due to the starter using a lot of juice.

I'm encouraged that the car didn't shut off in the garage, but I'm not clear as to whether I have a charging issue or not.

[oab_au]

Check the fuse-able link. The alternator charges the battery through this link, it may have a high resistance.

[elemgee]

OK, I found the fusible link in the engine compartment fuse box. How do I test its resistance and what is considered out of spec?

[svxcess]

I would order one anyway. PN 82301PA000. Less than $6.00.

If yourd turns out to be bad, you have a spare.
.These are nice to have around
.

[svxcess]

I believe everything, except the head lights, is supplied via the fusible link. Obviously resistance within this link would cause voltage drop throughout the system, dependent on the current load and associated problems. But no other malfunctions or symptoms are mentioned.

The alternator wiring modification should provide a direct connection between the alternator and the battery and bypasses the fusible link.

Provided that measurements are taken correctly, if at any time there is a difference in voltage at the main alternator terminal and the battery post, this circuit must involve resistance. In this event the reason for what must amount to a poor connection must be found and corrected.

All things considered, I would suspect a wiring modification issue.
.

[elemgee]

With the engine running I attached the voltmeter leads to the alternator body and negative battery post and it showed a negligible amount of resistance. I then attached the leads to the positive alternator connection and the positive battery post and it showed several volts of resistance which would account for the problem. So I first checked all fuses and they were fine. i then cleaned all positive battery clamps and the battery post and that seemed to have solved the problem. With the engine running the battery now shows around 14 volts, alternator shows 14.5 volts.

Thanks to everyone for their help.

[svxcess]

Originally Posted by elemgee

I attached the voltmeter leads to the alternator body and negative battery post and it showed a negligible amount of resistance. I then attached the leads to the positive alternator connection and the positive battery post and it showed several volts of resistance which would account for the problem.

Glad you got if figured out. Wise to be looking for a voltage drop than looking for resistance in ohms.

.

[elemgee]

Wanted to close the loop on this. My engine died a couple of miles from my house a couple of days ago. Oddly enough, I'd just taken a 60 mile round trip at night a couple of nights prior with no problem.

When I got the car home on Friday evening I rechecked the charging system and there was clearly the same problem as before - with the engine running the voltage at the battery was lower than with the engine off, so there was resistance somewhere.

After replacing the positive battery to the starter cable with no noticeable change, I then replaced the cable going from the alternator to the battery. That was the problem. After replacing that cable (which is only a couple of years old - included in an alternator upgrade kit I used when upgrading the stereo) the voltage at the alternator and at the battery when idling, were all within spec.

Just wanted to post this so any future searches on this topic may be helped by this.