Charging Circuit

[eeyore]

Hi everyone,

I'm trying diagnose the problem with my 4bd1 ute's charging circuit, and I could really do with some help :(. OEM 40amp Nippon Denso alternator has been rebuilt by local auto electrician last week. Regulator is 6 months old, solid state, internal fuse good. Pulled dash apart (a mistake, since it was held together with self-tappers, silicone and hope) to check indicator light and found that it's wired differently to the manual's circuit diagram. The Batt/Alt indicator lamp isn't connected back to the regulator harness at all, and the wires that should form that circuit are connect together via a very heavy fuse. Weird, since I thought it wouldn't have ever worked without the indicator lamp in the regulator circuit?

Anyway, since it wasn't working anyway, I wired it up as per the diagram - power from 'ign on' to indicator light with correct (Brown/yellow) wire to regulator - and lamp I substituted into the circuit works as expected - ie comes on with ignition, start engine and flickers at very low idle, touch throttle and permanently goes out. However, no charge to battery. I make a temporary patch harness in engine bay, power to regulator direct from battery, both with lamp and without, lamp behaves as it should and I do get some response at battery, reading goes from 12.1v at idle to about 12.9 at max revs (regardless of whether lamp is in circuit or not though).

Final test is to bypass regulator entirely and jump sense wire to battery. If I understand some of the stuff I've read, I should get full voltage from alternator - 15-16+ v - to battery? Instead, only get about 13.5, and that's at very high revs. So could all the problems be that the alternator is simply not showing enough voltage to the regulator? Can't work out why it should be the alternator though; newly rebuilt, belt is tight. Also wondered if there as a bad connection between alternator output and the battery at the starter solenoid but voltage readings at the battery terminals and at the output stud on the alternator are virtually identical.

Anyone have any suggestions? Is there something obvious I'm missing. I really don't understand auto electrics at all and after a couple of days with this, I'm ready admit defeat and take to an auto electrician :mad:

Thanks

[drivesafe]

Hi eeyore and although you have posted up a fair bit of info, still need a bit more.

From what you have posted, to get only 12.1v reading, if this is with the battery connected and it should be, then you probably have a problem with your battery.

Never run your motor and disconnect the battery, this can in a very short time period, stuff your alternator.

Now back to the voltage.

If your battery is in a low state and as you only have a 40 amp alternator, that low voltage could easily be caused by the battery pulling more current than the alternator is capable of producing.

In situations like this, and this is very commonplace, when an alternator’s maximum current production is exceeded, an alternators voltage drops. Again, this sort of situation is commonplace.

Again, if your battery is low, and as your alternator would be unlikely to produce as much as 15 amps at idle, it would be easy for your battery to try to pull way over 15 amps if it was in a low state.

Try leaving everything alone over night and before you do anything else to the vehicle in the morning, measure the battery’s voltage.

[eeyore]

Thanks for the reply :). (And I was a bit hesitant about posting about this problem because of how much info seems required in order to diagnose electrical problems!)

What you say about the battery state of charge and the effect on the alternator output is very helpful. Of course, now that you say it, it makes sense that excessive amp draw from that battery, especially with a small alternator, is going to drag the voltage down. You could be very right about the battery; I have had it on a recharger overnight during the last few days and the voltage never reads more than just over 12.1 in the morning. The battery is only about a year old but perhaps I'll take it to a battery place tomorrow and get it properly tested / recharged. Then I can see it that makes a difference...

Again, thanks for your help, much appreciated :)

[steveG]

I've had exactly that situation on my County in the past. With a couple of decent size batteries trying to charge after being stopped for a couple of nights camping, it would take 6 hours or more of highway driving before the voltage made up above 13v.

The 120A alternator that's fitted now doesn't have that issue :)

Steve