alternator issues

[elbundi]

I recently (well within the last 6 months) bought a Powermaster 140 amp one wire alternator. I've had nothing but less 11.5v at the dash since.

There's a two spade connector on the alt. I put one to the positive pin out on the alt and the other to the tan ignition wire via a dash light (using the glow plug lamp) seen in the diagram. Ran a 2 awg wire from the alt to the isolator. Isolator is new. Battery was checked and holds a load, alternator was removed and checked and is working fine.

When I start the engine the dash light (glow plug) lights up. Checking the voltage at the isolator I get 13.6V from the alt, and 12.56V from the auto and the house batteries. If I disconnect the alt wire from the isolator and test I get 24V!

I've attached 3 diagrams, one of my setup and two others of a before and after belt configuration. The other alternator died soon after I removed the pulley on the smog pump and ran a shorter belt. Could this be the issue? I've asked numerous mechanics and some say it'll spin the wheel faster , others say so long as the crank pulley wheel is the same it shouldn't be an issue.

What should be a simple repair has brought me to my knees. Any suggestions?

[barts]

The length of the belt has no effect; all that matters is direction of rotation and relative pulley sizes.

Diode type isolators can result in low charge in the batteries due to the .7 volt forward voltage drop on the diodes. The relay type (battery combiner) isolators are often preferred for this reason.

It also sounds like you have some ground/corrosion issues somewhere; I would spend some time looking at voltages across connections.

- Bart

[bkahler]

I agree with Bart. Unless you changed the crank pulley diameter your belt speed to the alternator is not going to change. My guess is the tension on the alternator pulley/shaft changed which probably caused your failure. Also your alternator may well have been on its last leg anyway.

As for your voltage problem many of us have voltage problems to the dash also. With only the engine running and NO accessories being powered I read about 13 volts. Once I gurn on lights or A/C, heator or whatever my dash voltage drops to 11 or even less at times. There is a definite wiring issue that needs to be dealt with.

Bart has a good suggestion troubleshooting which is to check the condition of ALL ground connections on your motorhome. Believe it or not I have found that a bad ground connection is the ususal culprit.

Definitely keep us posted as to what you find the problem.

Brad

[richinny]

make sure you have a good ground from the engine to the chassis.

follow the alternator wire with the volt meter until you see the drop. it might be the bulkhead connection on the firewall.

i've seen posts indicating that the ignition switch may be under capacity when used in these rigs. chech the voltage going in and out and compare it.

[barts]

Originally Posted by richinny

make sure you have a good ground from the engine to the chassis.

follow the alternator wire with the volt meter until you see the drop. it might be the bulkhead connection on the firewall.

i've seen posts indicating that the ignition switch may be under capacity when used in these rigs. chech the voltage going in and out and compare it.

All good suggestions; I've seen the engine ground problem before.
A good flexible ground (welding cable works well) can really help.

As regards the ignition switch, 80 amp automotive relays are really cheap and solve a lot of problems.

- Bart

[bkahler]

Originally Posted by barts

As regards the ignition switch, 80 amp automotive relays are really cheap and solve a lot of problems.

- Bart

Bart,

Can you recommend a source and/or part number for the 80 amp relay?

Thanks!

Brad

[barts]

Originally Posted by bkahler

Bart,

Can you recommend a source and/or part number for the 80 amp relay?

Thanks!

Brad

My previous Bosch source has disappeared (or I misremembered it), but:

High Power 80 Amp Relay Single Pole, Double Throw: eBay Motors (item 150306790794 end time Sep-19-10 08:52:42 PDT)

Of course, if you can use separate smaller relays for the different circuits, you're better off.

- Bart

[elbundi]

Well I did start on the trace today. The wire going back from the isolator to the engine battery goes via the starter. What looked like a loose connection on the solenoid crumbled when I tried to tighten it, so had to buy a new starter (see before and after pics) Now I'm getting a consistent 12.7v at the battery end when running but still 11.5v at the dash
Another good thing is I've now reconnected with the 345 and decided not to sell! Sorry to have disappointed the guy in TX but if anyone's wanting to sell I know someone eager to join the club

[elbundi]

If I'm understanding the second post in the link below correctly I add a diode on the charge light wire with equivalent .7v drop?
Battery combiner vs battery isolator - SailNet Community

[Robfike]

Glad to hear you are going to keep the 345. I just can't imagine not having one.

[elbundi]

[QUOTE=Robfike;899525]Glad to hear you are going to keep the 345. I just can't imagine not having one.[/

When a potential sale became real I had 2nd thoughts! I still updated the 6 rear maypops with new 8R19.5's though

"As regards the ignition switch, 80 amp automotive relays are really cheap and solve a lot of problems. "

Good call. I got 13.5 at the dash yesterday, woohoo, I stopped at an auto store to buy some gloves for the tire updates but only got 11.5 on at the dash on restart
Couldn't find the ignition relay today, but didn't spend much time looking. It has to be there somewhere right!

As for the .7 voltage drop on the isolator (which I bypassed yesterday) need to figure what size resistor needs to go on the sense wire to the alt.

Strange how we still become attached to these classics

[dljosephson]

Originally Posted by elbundi

Good call. I got 13.5 at the dash yesterday, woohoo, I stopped at an auto store to buy some gloves for the tire updates but only got 11.5 on at the dash on restart
Couldn't find the ignition relay today, but didn't spend much time looking. It has to be there somewhere right!

I don't think there *is* an ignition relay, that's the problem. From the ignition output of the key switch it goes to the fuse block through a bunch of old crimped connections on both sides of the firewall. All the current flows through the key switch. As Bart suggests, the fix is to *install* a relay that feeds the high-current loads directly, through a new fuse block that isn't corroded and worn. These used to be called Bosch relays but they are made by Tyco now and cost about $4.

As for the .7 voltage drop on the isolator (which I bypassed yesterday) need to figure what size resistor needs to go on the sense wire to the alt.

Why do you need a resistor? Is there even a sense wire on a "one-wire" alternator? Forget the light for now, check that you have a heavy (4 ga or bigger) wire from the alternator output post to the positive post of the battery, and be sure that the bolts holding the alternator make a solid enough connection that you can't measure any voltage between the case of the alternator and the engine block, when it's charging (all fans and headlights on, >1500 rpm). Powermaster alternators I've seen have no charge light or sense wire, that's another reason it's so important to have a fat wire (low resistance) between it and the battery.