One wire alternator

[85lebaront2]

I'm not a Powermaster alternator fan. Big Blue had one when I acquired him and it failed soon thereafter. Called Powermaster to get parts and was informed that they don't sell parts - you return the alternator to them for repair.

I'm not into that. I want to be able to get repair parts at the local auto parts if the thing fails while I'm on the road. So now I'm running a box stock 3G. But any 3G, even a souped-up one like Bill's 160A unit, would be fine because you can always drop another 3G in its place for the trip home. Like maybe even from a salvage Not true of the 1-wire Powermasters as you have to wire specifically for a 1-wire.

I'll let Scott/kramttocs persuade you that the Powermasters are the way to go. He's the Powermaster czar as I think he now has three of them - inc my bad one. Took me several years to find someone that would take it off my hands - for free.

My "souped up" 3G is essentially a Taurus 3.8L 130 amp 3G (which is an easy way to get one) It uses two wires, a big output wire through a 200amp megafuse and a small LG/R from the instrument cluster idiot light. I can get a 130 amp one easily (I actually have a spare) if I need it.

The reason I am not a huge fan of one wire units, if your gauge, be it the original "I might actually read" unit or a converted to a volt meter one, unless you watch it on starting and keep an eye on it driving, you may not realize the alternator isn't charging. The idiot light gives a real fast "it's charging" on start up and a pretty quick "oh crap" if it quits.

[Gsmblue]

My "souped up" 3G is essentially a Taurus 3.8L 130 amp 3G (which is an easy way to get one) It uses two wires, a big output wire through a 200amp megafuse and a small LG/R from the instrument cluster idiot light. I can get a 130 amp one easily (I actually have a spare) if I need it.

The reason I am not a huge fan of one wire units, if your gauge, be it the original "I might actually read" unit or a converted to a volt meter one, unless you watch it on starting and keep an eye on it driving, you may not realize the alternator isn't charging. The idiot light gives a real fast "it's charging" on start up and a pretty quick "oh crap" if it quits.

Wow, so much info!!!

I am not sure i will keep this 1 wire. It is amazon so returns are easy.

[Gary Lewis]

Wow, so much info!!!

I am not sure i will keep this 1 wire. It is amazon so returns are easy.

If you go with a 3G THEN you can clean up the old wiring. Remove the regulator from the fender. Get rid of the undersized charge wire, etc. 'Cause wherever you go you can get a replacement.

I don't know about the Powermaster, but a bog stock 3G puts out as much at idle than a 1G does at full tilt. Your lights will stay bright. The HVAC fan stays spinning rapidly, etc.

[Gsmblue]

If you go with a 3G THEN you can clean up the old wiring. Remove the regulator from the fender. Get rid of the undersized charge wire, etc. 'Cause wherever you go you can get a replacement.

I don't know about the Powermaster, but a bog stock 3G puts out as much at idle than a 1G does at full tilt. Your lights will stay bright. The HVAC fan stays spinning rapidly, etc.

Tonight I pulled out my 1981 EVTM and and started to look at this more closely. The picture below is the actual wiring harness for my 1G alternator.

NOTE: I have only pulled the harness out to make it easy to see what is going on and to fix that S202 splice properly. It will get a nice cover go back in.

My big question is how to disable the shunt in a way that doesn't butcher the harness. It looks like I can just remove it from S202 and tape it up. Is that all I really need to do?

It also looks like power will still get to the voltage regulator, should I leave that disconnected?

Does anyone have any thoughts?

 

[Gary Lewis]

Tonight I pulled out my 1981 EVTM and and started to look at this more closely. The picture below is the actual wiring harness for my 1G alternator.

NOTE: I have only pulled the harness out to make it easy to see what is going on and to fix that S202 splice properly. It will get a nice cover go back in.

My big question is how to disable the shunt in a way that doesn't butcher the harness. It looks like I can just remove it from S202 and tape it up. Is that all I really need to do?

It also looks like power will still get to the voltage regulator, should I leave that disconnected?

Does anyone have any thoughts?

Depending on what you are going to do you may not need to remove the shunt. It is just a smaller wire and is capable of handling the full output of the 70A 1G alternators, so if you move the alternator output to the starter relay then the shunt will only be seeing the current into the cab. And it is very unlikely that you'll pull over 70A in the cab.

As shown on the page at Documentation/Electrical/Ammeter I measured the voltage required to peg 4 different ammeters, and it took from .102 volts to .156 volts depending on the ammeter. In other words, that's probably the voltage drop across the shunt when carrying 60 - 70 amps. And that isn't much voltage drop.

But, if you really want to eliminate the shunt just cut it out and put a larger piece of wire in its place between S201 and S202.

[Gsmblue]

Depending on what you are going to do you may not need to remove the shunt. It is just a smaller wire and is capable of handling the full output of the 70A 1G alternators, so if you move the alternator output to the starter relay then the shunt will only be seeing the current into the cab. And it is very unlikely that you'll pull over 70A in the cab.

As shown on the page at Documentation/Electrical/Ammeter I measured the voltage required to peg 4 different ammeters, and it took from .102 volts to .156 volts depending on the ammeter. In other words, that's probably the voltage drop across the shunt when carrying 60 - 70 amps. And that isn't much voltage drop.

But, if you really want to eliminate the shunt just cut it out and put a larger piece of wire in its place between S201 and S202.

Thanks for the feedback. I am going to run a 6 gauge wire to to battery side of the starter relay and I want to change the ammeter for a voltmeter. The rocket an upgrade.

Looks like I don’t need to worry about the shunt but I can replace some of that wiring to the alternator and fix the S202 splice then put one of those nice corrugated covers on and tie it away.

I have read that the external regulators should be disconnected so I will probably remove the regulator from the fender and tape up the connector. The theory being that if I need to buy a 1G alternator I should be able to source a regulator too.

[Gary Lewis]

Thanks for the feedback. I am going to run a 6 gauge wire to to battery side of the starter relay and I want to change the ammeter for a voltmeter. The rocket an upgrade.

Looks like I don’t need to worry about the shunt but I can replace some of that wiring to the alternator and fix the S202 splice then put one of those nice corrugated covers on and tie it away.

I have read that the external regulators should be disconnected so I will probably remove the regulator from the fender and tape up the connector. The theory being that if I need to buy a 1G alternator I should be able to source a regulator too.

If you are going with a 1-wire then yes, I'd leave the 1G wiring in place and tape it up. And it would be wise to buy a new regulator at the same time as the new alternator, so remove the regulator and tape its connector up.

But if you are converting the ammeter to a voltmeter you have one other change to make in the original wiring. You need to provide both battery voltage and ground to the voltmeter, but only when the key is on or you'll run the battery down powering the voltmeter 24x7. One way is shown below. It uses the original wiring that runs to the ammeter, but you remove the yellow/light green wire from S202 and take it to a relay that grounds it when the key is turned on.

Another, probably easier, way to do that is shown below. Don't mind that it shows a 3G alternator, you can still wire the 1-wire as in the previous schematic with the large wire going to the battery side of the starter relay, although I'd recommend installing a fuse in the circuit. But if you wire the voltmeter this way you won't have to have the relay in the previous approach.

[Gsmblue]

If you are going with a 1-wire then yes, I'd leave the 1G wiring in place and tape it up. And it would be wise to buy a new regulator at the same time as the new alternator, so remove the regulator and tape its connector up.

But if you are converting the ammeter to a voltmeter you have one other change to make in the original wiring. You need to provide both battery voltage and ground to the voltmeter, but only when the key is on or you'll run the battery down powering the voltmeter 24x7. One way is shown below. It uses the original wiring that runs to the ammeter, but you remove the yellow/light green wire from S202 and take it to a relay that grounds it when the key is turned on.

Another, probably easier, way to do that is shown below. Don't mind that it shows a 3G alternator, you can still wire the 1-wire as in the previous schematic with the large wire going to the battery side of the starter relay, although I'd recommend installing a fuse in the circuit. But if you wire the voltmeter this way you won't have to have the relay in the previous approach.

Gary,

That last diagram has confused me a little bit. I get the grounding of the Y/LG on one side of the Ammeter (to be voltmeter), no problem.

The other +Ve side has me confused the LG/R wire is normally connected to the external voltage regulator then on to the dash cluster. But now it is not connected to anything that I can see. Where is it getting it's +Ve from?

[Gary Lewis]

Gary,

That last diagram has confused me a little bit. I get the grounding of the Y/LG on one side of the Ammeter (to be voltmeter), no problem.

The other +Ve side has me confused the LG/R wire is normally connected to the external voltage regulator then on to the dash cluster. But now it is not connected to anything that I can see. Where is it getting it's +Ve from?

That LG/R wire is the key-on power to the alternator. It bootstraps the alternator in. (There's the difference in a 1-wire and a normal alternator.)

Note that it says "Continued on Page 16". Here's Page 16: (NB: This is from the 1986 EVTM as it is showing the 2G firestarter alternator, and the '86 trucks were the only Bullnose trucks afflicted with them. And, btw, you are one of the few on here that understands "NB". )

[Gsmblue]

That LG/R wire is the key-on power to the alternator. It bootstraps the alternator in. (There's the difference in a 1-wire and a normal alternator.)

Note that it says "Continued on Page 16". Here's Page 16: (NB: This is from the 1986 EVTM as it is showing the 2G firestarter alternator, and the '86 trucks were the only Bullnose trucks afflicted with them. And, btw, you are one of the few on here that understands "NB". )

Ah! I thought it was an output from the voltage regulator to the dash, but it is the other way around!

Thanks Gary, as always invaluable help!

I will grab a mega fuse later on today and hopefully I can get this all wired in :)