install 6 volt positive ground alternator

[Keefer]

Hello all.Want to install alternator on my 1939 P8 with ammeter but not quite sure how to wire it.Any info is very much appreciated.Thanks

Edited July 15, 2024 by Keefer

[Plymouthy Adams]

the use of the older limited ampmeter with the use of new (normally high output)  alternator is considered a risk to damage overheat/fire etc and why today they defer to a volt meter.  In the early period of ampmeter and alternators these were changed to shunted (mopar) and sampled the current flow to show discharge and charge only with no true indication of actual current only direction of current flow.   IF your alternator is an output equiv to stock and staying positive ground....should stay as is.    Exceeding the capacity of your amp gauge is not considered wise.

[Sniper]

A couple of points to bring out. What determines current flow in the charging system is the load. Not the alternator not the ammeter. As long as th OP doesn't add any additional electrical items this should be no increase in current through the system. That said old systems tend to have dirty connections which increase the load. A properly designed and calibrated shunted ammeter can most definitely show you accurate current values. Which is not to say the factory ones are like that because frankly it's really unnecessary. All they need to be able to do is show you whether or not it's charging or discharging and the relative amount of charge which they do just fine. One other thing to understand is that the only two loads going through the ammeter and a properly functioning vehicle is the current necessary to charge the battery and for some odd reason the horn. So I don't really think this is a concern

[Sam Buchanan]

3 hours ago, Keefer said:

Hello all.Want to install alternator on my 1939 P8 b=with ammeter but not quite sure how to wire it.Any info is very much appreciated.Thanks

 

I don't know the answer to the issue that has been raised in regard to whether or not your 1938 has the same type of ammeter as my 48. What I can tell you is the modern 6v alternator works beautifully in my car using the original ammeter. Connecting the alternator to your wiring architecture is straightforward because the new alternators are "single wire" and internally regulated which eliminates the old voltage regulator. There are several threads in the forum on this subject and we can walk you through this simple process if you decide to pursue it. Here is the vendor I and several other forum members have used to source our alternators:

 

https://www.ebay.com/str/HowardEnt?_trksid=p2047675.l2563

[Keefer]

Thank you.I have a one wire already installed in my var but not wired up yet.Also i have a fusible link in case i need it.Do i connect alternator to batt, terminal on voltage regulator or to battery or to battery lug on starter.

[Dave72dt]

The instructions from one vender shows it going to the voltage regulator BAT terminal with the FLD and ARM terminal wires disconnected.  Your vender should have had instructions with the alternator or a tech number to call.

[Sam Buchanan]

2 hours ago, Keefer said:

Thank you.I have a one wire already installed in my var but not wired up yet.Also i have a fusible link in case i need it.Do i connect alternator to batt, terminal on voltage regulator or to battery or to battery lug on starter.

 

BAT terminal on regulator or the actual battery terminal will work, they are electrically at the same potential. I'm not sure how the early stomp starters are wired. Most of us connect the single wire to the wire that was on the BAT terminal of the old voltage regulator. Your fuse can go between the alternator and where you connect the single wire. Its purpose is to protect the car's harness in the remote case something in the alternator shorts to ground. The link should be rated a little lower than the harness wires so it will open before smoke escapes from the harness.

 

Get ready to enjoy bright lights at idle and a battery that stays fully charged with none of the aggravation of keeping an old genny and regulator in working order! 

Edited July 15, 2024 by Sam Buchanan

[Keefer]

Thank You thats what needed to be done.

[denmopar]

On 7/15/2024 at 2:15 PM, Sniper said:

A couple of points to bring out. What determines current flow in the charging system is the load. Not the alternator not the ammeter. As long as th OP doesn't add any additional electrical items this should be no increase in current through the system. That said old systems tend to have dirty connections which increase the load. A properly designed and calibrated shunted ammeter can most definitely show you accurate current values. Which is not to say the factory ones are like that because frankly it's really unnecessary. All they need to be able to do is show you whether or not it's charging or discharging and the relative amount of charge which they do just fine. One other thing to understand is that the only two loads going through the ammeter and a properly functioning vehicle is the current necessary to charge the battery and for some odd reason the horn. So I don't really think this is a concern

 

"That said old systems tend to have dirty connections which increase the load."

With due respect, dirty connections from a power source to the load provides _increased resistance_ which causes a lesser load on the circuit.

That's why lights glow dimmer than they should, or starters turn slower than designed.

[Sniper]

1 hour ago, denmopar said:

 

"That said old systems tend to have dirty connections which increase the load."

With due respect, dirty connections from a power source to the load provides _increased resistance_ which causes a lesser load on the circuit.

That's why lights glow dimmer than they should, or starters turn slower than designed.

 

We can argue semantics, but any increased resistance in a circuit is a load increase.  Total voltage drop will remain the same, current drop across EACH source of resistance will change in the circuit as unwanted resistance will consume it's share of current.  Remember V=IR  So, as the unwanted sources of resistance consumes it's share of current, in the circuit, less is available to the wanted sources. 

 

The ammeter will increase it's output because it is voltage regulated, not current regulated.  So until you hit the upper limit of the alternator's output it will overcome.  That's what gives you the dim lights at idle symptom.  My 65 Cuda had that issue, till I cleaned up all the connections and it went away.  Original style mechanically regulated setup.  Now you can see the headlights flicker as the mechanical regulator cycles on/off but the lights do not go dim.

 

Not sure why you bring up starting, the charging system is not involved except indirectly insomuch as it is what keeps the battery charged.  Being that the starter is the biggest load on in the system any unwanted resistance's effect in the starting circuit is magnified and will negatively effect starting.  But that isn't part of the charging system and has no effect on how the charging system works except for the drain on the battery that needs to be replenished after starting is complete and that is matter of increasing the amount of time it will take to recharge the battery.

[desoto1939]

So on my 39 Desoto the volt reg has the original autolite tag and it is rated at 28 AMPS.  So if I installed the base alternator positive ground that is rated at 60 amps would I have any issues since it is rate at 30+ amps more that the original regulator?

 

Everyone is having their points of interest and input. ALso they make a fuse that can be directly attached to the battery tab on the volt regulator so that you do not blow out the VR.  I have several that I have in stock and they are rated at around 22 amps.  So could this also be used on the VR at the battery terminal tab with the 6 volt positive grnd alternator?

 

I still have the original 6v generator.

 

Rich Hartung

desoto1939@aol.com

 

Edited Saturday at 09:46 PM by desoto1939

[Sniper]

I do not know the intricacies of a generator's regulator setup.  I do know that on the alternator's setup the VR has to be capable of handling the field current of the alternator.  I assume something similar in a generator setup.

 

But as with anything, input determines output.  You aren't going to need that extra amperage if the load for it is not there so a fuse protecting it is probably a good idea.

[soth122003]

The biggest problem with the genny was it's variable speed out put. At idle the genny did not produce enough power to run the lights, radio and other system draws, which is why they installed the fast idle cable. The alternator on the other hand produced max power at idle. The genny was also DC current while the alternator was AC with a rectifier to change AC to DC.

 

Now with that said, just because the power was produced (either Genny or alternator) it was not all needed or used. That was the job of the voltage regulator for the genny and the rectifier for the alternator. Both supplied the needed volts/current to recharge the battery and stopped the extra power so it did not fry the electrical system.

 

The generator was capable of producing 30,40, 50 amps and so on, but it had to run at faster rpms to do so. The alternator did the same but it's max output was set at a predetermined rpm (usually low speed) so no matter how fast it ran (rpm) it would never increase it's rated output.

 

I switched to the Pos grnd alternator and have been very happy with it. Hooked the wire from the alt to the bat connection on the VR to maintain the look of the period. Sniper is also right that the ammeter is just a visual indication of charge/discharge. The more the needle moved the bigger the charge or discharge. The only numbers on the gage are the max number (usually 30) to indicate the output of the max load the electrical system can handle (I think, might be the genny size also). 

 

This is my layman's explanation of the system (not to include such things as corrosion, frayed wires and so on). If I got anything wrong feel free to correct me. (Still working on the FTL problem in my spare time).

 

Joe Lee

Edited Sunday at 06:22 PM by soth122003

[Sam Buchanan]

21 hours ago, desoto1939 said:

So on my 39 Desoto the volt reg has the original autolite tag and it is rated at 28 AMPS.  So if I installed the base alternator positive ground that is rated at 60 amps would I have any issues since it is rate at 30+ amps more that the original regulator?

 

 

Short answer....no. The alternator, regardless of its max rating, will not put out more current than needed to satisfy the loads on your electrical system. In other words, if your old genny put out 30a to accommodate the max load, then the new alternator will output similar current. Nothing gets fried and you can use your existing ammeter.

Edited Sunday at 07:19 PM by Sam Buchanan