vette-kid Posted January 23, 2022 Share Posted January 23, 2022 We recently required my 36 P2. Everything functions great, but dad drove it today and says it looks backwards. With the engine on and ALL electrical of it shows a discharge, but with all on it shows a charge. That would seem backward, but I don't see how we could have them switched without creating a short, and since everything works then there clearly isn't a short. Are we reading the gauge wrong? Or do I have something mixed up? Link to comment Share on other sites More sharing options...
vette-kid Posted January 23, 2022 Author Share Posted January 23, 2022 This is at idle with nothing on Link to comment Share on other sites More sharing options...
vette-kid Posted January 23, 2022 Author Share Posted January 23, 2022 (edited) Engine off, lights on Edited January 23, 2022 by vette-kid (see edit history) Link to comment Share on other sites More sharing options...
vette-kid Posted January 23, 2022 Author Share Posted January 23, 2022 Idle with lights Link to comment Share on other sites More sharing options...
vette-kid Posted January 23, 2022 Author Share Posted January 23, 2022 High idle with lights Link to comment Share on other sites More sharing options...
broker-len Posted January 23, 2022 Share Posted January 23, 2022 (edited) this car is positive ground is the battery wired correctly ???? are there any shorts in wire system kind of hard to diagnose. from computor Edited January 23, 2022 by broker-len (see edit history) Link to comment Share on other sites More sharing options...
vette-kid Posted January 23, 2022 Author Share Posted January 23, 2022 No indication of a short. Everything functions just fine, aside from the ammeter reading anyway Link to comment Share on other sites More sharing options...
Matt Harwood Posted January 23, 2022 Share Posted January 23, 2022 Wires reversed on the ammeter? Link to comment Share on other sites More sharing options...
vette-kid Posted January 23, 2022 Author Share Posted January 23, 2022 11 minutes ago, Matt Harwood said: Wires reversed on the ammeter? That's what my thought is too, just want to make sure i I'm not missing something else Link to comment Share on other sites More sharing options...
TerryB Posted January 23, 2022 Share Posted January 23, 2022 1. Measure battery voltage with engine off and no lights or other electrical accessories on. 2. Measure battery voltage with engine off and headlights on. 3. Measure battery voltage with engine running at idle and headlights off. 4. Measure battery voltage with fast idle and headlights off. 5. Measure battery voltage with fast idle and headlights on. Step 1 is the baseline for battery voltage. Step 2 should show a drop in battery voltage with the headlights on. Step 3 should show the if the battery is getting a charge at idle speed, maybe and maybe not depending on idle speed. Step 4 should show if the regulator is charging the battery. An increase in battery voltage is expected here. Step 5 checks to see if regulator is functioning correctly by compensating for increased electrical load due to headlights. Battery voltage should be close to that in step 4. If the voltage checks make sense then the ammeter wiring is suspect. 1 1 Link to comment Share on other sites More sharing options...
vette-kid Posted January 23, 2022 Author Share Posted January 23, 2022 Thank you for that! We will check all that. Link to comment Share on other sites More sharing options...
vette-kid Posted January 26, 2022 Author Share Posted January 26, 2022 test results below. I expected a bit more variation I guess. The numbers check out in as much as they are at least moving the correct direction. But I would have expected more than 6.25 at idle. Do those appear to be normal readings? 1. 6.33 2. 6.18 3. 6.25 4. 6.45 5. 6.44 1 Link to comment Share on other sites More sharing options...
JACK M Posted January 26, 2022 Share Posted January 26, 2022 I think those numbers show that your system is working. I assume that you are taking these readings at the battery and your amp gauge disagrees. If you have the battery installed with the positive to the ground then you must have the ammeter wired backwards. (this is a pos ground car right?) Is your first comment a typo? Required/rewired ? 1 1 Link to comment Share on other sites More sharing options...
Bloo Posted January 26, 2022 Share Posted January 26, 2022 (edited) 17 minutes ago, JACK M said: If you have the battery installed with the positive to the ground then you must have the ammeter wired backwards. (this is a pos ground car right?) I second that, and I am 99.9% sure this is supposed to be positive ground. Hey @ply33 are you reading this? Is the battery fully charged? I would charge it and recheck before getting too excited, but it looks as if your regulator may be set too low, assuming this car has a regulator. Since it is a p2, I think it should have a regulator. 7.5v is typical on 6 volt cars, but I'm thinking I read somewhere that these cars ran slightly over 8 volts, which is unusual. In any event, 6.45v on line 4 would be too low with a fully charged battery. Edited January 26, 2022 by Bloo (see edit history) 3 1 Link to comment Share on other sites More sharing options...
TerryB Posted January 26, 2022 Share Posted January 26, 2022 Vette kid, is this a three brush generator with a cut out relay mounted on top? If it is I think it needs to be readjusted to get closer to 7.0 volts when it’s charging the battery. Even if it’s not a three brush generator, the output seems low. A good battery should be around 6.3v with no load and you have that. Charging volts is typically around 7.0v for a 6 volt battery. Since the readings on the battery make sense, I would guess the ammeter wires are backwards. The car is positive ground if it’s in stock condition. Remember the battery cables need to be much larger on 6v systems as they carry more current than 12v electrics. 1 Link to comment Share on other sites More sharing options...
vette-kid Posted January 26, 2022 Author Share Posted January 26, 2022 Yes, it is original 6v, +ground. It has been rewired (sorry about the earlier typo) with a rhode island wire harness to original spec. Original generator. I think dad has a guy that works on those so I might have him look at the regulator. 1 Link to comment Share on other sites More sharing options...
31plymouth Posted January 26, 2022 Share Posted January 26, 2022 The adjustment would be on the generator( third brush) to raise the output. Correct? That's the way it is with my 1931 Plymouth with 3 brush generator. My 31 has a generator cutout on the top but it is not a regulator. Or the terms cutout and regulator the same? 1 Link to comment Share on other sites More sharing options...
ply33 Posted January 26, 2022 Share Posted January 26, 2022 4 hours ago, Bloo said: I second that, and I am 99.9% sure this is supposed to be positive ground. Hey @ply33 are you reading this? Yes, that vintage Plymouth should be 6v positive ground. 1 Link to comment Share on other sites More sharing options...
vette-kid Posted January 26, 2022 Author Share Posted January 26, 2022 24 minutes ago, ply33 said: Yes, that vintage Plymouth should be 6v positive ground. Yes it is. I'm certain the battery is correct as all the l lights work and t the y are pos ground lights that won't work the other way. 1 Link to comment Share on other sites More sharing options...
ply33 Posted January 27, 2022 Share Posted January 27, 2022 2 hours ago, vette-kid said: Yes it is. I'm certain the battery is correct as all the l lights work and t the y are pos ground lights that won't work the other way. Positive ground lights? So all have been replaced with LEDs? An old fashioned incandescent or quartz-halogen will work positive ground, negative ground or even AC as long as the voltage is correct. 1 Link to comment Share on other sites More sharing options...
Bloo Posted January 27, 2022 Share Posted January 27, 2022 (edited) 3 hours ago, 31plymouth said: The adjustment would be on the generator( third brush) to raise the output. Correct? That's the way it is with my 1931 Plymouth with 3 brush generator. My 31 has a generator cutout on the top but it is not a regulator. Or the terms cutout and regulator the same? I don't believe it is exactly like that, because he called it a P2. I could be wrong but it is my understanding that the P1 has a third brush generator with a cutout, and a P2 has a third brush generator and a voltage regulator. On a third brush generator with a cutout, you can only adjust current regulation with the third brush. The voltage falls where it may because it is unregulated. On a third brush generator with a voltage regulator, the third brush is just set to the maximum value of current that will not burn up the generator. The voltage regulator is then set to some specific voltage at room temperature, and it does most of the regulating. It's usually about 7.5 volts, but I think it might be higher on this car. Edited January 27, 2022 by Bloo (see edit history) 2 1 Link to comment Share on other sites More sharing options...
ply33 Posted January 27, 2022 Share Posted January 27, 2022 3 hours ago, 31plymouth said: The adjustment would be on the generator( third brush) to raise the output. Correct? That's the way it is with my 1931 Plymouth with 3 brush generator. My 31 has a generator cutout on the top but it is not a regulator. Or the terms cutout and regulator the same? Cut out and regulator are not the same though usually a regulator contains a cutout within it. There were several steps along the way for generator regulation: Typical 1920s and early 1930s used "3rd brush regulation". Basically the field coil is powered by an adjustable third brush. As the current increases the shape of the magnetic field changes inside the generator and that changes the intensity of the field at the point the third brush picks up power and thus affects the field current in turn affecting the generator output. The general effect was to turn the generator into a relative constant current source. On a generator with only third brush regulation there was a cut out, generally mounted on the generator, that disconnects the generator when its output is low. The cut out is a relay with two coaxial coils that acts as a electro-mechanical diode to keep the battery from discharging through the generator when the generator output is very low or non-existent. Adjustment for current output is by changing the position of the 3rd brush. Voltage regulation was basically the battery fighting for its life against all odds. In the early to middle 1930s they kept the 3rd brush current regulation and added a voltage regulation stage, often in the same box as the cut out. This was basically another relay that cut the field current if the voltage went above a set point. At least on the cars I recall, this box with two sets of relay looking things inside was usually mounted on the generator. So half the regulation (voltage) was in a box that could now be called a regulator and the other half (current) was intrinsic to the 3rd brush generator. You might hear these referred to as "two stage" because they had two relay looking things in side the box even though one is a cutout and the other is for regulation. The last iteration, in the late 1930s or early 1940s, ditched the 3rd brush current regulation in favor of a third relay looking thing inside the box (now definitely called a regulator instead of cutout even though it contains a cutout stage) to adjust the field current based on generator output current. Seems like most vehicles mounted this box on the firewall instead of the generator. My 1936-42 Plymouth Factory Service manual indicates that the 1936-39 Plymouths all had 3rd brush current regulation. The P2, P4, P6 and P8 (basically Deluxe models) had a voltage regulator. (1933 and earlier Plymouths were simply 3rd brush regulation only, 1934 PE (Deluxe) was the first to have a voltage regulation stage.) 2 1 Link to comment Share on other sites More sharing options...
vette-kid Posted January 27, 2022 Author Share Posted January 27, 2022 1 hour ago, ply33 said: Positive ground lights? So all have been replaced with LEDs? An old fashioned incandescent or quartz-halogen will work positive ground, negative ground or even AC as long as the voltage is correct. Yes, all LED except the headlights. Link to comment Share on other sites More sharing options...
TerryB Posted January 27, 2022 Share Posted January 27, 2022 14 hours ago, vette-kid said: Yes, all LED except the headlights. LED lights draw a lot less current than the old filament style incandescent bulbs so your generator will thank you for that. My 1937 Dodge 1/2 ton pickup used the cutout relay on top of the generator and the third brush adjustment setting inside the generator to control the battery charging. This system is very simple in design but the downfall is it’s set to always charge the battery if it needs it or not. The recommendation was to set the charge voltage to about 7.0v for normal use using the movable third brush and a bit higher if you drove a lot at night. Setting the the generator voltage too high results in overcharging the battery which is evident by it needing water a lot more often. Good luck with your car! 1 Link to comment Share on other sites More sharing options...
JACK M Posted January 27, 2022 Share Posted January 27, 2022 15 hours ago, vette-kid said: Yes, all LED except the headlights. With this in mind I would simply reverse the ammeter leads and drive it. If the battery goes down over time, then worry about the regulation. Be sure and unhook the battery first. I know, I know just a reminder for the absent minded. 1 1 Link to comment Share on other sites More sharing options...
vette-kid Posted January 27, 2022 Author Share Posted January 27, 2022 Thanks for all the information gentlemen. This had been very informative and helpful. 1 Link to comment Share on other sites More sharing options...
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