With the ignition switch on & before starting the engine, the battery gauge needle does NOT rise above the lower mark on the gauge. The engine must be at a sustained high idle to even keep the needle just the thickness of the needle below the N (normal) range (will NOT go into the "normal" range). The belt is tight. Wire connections at the alternator (one of those alternators disguised as a generator) and the voltage regulator are clean & tight. Brand new 6V Diehard battery with 878 CA. Terminals are clean & tight. Voltage readings at the battery: Engine off: 6.35V Engine idling: 6.37V and engine idling with the headlights & directional on: 6.14 V. Is there any way to tell if the problem is the alternator, the voltage regulator or possibly something else?
1939 model 91a charging
- Thread starter MCB-12NAM
- Start date
What are the readings when you speed the engine up? Voltage at the battery should increase well above 6.37 volts.
What type of regulator is it? How many wire from the alternator?
Bill
So um, what's the issue?
To test alternator connect your voltmeter between a clean ground and the alternator main output terminal and bring the RPM up to about 2000 to 3000 . Voltmeter should be reading approx 7.2 to 7.5 volts. If it is not over 7 volts then the alternator is faulty. The voltage regulator should be inside the alternator normally. Regards, Kevin.
Test voltage at dash gauge. This will be easier if you run a jumper wire off back of gauge to your meter and ground other lead. If you are getting 7+ volts to gauge and it still reads low there is nothing wrong with charging system. Just note what gauge reads and that will be the normal. My 39 does the same thing and I got a nos. gauge but have not installed it yet.
I would be satisfied 6.89 at the battery ,that will keep it charged. Run the same test with the lights on. Sounds like your dash gauge is not to accurate.
Bill
drolston
Well-known member
Couple of things.
First, if you are using an alternator, you do not need the regulator at all. It can be used as a junction point. The wire that used to come from the generator hooked to the "A/armature" post on the regulator. That wire should be attached along with the wire connected to the "B/battery" terminal on the regulator. The "F/field" wire to the regulator is unused.
Second, I bought one of those look-alike alternator inside a generator case things. It did not last 2,000 miles. I had it rebuilt by a local alternator shop; they replaced the guts with a small alternator from a Japanese car inside there. I do not expect it to last either, due to heat inside that case.
First, if you are using an alternator, you do not need the regulator at all. It can be used as a junction point. The wire that used to come from the generator hooked to the "A/armature" post on the regulator. That wire should be attached along with the wire connected to the "B/battery" terminal on the regulator. The "F/field" wire to the regulator is unused.
Second, I bought one of those look-alike alternator inside a generator case things. It did not last 2,000 miles. I had it rebuilt by a local alternator shop; they replaced the guts with a small alternator from a Japanese car inside there. I do not expect it to last either, due to heat inside that case.
First, thanks to all for pointing me in the right direction. Here is an update:
I rolled the dice & disconnected the positive ground while the engine was running. It kept firing & the batt gauge needle went up to the top of the normal range on the gauge (I suspect due to the battery load being off-line but at least I know the alternator is charging) (how well it may be charging is another story). To eliminate the voltage regulator as part of the problem (I had not at that point read the post from D Rolston),I swapped it out. No change on the batt gauge readings but to look at the glass as being half full, at least I have a spare regulator. On the other hand, now that I know alternators have a self-contained regulator I guess I will just chalk it up to experience - nothing ventured- nothing gained! I also idled up the engine some as a little charging insurance during an extended idle (as an added bonus, the engine sounds a lot better at idle).
Going forward:
From your suggestions & what I am seeing, probably safe to assume the batt gauge is out of calibration. I am wondering if what I should do is go to an under dash set of Volt, Temp & Oil Pressure gauges. Switching to an analog multimeter! Lastly, if the existing alternator calves at some point, I will revert to a conventional alternator & use the existing voltage regulator as a junction device as suggested.
I rolled the dice & disconnected the positive ground while the engine was running. It kept firing & the batt gauge needle went up to the top of the normal range on the gauge (I suspect due to the battery load being off-line but at least I know the alternator is charging) (how well it may be charging is another story). To eliminate the voltage regulator as part of the problem (I had not at that point read the post from D Rolston),I swapped it out. No change on the batt gauge readings but to look at the glass as being half full, at least I have a spare regulator. On the other hand, now that I know alternators have a self-contained regulator I guess I will just chalk it up to experience - nothing ventured- nothing gained! I also idled up the engine some as a little charging insurance during an extended idle (as an added bonus, the engine sounds a lot better at idle).
Going forward:
From your suggestions & what I am seeing, probably safe to assume the batt gauge is out of calibration. I am wondering if what I should do is go to an under dash set of Volt, Temp & Oil Pressure gauges. Switching to an analog multimeter! Lastly, if the existing alternator calves at some point, I will revert to a conventional alternator & use the existing voltage regulator as a junction device as suggested.