The Ford Barn

MCB-12NAM · 06-23-2021, 08:05 PM

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?

bbrocksr · 06-23-2021, 08:32 PM

Quote:

Originally Posted by MCB-12NAM

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?

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

Kube · 06-23-2021, 08:41 PM

Quote:

Originally Posted by MCB-12NAM

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?

So um, what's the issue?

koates · 06-23-2021, 09:25 PM

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.

marko39 · 06-24-2021, 08:26 AM

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.

MCB-12NAM · 06-24-2021, 06:28 PM

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Thanks for responding. The voltages at the battery at idle & fast idle (no tach but guessing around 2000RPM) are essentially the same - 6.87/6.89. The regulator is the newer rectangular version as opposed to the older square version. No visible part/model #.

MCB-12NAM · 06-24-2021, 06:30 PM

There is one wire from the alternator that goes directly to the voltage regulator.

MCB-12NAM · 06-24-2021, 07:23 PM

Went right to the battery ground at the firewall for the ground. Set the multimeter on voltage & DC and then got scattered readings. Not sure what that is all about but going to try again with another multimeter.

MCB-12NAM · 06-24-2021, 07:40 PM

Thanks for the suggestion about testing at the gauge. Will give it a try if I can maneuver sufficiently to access the terminal. Might try to reach up there and hook on with an alligator clip lead.

bbrocksr · 06-24-2021, 08:06 PM

Quote:

Originally Posted by MCB-12NAM

Thanks for responding. The voltages at the battery at idle & fast idle (no tach but guessing around 2000RPM) are essentially the same - 6.87/6.89. The regulator is the newer rectangular version as opposed to the older square version. No visible part/model #.

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

Bill OH · 06-25-2021, 11:12 AM

I would use an analog meter - digital meter will give readings all over the place. Your readings of two decimal points tells me you are using a digital meter - inaccurate

drolston · 06-25-2021, 12:35 PM

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.

Bob C · 06-25-2021, 01:34 PM

Is this what you have??

MCB-12NAM · 06-27-2021, 10:13 AM

It does not look like one of those four. The engine mount is similar but there is no device mounted on the top.

MCB-12NAM · 06-27-2021, 11:06 AM

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.

06-23-2021, 08:05 PM	#1
MCB-12NAM Junior Member Join Date: Sep 2020 Posts: 23	1939 model 91a charging 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?

06-23-2021, 09:25 PM	#4
koates Senior Member Join Date: May 2010 Location: Melbourne Australia. Posts: 2,079	Re: 1939 model 91a charging 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.

06-24-2021, 08:26 AM	#5
marko39 Senior Member Join Date: Oct 2016 Location: harpursville ny Posts: 1,040	Re: 1939 model 91a charging 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.

06-24-2021, 06:28 PM	#6
MCB-12NAM Junior Member Join Date: Sep 2020 Posts: 23	Re: 1939 model 91a charging Sponsored Links (Register now to hide all advertisements) Thanks for responding. The voltages at the battery at idle & fast idle (no tach but guessing around 2000RPM) are essentially the same - 6.87/6.89. The regulator is the newer rectangular version as opposed to the older square version. No visible part/model #.

06-24-2021, 06:30 PM	#7
MCB-12NAM Junior Member Join Date: Sep 2020 Posts: 23	Re: 1939 model 91a charging There is one wire from the alternator that goes directly to the voltage regulator.

06-24-2021, 07:23 PM	#8
MCB-12NAM Junior Member Join Date: Sep 2020 Posts: 23	Re: 1939 model 91a charging Went right to the battery ground at the firewall for the ground. Set the multimeter on voltage & DC and then got scattered readings. Not sure what that is all about but going to try again with another multimeter.

06-24-2021, 07:40 PM	#9
MCB-12NAM Junior Member Join Date: Sep 2020 Posts: 23	Re: 1939 model 91a charging Thanks for the suggestion about testing at the gauge. Will give it a try if I can maneuver sufficiently to access the terminal. Might try to reach up there and hook on with an alligator clip lead.

06-25-2021, 11:12 AM	#11
Bill OH Senior Member Join Date: May 2010 Posts: 426	Re: 1939 model 91a charging I would use an analog meter - digital meter will give readings all over the place. Your readings of two decimal points tells me you are using a digital meter - inaccurate

06-25-2021, 12:35 PM	#12
drolston Senior Member Join Date: Jun 2014 Location: Williamsburg, VA Posts: 1,627	Re: 1939 model 91a charging 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.

06-27-2021, 10:13 AM	#14
MCB-12NAM Junior Member Join Date: Sep 2020 Posts: 23	Re: 1939 model 91a charging It does not look like one of those four. The engine mount is similar but there is no device mounted on the top.

06-27-2021, 11:06 AM	#15
MCB-12NAM Junior Member Join Date: Sep 2020 Posts: 23	Re: 1939 model 91a charging 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.