The Stovebolt Site Forums The Shop Area The Electrical Bay 12 volt Generator questions

Hello everyone. Hope everyone's summer is going well. I have gotten some time to work on my 49 truck and I believe my generator is either not working or the Regulator isn't working or maybe both?

Let me start off by saying the previous owner converted it to 12 volt system. I have a fully charged optimum battery and the belt is tight. My gauge is either showing nothing or a slight discharge. It is definitely not showing a Charging position. So with that being said what should I check first and what possibly have I missed? I do have a digital Volt meter.

Thanks in advance.
Brian

Check the battery terminal voltage with the engine running at a fast idle, maybe 2K RPM (at the battery posts, not the cable connectors) with your voltmeter. Against a fully charged battery, the voltage should be in the 13.5-14.5 range. At rest, engine off and no accessories like lights in use, the terminal voltage should be about 12.5-12.6 (2.1 volts per cell). Drop me a PM and I'll send a phone number- - - - -diagnosing a charging system is much simpler in a 2-wy conversation, as there are several tests that need to be made in the proper sequence. Also, sometimes a digital meter is too sensitive to check a DC voltage regulator- - - - -sometimes the digital readout shows confusing gibberish instead of a steady voltage reading. Analog (sweep needle) meters are sometimes more stable, accounting for the slow operating frequency of a vibrating point regulator.
Jerry

First thing you want to confirm is whether or not the generator is charging or providing any output, maybe the ammeter lying to you. Connect your voltmeter to the battery posts and read the voltage, should be somewhere around 12.6 volts with nothing running. Start the truck and run the engine at a fast idle, 1000 - 2000 rpm and read the voltmeter, hopefully you will see 13.00 - 14.00 volts. If the battery voltage starts to drop or stays at 12.5 you will move your meter to the generator. Disconnect both wires from the generator, connect a jumper wire from the field terminal "F" to ground, connect your voltmeter to ground and the armature "A" terminal, start the truck and run it at a high idle and read the voltage, should see 15 - 30 volts dc.

I wasted several billion electrons with a long reply to this thread, and the internet gremlin ate it when I hit "Post"! Before you do anything else- - - -polarize the generator. Use a short jumper wire to connect the BAT and ARM terminals of the regulator together momentarily. You'll get a pretty good flash, which is normal. 1/2 second or so is plenty. That wakes up the residual magnetism in the generator housing and makes it capable of flowing current in the field coil windings. Even a brand new generator won't charge unless it's polarized first. Engine running or stopped doesn't matter. Then measure the battery terminal voltage with the engine running at fast idle. Look up the tutorial I wrote several years ago in the Tech Tips area "6 Volt DC Charging systems". Most of that info also applies to 12V systems. No, I never got around to finishing the series of articles I had planned to do!

www.stovebolt.com/techtips/6v_charge_system/index.htm

Jerry

On my 1949 3600 (12V conversion, 235 engine, SM420) I get the same thing after it's sat a bit in the winter (wet and cold). My generator is original with the 235 (from some year in the '50's and never rebuilt) and my mechanical regulator is a two year old questionable reproduction that wishes it was a Delco-Remy.

Anyway, I get the same symptoms. A stiff whack on the cover of the voltage regulator gets it charging again, so that tells me it's cranky from sitting and oxidizing. Thereafter, cleaning all three contacts with very fine grit makes it work all summer just like it's supposed to.

I don't understand electrical magic like Jerry does, so I just clean up all three contacts. One of them is responsible for knowing the voltage to the battery and when it's time to turn on and off.

Always give it a whack first. If that doesn't work, call Jerry. ;-)

LOL! I've made a fair amount of pocket change over the past 65 years- - - - -by knowing what to whack- - - - -where to whack it- - - - -and how hard! If that doesn't work, then the test equipment comes out!

When I was running a Tennessee state trade school auto shop, the assistant director of the school told me his pickup wouldn't start. He lived about 20 miles from the school. I suggested that he might try to tap the starter with a hammer to seat the brushes temporarily. It came in on a wrecker the next day- - - - -with bunch of big dents in the WINDSHIELD WIPER MOTOR!
Jerry

Percussive Maintenance is one of my primary go-tos. But knowing where to whack is definitely important. LOL!

Here is an UPDATE. So I had to remove my generator so that I could repair the hairline crack in the block (water jacket). So since I had the generator off I figured I would take a look inside. Sure enough It just needed to be cleaned up. Which I did and now it seems to work fine. Thanks for all the help!