The Stovebolt Site Forums The Shop Area The Electrical Bay Charging issue

Can any one help me out with some ideas where to begin ..recently had my 1940 Chevy 1/2 ton rewired adding dash lights fog lights and a spot light. .. I’m running a single wire alternator which I recently had tested and passed all the tests .. after running truck for a couple miles using lights and fog lights battery goes completely dead ...per altenator guy the altenator is pushing out 85amps .. I’m running a smaller type battery that was just fine before rewire .. only fog lights and dash lights and spot light we’re added on rewire .. I checked the voltage at idle speed at battery and it’s getting 13 volts I checked the voltage on wire connecting to altenator and it’s 36volts can’t understand why I would be getting 36volts .. I did disconnect the ground terminal from battery and connected a volt meter to measure and with one lead on the ground post of battery and other to ground wire off the tranny I measure 10 volts .. is this right ?

With an alternator system ‘Hotrod’ tells us to never remove the load (battery) from the system while engine is running. The battery acts as a load for the alternator and without it, the alternator output will jump way up and can trash the regulator. You should see battery voltage using a voltmeter between a battery post and its connector, alternator output voltage if engine is running, but reread first part. Were some of your voltmeter readings (36 volts) taken with the alternator disconnected from battery?

When I measured 36 volts coming off altenator trucks was at idle speed and battery was still connected normal and I used a volt meter with one lead to frame ground and other lead to the altenator post where hot wire connects to alternator. When I measured 10 volts between frame ground and negative battery post truck was turned off. I left positive cable still connected to battery and disconnected frame ground from battery . I got a volt meter connected one lead to negative post of battery and one lead to frame ground and measured 10 volts. Is all this normal ?

10 volts is not normal for battery voltage. Measure across battery to the lead studs. If you see around 13 volts then I would think something is amiss in your wiring. I would make sure of the grounds. 1. Is the engine well grounded to the frame. 2. Is the alternator grounded to the engine. I had that happen once when I powered coated the alternator bracket. Use your voltmeter on the ohm scale or a test light works well for these tests.

If you're getting 10 volts between the frame and the negative battery post you've got a very bad ground somewhere. It should be zero. Be sure there's a good ground strap from the engine block or the alternator housing to the frame, and attach the negative battery cable to the engine block somewhere, NOT the frame or body. It sounds like there's an insufficient, or maybe nonexistent ground from the engine to the body/frame assembly. Never, ever disconnect a ground or a hot cable with the engine running- - - -I've seen voltage spikes of over 100V on an oscilloscope just as the connection is broken.
Jerry

What the heck are you doing? You say you have a one wire alternator. That would be the battery cable. If a wire or cable goes from the alt to the battery, it will show the same voltage anyplace you measure. It is a known fact that a one wire set up will have problems with big draw accessories like you listed. The sensing is too close to the alt....as in: right inside or none.
Without anything on, and motor at high idle, you need to see approx 13.8 minimum, (14.5 is good) when touching the cable clamp, not the battery post. If not, you got alternator troubles. There is nothing else to blame if the alternator case is well grounded. No paint, no plating, no corrosion, no grease at the bolts.

Do you have an actual one wire alternator or a normal alternator just wired as a one wire? Is it a 10Si? How is it wired? 12V right? What motor? What the heck is a "smaller type battery"? you could actually have TOO small of a battery or a bad battery. Hope it is name brand.

"I checked the voltage on wire connecting to altenator and it’s 36volts can’t understand why I would be getting 36volts" is this the "one wire" the only wire, on the one wire alternator?

CLEAN and wire brush all the battery posts and clamps. Be sure clamps are tight

Bartamos to answer all your questions .. yes it’s a true one wire alternator from shop 10Si. I’m running a 12volt system with a 216 motor . By smslller type battery just meant it’s not a average size it seems to be Smaller housing than avg but it is rated at 640 CCA and 800CA .. that was my wonder why am I pulling 36 volts from altenator at idle speed and 13v at battery ? I’m going to make sure my alternator is getting a good ground before anything else seems to be every one who replied suggestion. Thanks for the reply

Google "over charging alternator" after you check all the grounds and such.

Somehow your alt. is not connected to the battery or not returning to ground. If you are going through an ammeter it might be a bad shunt. You should have heavy gauge wire from the alt to the battery & like said before, a good ground. Check connections at the starter post & any junction blocks. Check any fuseable links. They can be burned out inside the insulation & you cant tell by looking. If your old gen. type regulator is still in the circuit make sure you are not trying to go through the cutout.
George

George ... you nailed it.. thanks to Bartamos input on “ if a wire goes from battery to alternator it should measure the same voltage anyplace you measure it “ got to thinking I never checked the voltage on cable conecting to altenator. I disconnected wire from alternator turned ingnition on and got zero volts on cable checked it at ammeter and had 12v the wire had heat shrink around the lug term and the wire slipped out the crimp on lug .. I don’t have the correct lug to recrimp and terminate but I’m positive that is my problem 🙄.. something so simple thanks for every ones input ..

In the future when you have problems like that, don't disconnect anything. Check out with everything connected. I don't know where you got the idea to start disconnecting powers and grounds. Glad you found a good possible.

On heavy current connections like the main output circuit of an alternator, crimped connections are a poor substitute for soldered ones. It takes a little more time and effort, which is why the commercial wire harness builders don't do it, but on individual connections that really need to be low resistance, it's still the best way to go.
Jerry