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shortyx250
03-25-2011, 06:02 PM
I have a 1980 S&S with a 351 and all standard ignition. I can go out for several days and run lots of gas. But eventually the battery will drain. Its a new battery so I know that's not the issue. The amp meter is above the 0 mark showing that its getting a positive charge. Sometimes it will go negative though. I think this happens when i am at low RPM's. I had the alternator rebuilt, and a new voltage regulator also. Any ideas on this?

ahhudgins
03-25-2011, 06:15 PM
Always use a digital volt meter to test your charging system rather than using the amp meter or just guessing. Check the voltage at the battery when the engine is off and make sure it is at least 12.0 to 12.3V Then check the voltage when the engine is running to see if the alternator is working. The voltage shoud be above 13V. As always, check all of your terminals and ground connections.

Have your battery tested too. If it seems to drain down when it is not in use, you may have something running down the battery.

thatsmrmastercraft
03-25-2011, 06:35 PM
If I don't hit about 1100 RPM's, my alternator doesn't start charging. Once I initially hit that RPM it will charge at idle speed no problem.

ctjahn
03-26-2011, 01:03 AM
I have a 1980 S&S with a 351 and all standard ignition. I can go out for several days and run lots of gas. But eventually the battery will drain. Its a new battery so I know that's not the issue. The amp meter is above the 0 mark showing that its getting a positive charge. Sometimes it will go negative though. I think this happens when i am at low RPM's. I had the alternator rebuilt, and a new voltage regulator also. Any ideas on this?

Sounds just like the symptoms I had.... Battery would charge but weak.

Replaced the terminals with new ones and it fixed the problem (My terminals were trashed by the previous owner). Charges STRONG now...but as stated above you have to check the alternator and other typical sources of issues (bad grounds, etc).

Dont forget to clean and protect them...
Cj

Matt L.
03-26-2011, 12:19 PM
This is an old post of mine for what I did a few years ago. My 1990 MC was wired with straight up copper automotive grade crap wire. After 20 years every connection was very corroded. I don't carry much H2O in the bilge at any time, and the wiring has never been wet, ever! I was only getting 7.5V to the coil causing the EI to fail. Replacing all of this wire with marine grade fine strand tinned copper was the best thing I've ever done to my boat! 2+ years on and every connection looks brand new!

www.genuinedealz.com is a great place to get boat wiring stuff. I just rewired my boat from the batts to the Distributor with their stuff. Less than half the price of Westmarine.com and great quality marine grade stuff. they ship quickly and it is free shipping. I bought the $29? hammer crimper it worked great. I also soldered everything and shrink wrapped with their self sealing shrink tubing. I used the milspec stuff on all battery connections. I also used Deoxit products to clean and Deoxit Gold liberally on all connections to hold off future corrosion issues. http://store.caig.com/s.nl/sc.2/category.188/.f

Good luck,

Matt

shortyx250
05-16-2011, 10:38 AM
I tested my battery and it was 12.4 volts before starting. I had my buddy with a multi meter checking it as I started up and accelerated. It did start to go up to 12.7 volts but never got up to 13. Also none of my gauges are working now.

chawk610
05-19-2011, 03:41 PM
The guage issue sounds like a grounding prob. I replaced my dash last year and one ground wasn't making a good connection. I finally found it and now all is well.

ctjahn
05-19-2011, 04:53 PM
Also none of my gauges are working now.

Dont forget to check the PCB (printed circuit board or fuse pannel) under the dash... My connections were all in really poor shape. Someone attempted to resolder them and did a terrible job. When I replaced the fuse panel with a new one; I also replaced all the terminals on all the wires which were in equally bad shape due to age. I was going to rewire it this winter but ended up band-aiding the wires to get though this season.

Best wishes.
Cj

EricB
05-19-2011, 06:48 PM
Before you tear everything apart then put it back together and it all magically works, you need to find the issue. Since the Alternator is doing something, the first tests should be to do voltage drop tests on the feed side then the ground side.
Voltage drop test is a simple test. Set your DVOM to the DC volts scale. Connect one lead of your DVOM to the positive terminal of the battery (terminal of battery, not the cable clamp), and the other lead to the Alt. output terminal. Start engine and read the voltage on the DVOM. Should read less than .4v.
Then hook the DVOM meter lead to the alternator case and the other to the negative terminal of the battery. Run the engine and the meter should read less than .4v.

How this works: The DVOM in the volts position reads/measures the voltage (pressure) difference between the 2 leads. If you connect the meter on the same side of the circuit you are testing and operate the circuit, it will tell you the pressure difference it sees between the leads and connections. If (for example) the feed side circuit is clean and free of corrosion and bad connections, the pressure difference between the battery positive terminal and the alt. output terminal should be almost nothing. If it above .3 to .4 v it has excessive resistance and that is the pressure lost (or consumed) attempting to get back to the battery. Same true for the ground side test.
Tyr it and let us know how it goes.

shortyx250
06-01-2011, 02:23 PM
So I checked the 2 grounds and they were a little corroded and had some paint. I cleaned them up. I also found a black ground wire that goes from the intake ground to the alternator. This wire is not hooked up to nothing, just laying loose around the front of the intake manifold. Does this ground the Alternator? Maybe this is my problem.