Alternator Loading
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Alternator Loading
Hello folks. I have been a member for a while now, but haven't been very active. I recently came across a problem that is bugging me.
My 1977 F-150, (300 engine) wouldn't start Sat. The battery is only a few weeks old. It wouldn't even trip the solenoid. So I put a 1 amp charger on it over night and tried the next day. Nothing. I swapped the battery from our Explorer and it cranked right up. I put the F-150 battery in the Explorer and it cranked right up as well. I guess that eliminates the battery.
So I checked the output of the alternator. At idle, 13.6 volts. High idle, 15.9.
Here is the wierd part. When I disconnect the battery cable, the RPM's jump up. At a low idle, when I put the cable back on, it nearly kills the engine because it loads it so much.
I took the alternator off, and it spins freely. Could it be the regulator that is telling it that it needs alot of juice when it actually doesn't? Why would this prevent it from cranking?
Thanks,
J in VA
My 1977 F-150, (300 engine) wouldn't start Sat. The battery is only a few weeks old. It wouldn't even trip the solenoid. So I put a 1 amp charger on it over night and tried the next day. Nothing. I swapped the battery from our Explorer and it cranked right up. I put the F-150 battery in the Explorer and it cranked right up as well. I guess that eliminates the battery.
So I checked the output of the alternator. At idle, 13.6 volts. High idle, 15.9.
Here is the wierd part. When I disconnect the battery cable, the RPM's jump up. At a low idle, when I put the cable back on, it nearly kills the engine because it loads it so much.
I took the alternator off, and it spins freely. Could it be the regulator that is telling it that it needs alot of juice when it actually doesn't? Why would this prevent it from cranking?
Thanks,
J in VA
Postmaster
Joined: Jan 2003
Posts: 4,417
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From: Durham, NC
With battery voltages that high, I would say your voltage regulator has fried!!!! Yes, your alternator is in FULL OUTPUT
mode, which is loading your engine. I hope you haven't ruined your new battery yet.
mode, which is loading your engine. I hope you haven't ruined your new battery yet.
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Joined: Jan 2004
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From: Bay Area, California
I agree
The system voltage with the battery connected at fast idle should be around 14.3 MAX unless you have a 1970 Boss 302 in which case it would be around 15 volts. Almost 16 volts is a sure sign that the regulator is not working properly.
John
John
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From: Louisville,Ky.
Yes, and removing the battery cable while it is running is a good way to fry the alt, and blow out all of the light bulbs that are on if the alt is overcharging. This creates a voltage spike that can damage anthing electrical in the truck.
That being said, replace the regulator. If it is stuck open, it will overcharge. Then when it isn't running, it will drain the battery by feeding voltage back to the alt.
Jimmy
That being said, replace the regulator. If it is stuck open, it will overcharge. Then when it isn't running, it will drain the battery by feeding voltage back to the alt.
Jimmy
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Thanks guys. I don't think the new battery is toast yet. I just wish I found the problem before I changed it. I didn't have any other symtpoms at the time. I think you all saved me alot of time. I will get a new regulator at Autozone (9.95).
J in VA
J in VA
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From: Louisville,Ky.
If ever in doubt, AutoZone will test the vehicle for free! A voltmeter is a cheap investment also. An overcharging alternator can explode a battery. And that ain't a pretty sight!!!!
Jimmy
Jimmy
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Okay, guys here's the scoop. I replaced the regulator and in doing so noticed that the connections were corroded. So I cleaned them up the best I could and the truck fired right up.
I didn't see the "do not take the cable off" reply. So I checked voltage again (duhh, see, I have a volt meter!) 14.5 at high idle and 13.8 low idle. I took the cable off while running, and the output at the cable was 12.08v. So I defintely helped something.
But it still loads the engine when I hook it back up. Yeah, yeah its a no, no. But what the hell is loading it?
I didn't see the "do not take the cable off" reply. So I checked voltage again (duhh, see, I have a volt meter!) 14.5 at high idle and 13.8 low idle. I took the cable off while running, and the output at the cable was 12.08v. So I defintely helped something.
But it still loads the engine when I hook it back up. Yeah, yeah its a no, no. But what the hell is loading it?
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From: lino lakes, mn
a short circuit probably in your aternator diode bank or in the feild wire to the regulator shut everthing off make sure EVERYTHING is of dome light to put a volt meter in series with you positive batterey cable if you get a voltage reading you got a short pull fuses to see if its on a fused circuit
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Okay I will check the voltage in series with positive terminal.
The battery was charged and reading about 13 volts with no cable on it.
Hell, could probably use a new alternator anyway. It looks old and is a Motorcraft. If not bad yet, could be soon.
>>>>>>>>>>>>>>>>>>>>>>>>
If your battery isn't fully charged, it will be loaded until it is completely charged again.
Jimmy
a short circuit probably in your aternator diode bank or in the feild wire to the regulator shut everthing off make sure EVERYTHING is of dome light to put a volt meter in series with you positive batterey cable if you get a voltage reading you got a short pull fuses to see if its on a fused circuit
The battery was charged and reading about 13 volts with no cable on it.
Hell, could probably use a new alternator anyway. It looks old and is a Motorcraft. If not bad yet, could be soon.
>>>>>>>>>>>>>>>>>>>>>>>>
If your battery isn't fully charged, it will be loaded until it is completely charged again.
Jimmy
a short circuit probably in your aternator diode bank or in the feild wire to the regulator shut everthing off make sure EVERYTHING is of dome light to put a volt meter in series with you positive batterey cable if you get a voltage reading you got a short pull fuses to see if its on a fused circuit