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Discussion Starter #1
Well my brand new battery, fully charged with charger, went dead overnight, again. I went and bought one of those 12v testing light sticks and put it between POS cable end and POS battery post after fully charging it again. The light went full constant bright right away, telling me something is drawing current. The regulator had a minor hummm to it, so I unplugged the 4 prong clip and the light went out. I had bought a new regulator, so I got that out and when I plugged in the 4 wire clip the test light now blinked off and on constantly and the regulator had a on and off buzzing to it. Im guessing something connected to that 4 wire clip must be shorted but Im lost now on which way to look further. Any of you elec. gurus able to help quide me on this?
The old battery went dead on me last fall after a short cruise but then would not take a charge a few weeks ago, so I returned it and they said it was toast and replaced it free. This new battery then went dead just sitting overnight. Alternator was rebuilt a year ago and things seemed to work fine. Its a standard Alt 61amp.
Ideas? Thanks for any hints.

 

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sounds like it could be the alternator. the diodes in my alternator went bad a while back and cooked the voltage regulator and drained the battery. but my gen light constantly stayed on even without the key. maybe pull the harness from the back of the alternator and see if that changes anything? good luck
 

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I agree with Zach. The good news is that a replacement diode module is pretty cheap.
 

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Discussion Starter #4
Is the diode problem common? Does it just 'blow' or does it die slowly? Since I had the alt. rebuilt last year would they have checked that diode?
all these tests are done with the engine NOT running of course. Does a bad diode play the same tricks with engine off or on?
Im trying to make sure the conditions Im experiencing are fully set forth. The key is NOT on, no reading on the console guage at all. Just the light stick is blinking off and on. I can have the Alt. re-checked by the rebuilder easily enuf.
Thanks for the input fellas.
 

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Zach's advice of removing the big red wire from the back of the alternator is the most conclusive test you can do. Just be carefull not to let it touch ground. I'd remove the negative battery cable, then remove the red wire on the alt. and tape it up. The put the test lamp between the negative post and cable clamp. Does the light illuminate any longer? If so, try unplugging the field connection (2 prong plug presuming stock alternator). If the light goes out then, you could have either a bad alternator or regulator.

Perhaps one of the simplest things you can do is take your alternator to an autoparts store for a free test. But in short, the alternator has three windings in it which generate an AC voltage at 120* phase angles. The diode module contains six diodes. Two diodes each are connected to each of the three windings. One diod goes to ground while the other goes to the big lug on the back of the alternator. Diodes usually short circuit or open circuit. But they can get leaky. In effect if a diode begins to leak it will slowly drain the battery. But a bad regulator can do a similar trick. The regulator should not energize the field coil when the engine is off. But a bad one or a miswired one may, causing a slow drain.
 

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Discussion Starter #6
Thanks for the detail Dave. company left after easter dinner so I pulled the red plug from the Alt. and then tried the test light again with regulator plugged in, presto, NO LIGHT...no humm from the reg., I tried my old regulator and same thing, NO LIGHT. So tomorrow I will take the Alt. back to the elec. shop that rebuilt it and have it bench tested again. Im betting the diodes are gone as you both stated. This helped alot as I would have been looking all over for shorted wire.
Appreciate the heads up.
 

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Discussion Starter #7
Update for future reference, I took the alternator into the shop that rebuilt it last summer. On the bench test it showed 14v and no shorts to him but he agreed to take it apart and double check diodes. I called today and he said all 3 diodes were blown apart, the pos. leg of them fried. The stator was also shot. He said only thing that can do that much harm is pos to neg and neg to pos, like when jump starting. Ive never done that but last fall when it first went dead, I had a buddy jump start me in a parking lot. I didnt check his connections but he might have hit the wrong ones.
Anyway, the elec. guru said it was toast but weird it still benched out 14 volts.
He said, 'no charge' to fix it but I said let me pay at least half since someone on my end did something wrong. He said, NOPE, just bring more business. What a guy. Im taking pizza over there when I pick it up tomorrow.
 

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His DC meter was showing 14 volts DC. But, I bet if one hooked up an oscilliscope to the same place, there would be plenty of an AC signal, unrectified DC displayed.

No diodes to rectify, no DC, just AC. Hopefully, it didn't damage the radio/electronics.

Good business tactics on his part, darn right I'd give'em a pizza.
 

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Discussion Starter #9
Update finally. Last night I finally got the rebuilt alternator put back in ole Thunder. I installed the new regulator at the same time. Hooked it all up and presto, no short. Test light was dark again.
I then checked the battery and it was down to 30% so I put my charger on it. The needle started at 30% and flicked up to 100% then back to 30% and just kept repeating this over and over. It should have a steady needle slowly moving up the chart to 100%.
What might make this charger do this? Its set on 10amp setting.
:confused:
 

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Battery chargers will kick off under a heavy load. Perhaps your charge meter is showing voltage instead of current. Basically, the battery is demanding so much current that the charger's internal breaker gets hot and pops off. Then a few seconds or a minute later, it cools off enough and pops on again. Leave it on for an hour and see if it settles down.
 

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As dnult suggests, the internal circuit breaker heats up and pops open. During the heavy charge cycle, measure with DMM across battery terminals.
If reading is above 16 volts, battery may be bad.

When charging a battery, the colder temperature it is, the more voltage needed to recharge it. Once the battery is starting the chemical process and taking a charge, it heats up. As the battery gets hotter, the more recharging current it accepts, the higher the voltage.

Battery chargers are current sensitive, they could care less about voltage, its not monitored, as least for the cheaper models. Alternators on the other hand, are voltage sensitive. Read your ammeter. High charge at first, then levels off. As battery heats up, less current is provided for recharge because alt is regulating voltage, not current.

As long as it not boiling the electrolyte out, it should be good to go. Have a battery load test done once you get it on the road.
 

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Discussion Starter #12
Well after 2 hours the needle on the charger was at 100% and cycling down to 30% every 30 seconds,then back to 100%. I pulled off the cables and let it sit for half an hour, then put my battery reader guage on it that tells if the batter is fully charged or half etc. It read only 70% full.
Well I put it all together and wife and I took our maiden voyage for the year out around town, burger joint etc for almost 2 hours.
Now I notice the console Amp guage doesnt move a bit. I turned on the headlights and high speed blower fan, still the AMP guage didnt budge at all. I always recall it moved alot depending on the load, but now it acts like its dead.
If the diodes in the Alt. blew, could that have blown the AMP guage too?
I got home, put the multi meter on the engine at idle and I have 13.5 volts at idle on the big red HOT wire on the back of the alternator. I also have 13.5 on the battery terminals. The battery is now reading 100% full as well, so the alternator charged it up the rest of the way on our ride.
Thanks for any ideas on this guage now.
 

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You'll find plenty in the archives for amp guages. Basically, the wire that connects between the terminal block behind the battery and the buss bar on the horn relay, serves as a shunt for the ampmeter.

Ampmeters are sensetive volt meters. When current flows through a resistance, a voltage drop is formed accross the resistance. The wire I spoke of is that resistance or shunt. It probably has a resistance of 0.01 ohms for example. If 10 amps flow through it it will create a voltage drop of 10 * 0.01 = 0.1 volt.

Notice how small that voltage is. If an amp meter sees more than a volt or so accross it's terminals it will open circuit like a fuse. So it's possible that has happened at some point. In the archives a guy explains how he repaired his open amp meter and how to test it as well.
 
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