Quick parasitic draw question
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From: spokane
Quick parasitic draw question
Using the negative terminal and negative bat cable, I'm having power drawn backwards through the battery (ie: I have to have the red, 10A DC probe on the cable and the black com probe on the terminal) to get a positive reading.
Would this be an indicator of a bad diode in the alternator drawing current backwards while the engine is not running?
Would this be an indicator of a bad diode in the alternator drawing current backwards while the engine is not running?
More Turbo
Joined: Sep 2016
Posts: 559
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From: Australian Outback
Er... what? Sounds normal??? The terminal is *THE* ground, anything further away from it is part of the completed 12v circuit and will read as such when you put a positive probe on it while keeping the negative probe at the terminal.
When is the current draw happening, and what voltage and current are we talking here?
What is the problem you are trying to isolate (poor starting/running, battery goes flat after a few days) and what does the voltage sit at when you are idling?
- boingk
When is the current draw happening, and what voltage and current are we talking here?
What is the problem you are trying to isolate (poor starting/running, battery goes flat after a few days) and what does the voltage sit at when you are idling?
- boingk
Post Fiend
Joined: Apr 2002
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From: Waterloo, Iowa
I'm not sure what you mean by your measurements, but as a practical matter put your hand on the alternator and see if it's getting warm after sitting overnight.
Post Fiend
Joined: Feb 2008
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From: St Albert, Alberta
Use the Positve terminal not the negative to determine draw on the battery.
Most low meters will not show what direction the current is flowing just that it is. If current was flowing in to the battery it would be charging it. Remember actual election flow is from negative to positive.
Not positive to negative as dictated by conventional current flow. That convention was chosen during the discovery of electricity. It is wrong.
It could be many things besides the Alternator. It could be the regulator, a wiring fault a device fault....
First thing to check is the regulator. Disconnect the POS battery cable and place your (meter set to amps) between the battery post and the cable.
Note the amp draw. Then disconnect the regulator, check the amp draw. If it falls that is your culprit. If not move on to the alternator. Disconnect it and see if the amp draw drops.
If neither of those reduce the amp draw there is something else wrong.
Most low meters will not show what direction the current is flowing just that it is. If current was flowing in to the battery it would be charging it. Remember actual election flow is from negative to positive.
Not positive to negative as dictated by conventional current flow. That convention was chosen during the discovery of electricity. It is wrong.
It could be many things besides the Alternator. It could be the regulator, a wiring fault a device fault....
First thing to check is the regulator. Disconnect the POS battery cable and place your (meter set to amps) between the battery post and the cable.
Note the amp draw. Then disconnect the regulator, check the amp draw. If it falls that is your culprit. If not move on to the alternator. Disconnect it and see if the amp draw drops.
If neither of those reduce the amp draw there is something else wrong.
Senior User
Joined: Mar 2008
Posts: 273
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Check all your switches first to make sure everything is off. Dome lights have been known to go unnoticed.
Also, if you have a modern digital radio you will have a slight draw while the truck is not running, (memory and clock).
Robert
Also, if you have a modern digital radio you will have a slight draw while the truck is not running, (memory and clock).
Robert
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From: spokane
Er... what? Sounds normal??? The terminal is *THE* ground, anything further away from it is part of the completed 12v circuit and will read as such when you put a positive probe on it while keeping the negative probe at the terminal.
When is the current draw happening, and what voltage and current are we talking here?
What is the problem you are trying to isolate (poor starting/running, battery goes flat after a few days) and what does the voltage sit at when you are idling?
- boingk
When is the current draw happening, and what voltage and current are we talking here?
What is the problem you are trying to isolate (poor starting/running, battery goes flat after a few days) and what does the voltage sit at when you are idling?
- boingk
Thread Starter
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Senior User
Joined: Dec 2014
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From: spokane
I'll give that a go. I can't leave it plugged in over night, its dead by morning at that rate. Have to be a bit more time controlled than that.
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From: spokane
Use the Positve terminal not the negative to determine draw on the battery.
Most low meters will not show what direction the current is flowing just that it is. If current was flowing in to the battery it would be charging it. Remember actual election flow is from negative to positive.
Not positive to negative as dictated by conventional current flow. That convention was chosen during the discovery of electricity. It is wrong.
It could be many things besides the Alternator. It could be the regulator, a wiring fault a device fault....
First thing to check is the regulator. Disconnect the POS battery cable and place your (meter set to amps) between the battery post and the cable.
Note the amp draw. Then disconnect the regulator, check the amp draw. If it falls that is your culprit. If not move on to the alternator. Disconnect it and see if the amp draw drops.
If neither of those reduce the amp draw there is something else wrong.
Most low meters will not show what direction the current is flowing just that it is. If current was flowing in to the battery it would be charging it. Remember actual election flow is from negative to positive.
Not positive to negative as dictated by conventional current flow. That convention was chosen during the discovery of electricity. It is wrong.
It could be many things besides the Alternator. It could be the regulator, a wiring fault a device fault....
First thing to check is the regulator. Disconnect the POS battery cable and place your (meter set to amps) between the battery post and the cable.
Note the amp draw. Then disconnect the regulator, check the amp draw. If it falls that is your culprit. If not move on to the alternator. Disconnect it and see if the amp draw drops.
If neither of those reduce the amp draw there is something else wrong.
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From: spokane
I have no radio at all. Dome light circuit has no fuse. I have no added in switches to leave on and everything else factory is off.
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Senior User
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From: spokane
This or the alt it self seems to be the most common culprit with these trucks.
More Turbo
Joined: Sep 2016
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From: Australian Outback
Replace both and you are set!
Electrical gremlins are the worst... I once had to stay overnight at my fathers while I charged the battery on my motorcycle as the reg/rec had failed and wouldn't charge it. I bought two big 6v torch batteries as a backup to keep the ignition fired and got the 80 miles home without having to use them.
Electrical gremlins are the worst... I once had to stay overnight at my fathers while I charged the battery on my motorcycle as the reg/rec had failed and wouldn't charge it. I bought two big 6v torch batteries as a backup to keep the ignition fired and got the 80 miles home without having to use them.
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From: spokane
So, I've known of a few spots of bad electrical work in my engine bay. Now I dont know for sure, but as a 76 am I supposed to have a 1g alt? Because for the life of me, I cannot find an external voltage regulator, and I'm thinking it might have been converted to a 2g due to some funky, obviously not factory, rewiring done in the alternator portion of the harness.
Is 76 a cross over year where some got 1g and some got 2g? It (the alternator) has an external fan so its for sure not a 3g. Or is this in fact just a bad 2g conversion?
Edit: also on the O'Reily auto website it calls for an alternator with an external regulator. All 3 options were externally regulated, which furthers my thoughts of this being a 2g upgrade.
Edit again....: if it matters, this is a ranger xlt, I don't know if they maybe got different alts... There's minimal options though, no ac or any other kinds of bells or whistles. I dunno, just putting my thoughts and more info out there.
Is 76 a cross over year where some got 1g and some got 2g? It (the alternator) has an external fan so its for sure not a 3g. Or is this in fact just a bad 2g conversion?
Edit: also on the O'Reily auto website it calls for an alternator with an external regulator. All 3 options were externally regulated, which furthers my thoughts of this being a 2g upgrade.
Edit again....: if it matters, this is a ranger xlt, I don't know if they maybe got different alts... There's minimal options though, no ac or any other kinds of bells or whistles. I dunno, just putting my thoughts and more info out there.
Tuned
Joined: Jul 2016
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I admittedly don't know about the different types of alternators but the voltage regulator is between the radiator and battery about the size of a cigarette box
76 is a crossover year if I'm remebering correctly I've never messed with the newer style though
76 is a crossover year if I'm remebering correctly I've never messed with the newer style though
More Turbo
Joined: Sep 2016
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From: Australian Outback