Parasitic draw

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Bextreme04

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fast 99 said:
Thats an option but have to be careful the load doesn't exceed the fast blow fuse. Last I knew they were about $10. After buying several I use the shunts.

Remove negative cable, one clamp on the cable other on the battery. I say negative because no grounding issues. That is unless it is an older British car. In that case positive side.
Click to expand...
Yeah, you have to make sure you have the terminals in the right spot of the multimeter. My fluke will handle up to 10A, and if you have that much draw... you would know it. Just use a light at that point. A 10A parasitic draw will pull a modern battery down from full charge to completely dead in just a few hours.
 
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fast 99 said:
Thats an option but have to be careful the load doesn't exceed the fast blow fuse. Last I knew they were about $10. After buying several I use the shunts.

Remove negative cable, one clamp on the cable other on the battery. I say negative because no grounding issues. That is unless it is an older British car. In that case positive side.
Click to expand...
A couple of things I can add to this, in training ac/delco our instructor told us to make a fused lead for our meters with a fuse lower than the meter fuse,that way a failure was cheap and easy to repair. I usually just use a test light between negative cable and negative battery post. I think @fast 99 already mentioned that. If the lights lit disconnect the alternator,if the light is still lit pull fuses 1 at a time until the light goes out. When you pull the fuse that puts the light out replace that fuse with a 194 bulb,hook the battery back up and start taking loads off that fuses circuit until the 194 bulb goes out. I've got a pic of my 194 bulb I'll put up in a minute.
 

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fast 99

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agree, but sometimes I forgot that and turned the headlights or another high amp circuit on. Yes, a 10-amp draw is very excessive and normally much less.
 
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Bextreme04 said:
Disconnect negative battery cable. Set digital Mulitmeter to read "A". Connect one lead to the battery cable, connect other lead to the negative terminal on the battery. If you have a parasitic draw you should see something more than 0.5A on the meter with the key off. Start pulling fuses one by one and look at the multimeter after pulling each one. When the draw drops below 0.5A, you have found the circuit that has the draw in it.
Click to expand...
fast 99 said:
Thats an option but have to be careful the load doesn't exceed the fast blow fuse. Last I knew they were about $10. After buying several I use the shunts.

Remove negative cable, one clamp on the cable other on the battery. I say negative because no grounding issues. That is unless it is an older British car. In that case positive side.
Click to expand...
Thanks, guys. I'll definitely do this this weekend. I need to check the max on my multimeter as I don't have a shunt yet. I'm really tired of the battery losing voltage in three or four days.

(Sorry Buddhabelly I don't mean to hijack your thread)
 
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Ricko1966 said:
A couple of things I can add to this, in training ac/delco our instructor told us to make a fused lead for our meters with a fuse lower than the meter fuse,that way a failure was cheap and easy to repair. I usually just use a test light between negative cable and negative battery post. I think @fast 99 already mentioned that. If the lights lit disconnect the alternator,if the light is still lit pull fuses 1 at a time until the light goes out. When you pull the fuse that puts the light out replace that fuse with a 194 bulb,hook the battery back up and start taking loads off that fuses circuit until the 194 bulb goes out. I've got a pic of my 194 bulb I'll put up in a minute.
Click to expand...
Ricko1966, are you saying that a bad alternator could cause a draw? Even if the alternator is working properly otherwise it could cause a draw?
 
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Uberbeans said:
Ricko1966, are you saying that a bad alternator could cause a draw? Even if the alternator is working properly otherwise it could cause a draw?
Click to expand...
I am not an electrical guru but can promise you from experience on a 79 Trans AM that, yes, it can. It would drain the battery in 12 hours and test AOK on the parts house machine.
 
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QUOTE="Uberbeans, post: 939519, member: 41860"]
Ricko1966, are you saying that a bad alternator could cause a draw? Even if the alternator is working properly otherwise it could cause a draw?
[/QUOTE]
Absolutely. It's the first thing I'd disconnect. And didnt you say you changed the pigtail? Make dam sure you didn't flip the 2 wires
 
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An alternator on my 76 took a dump, when it did it began to back feed. I came outside and saw the cab lights were [dimly] illuminated. On these trucks the cab lights are wired to be on with key on, no bypass or switch for them. I’m sure other things were being back fed, but that was a visual indicator.
 
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Ricko1966 said:
QUOTE="Uberbeans, post: 939519, member: 41860"]
Ricko1966, are you saying that a bad alternator could cause a draw? Even if the alternator is working properly otherwise it could cause a draw?
Click to expand...
Absolutely. It's the first thing I'd disconnect. And didnt you say you changed the pigtail? Make dam sure you didn't flip the 2 wires
[/QUOTE]
Not the pig tail the power lead is what I am considering. I would be interesting if it was the alternator....I will definitely check this out. A simple fix.
 
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legopnuematic said:
An alternator on my 76 took a dump, when it did it began to back feed. I came outside and saw the cab lights were [dimly] illuminated. On these trucks the cab lights are wired to be on with key on, no bypass or switch for them. I’m sure other things were being back fed, but that was a visual indicator.
Click to expand...
good advice, though I haven't had this symptom. I wondered if the door switches could allow a parasitic draw even if "open" (doors closed)
 
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Uberbeans said:
Ricko1966, are you saying that a bad alternator could cause a draw? Even if the alternator is working properly otherwise it could cause a draw?
Click to expand...

Yes - my friend Dave had that happening on his 1987 C30. If there is a miswiring that keeps the exciter circuit live, that can cause it to happen even with a perfectly functioning alternator. A bad diode in an otherwise working alternator could do it too - it will charge perfectly fine but when the engine is off it can leak current back through the coils.
 
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I'd never heard of an alternator doing this. Good info to know!!
 
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