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Old 07-24-2021, 08:32 AM   #1
Youngblood
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Default Parasitic Drain?

Hi; I have a 1930, 6 volt positive ground. If I leave the fuse in after shutting off the car, I am experiencing about .2 volt drop in voltage at the battery over about 6 hours. Is that normal?
If not;
Do I need to just start disconnecting wires from the horn, lights etc. to find the drain?

Or, can I check various wires with a clamp amp meter to determine the drain or will all of the wires show an amperage reading if there is a drain?

Thanks for your help.

Mike
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Old 07-24-2021, 08:42 AM   #2
BRENT in 10-uh-C
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Default Re: Parasitic Drain?

Mike, do you have a generator or alternator? Did you disconnect the wire from the alt/gen and see if your draw is eliminated? A self-exciting regulator in the alternator does have a draw.

Yes, just begin eliminating circuits. The original type ignition switch can also see leakage as the ignition coil stays 'hot' all the time.

You can remove a circuit and then use a test light in that circuit to see if there is a draw as it will dimly illuminate if there is a draw downstream.
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Old 07-24-2021, 09:36 AM   #3
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Default Re: Parasitic Drain?

Thanks Brent. Yes, I have an alternator and I checked it. It shows a draw of .9 amps so I believe that would be the reason the battery draws down if I leave power to the system. I will just need to make sure I cut the power to the car when I shut it off for a period of time.

Thanks,
Mike
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Old 07-24-2021, 09:40 AM   #4
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Default Re: Parasitic Drain?

If your alternator has a bad diode in the rectifier it will show a draw. You might think about having it checked?
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Old 07-24-2021, 10:12 AM   #5
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Default Re: Parasitic Drain?

Alternators have a parasitic draw, its just in their nature.

So, a heavy main disconnect switch that is easily accessible may be a good addition.
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Old 07-24-2021, 10:18 AM   #6
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I will do that. Thanks for the help.

Mike
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Old 07-24-2021, 10:25 AM   #7
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Default Re: Parasitic Drain?

Alternators with a bad diode can have a parasitic draw but a well functioning unit will have no draw at all. It is not in their nature to have a problem like that but it can happen over time with electrical spikes or excessive jumping of a worn out battery. I really can't speak to the reliability of the conversion parts. I only tried an alternator once before going back to a generator on my old 29 Ford. The 10si is very reliable using 12-volt negative ground (normal) components in a 3-wire configuration.

The kits used to convert a Delco 10si to 6-volt have a new diode bridge & regulator plus all the parts to overhaul one of these units. These parts and the polarity jumper are all thats needed in a conversion.
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Old 07-24-2021, 11:10 AM   #8
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Default Re: Parasitic Drain?

This may be unrelated, but it is normal for a battery to loose a little voltage when sitting after being charged.

When I am away from my car for more than a week I will disconnect the battery with the main switch and put a battery maintainer on the battery.
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Old 07-24-2021, 11:32 AM   #9
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Default Re: Parasitic Drain?

Quote:
Originally Posted by rotorwrench View Post
Alternators with a bad diode can have a parasitic draw but a well functioning unit will have no draw at all. It is not in their nature to have a problem like that but it can happen over time with electrical spikes or excessive jumping of a worn out battery. I really can't speak to the reliability of the conversion parts. I only tried an alternator once before going back to a generator on my old 29 Ford. The 10si is very reliable using 12-volt negative ground (normal) components in a 3-wire configuration.

The kits used to convert a Delco 10si to 6-volt have a new diode bridge & regulator plus all the parts to overhaul one of these units. These parts and the polarity jumper are all thats needed in a conversion.
Are you sure? I have yet to find a 10si self-exciting regulator that did not have an electric draw, -even brand new out of the box.
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Old 07-24-2021, 12:46 PM   #10
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Default Re: Parasitic Drain?

Quote:
Originally Posted by BRENT in 10-uh-C View Post
Are you sure? I have yet to find a 10si self-exciting regulator that did not have an electric draw, -even brand new out of the box.




I better keep my mouth shut.
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Old 07-24-2021, 02:49 PM   #11
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Default Re: Parasitic Drain?

I've worked on many old GM vehicles that had the 10si and repaired dome light switches that showed a current draw but there was never a draw after the repair completion. Now I'm not a fan of the 6-volt conversions so that's why I can't vouch for them. I converted my Ford 850 to 12-volt so I could get the reliability and there has not been a parasitic draw problem with it yet. I use all three wires and a warning light. After I shut it down the ammeter is at zero.
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Old 07-24-2021, 02:52 PM   #12
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Default Re: Parasitic Drain?

Quote:
Originally Posted by rotorwrench View Post
Alternators with a bad diode can have a parasitic draw but a well functioning unit will have no draw at all. It is not in their nature to have a problem like that but it can happen over time with electrical spikes or excessive jumping of a worn out battery. I really can't speak to the reliability of the conversion parts. I only tried an alternator once before going back to a generator on my old 29 Ford. The 10si is very reliable using 12-volt negative ground (normal) components in a 3-wire configuration.

The kits used to convert a Delco 10si to 6-volt have a new diode bridge & regulator plus all the parts to overhaul one of these units. These parts and the polarity jumper are all thats needed in a conversion.
I have to disagree with " a well functioning unit will have no draw at all."
A brand new alternator will have a minimal draw.

Diodes do not resist backflow 100% nor do they conduct current 100%.
Bill

P S I hate to agree with Brent but he's right.
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Old 07-24-2021, 03:34 PM   #13
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Default Re: Parasitic Drain?

I guess one could mount an original style generator cutout on top of the alternator. Once the contacts are open, there is no current flow.
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Old 07-24-2021, 05:15 PM   #14
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Default Re: Parasitic Drain?

I don't know about you all but less than 50 milliamps is negligible. An electric clock draws more than that. A car should be able to set for 14 days with little or no loss of starting capability.

A lot of generator cars use a diode instead of a cut out and they don't lose there charge quicky either. Negligible is just that.

Last edited by rotorwrench; 07-24-2021 at 05:21 PM.
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Old 07-25-2021, 07:17 AM   #15
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Default Re: Parasitic Drain?

PatrickL hit the nail on the head. Some alternators such as the single wire GM10Si may have a natural small current draw that charges the field coils. I put a diode in the output wire of mine.
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Old 07-25-2021, 07:31 AM   #16
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Default Re: Parasitic Drain?

Alternators also have residual magnetism in the rotor & stator. This is similar to the residual magnetism in the generator field pole shoes. This is generally what excites the field to start with. This is why a lot of self excited alternators have to have higher rpm to come on line when they are set up as a single wire connect. They self excite much faster when the voltage sense wire and the warning light system are connected as was originally intended. The diode bridge serves to limit full AC output to a DC equivalent during operation and prevent return flow from the battery after shut down with key off. Another diode in the output line certainly will not hurt anything but it is redundant.

A battery has a tendency to sulfate if not used for longer periods than 14-days. If a person lets it set unused for a month or longer without a start or a deep cycle to knock the sulfates off the plates then it won't last very long before the build up is so thick that it won't come off.

Last edited by rotorwrench; 07-25-2021 at 10:51 AM.
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Old 07-25-2021, 08:13 AM   #17
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Default Re: Parasitic Drain?

I tend to get self-excited, happens all the time.
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Old 07-26-2021, 12:15 AM   #18
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Default Re: Parasitic Drain?

Quote:
Originally Posted by nkaminar View Post
I guess one could mount an original style generator cutout on top of the alternator. Once the contacts are open, there is no current flow.
There you go, and that should would have a lot of people asking questions!
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Old 07-26-2021, 09:34 PM   #19
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Default Re: Parasitic Drain?

I have a 6v alternator and many years ago our own Tom Endy told me how he prevents a slow drain…..he pops up one end of the fuse on top of the starter……he even gave me half of a wooden close pin to easily pry it up. I recently left my car unstarted for 2 months and no problem.
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Old 07-27-2021, 02:07 AM   #20
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Default Re: Parasitic Drain?

[QUOTE=Youngblood;2039071]Hi; I have a 1930, 6 volt positive ground. If I leave the fuse in after shutting off the car, I am experiencing about .2 volt drop in voltage at the battery over about 6 hours. Is that normal?
If not;
Do I need to just start disconnecting wires from the horn, lights etc. to find the drain?

Or, can I check various wires with a clamp amp meter to determine the drain or will all of the wires show an amperage reading if there is a drain?

Thanks for your help.

Mike[/QUOTE

Hey Mike ,
A lot of thoughts/ talk as to where and why parasitic draw may exist.
This ‘drain’ can be eliminated….as a problem… by installing a master cut off switch in your old car. Simple.
My old cars have sat unused for months with no problem. A clean charged battery can sit without sulfating for long periods of time.
Conversely, a dirty new battery put out of service can / will eventually discharge… from electrolysis across it’s top… post to post.
So CLEAN top of battery occasionally and install cut off switch, to resolve any such concerns.
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