Parasitic Drain?

[Youngblood]

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

[BRENT in 10-uh-C]

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.

[Youngblood]

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

[Ruth]

If your alternator has a bad diode in the rectifier it will show a draw. You might think about having it checked?

[Patrick L.]

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.

[Youngblood]

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I will do that. Thanks for the help.

Mike

[rotorwrench]

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.

[nkaminar]

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.

[BRENT in 10-uh-C]

Originally Posted by rotorwrench

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.

[Patrick L.]

Originally Posted by BRENT in 10-uh-C

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.

[rotorwrench]

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.

[bbrocksr]

Originally Posted by rotorwrench

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.

[nkaminar]

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.

[rotorwrench]

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.

[Bob Bidonde]

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.

[rotorwrench]

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.

[Patrick L.]

I tend to get self-excited, happens all the time.

[Tom Wesenberg]

Originally Posted by nkaminar

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!

[TerryH]

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.

[hardtimes]

[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.

[rotorwrench]

A 6-volt lead/acid battery will have a higher voltage reading right after a full charge but will lose a tenth of a volt after it sets a while. This is normal from my experience.

The newer the battery, the less it will drop off. As long as it's above 6-volts, it should start the car but condition largely depend on how long it has been in service and how often it is used.

[Badpuppy]

Originally Posted by Youngblood

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

.9 amps is rather a lot. Most likely a rectifier diode has failed (there are three of them, pressed into the finned assembly). Rectifiers are available for not a lot of money, just be sure you get the right polarity.

https://www.ebay.com/itm/10SI-Delco-...3587816?_ul=IL

[JKY]

Originally Posted by bbrocksr

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.

Yep, he is.

[Patrick L.]

Originally Posted by Badpuppy

.9 amps is rather a lot. Most likely a rectifier diode has failed (there are three of them, pressed into the finned assembly). Rectifiers are available for not a lot of money, just be sure you get the right polarity.

https://www.ebay.com/itm/10SI-Delco-...3587816?_ul=IL

Thats a draw that should be addressed. And, yep, its an easy fix and parts should be available.

[Youngblood]

Hi; I called Nu-Rex and asked them about the draw. There is a draw on the alternators. There is always a small draw when the Battery is connected. 1 - 2 amps is not uncommon but they said it should not cause a significant voltage loss at the battery over time.

Mike

[gdmn852]

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Master switch are nice to have, extra protection from theft and electrical draw, have one in every collector type car I own.

[Patrick L.]

Originally Posted by Youngblood

Hi; I called Nu-Rex and asked them about the draw. There is a draw on the alternators. There is always a small draw when the Battery is connected. 1 - 2 amps is not uncommon but they said it should not cause a significant voltage loss at the battery over time.

Mike

Well, Nu-Rex is right. But I think that amount is a bit high, but, regardless they draw.

As mentioned, a good shut-off in a convenient location is a good thing.

[rotorwrench]

On most alternators 50 miliamps is considered normal leakage. Anything above 80 miliamps in too much.

I quit using the 6-volt conversion alternators due to the high charging level of the voltage regulator. They just don't work like a normal alternator when they start messing with the original design.

[Bill G]

I have a Nu-Rex which is essentially a 10si and I can park it for weeks with no significant drain. I do get a very slight reading on the electronic DVM, but still not enough to drain it, but I usually drive it several times a week. I do use the shut off switch when I park when I go out of town or on vacation.

[Special Delivery]

At what point does it become non-parasitic. My 1930 Special Delivery has gremlins under the hood. If I leave my Nu-Rex 12V alternator connected I drain multiple volts from the battery in a matter of hours. Bad diode(s)? Bad regulator? Any suggestions from the sages in here?

[Bill G]

Originally Posted by Special Delivery

At what point does it become non-parasitic. My 1930 Special Delivery has gremlins under the hood. If I leave my Nu-Rex 12V alternator connected I drain multiple volts from the battery in a matter of hours. Bad diode(s)? Bad regulator? Any suggestions from the sages in here?

If everything is stock and no additional add-ons, I would definitely suspect the alternator and have it checked out for either diodes or its internal regulator.


If you have a lot of add-on stuff, I would probably start there. Disconnect each one at a time and use an the ammeter of a VOM in series with each to see what kind of current each item draws when the car is off. You would hope zero, but ya never know.....


For that matter, you can also use the same ammeter connected in series with the alternator output pole to check for draw. It could be milliAmps which is too small to show up on the dash ammeter.

[old31]

Originally Posted by Patrick L.

I tend to get self-excited, happens all the time.

Ya but at your age what good does it do you!

[rotorwrench]

Another common problem is the brake light switch. Some of the reproductions don't work well and can just have enough contact to allow juice to flow to the brake light. I've seen more than one with a dim glow at night with the car setting at rest. Another problem can be with a pop out or ignition switch that doesn't completely break the circuit when shut off. If the points are closed, it can drain through the ignition coil.

I have a fuse puller and just pull the fuse out when the car is going to set for a while. This requires a fuse kit to be installed at the battery.

[Big hammer]

If’ing my A is not going to be started for awhile, I flip up the mat, pop the metal cover, wiggle the positive ground battery terminal off of the battery. I’ve done this for over 50’years! It works in an emergency like when at a car wash clean up the engine bay ( over 50 years ago) or when a starter switch sticks on ! Tom Wesenberg did this also RIP

[Jim M]

The way I solved the problem was to put a cut out switch on the positive battery cable. Every time I park my roadster I snap the switch off. It eliminates ANY draw! Battery is always up when I go to start the car.

[nkaminar]

You will notice that the "good old boys" will always park their trucks on hills, especially if they will be parked for any length of time.

[Special Delivery]

I measured voltage across the diodes and get roughly 0.5 volts BOTH ways. That sure seems like bad diodes and the likely gremlin under my hood. Kinda sad because it’s a 4 year old Nu-Rex 12V. Would’ve expected better quality from them.

[31Tudor]

I guess I must just be lucky then, I have an alternator on a 6 volt system, and the car sits for 6-8 months, and it starts right up every time. In my case, the alternator obviously does not drain the battery.

[Flathead]

I don't have any parasitic draw with my generator, should I be worried?? Sorry, couldn't help myself.

[ndnchf]

I think some folks forget how well the original electrical system can work when it is properly maintained ��

[Special Delivery]

I’d agree with you all. This was my dad’s and he made some changes so I am running with his past decisions. Crossing my fingers and hoping a new alternator will solve my headaches.

[Bob Bidonde]

A battery cutoff switch will solve the problem.

[Benson]

Dash light #63 lamp .63 amps

I see that this an old thread ... I wonder what fixed it?

[Jim M]

I think everyone has this problem. I bought a cut out switch from NAPA and installed it just under the fire wall on the positive battery cable. When I shut the A down I turn that switch off and now there is NO juice flowing in the car while it is parked in the garage. Works like a charm. Never have a battery issue.

[Kurt in NJ]

Stock cars with generator don’t have the parasitic drain, I can let my car sit 6-8 months, no maintainer charging in between and I expect it to start,

[larrys40]

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Benson, had this happen on a customer car today. Drain on battery and started looking and got out my meter in series and discovered draw was .667 Amps which was the 30/31 dash light. Turned it off problem solved. His battery voltage was so low that even when lamp was on the light wasn’t visible and I only saw the car in daylight.
Easy to find issues if you know how to use your voltmeter. I have given Marc seminars several times entitled “ voltmeter “ best tool in your toolbox. I had a Full house both times…. I know this is an old thread but I always enjoyed Tom Wesenberg’s Model A friendship and wisdom and it’s great to read his comments still.
Larry Shepard

[katy]

Multimeter

[Benson]

Yes Larry,

As soon as I saw that the drain was around 0.6 amps a light went off in my head for me.

I looked up the current draw on the #63 light bulb which is why my post reads #63 lamp .63 amps.

Yes, Tom was an old time Army trained Tech as I remember.


I think that he repaired "Deuce and a Half's" at Ft Bliss, TX about the time that I was there.

Last week the new battery on the 1988 Cressida went dead.


A VOM showed .95 amps drain after battery was charged ... The switch on the Map Light above the driver's seat was on. This car sits for weeks at a time sometimes without being driven.

Originally Posted by larrys40

Benson, had this happen on a customer car today. Drain on battery and started looking and got out my meter in series and discovered draw was .667 Amps which was the 30/31 dash light. Turned it off problem solved. His battery voltage was so low that even when lamp was on the light wasn’t visible and I only saw the car in daylight.
Easy to find issues if you know how to use your voltmeter. I have given Marc seminars several times entitled “ voltmeter “ best tool in your toolbox. I had a Full house both times…. I know this is an old thread but I always enjoyed Tom Wesenberg’s Model A friendship and wisdom and it’s great to read his comments still.
Larry Shepard

[JKY]

Originally Posted by BRENT in 10-uh-C

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 would agree. That diode will have a very small leak (draw) even when brand new. When it goes you will see a big draw.

[Y-Blockhead]

Considering a 10si alternator has 6 diodes in the rectifier, there is no doubt it will have a small amount of leakage.

[Flathead]

Back in the dark ages it was common to use a test light, disconnect the battery cable and hook the light between the battery post and the cable, if the light comes on you have a draw that is excessive, if the light does not come on you are OK in draw department. Of course the first step when using a test light is to be sure it works.

[Bill G]

The Nu-Rex alternator I have is basically a 10si, but probably made in China or somewhere else. It's parasitic draw is so slight, I have left the car with the shut-off switch on for weeks and not had a problem. I usually turn it off when parked overnight, but I have been known to forget, just like everyone else. The main reason I have for shutting it down is just because you never know when a diode is going to fail. That being said, I never bother shutting off the shut-off switch if I am just parking for short times.

[CarlG]

I always use a battery maintainer if it is going to sit idle for more than a couple of weeks. Has helped my 2-year battery last 12 years and going.

[Y-Blockhead]

Originally Posted by CarlG

I always use a battery maintainer if it is going to sit idle for more than a couple of weeks. Has helped my 2-year battery last 12 years and going.