Parasitic battery drain

[Silvertip]

I have a slow battery drain that has been there for a long while that I have been putting up with, and finally decided to take care of.
The total drain is 7.5 mA, just enough to require a jump if the car isn’t driven for a few weeks. None of the fuses had any impact when removed, so I went about isolating the “hot” feeds. One of them contributed 3.5 mA to the total, I assumed it was the radio lead and didn’t look further. The surprise came with the other 4 mA current - it was on the huge cable for the starter.
Question is what in the starter could be causing a tiny 4mA drain on the battery? I mean it’s pretty simple electrically - relay kicks in and 12v turns it round and round. Should be no current draw without the starter relay engaged.
Can someone please advise?
Thanks!

[ErrorMargin]

Originally Posted by Silvertip

One of them contributed 3.5 mA to the total, I assumed it was the radio lead and didn’t look further.

I would look into that. It should not be drawing current with the car off.

The aftermarket radio and amplifiers in my car were installed incorrectly by a PO and drawing current while the car is off. The current draw (and the PO) was so bad the PO installed a battery disconnect and disconnected the battery from the car every time he stopped anywhere instead of fixing the problem.

I rewired it correctly so that it does not draw current while the car is off.

Originally Posted by Silvertip

The surprise came with the other 4 mA current - it was on the huge cable for the starter.

It could be a short in the solenoid. I would disconnect the wiring from the starter and see if the current draw goes away.

If it does, then I would clean up all the contacts and re-connect the cables. If the current draw remains it is probably time to replace the starter.

[30westrob]

Something to consider, the battery power lug on the starter also powers the engine harness, which incorporates the alternator. A leaky diode could be your issue. Rob

[PeteKz]

^^^ This. Disconnect the heavy red wire from the starter to the alternator and recheck for current drain.

[917_Langheck]

Originally Posted by 30westrob

Something to consider, the battery power lug on the starter also powers the engine harness, which incorporates the alternator. A leaky diode could be your issue. Rob

This^^^

[Dpmulvan]

Starter solenoid

[mysocal911]

Originally Posted by Silvertip

I have a slow battery drain that has been there for a long while that I have been putting up with, and finally decided to take care of.
The total drain is 7.5 mA, just enough to require a jump if the car isn’t driven for a few weeks. None of the fuses had any impact when removed, so I went about isolating the “hot” feeds. One of them contributed 3.5 mA to the total, I assumed it was the radio lead and didn’t look further. The surprise came with the other 4 mA current - it was on the huge cable for the starter.
Question is what in the starter could be causing a tiny 4mA drain on the battery? I mean it’s pretty simple electrically - relay kicks in and 12v turns it round and round. Should be no current draw without the starter relay engaged.
Can someone please advise?
Thanks!

Most don't consider 12 ma as a problem. Typically the battery should be good for 2-3 months to start the engine. A draw over 10X that value becomes a concern. Are you sure the measurement is correct and not over 100ma?

[PeteKz]

Originally Posted by Dpmulvan

Starter solenoid

Very unlikely. Even a partial short through the solenoid almost certainly would draw far more than a few milliamps.

[Silvertip]

Thanks all. I will check the starter wiring when I can get it up in the air. Right now I am replacing the interior carpet and I don’t want to get distracted.

[John W.]

Say a typical battery is rated at 40 Ahr. If you have a parasitic drain of 7.5 mA, it would take over 6 months to die.

(40 / 0.0075) / (24 * 30) =7.4

Could the drain be more than 7.5 mA?

[mysocal911]

Originally Posted by John W.

Say a typical battery is rated at 40 Ahr. If you have a parasitic drain of 7.5 mA, it would take over 6 months to die.

(40 / 0.0075) / (24 * 30) =7.4

Could the drain be more than 7.5 mA?

A more practical estimate would half that number to assume a usable battery for cranking. In any case, thinking 7.5 ma is problematic, is laughable!

[ant7]

As for the radio,
Depending on the type fitted, there are often two lives, one is switched through the ignition, the other is connected to a constant live, this is for the memory, i.e. to keep programmed stations and other features that may need a constant live, worth checking.
I agree with others though, if it is indeed 7.5 MA then it could just be leakage in the starter solenoid, or a diode in the alternator, try disconnecting things one by one, and see if you can identify the source, start with the radio.
Ant.

[wazzz]

Also, I don't see any mention of the clock, which is continuously on and drawing current.

[ant7]

Originally Posted by wazzz

Also, I don't see any mention of the clock, which is continuously on and drawing current.

[mysocal911]

Originally Posted by wazzz

Also, I don't see any mention of the clock, which is continuously on and drawing current.

You bring up a good point, but why hasn't the OP indicated yes/no on whether the vehicle has a clock?

[pmax]

Aren't there two batteries in a 72 ?

[Silvertip]

Hey all!
Just got around to checking the post, had a chuckle on the clock. Mine hasn’t worked since I bought the car - I have it set at 6:30 to lower the center of gravity. I switched to a single AGM battery some time ago.
I agree that 7.5 mA should not be a concern, but the fact is that the battery will drain if left in the garage for an extended length of time. It was in a shop for several months a bit ago and the battery was doa - wouldn’t even run after a jump.
I guess I could just drive it more and I wouldn’t have a worry in the world

[eastbay]

Alternator diode drain happened to me..... Car still ran fine and charged

$7 fix until you have time to chase it and don't want to kill your battery

[creaturecat]

use a multimeter across the fuses to narrow down the location of the draw.

[brp914]

My clock was draining the battery and it didn't even work. The draw was periodic, like 1/sec. Don't recall the amperage. I was using an Odyssey 925 which was plenty to crank the engine but not enough for weeks of low draw.