Battery Parasitic Draw comes up with no results

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Battery Parasitic Draw comes up with no results

Post by SensibleInvestment » 06/07/19 20:31

I have been trying to diagnose a potential battery leak in my import 1991 G-limited.

Getting the multimeter over the negative terminal gives a reading between 0.1A and 0.13A, which I was lead(hah) to believe isn't terrible. However when I first put the battery in, it drained after sitting in there for 3-4 days.

I checked the 3 fuse boxes to see the current over each fuse and each came up with 0.

Now the radio loom, antenna, and fog lights have been bodged with random connectors, new cables, and god knows what else over the years. However I can't seem to find where the power is draining.

Am I missing a trick here?



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Re: Battery Parasitic Draw comes up with no results

Post by jimi » 06/07/19 21:36

With the ignition off, lights off and doors shut, disconnect the positive lead from the battery, put the multi meter (set to DC amps, you may also need to change one of the meter leads to a different socket on the meter) in series with the battery and positive lead ie one meter probe (negative) on the battery posItive and the other (positive) on the positive lead and see what you get, if your still getting 100/130 mA then it sounds like your battery is U/S. A good battery with that kind of load should last closer to 3 weeks not 3 or 4 days.
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Re: Battery Parasitic Draw comes up with no results

Post by MR2DI4 » 06/07/19 23:27

Having a few issues myself, but the draw may be random as when I checked with a decent multimeter the draw was 25mA or 0.025A, which would be normal.

The draw you are experiencing is a problem, the battery will be flat in less than a week. I had 250mA in my subaru because someone had wired a TV amp into the 12V that was there all the time and not switched. The brand new battery was dead in 2 to 3 days.

The best way to test would NOT to break the connection to the battery while inserting the multimeter.

With one lead connected to the battery lead with a alligator clip and the other lead a probe pressing on top of the battery through the top of the battery lead, raise the lead over the top of the probe so at no point do you make a disconnection.

Essentially your typically backing up the clock, the clock/radio stations in the stereo and the alarm as well as the ram in the ECU, total current draw should be really low. Its an older car so possibly not as low as a new car these days but 15 to 35mA should be the range depending on what you have connected.

If its not this low, with the multimeter connected, start pulling fuses to equipment that has 12V all the time like the radio and the ECU etc until it drops.

One problem can be the regulation diodes in the alternator, the alternator has a thick wire permanently connected to the battery. Pull this or the huge 120A Alternator fuse and see if the fault clears.

Just start pulling fuses until the fault clears. Its unlikely to be a loom wiring fault, that would draw alot of current and blow a fuse if there was a 12V short to ground anywhere.
Last edited by MR2DI4 on 07/07/19 0:23, edited 1 time in total.

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Re: Battery Parasitic Draw comes up with no results

Post by jimi » 07/07/19 0:23

The average battery for a MK2 is around 60AH, a demand of 100mA isn't going to flatten it in less than a week.
As for not breaking the connection, all he will lose is the clock setting and any saved stereo settings, if his battery is going flat then he's losing them anyway, so no real loss and a lot easier to do.
However each to his own, I'll stick stick with my method, it's served me well over a couple of years ;)
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Re: Battery Parasitic Draw comes up with no results

Post by MR2DI4 » 07/07/19 3:27

I really don't have time to start giving lessons in electronics on here so I keep the posts as brief as possible with just the possible solution.

Plenty of specific technical information on the Web if you need the why and take the time to do some research.

I prefer not to make s@#t up or guess so any numbers come from actual measurements.

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Re: Battery Parasitic Draw comes up with no results

Post by jimi » 07/07/19 4:13

:rofl: Nice :th:
I won't bore you with details of my job or experience.
I will say this 130 X 24 X 7 = 21840
I'm sure you can work out the rest yourself.
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Re: Battery Parasitic Draw comes up with no results

Post by jeff » 07/07/19 8:56

MR2DI4 wrote:
07/07/19 3:27
I really don't have time to start giving lessons in electronics on here so I keep the posts as brief as possible with just the possible solution.

Plenty of specific technical information on the Web if you need the why and take the time to do some research.

I prefer not to make s@#t up or guess so any numbers come from actual measurements.
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Re: Battery Parasitic Draw comes up with no results

Post by SensibleInvestment » 07/07/19 13:04

Must admit I am a little confused by MR2DI4's method, are you saying to essentially connect the multimeter in parallel with one of the battery terminals? Won't that make my multimeter nice and toasty? I might've read it wrong.

Went to Haynes this morning but before I left I noticed the Positive terminal connection was pretty poor, the band that goes over the batter terminal is split into 2? and the top one wasn't really connecting, so I'm wondering if it had anything to do with it.

Put the multimeter in series again and only read 0.11A. Don't even had the stereo plugged in at the moment (And don't think any connections are touching metal) So am still dumbfounded.

Not forgetting that these posts get searched by people who might not have any prior knowledge of electronics. Hell even I'm doing an Electronic Engineering Degree but don't really get involved in practical stuff like this.

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Re: Battery Parasitic Draw comes up with no results

Post by jimi » 07/07/19 14:03

All he is suggesting is to have one meter probe on the battery post and the other on the clamp, before removing the clamp from the battery so you never leave the car without power, this would ensure you don't lose any stored clock/stereo settings, it's a bit awkward to to do and if at any time your meter probe comes off the settings are gone, they will be gone anyway once you pull the appropriate fuse, so it is worth it ? I.M.O. in certain circumstances yes, in this case no.
If you want to eliminate the alternator, disconnect it it by pulling the plug out and disconnecting the power connection (disconnect the battery before doing this and ensure the cable terminal can't short to earth) may seem like a lot of work but it's easier than removing the 120A Alt fuse which is bolted in place (you need to access the underneath of the fuse box to remove it)

110mA is slightly high (again that's only my opinion, but I have worked on a few MK1's & MK2's with similar readings in the 50-100 mA range) a lot depends on what accessories you have connected and what type of alarm/immobiliser is fitted.

I've come across one car where the backup battery for the alarm was u/s, this was causing an increase in current as the alarm tried to charge it, replacing the battery reduced the current to normal (this wasn't on an MR2 but the principle could still apply)

My MK1 has a similar reading (AutoWatch alarm/immobiliser, clock and CD head unit) and the battery doesn't go flat in a week or even two, I used to be around week 3 that I would have problems starting it (in the summer, in winter it goes down quicker) so I built a little plug in charger (only puts out about 150mA @ 15v) which I connect for the 3 weeks I'm away at work, never had a problem starting it after 3 weeks since I started using it.
You don't really need any electronics knowledge to track down these type problems, it's basic electrics (in my opinion :) )
How old is your battery ?
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Re: Battery Parasitic Draw comes up with no results

Post by SensibleInvestment » 07/07/19 16:33

Brand new-ish? Got the car early 2019 and got a battery fairly close to then, it drained a few days later and was hoping it was just because Halfords might not keep them fully charged. Part of me did wonder whether it is just a dodgy battery, but I figured I trust that more than a 28yr old car...

I'll definitely give the alternator a check when the car isn't steaming from the heat and try and follow the immobiliser/Alarm cabling.

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Re: Battery Parasitic Draw comes up with no results

Post by jimi » 07/07/19 17:54

Worth sticking your meter across the battery with the engine running, at idle your looking for around 13.5v and above 1500 or so around 14.6v
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Re: Battery Parasitic Draw comes up with no results

Post by MR2DI4 » 07/07/19 19:15

Multimeter is in series as explained by Jimi.

The reason you do not want to disconnect the power is that you want to be 100% sure your testing it in the fault condition. Its not about loosing the radio stations its about not having everything that has a micro in it resetting and possibly clearing a fault when you disconnect then reconnect the power.

If you have a decent multimeter that is not wildly inaccurate, 100mA is still way to high but that said with a decent battery and if the car was being used as a daily driver you would be unaware of the fault. Clearly the 250mA fault didn't show up on my Subaru by the owner in Japan but when it got here and sat on a car lot, they thought the battery was stuffed so they replaced it and I could see where they had been jump starting the car from marks on the battery terminals.Even at 250mA if you drove it 6 days a week for a decent distance, then your wouldn't be aware of the problem.

I knew I had a problem with the Subaru just using a DC Clamp meter, no need to disconnect the battery at all. Not that accurate below 1A however, but it should be almost down at zero.

Recently rebuilt my alternator, its putting out 14.8 initially and 14.6V at idle. Its also possibly some of the diodes have gone in your alternator so its not charging properly compounding the problem. Got a whine coming from the alternator ?

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