Car battery parasitic drain.

kfoto · Post by **kfoto** » Thu Dec 30, 2021 6:20 pm

Hi everyone, just joined today with a dilemma with my Rover 45. But just to add as a very keen DIYer I have had a lot of experience in computing Windows, Mac and Android, building internal construction, plumbing, electrical installations, photography and videography, so will reply to posts on these.
Back to my unsolved problem. For the last 2 years I winterise my car from Nov to March. Each winter top up my car battery via an extension lead from a 1.8amp battery charger weather permitting because mains lead goes out the back door. But it was not enough to keep the new battery fully charged until I read about parasitic drain. So I decided to use a 40 watt solar panel connected this year to a charge controller in the boot and with a feed directly to the OBD socket. Was OK to start with until after 5 weeks another new Varta HD battery was down to 12.2v. Then with info checked for the drain between negative earth terminal and negative earth clamp it was 320ma. With weather bad waited till today for more checks. Connected it and again 320ma. PS solar panel is isolated. I have two multimeters so did a diode test on alternator. With one MM it gave a reading of 0.712 and in reverse 1(OL). Great I thought, so did the same test with another MM and got readings both ways. What the heck? The final test to see if the alternator was bad is to see if there is an AC current at the battery. Connected battery up and went to start the car. But it would not turn over as immobiliser was on, so switched it off via key fob and car started. Put MM into AC and touched both terminals and meter registered zero, but left them there for about 5 secs or so and meter leads got hot, so stopped. Stopped engine, disconnected earth clamp and ran the initial drain test and it said 30mah. So my dilemma is was it the immobiliser causing the drain? And why did my leads get hot on the AC direct test?

Someone-Else · Post by **Someone-Else** » Thu Dec 30, 2021 6:34 pm

You should not try to measure AC on a car battery, there is none.

Small solar panels are not worth using in winter as there is not enough sunshine.
Modern cars are meant to be driven everyday, this charges the battery up, you should be ok for at least a month but after that the battery will go flat because of all the things being used when your car is idle, then you have the cold, that does not do batteries any good either. The only real solution other than to trickle charge the battery is disconnect it. (But make sure you have your "Entertainment system unlock code first")

kfoto · Post by **kfoto** » Thu Dec 30, 2021 7:12 pm

Thanks for the reply, but you are wrong, solar panels do not just need sunshine. The name solar confuses so many people and you as meaning sunshine, but actually it means "energy" from the sun. Solar panels can accumulate power on a cloudy day thanks to ultra violet light and infra red. I know this as fact from my solar panel, on a cloudy day it will produce 100ma and semi cloudy days 200ma. But sadly this did not directly answer my question. But for your info, if a faulty alternator has bad diodes then some leakage of AC current will go to the battery along with DC and it will show with a test.

dewaltdisney · Post by **dewaltdisney** » Thu Dec 30, 2021 7:12 pm

All modern cars drain power whilst left parked up. I suspect the drain might relate to an alternator defect as one of the diode packs is earthing out. I would check that out

DWD

kellys_eye · Post by **kellys_eye** » Thu Dec 30, 2021 7:23 pm

You mentioned the immobiliser. They don't work without power. Measure the current drain with all systems off then start pulling fuses until the drain stops/lowers then investigate the systems that fuse powers.

Your solar recharger should deliver at least 14.2V for the battery to take a charge. 12V won't cut it.

Someone-Else · Post by **Someone-Else** » Thu Dec 30, 2021 7:39 pm

kfoto wrote: ↑Thu Dec 30, 2021 7:12 pmThanks for the reply, but you are wrong

If you say so. But wasn't it you who said

kfoto wrote: ↑Thu Dec 30, 2021 6:20 pm left them there for about 5 secs or so and meter leads got hot, And why did my leads get hot on the AC direct test?

I wish you luck.

aeromech3 · Post by **aeromech3** » Fri Dec 31, 2021 6:20 am

My typical standard MM does not measure AC ampere and in fact will only measure up to 10amp DC with internal fuse for overload which I am pretty sure would happen if I put it across a car battery; if you put ACV across the battery you are lucky not to have damaged the meter. I have a clamp type AC ampere meter but nowhere on the car it can fit!
I understood when diodes fail open this does not change the max DC wave V output from a car alternator but causes a time shift, half wave, with a much lower DC V low wave point; then I guess the charge rate is slower. We also used to say that if an alternator diode fails (perhaps in the short mode) there is a possibility of the battery driving the alternator as if it were a motor; in any case a shorted diode will soon destroy itself or other components but nowhere can I envisage ACV getting through to the battery.
I have a 1972 VW Beetle, it is only on its second battery, and as there is no live circuits when I park it up, I give the battery a charge every couple of months or just before I give it a start. Now my 2021 mini has a few continuously powered circuits so parked I use a low power charger, charge controller, but not content I have a timer switch to give it just 3 short On cycles a day. Will find out the results of this combination after my travels, but for the short test days before leaving, it seemed to keep the battery about 12.6v (DC).

kfoto · Post by **kfoto** » Fri Dec 31, 2021 11:36 am

kellys_eye wrote: ↑Thu Dec 30, 2021 7:23 pm You mentioned the immobiliser. They don't work without power. Measure the current drain with all systems off then start pulling fuses until the drain stops/lowers then investigate the systems that fuse powers.

Your solar recharger should deliver at least 14.2V for the battery to take a charge. 12V won't cut it.

Thanks for the info. I did the drain test after installing the battery which had a charge of 12.81v after left standing for a week outside following a charge and it was 320ma. But after doing all the tests, then starting the car and left ticking over to normal running temperature, I switched off. Disconnected the negative clamp and did drain test again and it was 0.03ma which is normal. But a mystery for me to as to why it went from 320 to 30ma. Output of my solar panel is 22.45v Voc and 18.30v Vmpp. The charge controller produces an equalisation charge of 18v and then a float charge of 14v. In the summer at 18 v I get 500ma and now just 13v at 100ma.

kfoto · Post by **kfoto** » Fri Dec 31, 2021 11:59 am

aeromech3 wrote: ↑Fri Dec 31, 2021 6:20 am My typical standard MM does not measure AC ampere and in fact will only measure up to 10amp DC with internal fuse for overload which I am pretty sure would happen if I put it across a car battery; if you put ACV across the battery you are lucky not to have damaged the meter. I have a clamp type AC ampere meter but nowhere on the car it can fit!
I understood when diodes fail open this does not change the max DC wave V output from a car alternator but causes a time shift, half wave, with a much lower DC V low wave point; then I guess the charge rate is slower. We also used to say that if an alternator diode fails (perhaps in the short mode) there is a possibility of the battery driving the alternator as if it were a motor; in any case a shorted diode will soon destroy itself or other components but nowhere can I envisage ACV getting through to the battery.
I have a 1972 VW Beetle, it is only on its second battery, and as there is no live circuits when I park it up, I give the battery a charge every couple of months or just before I give it a start. Now my 2021 mini has a few continuously powered circuits so parked I use a low power charger, charge controller, but not content I have a timer switch to give it just 3 short On cycles a day. Will find out the results of this combination after my travels, but for the short test days before leaving, it seemed to keep the battery about 12.6v (DC).

Sorry my mistake saying AC current as it refers to amps, I should have typed supply or volts. Yes my meters do not measure AC amps with leads. Well yes the hot leads then made me think that it could have damaged the meter, but no it is intact and the fuse did not blow thankfully. It is a digital MM from Maplins I bought donkey years ago when they were only in Southend. I have just bought a clamp one a UNI-T 210E and it is very compact and more sensitive than the Maplin one. This test to check for AC volts at the battery with engine running is shown on many websites to see if AC is escaping through a bad regulator.

kellys_eye · Post by **kellys_eye** » Fri Dec 31, 2021 2:03 pm

Does the measured current (parasitic) value change if you change ranges? i.e. 320mA will show as 0.32A on a higher range.

kfoto wrote: ↑Fri Dec 31, 2021 11:36 am I did the drain test after installing the battery which had a charge of 12.81v after left standing for a week outside following a charge and it was 320ma.

If the measured parasitic loss was 320mA after a week then assuming it was that value all week would have left you with a completely drained battery. 0.32A multiplied by (7x24hours) = 53.6Ahr drain. The car battery is what..... 65Ahr?

Sure you 'opening' the car isn't putting a load on somewhere? Interior light perhaps? (0.32A @ 12V = 4Watts - a typical interior light rating. Glove box perhaps - a common fault on older cars).

12.8V is a typical fully-charged (after a short period of time) value. A battery coming off charge will measure 13.8V when new, dropping to anything between 13V and 12V as it ages and is left unloaded i.e. parasitic loss.

The battery needs 13.8 to 14.2V to charge properly - nothing more! If, as you state, you're banging 18V into it you are going to ruin it.

I would suggest a proper battery isolation switch be fitted and have done with it..... or find the fuse that's related to the parasitic draw and pull it.

SilverfoxUK · Post by **SilverfoxUK** » Tue Jan 04, 2022 5:08 pm

So guys you are right we shouldn't try to measure AC from a battery. But if you consider a rectifier (changes AC to DC) it will pass the DC but with a voltage loss of 0.7V.
We seemed to be getting mixed up with volts and amps a bit. So the voltage on a car battery is around 12V. That is the pressure available. Only when you connect some sort of a circuit will you get current flow which we measure in amps. Now if select a high current on your ammeter and connect is across the battery unless its good for about 800A you are going to be looking towards a new meter ! Remember volts times amps gives watts - watts is heat which is what you got.
I would suggest the electronics in your car is drawing more current than you realise it is. The electronics don't really sleep whether it be the alarm system of the entry system. Bottom line is need to use the car more often of pop the battery on charge probably once a fortnight. Cold weather wont help your cause either.

kellys_eye · Post by **kellys_eye** » Tue Jan 04, 2022 5:54 pm

SilverfoxUK wrote: ↑Tue Jan 04, 2022 5:08 pm Now if select a high current on your ammeter and connect is across the battery unless its good for about 800A you are going to be looking towards a new meter !

Nope - a new fuse for the meter.

ericmark · Post by **ericmark** » Wed Jan 05, 2022 9:28 am

I used a smart charger for my wife's Jaguar XE during the lock down, and put it on an energy monitor as more than one car so was swapping it car to car, it would kick in same time every day, clearly some thing in car was connecting at that time.

David_Baratheon · Post by **David_Baratheon** » Sat Feb 05, 2022 6:39 pm

By parasitic drain, do you mean quiescent current? I.e. current that passes around the circuit whilst it's in an off state, due to components slowly leaking current?

Why were you testing the alternator etc? Is this with the engine running? I'm not clear what testing a DV battery for AC current would tell you about quiescent drain

David_Baratheon · Post by **David_Baratheon** » Sat Feb 05, 2022 6:41 pm

ericmark wrote: ↑Wed Jan 05, 2022 9:28 am I used a smart charger for my wife's Jaguar XE during the lock down, and put it on an energy monitor as more than one car so was swapping it car to car, it would kick in same time every day, clearly some thing in car was connecting at that time.

What model year is it? Does it have SOTA? if its a modern vehicle it will have over 100 ECUs on the vehicle and something could be kicking in at a certain time of day. Is it a plug in hybrid?