Measuring accessories draw on battery

cappers · Dec 23, 2023

Ninety 3.5V8 Efi auto (originally 2.5P LT77).

Had some problems with battery losing charge over time when unused and I wanted to see what might be draining it.
The components I can think of that are live when the ignition is off are the clock, radio memory, alarm's ignition, motion and ultrasonic sensors and warning LED and possibly the ECU (14CUX).

I removed the negative battery lead and connected the -ve probe of a DVM set to amps to the earth strap and the +ve probe to the battery -ve post.
Got a reading of 0.004A or 4mA which doesn't seem excessive. But as the battery earth was not connected I couldn't activate the alarm fob or radio to check their draw.

What am I doing wrong and how do I achieve my goal? Should I just put the DVM set to V across the battery and turn things on and off? Won't tell me current draw but will show voltage?

TIA

Def90man · Dec 23, 2023

A faulty alternator can drain the battery as well I think

cappers · Dec 23, 2023

Alt. less than a year old (A127) and was putting out ~14.5V at idle (new fully charged battery)

cappers · Dec 23, 2023

cappers said:
But as the battery earth was not connected I couldn't activate the alarm fob or radio to check their draw.

Just realised, the battery earth was connected via the meter

I was using the mA socket, perhaps the ~10A socket would better to detect the alarm draw?

lynall · Dec 23, 2023

Check out youtube, search for parasitic draw, you can tst at the fuse box without removing anyhting, Think @gstuart had some doings with his car?

gstuart · Dec 23, 2023

lynall said:
Check out youtube, search for parasitic draw, you can tst at the fuse box without removing anyhting, Think @gstuart had some doings with his car?

hi mate

indeed had to make up some fused leads to allow me to test the fuses as found that u wasn’t able to pull the fuses out to test otherwise it would wake up the modules , locked out the bonnet and door catches in order for me to test each fuse one by one until I found the issue

also found a clamp meter very useful , do remember it took 30 x mins for mine to go into a sleep state and had to read under 22 Ma, in the end for me it was the electric seat memory module, removed it and made all new looms for each seat

alas not sure if the same type of tests can be done on the earlier FFRR

kermit_rr · Dec 24, 2023

ER1C · Dec 24, 2023

For what its worth I had similar and picked up a volt meter/fuse adaptor then just went through the fuses to see which was pulling. It was pennies on Amazon.

lynall · Dec 24, 2023

gstuart said:
hi mate

indeed had to make up some fused leads to allow me to test the fuses as found that u wasn’t able to pull the fuses out to test otherwise it would wake up the modules , locked out the bonnet and door catches in order for me to test each fuse one by one until I found the issue

also found a clamp meter very useful , do remember it took 30 x mins for mine to go into a sleep state and had to read under 22 Ma, in the end for me it was the electric seat memory module, removed it and made all new looms for each seat

alas not sure if the same type of tests can be done on the earlier FFRR

View attachment 305674 View attachment 305675 View attachment 305676

In think them chunky fuses are called slow blow or something like that!

Measuring accessories draw on battery

cappers

Well-Known Member

Def90man

Percy the Pedant

cappers

Well-Known Member

cappers

Well-Known Member

lynall

Well-Known Member

gstuart

D3 Grandad

kermit_rr

Very

ER1C

Well-Known Member

lynall

Well-Known Member

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