Battery drawdown

Submitted: Tuesday, Dec 16, 2008 at 19:41

ThreadID: 64331 Views:3384 Replies:6 FollowUps:9

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Battery Power

In this article we explain why you might need an additional power source independent of the starting battery installed into your vehicle and we look in detail at types of batteries,

Campy

How to I check for battery drawdown/loss? All I have is a multimeter....

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Reply By: Member - Roachie (SA) - Tuesday, Dec 16, 2008 at 20:03

Tuesday, Dec 16, 2008 at 20:03

Set the multimeter on 20VDC, attach red probe onto positive battery terminal and black probe onto negative.

Do this whenever you want to know what the battery's voltage is. Do it at the beginning (after you stop charging or when you pull-up after a day's driving etc) and then check it again as often as you like.

If you see the voltage drop down to around 12 volts, your battery is (as far as I'm concerned), in immediate need of re-charging.

Hope this helps...... I've gone a different way and have permanently attached digital voltmeters to my battery banks in both the Patrol and the camper trailer.

Roachie

AnswerID: 340017

Follow Up By: jdbb - Tuesday, Dec 16, 2008 at 20:11

Tuesday, Dec 16, 2008 at 20:11

So with the same multimeter, how do I see how many amps are being used by a particular appliance?

John

FollowupID: 607584

Follow Up By: Member - Roachie (SA) - Tuesday, Dec 16, 2008 at 20:16

Tuesday, Dec 16, 2008 at 20:16

See the below response....that's how to check for amp draw.... Just be aware that most small multimeters have only a small amp-reading capacity. Don't try to measure the draw of a starter motor or winch...hahahaha

FollowupID: 607587

Reply By: Dunaruna - Tuesday, Dec 16, 2008 at 20:05

Tuesday, Dec 16, 2008 at 20:05

And that's all you need.

Disconnect the positive battery lead, Connect the black test lead to the battery post and the red test lead to the disconnected battery cable. Set the MM to amps.

Depending on the vehicle and the amount of control modules, you could expect to see anything up to 300 milli amp (mA) parasitic drain. If you suspect a problem, disconnect fuses one by one and see if the amp draw reduces (boot lights and glovebox lights are a classic faulty draw).

AnswerID: 340018

Follow Up By: Dunaruna - Tuesday, Dec 16, 2008 at 20:06

Tuesday, Dec 16, 2008 at 20:06

I should add - this is a test for parasitic drain. It does not test the condition of the battery or the charging system.

FollowupID: 607582

Follow Up By: Peter 2 - Tuesday, Dec 16, 2008 at 20:16

Tuesday, Dec 16, 2008 at 20:16

Also DO NOT have the vehicle ignition on or the engine running when doing this test as you WILL fry the multimeter and the alternator.
also ensure the multimeter has a current capability of at least 10 amps to be on the safe side.

FollowupID: 607586

Reply By: Member - Mike DID - Tuesday, Dec 16, 2008 at 20:21

Tuesday, Dec 16, 2008 at 20:21

"How to I check for battery drawdown/loss? All I have is a multimeter...."

???? Do you want to measure the amount of charge remaining in the battery OR how much current is being drawn from the battery right now.

AnswerID: 340021

Reply By: Campy - Tuesday, Dec 16, 2008 at 20:21

Tuesday, Dec 16, 2008 at 20:21

Thanks guys - it seems so simple when someone explains it....

AnswerID: 340022

Reply By: Member - Kiwi Kia - Wednesday, Dec 17, 2008 at 06:58

Wednesday, Dec 17, 2008 at 06:58

If you want to see what current a heavy device like a winch etc. is drawing then get hold of a mate who is an electrician or auto electrician and see if you can borrow a DC clamp meter. No hook-up required just clip it around the outside of a battery cable.

.

AnswerID: 340056

Follow Up By: Ray - Wednesday, Dec 17, 2008 at 07:48

Wednesday, Dec 17, 2008 at 07:48

Commonly known as a tong tester

FollowupID: 607653

Follow Up By: Member - Kiwi Kia - Wednesday, Dec 17, 2008 at 08:11

Wednesday, Dec 17, 2008 at 08:11

Yes, but more commonly known these days as a "DC Clamp Meter' to distinguish it from the old 'Tong Tester' that was only used on AC

.

FollowupID: 607655

Follow Up By: oldtrack123 - Wednesday, Dec 17, 2008 at 15:23

Wednesday, Dec 17, 2008 at 15:23

Hi
50years ago there were tong testers [so called by the manufacturers] that measured AC & DC [Plugin movements according to range required moving iron instrument]

FollowupID: 607717

Follow Up By: Member - Kiwi Kia - Wednesday, Dec 17, 2008 at 15:39

Wednesday, Dec 17, 2008 at 15:39

Hi Oldtrack123,
I don't think you could find me a 50 year old tong tester that measured DC ! The old tong tester could only register AC.

FollowupID: 607721

Follow Up By: oldtrack123 - Thursday, Dec 18, 2008 at 13:20

Thursday, Dec 18, 2008 at 13:20

Hi Kiwa
Well, I have one sitting in front of me right now" GEC" brand "200a ac/dc dial ".It is moving iron type meter works straight from magnetic flux in tongs.You change dials / movements for different ranges.
Dials available which I have are 15a, 75a, 200a,400a , 800a
. It is not transformer type with switchable ranges THEY came out later.
Crompton also had a similar product ,with various shaped tongs but range did not go to 800a.
Some were limited in the current range due to being thin tongs [ magnetic saturation limited their range]
The Crompton was 1st on the market late 40s ,GEC came out early 50s.

FollowupID: 607877

Reply By: Member -Dodger - Wednesday, Dec 17, 2008 at 16:31

Wednesday, Dec 17, 2008 at 16:31

If you want to tell the state of the battery and not the amps out you can use your MM to check the voltage of the battery and the info below wiil give you a good Idea.
Make sure that all charging actions have ceased and the battery has been at rest for a good while.
You can shorten the waiting time by putting a load on the battery such as a camping light for a couple of minutes then check the battery with the light still on it.

State of Charge Volts per Cell
100% 12.7 2.12
90% 12.5 2.08
80% 12.42 2.07
70% 12.32 2.05
60% 12.20 2.03
50% 12.06 2.01
40% 11.9 1.98
30% 11.75 1.96
20% 11.58 1.93
10% 11.31 1.89
0 10.5 1.75