Checking battery voltage using a multimeter

[silver1011]

Hey all,

 

I've had a multimeter tucked away in the garage for several years and never really properly read up on how to use it properly.

 

Being stuck at home and looking for jobs I thought I'd use it to check the battery health on my two cars.

 

A quick Google search suggested I should set the dial to DC...

 

 

...and to '20', being the closest to the battery voltage of between 12V and 14V...

 

 

I then touched the positive terminal on the car battery with the red probe, and then the negative terminal (both the seperate jump start contact point, and the battery terminal itself) with the black probe.

 

The voltage was reading on the multimeter display somewhere between 3V and 4V, which threw me.

 

The engine was off, the engine hadn't been started since a few days prior. The ignition was off and again hadn't been turned on for a few days.

 

Later today I used to car to pop to the supermarket and it started fine, so presumably the battery is OK.

 

With the engine off I was expecting to see something close to 12.6V, with 12.2V or below sign of a severely or dead battery.

 

So 3V has me confused. What was I doing wrong?

[lol-lol]

4 minutes ago, silver1011 said:

Hey all,

 

I've had a multimeter tucked away in the garage for several years and never really properly read up on how to use it properly.

 

Being stuck at home and looking for jobs I thought I'd use it to check the battery health on my two cars.

 

A quick Google search suggested I should set the dial to DC...

 

 

...and to '20', being the closest to the battery voltage of between 12V and 14V...

 

 

I then touched the positive terminal on the car battery with the red probe, and then the negative terminal (both the seperate jump start contact point, and the battery terminal itself) with the black probe.

 

The voltage was reading on the multimeter display somewhere between 3V and 4V, which threw me.

 

The engine was off, the engine hadn't been started since a few days prior. The ignition was off and again hadn't been turned on for a few days.

 

Later today I used to car to pop to the supermarket and it started fine, so presumably the battery is OK.

 

With the engine off I was expecting to see something close to 12.6V, with 12.2V or below sign of a severely or dead battery.

 

So 3V has me confused. What was I doing wrong?

 

Could be a knackered battery in the multimeter.

Should be 12 to 12.6 if healthy and about 14 to 14.5 when engine running after initial dip starter motor takes or lift revs to 2k and it should show 14 volts or so.

 

Is the red lead in the right hole ?

Edited 29 April, 2020 by lol-lol

[silver1011]

It could well be, the batteries are likely to be the originals, I just assumed that as the display was working, then so were the batteries, I'll replace and check again.

 

The probes were plugged into (from the top) the second and third sockets (red into red and black into black)...

 

[lol-lol]

16 minutes ago, silver1011 said:

It could well be, the batteries are likely to be the originals, I just assumed that as the display was working, then so were the batteries, I'll replace and check again.

 

The probes were plugged into (from the top) the second and third sockets (red into red and black into black)...

 

 

Not super clear but maybe it should be top connector and bottom one ?

[john999boy]

5 minutes ago, lol-lol said:

Not super clear but maybe it should be top connector and bottom one ?

The top one is to measure current and not voltage.

[Kenny R]

The leads are connected correctly for measuring voltage, the top red connector is for measuring current. 

If you turn the selector to the 200 ohm position and touch the two probes together, what is the resistance of the leads?

[silver1011]

Without the probes touching...

 

 

With the probes touching...

 

[Kenny R]

4.1 ohms not perfect but close enough not to influence voltage readings by much.

Have you tried measuring the voltage of say an AA battery or such likes to see how much the readings are out.

Also If testing using probes on the car battery terminals you might need to rub the probe across the surface to make good contact, or test on the bright battery cable connectors.

[silver1011]

Good idea Kenny.

 

A brand new 1.5V AA battery...

 

 

I'm clearly not getting a proper connection from the car battery terminals, although aside from loosening them and squeezing the probes down the sides of the terminals I'm not sure what more I can do.

 

I'll have another go in the morning.

[Breezy_Pete]

The terminal posts are soft, just scrape the surface a little with the probes to reveal shiny fresh metal to contact.

[mac11irl]

little bit of sand paper and rub the tops of terminals. and press the probes hard onto them.  should give a decent connection

 

@Wino snap

[peter3197]

I have the same multimeter. black in the top one, red in the middle gives correct readings on voltage and resistance.

[john999boy]

25 minutes ago, peter3197 said:

I have the same multimeter. black in the top one, red in the middle gives correct readings on voltage and resistance.

Maybe you need to re-check?

This is in essence exactly the same as the OP's meter.

 

[peter3197]

23 minutes ago, john999boy said:

Maybe you need to re-check?

This is in essence exactly the same as the OP's meter.

 

Mine is the same generic one. The DC voltage and resistance work with the black lead in either the top or bottom positions, just checked it.

[xman]

5 hours ago, lol-lol said:

 

Not super clear but maybe it should be top connector and bottom one ?

Do not under any circumstance try to measure your battery voltage using the top connector marked 10A!! This connection is joined to the bottom black connector via a very low resistance current shunt, its unfused and is used for high current range measurement only. If you did try to measure your car battery with leads connected top and bottom connectors you would be effectively shorting the battery out! You will then briefly see some sparks, an interesting combination of melting meter and leads and weld the probes to the battery posts at which point you will probably start screamimg before things start glowing red and.....💥   🚑

 

1 hour ago, peter3197 said:

Mine is the same generic one. The DC voltage and resistance work with the black lead in either the top or bottom positions, just checked it.

 

Thats because of the current shunt. But it is the incorrect way to connect it.

 

To measure ac or dc volts or resistance use the bottom two connectors only.

 

Meter probes don't work well on lead posts unless you prod hard, instead use the tensioning bolt on the +ve terminal connector and the charging ground tab for the -ve probe.

 

[NJRJ]

2 hours ago, peter3197 said:

Mine is the same generic one. The DC voltage and resistance work with the black lead in either the top or bottom positions, just checked it.

 

Use only the terminals for what they are labelled as, also make sure the setting on dial is correct before testing - else the magic smoke escapes, sometimes noisily ⚡ 🌟🌪️

[peter3197]

7 hours ago, xman said:

Do not under any circumstance try to measure your battery voltage using the top connector marked 10A!! This connection is joined to the bottom black connector via a very low resistance current shunt, its unfused and is used for high current range measurement only. If you did try to measure your car battery with leads connected top and bottom connectors you would be effectively shorting the battery out! You will then briefly see some sparks, an interesting combination of melting meter and leads and weld the probes to the battery posts at which point you will probably start screamimg before things start glowing red and.....💥   🚑

 

 

Thats because of the current shunt. But it is the incorrect way to connect it.

 

To measure ac or dc volts or resistance use the bottom two connectors only.

 

Meter probes don't work well on lead posts unless you prod hard, instead use the tensioning bolt on the +ve terminal connector and the charging ground tab for the -ve probe.

 

 

6 hours ago, NJRJ said:

 

Use only the terminals for what they are labelled as, also make sure the setting on dial is correct before testing - else the magic smoke escapes, sometimes noisily ⚡ 🌟🌪️

Noted, thank you both.

[Robbydazzler]

Similar to Silver1011 I have been looking round for something to do. Therefore , since my car gets  little use at present, I decided that I would research all things car battery especially how to test its health. Tried a multimeter on my own 18 month old Seat Toledo today and got 11.92V. This confused me greatly as according to most things I have read  (some articles are contradictary) this suggests the battery needs a recharge. I have noticed on my weekly 5 mile trip that the start/stop has ceased to function. I went out in the wife's Dacia the other day and the start stop was working and hence I decided to try the battery voltage expecting it to be far higher than the Seat. It read marginally higher at 11.98V. Both batteries are EFB and the Dacia is a year older. Both cars start immediately. To paraphrase  Alice  in Alice through the looking glass the more you look at things the curiouser they get !

[Breezy_Pete]

Checking a battery ideally needs to be done with nothing but the meter connected to it, and after a good hour or two since there was zero load on it (disconnecting battery negative is one way to achieve this). 

As soon as you unlock/open the car, various systems wake up, draw current and depress the voltage measured at the battery or ciggie lighter or wherever. So you're not getting a true indication of the off-load voltage.

 

What you can do to get the closest possible to a 'true' off-load reading without disconnecting the battery is to open the bonnet, flick the latch over with a screwdriver so that the car 'thinks' the bonnet is closed; close and lock all doors, wait a couple of hours to make sure everything is dormant, then measure across the battery terminals.

 

Once you're done, open the car again, pull the bonnet opening lever to reset the latch so you can close the bonnet fully again.

 

It sounds like both cars could do with a charge though.

Edited 30 April, 2020 by Wino

[Breezy_Pete]

19 hours ago, xman said:

Do not under any circumstance try to measure your battery voltage using the top connector marked 10A!! This connection is joined to the bottom black connector via a very low resistance current shunt, its unfused and is used for high current range measurement only. If you did try to measure your car battery with leads connected top and bottom connectors you would be effectively shorting the battery out! You will then briefly see some sparks, an interesting combination of melting meter and leads and weld the probes to the battery posts at which point you will probably start screamimg before things start glowing red and.....💥   🚑

 

 

Whilst I agree that it isn't something you should deliberately, nor misguidedly do; the outcome isn't very likely to be as dramatic as described above. 

A few weeks ago while checking elderly neighbours' batteries I was swapping between current measurements and voltage measurements with insufficient care and attention when I managed to do this faux-pas on a cheap meter.  There was the subtlest of 'phut' noises from within the meter followed by an unexpected reading of 0.  Realising what I'd done, there was a slightly louder sound approximating 'phut'...

 

I finally got round to fixing it just now.  A not-so-wide PCB track links the 10A DC socket to one end of the current shunt, and it had 'popped' as it would be expected to when presented with lots and lots of amperes.

 

A thin bit of wire soldered in its place and all is back up and running.  Including a picture of the current shunt (thick bridge of wire linking common and 10A input skts, top and bottom ones in last, blurry pic) for the hell of it while I have it apart, to show what xman means.  That wire has a small, but known resistance which causes a voltage to be developed between its ends when a large current flows through it, which the meter measures and converts into a current value.

Edited 30 April, 2020 by Wino

[silver1011]

I had another quick try, no real improvement...

 

Tried several different locations for the probes, none of which seemed to make any discernible difference.

 

The only potential positive is that the voltage was fluctuating between 0.5V to 1V every second or so, each time it returned to the higher voltage reading it was slightly higher. In the 2 or 3 minutes I left the multimeter connected the voltage increased from around 2V to just over 4V. If I'd left it connected it might have eventually reached a normal reading, but not one I'd probably be able to trust as being accurate...

 

 

 

 

I'll try my other car tomorrow to see if that results in the same readings...

[J.R.]

Fubar!

[chimaera]

3 minutes ago, J.R. said:

Fubar!

BUNDY?

[xman]

See what reading it gives on the 200 volt range. (thats what you used with the AA battery test)

 

Could be the 20 volt range is fubared.

 

Change the battery in the meter for a fresh one and definitely if the battery has been tucked away for several years along with the meter!

 

Other than that, throw it away and buy a decent multimeter.

Edited 3 May, 2020 by xman