How to carry out parasitic drain check with twin batteries ? (2 Viewers)

[Paulpen]

Hi guys

Having had my 100 a couple of months now the alarm does seem to go off randomly once ever few weeks and also the battery gauge can sometimes read 12v at idle rather than 14v.

With this in mind if like to carry out a battery drain test which I've done on cars before but never anything with twin batteries.

Can I do the test on either battery or do o have to do it on a specific one ? Also do I have them both connected when doing it or one disconnected ?

Sorry for what I imagine is a silly set of questions but if rather do it correctly and get a real figure than chasing ghosts by doing it wrong

 

[hoser]

The factory dual battery set-up is wired in parallel. Remove/disconnect one battery and proceed with normal trouble shooting.

 

[Paulpen]

So fully disconnect battery one and do the amp draw on battery two
Would you then do the amp draw on battery one with battery two disconnected or will o get exactly the same result ?

 

[hoser]

Your charging system should never read 12v at idle. Use a voltmeter at the battery terminals. There's likely an issue with the alternator, the battery or the battery cables. Still, disconnecting one battery will help isolate issue.

 

[Paulpen]

I mentioned it on a 100 series Facebook group before I found this forum and they all said it's normal !

I'm not sure where to upload the video so you can see what I mean.

Guess I'll be do a drain and then a charging test - all I've got is a multimeter

 

[uHu]

Assuming you 100 is a HDJ (being in the UK), you would see a low voltage (~12v) at idle for 90 sec after starting a cold engine, unless you have disconnected the useless intake heating grid.

When checking the resting amp draw, wait for a minute after turning off ignition and locking doors before reading the meter.

 

[hoser]

Yes, Listen to uHu, we don’t get the HDJ here.

 

[Paulpen]

I am in the UK with the HDJ and assumed you guys got it too but with fuel being cheaper mainly had the V8 !

Handy to know - it must draw a fair current then !

It's certainly been fiddled with before going by the state of the wires and connector

 

[e9999]

and here I assumed all along that the diesel engines have a 24V starting system... oh well...

 

[Paulpen]

I was unsure tbh

I'm learning all the time thanks to this forum

 

[Paulpen]

Finally managed to start doing this today after realizing it was flat

Fully disconnected one battery (the one on the left of the engine bay from the driver's seat).

Setup the multimeter on the other battery negative terminal and negative lead (right side from the driver's seat) and waited a few minutes.

0.05A - 0.07A

Same result of I test the other way round (other battery)

Now I'm a bit stuck as how to proceed as the batteries are not that old and were replaced as a paid by the previous owner

Also best / easiest way to disconnect the heating grid setup ?

 

[uHu]

Also best / easiest way to disconnect the heating grid setup ?

Just unplug the small plug next to the intake heater grid relay. (located on top of fender, close to the heater grid)

 

[Paulpen]

I'll have a look tomorrow and see if I can find it as won't get cold enough for it here.

Guess my next option is somehow check all is charging correctly ?

 

[uHu]

I'll have a look tomorrow and see if I can find it as won't get cold enough for it here.

The intake heater grid comes on whenever you start with a coolant temp of under 40 C; which, even in old England, means every morning. It stays on for 90 sec, or until the temp is above 40.

 

[Paulpen]

The intake heater grid comes on whenever you start with a coolant temp of under 40 C; which, even in old England, means every morning. It stays on for 90 sec, or until the temp is above 40.

Maybe I'll try with it disconnected and see if it makes any difference to starting

Still need to work out why my batteries went flat

 

[e9999]

around 50mA of "parasitic" drain seems normal to me. So that's not the cause of them going flat, probably.

 

[Paulpen]

Yea I don't think that's the cause so it must be charging, storing or an intermittent drain ?

 

[e9999]

I don't know about those Diesel engines producing only 12V at idle but with the older trucks I'm familiar with, if the battery is reasonably low at start (say a bit above 12V), the alternator will go up to 14.4V or so right away and then slowly decrease to somewhere between 13.5 and 14V after the battery has gone back up enough.
What do you see your alternator do when it's been running for a while with low batteries?

 

[Paulpen]

So went out after leaving it overnight.

Battery voltage at 11.9 before doing anything although they were flat yesterday so not had a full charge.

Started fine and charging at 14.2v after a couple of minutes.

Headlamps on and it drops to 13.8v

With heating, lights etc all on it's at 12.4v

I'm not sure if this means I have a charging issue or that the batteries are poor ?

 

[Paulpen]

Also seems to get worse with either heat or running time.

15 minutes at idle and I'm now getting 11.8v under load and then turning the loads off the voltage slowly creeps up again but only to 12.8v

Tested the voltage drop between the alternator post and battery positive and get 0.08v so guess that means the cables are ok.

I must have an alternator or battery at fault but all I have to test them with is a multimeter