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[Brynjaminjones]

Good Morning all.

After being sat at traffic lights this morning with the heater fan on full whack, I noticed as I pulled away that the fan sped up.
At the next lights I looked and noticed that the voltage on the dashboard was dropping to about 11 Volts, then when I got moving again it was going up to just under 14.

After driving for a while it stopped dropping so much.

Is this simply a case of dying battery, or should I be looking at the alternator?

[bigjeepzj]

give the battery a charge
if you have being doing short journeys then it may not be charged that well
check the battery whit a proper meter if you have one



that would be a useful meter to have


http://www.ebay.co.uk/itm/VC97-3999-Auto-Range-Digital-Multimeter-Voltmeter-Tester-All-Function-AC-DC-OHM-/111487591451?hash=item19f52da41b:g:WnkAAOSwajVUQJD1
 

[Dave69]

if you switch everything on at once on a 1.8 escort (pre focus) then the engine would stall due to the electrical load

[Brynjaminjones]

Cheers Daves 

The ZJ does 2x 1.5 hour runs a day without turning the ignition off, and lots of shorter journeys between. I'd have thought that the longer journeys should be enough to give it a good charge, plus I try to not use any electrics with the ignition off as I don't trust the battery.

Also, when I had the issue this morning, the last run it had done had been 1.5 hours, so should have been charged.

I also don't have a charger or meter, but I guess it would make sense to try the known good battery from my XJ!

[Dave69]

Good Morning all.

At the next lights I looked and noticed that the voltage on the dashboard was dropping to about 11 Volts, then when I got moving again it was going up to just under 14.

After driving for a while it stopped dropping so much.

Is this simply a case of dying battery, or should I be looking at the alternator?

electric fans take alot of juice so slow running at idle is norm unless your boiling the water then it will kick into overdrive.

voltage increasing to 14v while driving is normal as it's replacing the lost lectricity due to idle and 14v also confirms your alternator is working due to the increase and decrese in voltage charge value

does the jeep start easy after a couple of days? if so the battery could still be fine.

if there is a drain on the battery check the amp value from the battery to body when engine is off. plenty of topics can be found after a google search

[Brynjaminjones]

Cheers Dave.
Just for clarification, it's the heater fan I'm on about, not the engine one (ZJs don't have an electric one).

It seems like alternator is okay then, I just think the battery might be a bit duff as that drop at idle isn't the norm for the ZJ or my XJ.

It's also really rare that the ZJ sits for more than 12 hours, so I'm unable to comment on how easily it starts after sitting!

Having thought about it, the ZJ had been sitting for 6 months until the day we bought it, and they had to charge the battery the night before. I'll try the XJ battery when I get a chance and update on here 

[Jonny Jeep]

that would be a useful meter to have

I bought for the similar VC99 for use in work, good meters for the money. It seems accurate as any other aside from the temp probe which I'm not so sure about. I'd need to test it with pure melting ice and steam above boiling water before I trusted it entirely. The min/max hold feature is useful as you can do things like hook it up to the battery, start the engine, and then go see what your voltage dropped to while cranking.

[LairdScooby]

Re the multimeter temperature probe, it's a K-type thermocouple and the standard "tolerance" for these is +/- 3C around the measured point.

As for the voltage drop, mine does exactly the same and the original volt meter in mine is "pessimistic" only just showing 14V when it is in fact 14.4V and usually shows about 12V when the real voltage is at least 13.8V.

[wildwood]

When I had the ZJ and it stood idle for 5 days on an older battery I found that starting was sluggish due to the draw caused by the alarm system.....

But you say the vehicle is almost constantly in use so unless the battery is bollixed you should be OK.
How about changing over batteries with your  XJ to give you a reference point.