Alternator output & battery voltage advice.

[Guest wunntenn]

I've just had installed two new Optimas with an IBS battery monitor charging system linking them, a yellow top and a red top. The yellow aux battery seems to be ok, retaining a healthy 12.75V but I'm a wee bit concerned about the red top main starter, which seems to dip quickly and this morning after not running the van for a few days was below 12V - around 11.84V. It started ok though without difficulty. The multimeter, and the IBS unit's built in indicators rough estimation, both agree on the voltage level.

I'm not sure if I've a voltage/charging problem. Can anyone tell me from the following figures if the alternator is doing what its supposed to? This is measuring across the red top with a proper multimeter:

At tickover:

Engine running, no lights 13.99V

Engine running, side lights on 13.98V

Engine running, head lights on, low beam 13.88V

Engine running head lights on, full beam (incl 2 spots) 13.04V

At 2000rpm or so:

Engine running, no lights 13.94V

Engine running, side lights on 13.93V

Engine running, head lights on, low beam 13.86V

Engine running head lights on, full beam (incl 2 spots) 13.73V

I've not given the main battery a full mains charge since installing it - it was showing 12.75V when I took it out of the box. I've just got a Ctek charger, arrived yesterday so will give it an overnight with that and see what transpires, but if any electro experts want to comment on the alternator that would help me sort this out. Thanks.

[Ex Member]

Assuming your meter is good, that all looks fine. The alternator should try and maintain 14 volts. At lower rpm and higher loads, the voltage drop as it can not keep up.

At rest a fully charged battery is around 12.5 volts, so you might have a power leak somewhere or a battery on the decline.

http://www.arttec.net/Solar_Mower/4_Electr...%20Charging.pdf

[suggs]

was the low reading taken with the ignition on or off, as the volts will drop when the key is turned before the engine fires up.

if your getting less than 12v with the ignition off then you probley have a drain somewere, i would use a multi meter direct to the battery and see what it reads..

[pat_pending]

Alternator seems a tad on the low side but not necessarily a problem, they normally kick out 14.5v.

Now i know two friends who both bought Optimas, both had problems with them self discharging if left for a while.

When i worked for a Chrysler dealer, they fit Optimas as standard, we used to change loads under warranty for the same problem. The general opinion was that they were carp. But... in the "off road" world everyone seems to rave about them.

Now you may have a current drain and the battery is fine, but that is my experience of Optimas.

To check for a current drain, disconnect the earth lead and connect a test meter set to 10 Amps between the battery - post and the disconnected lead. Should read about 0.05 amp max with everything off.

Most common causes of battery drain..interior lights not going off...Aftermarket alarm/immobilisers...faulty alternators.

Let us know how you get on.

[Guest wunntenn]

Thanks everyone.

Suggs "was the low reading taken with the ignition on or off, as the volts will drop when the key is turned before the engine fires up." Low reading <12v was with ignition off. All others readings with ignition on.

Will try the in-line metering and see what it gives.

[G_Cam]

Alternator seems a tad on the low side but not necessarily a problem, they normally kick out 14.5v.

Now i know two friends who both bought Optimas, both had problems with them self discharging if left for a while.

When i worked for a Chrysler dealer, they fit Optimas as standard, we used to change loads under warranty for the same problem. The general opinion was that they were carp. But... in the "off road" world everyone seems to rave about them.

Now you may have a current drain and the battery is fine, but that is my experience of Optimas.

To check for a current drain, disconnect the earth lead and connect a test meter set to 10 Amps between the battery - post and the disconnected lead. Should read about 0.05 amp max with everything off.

Most common causes of battery drain..interior lights not going off...Aftermarket alarm/immobilisers...faulty alternators.

Let us know how you get on.

Your comments are very interesting indeed.

I have a Red Optima that was bought new around 12 months ago - but now does not hold its charge for more than 3 days!

It is part of a split charge system in my Defender and the Yellow Optima now also appears to be failing after 18 months.

I have had to stick my trusty Samson lead acid battery back in while I test the system and see if the optimas still fully discharge when not fitted.

I have a cut-off switch fitted so there should be NIL leakage when its sitting unused!

It is VERY VERY frustrating.

Graham