Alternator output

[Cliffy]

 

I have got a voltage checker the plugs in to the cigar lighter socket, as recommended on this forum. I was expecting it to read around 14 volts but it is only reading between 13.4 and13 volts, revving the engine does not seem to make a great deal of difference.

 

Is this OK or do I need to have the alternator checked out by an expert?

 

 

 

 

[Derek Uzzell]

Your motorhome’s alternator should be charging the starter-battery at over 14V.

 

What you should do is check the starter-battery’s voltage at the battery’s terminals with a multimeter that you are confident is accurate.

 

If the multimeter’s readout is over 14V (when the motor is running) either your voltage checker is inaccurate or there’s a significant voltage drop between the starter-battery and the cigar lighter socket.

 

If the multimeter’s readout (when the motor is running) matches the readout of your voltage checker and is between 13.0V and 13.4V, you’ve got a problem!

[Alanb]

The voltages that you quote, are as you suggest rather low. A more typical output would be about 14.0 volts or slightly more. However partially charged batteries could be pulling the voltage down.

 

You do not mention vehicle make, but on my Ducato the cigarette lighter shares a control relay with the heater fan. In these circumstances the voltage at the socket could be lower if the heater fan was running.

 

Can you try your tester in another vehicle?

 

The best check is an accurate meter applied directly to the battery terminals. As has been frequently quoted on this site a fully charged battery will settle to about 12.6 volts after several hours.

 

 

[aandncaravan]

It seems like the Alternator is working, it wouldn't reach 13.4v otherwise, so I would suggest you may have some 'restriction' to the power flow?

 

My first suggestion would be to get someone to hold a wire, doesn't need to be heavy duty, between the engine and an unpainted part of the chassis while you watch the display. I suspect you will see the voltage rise to 14.4v? A battery jump lead works well clamped between the battery earth terminal and a unpainted engine bolt.

 

The well documented earth problems often result in a seemingly low Alternator output. Bridging between the engine and the body can 'bypass' the corroded connection on the Earth strap or wherever the poor earth is.

See the bottom of this page for more info : http://www.citroenhyonline.co.uk/6volt-to-12volt-conversion.php. Sorry the page is on our sister website of the Citroen H vans we restore, so it is right at the bottom, but I am working on creating a dedicated 'Poor Earth' page on the A and N Caravan web site.

 

[Cliffy]

Thanks for your help.

 

I have tried the Cigar socket voltage reader on two other vehicles and it reads over 14Volts so I need to do as suggested, check the battery charge with a multi meter at the battery and if necessary try earthing the battery to the engine.

 

Am I correct in assuming there is not a separate voltage regulator on modern vehicles.

 

If the alternator is not supplying 14 volts does that mean the alternator will have to be replaced or is there an integral regulator that can be causing a problem and can be replaced without replacing the alternator?

 

The van is a AT Tracker 2004 on a 1.9 Ltr Ducato.

 

Thanks

 

 

[Cliffy]

 

Thanks for the great advice, especially aandncaravan you were spot on.

 

Checking at the battery with a multi metre with the engine running returned 14,2 Volts.

Held a cable from the chassis to the engine and the cigar lighter voltmeter went up to 14.1.

I could not get hold of any webbed earthing lead as suggested on the link so bought a made up cable from the local motor factors and fitted it in 10 minutes.

The cigar lighter reading is now 14.2 to 14.5 volts with the engine running.

 

 

Result!!!!!

 

 

 

[aandncaravan]

Yes modern Alternators have a built in Regulator.

 

Glad it is sorted.

 

We think the Earth strap failure issue is hurting vehicles in ways long before it becomes noticeable with poor/none Starting issues.

 

Can we suggest you monitor your starter battery? It is possible it has not been getting a full charge for a while, as a result it may have been sitting for a time partially charged so the potential for Sulphation and deterioration?

We would suggest that at the slightest hint of sluggish starting you bin it rather than risk the Alternator which has almost certainly been stressed by the episode? Alternators are not that expensive but the Garage time fitting them is.

 

 

 

[Cliffy]

aandncaravan - 2016-03-05 9:23 PM

 

Yes modern Alternators have a built in Regulator.

 

Glad it is sorted.

 

We think the Earth strap failure issue is hurting vehicles in ways long before it becomes noticeable with poor/none Starting issues.

 

Can we suggest you monitor your starter battery? It is possible it has not been getting a full charge for a while, as a result it may have been sitting for a time partially charged so the potential for Sulphation and deterioration?

We would suggest that at the slightest hint of sluggish starting you bin it rather than risk the Alternator which has almost certainly been stressed by the episode? Alternators are not that expensive but the Garage time fitting them is.

 

 

 

Thanks for that, the battery is quite new and I had it checked out by the garage that fitted it when I first started having signs of a problem and it was good all round charge wise and starting power.

 

We have a solar panel and a battery master so the only time the battery has been a problem was when we were driving through Spain at 35+ deg and the battery died on us. Probably due to the problem we have just solved and the fact we had a lot of power being used, headlights, heater fan, fridge, radio.

 

I will keep an eye on it now you have pointed out the possible effects.

 

Thanks again.