Forums, Electrical Systems, Navigation and Safety equipment, Voltage Surge

Nick Martin at 10/04/2011 18:09:48
Could anyone please give us some advice about a problem that we are occasionally encountering when we fire up our Volvo 2003 27hp for the first time on a day’s sailing?

Though there appears to be no pre-heat facility, the engine fires up easily. The batteries hold their charge between our days out sailing (sometimes up to a week between trips). But shortly after the engine starts the volt meter indicates a charge of more than 17 volts surging through. We first noticed this when our Navman DSC radio sent out an alert about excessive voltage – and we quickly turned off all instruments. Within about a couple of minutes the charge returns to normal, and we can activate the instruments again. This voltage surge does not seem to happen if we need to use the engine during the trip or to enter harbour at the end.

Is this normal (in which case we need to be disciplined about not turning on instruments until the engine has settled its charge)? Does the altenator try to compensate quickly for the large load taken out of the battery on a cold start? Or does this indicate an alternator fault? Would there normally be a separate voltage regulator fitted – I used to have an old Citroen DS which had such a system!?

Having just had some fairly hefty bills for new engine mounts, morse control and other bits and bobs I am hesitant about contacting our marine engineer! Any advice from those of you who understand electrical systems would be much appreciated. Thanks.

Wisdish at 10/04/2011 20:00:03
No, this is not normal, and it puts your electronics and batteries at risk of permanent damage. The maximum voltage you should see from your alternator is 14.5V. If you are not getting this the alternator or associated control electronics are faulty. I would start by checking the integrity of all the connections to the alternator. Otherwise get it checked out professionally otherwise it could get very expensive.

Mark

davidmacdonald at 10/04/2011 20:15:55
It does sound like an alternator regulator problem. If you’re wanting to avoid marine engineers, you should be able to remove the alternator (a couple of bolts and three wires) and take it to a car alternator specialist to test/repair.

Simon Begley at 10/04/2011 22:39:26
If you have one of the intelligent regulators (ie Adverc or Sterling) fitted, the voltage sensing wire is usually run direct to the battery. Make sure this wire isn’t broken and the connections are ok. If not the regulator will detect no volts and therefore not limit the alternator output.

If you have a normal alternator setup with an in-built regulator then it sounds like the regulator is faulty, or something has caused a short which is by-passing it.

Either way, 17 volts could boil your batteries very quickly!

Nick Martin at 11/04/2011 17:10:19
Thank you all for your helpful advice. Sounds as if I need to remove the altenator and get it professionally checked out. Will post again when I get results of this!

Nick Martin at 23/04/2011 20:24:50
I got the alternator off the boat and took it to Tobay Auto Electrics where Rob Foster is locally known as an expert on alternators. He diagnosed a voltage regulator problem and quickly renewed the part. Total cost £36 including VAT. Have fitted it today and the volt meter shows 14 volts. Thanks to all who offered advice.

Nick