Electrical problem

Hightower · 16 October 2011, 13:19

Not RIB related but was hoping someone might have some ideas.

Was invited out on someones fishing boat powered by a Volvo Penta yesterday, it started fine and we motored round to the Loch in Port Solent, switched off and waited for the water to empty. When it came to restarting.....Nothing!

There was no power to any Dash instruments (not even a light), but all the accessories worked (VHF, Chartplotter, Depthfinder etc) after checking all the obvious like isolator and throttle wasn't in gear we still tried and still no power to the dash.

After a little bit of fiddling and a few turns of the key all the lights and gauges jumped to life but the engine wouldn't turn over, not even a click of the solenoid. When the power returned to the gauges I checked battery condition on both Batts 1 and 2. Both seemed a little lower than I would expect about 11.8V and went down to just over 10v when the key was turned to start so showing current draw.

Anyway we spoke to the marina staff and they organised a tow back to berth. After about 15 mins of waiting Steve turned the key and the engine started first time, no hint of slow starter motor or anything!

I can't help thinking the ignition switch wasn't one place to start looking at. You might be looking at two faults, ignition and starter relay.

Anyone got any thoughts?

martini · 16 October 2011, 14:15

That would be my suggestion, ignition key

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Erin · 16 October 2011, 15:32

Could be a few things, but ignition switch would be a primary candidate or possibly just a loose wire on the start battery circuit. Worth noting that just because the nav electronics are fine doesn't mean the start battery is ok. If properly wired up the domestic batts will be feeding the nav gear and will be totally independant from the start batt except for charging. Another possible cause if it is a modern engine is that the main relay is failing which stops power reaching the ecu and gauges. Some sophisticated engines also have negative isolator relays to separate the engine negative circuit from the boat fittings once the engine is started to minimise electrolysis.

Hightower · 16 October 2011, 18:03

Is an old tech diesel. I beleive that the the twin batteries are feeding the Isolator on Batt 1 and Batt 2, either or both can be used as a starting battery.

jyasaki · 16 October 2011, 23:48

Check for resistance on the entire motor to battery circuit (pos and neg, bot batteries). Sounds to me like a open/near open somewhere.

Out of curiosity, when you checked the batteries, was it from a dash panel meter, GPS status page or similar, or measured at the batteries themselves?

jky

Hightower · 17 October 2011, 00:18

Quote:

Originally Posted by jyasaki

Check for resistance on the entire motor to battery circuit (pos and neg, bot batteries). Sounds to me like a open/near open somewhere.

Out of curiosity, when you checked the batteries, was it from a dash panel meter, GPS status page or similar, or measured at the batteries themselves?

jky

The voltage readings were taken from the dash mounted volt meter guage so I guess the voltage was taken from the ignition. But I did select Batt 1 and Batt 2 using the Isolator switch to take the individual readings. We were limited to dash mounted gauge and visual checks due to an absence of tools. One thing I did notice however was that the radio, GPS and depthfinder when on lost power when the ignition switch was turned to start and nothing happened, this was the same time as the voltage on the gauge showed 10v. Very strange as it seemed that all the power was gone from the batteries. But later he had enough power to start the engine.

I might add that when back on the berth we had another failiure but after about 3/4 of an hour he started the engine again and then managed to start the engine without problem several times during the day trying to re-create the problem.

jyasaki · 17 October 2011, 05:47

Sounds like a continuity problem.

To clarify my other question, the voltage at my GPS reads fairly consistently about a half a volt lower than a reading taken at the battery. I should probably bounce that against the panel mounted voltmeter one of these days (can't remember ever checking both.)

jky

9D280 · 17 October 2011, 11:58

Sounds a bit like a sneaky problem I encountered on an Austin A40 once. Replacement wing had been welded on, and had in the oprocess part melted the insulation on a wire nowhere near the weld site. It occasionally vibrated to a point where it touched the body and shorted, taking out the ignition circuits, and inevitably after hunting around under the bonnet and then calling the AA/RAC it would happily start when they arrived to diagnose. Took months to find it, and a couple of wraps of insulting tape later it continued quite happily for years.

Doubt you'll have that exact scenario, but it's probably worth checking the loom where it goes through small holes & areas of viibration (more likely seeing as all the Aux stuff was working OK) etc for chaffing & partial shorts on the insulation.

biffer · 17 October 2011, 12:34

it's the wiring loom

Dirk Diggler · 17 October 2011, 13:31

I had similar on a customers boat this weekend, it was a loose connection on main power lead at the starter motor end.

Jizm · 18 October 2011, 12:35

I've had a similar thing on a race boat. Broken earth on the bus bar produced an intermittent fault that took a while to find.

Hightower · 23 October 2011, 21:27

Latest update is that perhaps the batteries could be a little bit tired so need replacing.

Twin 110 amps with suitable cranking amps for a diesel, anyone got an idea on which good value type to go for.

I suggested Squadron Energy SFL ones, but can't find any details of them on the internet any more