engine start battery voltage drops below 10v when starting engine

zikzik said:
its probably had it, but double check the terminal connections first. they might be good for a lower power item (though a heater usually draws plenty for the first few mins) but not good enough for the start load.
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Webasto/eber/Mikuni Glow plugs should draw around 15~20 amps so not "plenty". I had the Eber serviced recently. used to draw ~16 amp on startup but the new glow plug drew ~20 amp (old plug coil broke into bits so had to be replaced).
 
JumbleDuck said:
It's knackered, them to use a technical term. Time for a new one.
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Maybe not. Check and clean all connections from battery posts through to starter (or off-1-2-all switch at least. If the low voltage is measured across the battery posts then I would tend to agree the battery is buggered (provided there is sufficient electrolyte and the battery is in good state of charge). I had a similar problem and traced the fault to the earthlead connection on the block. Removed the bolt, cleaned the terminal, block and bolt, fitted new lock washers and reassembled. Electrical problem fixed. Low current draw items can function happily even when there is a bad connection in the circuit.
 
PowerSlapper said:
Maybe not. Check and clean all connections from battery posts through to starter (or off-1-2-all switch at least. If the low voltage is measured across the battery posts then I would tend to agree the battery is buggered (provided there is sufficient electrolyte and the battery is in good state of charge). I had a similar problem and traced the fault to the earthlead connection on the block. Removed the bolt, cleaned the terminal, block and bolt, fitted new lock washers and reassembled. Electrical problem fixed. Low current draw items can function happily even when there is a bad connection in the circuit.
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Very true, but the engine won't turn over on the start battery, but starts on the domestic. That doesn't sound like a bad neg connection.
 
PaulRainbow said:
Very true, but the engine won't turn over on the start battery, but starts on the domestic. That doesn't sound like a bad neg connection.
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Could be bad neg connection on the start battery terminal. or a bad +ve connection.. i would check all the connections before condemning the battery.
 
PaulRainbow said:
Looks like post #2 was fooled by the "voltage drop" in the title and, unaware that the engine battery only turned the engine half a revolution, failed to identify the true knackerdness of the battery :)
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Of course, silly me. :o

There was I foolishly thinking that the missing fact was whether the drop in voltage was actually accompanied by the engine turning over and starting ....... or not. How on earth did I miss that in post #2? ;)

Richard
 
RichardS said:
Of course, silly me. :o

There was I foolishly thinking that the missing fact was whether the drop in voltage was actually accompanied by the engine turning over and starting ....... or not. How on earth did I miss that in post #2? ;)

Richard
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You didn't. The OP didn't mention that until post #4 :)
 
The only function of the engine start battery is to start the engine. This is isolated so in the event you over-use your domestic bank you can still restart when required.

Good advice to check the connections, including at the 1 - Both - 2 - Off switch if you have one, but I suspect the dead battery diagnosis is fairly accurate. That's what happens when things operate independently, they just can't be relied upon, or I suppose it could be a British battery, eh Webbie !
 
All the cranking amps tests for a 12V battery involve it being well under 10V.
I'd expect a battery that was the sole cause of this problem to be under 6V when failing to turn a starter motor.
So, I'd be checking the wiring etc before exercising my credit card.

I had a similar problem when I bought my RIB. Traced to this 'orrible thing:
http://www.ebay.co.uk/itm/Battery-T...267691?hash=item4d5861846b:g:tSoAAOSwIWVY~79j
The steel screws had more or less dissolved and were no longer clamping the cable!
 
PaulRainbow said:
Apart from it only turning the engine half a revolution !
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Sir you miss my point, the OP was worried that the voltage was dropping below 10 volts because his peripheral kit turned off, otherwise everything was functioning normally. I suggested he reduce the stress by turning everything off and starting the the engine.
 
Sandy said:
I'm in the other camp and consider the 1-2-both switch is the pinnacle of simplicity, but not understood by 95% of the people who use them.
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I also have a routine, turn switch on, use boat, turn switch off, leave boat. My batteries are always charged, no chance of running the engine battery flat, no user intervention required. Simple.

What could be simpler than two switches, one for the engine battery and one for the domestics ? Arrive at boat, turn domestics on. Want to use the engine, turn it on, finished with it, turn it off or leave it on until you leave, doesn't matter either way. Throw in a third for emergency use and you're laughing.
 
superheat6k said:
The only function of the engine start battery is to start the engine. This is isolated so in the event you over-use your domestic bank you can still restart when required.

Good advice to check the connections, including at the 1 - Both - 2 - Off switch if you have one, but I suspect the dead battery diagnosis is fairly accurate. That's what happens when things operate independently, they just can't be relied upon, or I suppose it could be a British battery, eh Webbie !
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Rather a pointles dig, considering that the vast majority of "British" batteriies are badge -engineered and made in China! But heigh- ho, if it makes you feel good-----
 
Sandy said:
Sir you miss my point, the OP was worried that the voltage was dropping below 10 volts because his peripheral kit turned off, otherwise everything was functioning normally. I suggested he reduce the stress by turning everything off and starting the the engine.
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If he wasn't using a 1-2-both switch his electronics would be separate and would not be effected by any engine battery voltage drop. :)
 
Sandy said:
Sir you miss my point, the OP was worried that the voltage was dropping below 10 volts because his peripheral kit turned off, otherwise everything was functioning normally.
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Well, that's what it sounded like. Then he said that the engine wasn't starting, or even turning over.
 
PaulRainbow said:
I also have a routine, turn switch on, use boat, turn switch off, leave boat. My batteries are always charged, no chance of running the engine battery flat, no user intervention required. Simple.

What could be simpler than two switches, one for the engine battery and one for the domestics ? Arrive at boat, turn domestics on. Want to use the engine, turn it on, finished with it, turn it off or leave it on until you leave, doesn't matter either way. Throw in a third for emergency use and you're laughing.
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I have your set up on one boat and the 0-1-2-Both switch on the other. Both work perfectly well, although the rotary switch is more flexible in how I want to use the batteries. On the first boat we have guests often and some like to take part in the sailing and motoring and the domestic bank is far bigger than the engine start so I prefer the much safer and easier option. On the other it's usually just me on board and with identical engine start and domestic battery so like the flexibility.
 
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