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Inverter on....12v supply disappears a while later


JRT
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I'm still getting used to the foibles of the boat I purchased a couple of months ago. Nothing major, just me getting used to how things work and learning what to turn off and on and when. One thing has me puzzled though. While out cruising the other day I put the inverter on while we were moving so my better half could dry her hair. Everything worked fine for a while but then all the 12v supply inside the boat just disappeared - no voltage at all. Switched the inverter off and the 12v supply reappeared.

 

Electricity is not my strong point but I'm guessing the alternator/batteries just couldn't couldn't cope. Anyone got any other ideas? I'd be grateful for your views.

 

 

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Sounds like a battery problem. If by 12V disappeared you mean the inverter shut down then its definitely discharged batteries. The same could be said if the whole 12V system shut down but that could be related to dodgy isolators or fuse holders. If your isolator has a red key it would be a suspect as would dirty/loose battery terminals.

 

I am not clear why it shut down with the engine running as long as it was at 1200 rpm plus. If that was so then maybe your alternator is faulty or you have a slack drive belt.

 

We really need accurate voltage readings, preferably with as digital multimeter, now, tomorrow morning before and after starting and revving and just before shutdown tomorrow. Then again at least an hour later.

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Thanks Tony. If it was the alternator that problem has been removed as I had an uprated one fitted today. The batteries seem to hold charge well as we ran 12v appliances the evening before with no problems.

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I have a gut feeling its the domestic isolator switch as you lost all 12V except the inverter should have its own isolator if its of any power.

 

Definitely remove the domestic battery terminals (master switch and all equipment turned off, disconnect negative first and reconnect last) and   clean the clamps add posts to bright metal. Dress with Vaseline when refitting. Loose or dirty battery terminals    can give weird intermittent faults.

 

Are you aware that ideally you should avoid discharging the domestic back to below about 12.2 volts at least an hour after charging stops and with no loads on. Likewise about an hour after you shut down the voltage with no loads running should be in excess of 12.6 volts.

Edited by Tony Brooks
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Hmmm. Thanks everyone.  I'll check the isolator switch when I'm back on the boat at the weekend. The voltage at the front of the boat with the TV on is 13.1V so with voltage drop due to distance from the battery bank that's fine isn't it?

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1 minute ago, JRT said:

Hmmm. Thanks everyone.  I'll check the isolator switch when I'm back on the boat at the weekend. The voltage at the front of the boat with the TV on is 13.1V so with voltage drop due to distance from the battery bank that's fine isn't it?

 

Its not all about voltage, battery capacity is as critical.

 

You can have a 12v battery small enough to power a hearing aid, but it doent have enough power (capacity) to power a 12v vaccum cleaner. Or, you can have a 12v battery the size of a car. Both are 12v, but the capacity (measure in Ah) is very very different.

 

You boat batteries, when new, were probably 110Ah, with use and improper charging everytime you use them they start to produce 'sulphate' which sits in the bottom of the battery clogging things up, when you take the battery back up to 100% charge (every day) much of this sulphate is changed back to lead, but when you don't recharge it properly it gradually builds up reducing the capacity - eventually your 110Ah battery may be as low as 20Ah and unable to power the inverter and whatever was plugged into it.

 

Think of having a 5 litre bucket, it holds a usable 5 litres of water.

Put a litre of mud / concrete in the bottom of the bucket, it is still a 5 litre bucket but now has a usable capacity of 4 litres of water.

Put another litre of mud / concrete in the bottom of the bucket, it is still a 5 litre bucket but now has a usable capacity of 3 litres of water.

Put another litre of mud / concrete in the bottom of the bucket, it is still a 5 litre bucket but now has a usable capacity of 2 litres of water.

 

Eventually you get fed up with havig to refill the bucket so many times, you decide to buy a new one and get back to full capacity.

 

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We had one of the red handle isolators on the inverter and when my son was borrowing the boat his girlfriend tried her hair drier (I had no idea she had taken one), the load heated the isolator and the contacts opened losing power to the inverter. First and last time a hair drier was used on the boat.

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10 hours ago, JRT said:

Hmmm. Thanks everyone.  I'll check the isolator switch when I'm back on the boat at the weekend. The voltage at the front of the boat with the TV on is 13.1V so with voltage drop due to distance from the battery bank that's fine isn't it?

 

If that is withOUT any charging like a shoreline, solar, or the engine it suggests the meter is telling lies or you have just stopped charging. After the surface charge is taken off batteries (left to stand for an hour or more or having a modest load on for a while) the maximum voltage from lead acid batteries will be about 12.8 so 13.1 with the TV on is not credible.

 

Alan is correct, voltage is not everything but  the rested voltage (voltage after surface charge has gone) allows one to infer the state of charge and at other times the state of the alternator. If the rested voltage a while after charging stops is close to fully charged and the next morning its less that 50% charged one can infer that the bank is too small for your demands, the batteries have lost too much capacity to sulphation, or you have internal short circuits in a cell/cells.

 

 

Edited by Tony Brooks
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1 hour ago, JRT said:

Thanks again everyone. Time to get the multimeter out and do some measurements! ?

My advice and it will save you thousands and thousands over the years is to dispose of the female that needs use of a hair dryer. Very high maintenence females need hairdryers. There are models out there that can do all the washing up and cleaning that have shorter hair and have no need of land based gimmicks ?

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22 minutes ago, mrsmelly said:

My advice and it will save you thousands and thousands over the years is to dispose of the female that needs use of a hair dryer. Very high maintenence females need hairdryers. There are models out there that can do all the washing up and cleaning that have shorter hair and have no need of land based gimmicks ?

 

 

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Most hair driers are about 2000 watts....on full heat at 240 volts (roughly)

 

That will draw about 160 amps from your batteries at 12 volts .....

 

 

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1 hour ago, Bobbybass said:

Most hair driers are about 2000 watts....on full heat at 240 volts (roughly)

 

That will draw about 160 amps from your batteries at 12 volts .....

 

 

 

Much nearer 200 amps when you take the power the inverter itself uses, AND the inefficiencies in converting 12v to 230v.

 

(Its also easier to work on taking 1/10th of the watts and calling it amps)

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