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Old 16-05-2015, 13:11   #16
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Re: 12volt TV broken after starting boat motor

Why not just turn TV off when starting engine? Too simple?

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Old 16-05-2015, 15:07   #17

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Re: 12volt TV broken after starting boat motor

" I started the boat motor with the TV plugged into "
People don't believe it but the folks who make engines and electronics ALL say that during starting and shutdown, you can NORMALLY throw spikes in the electrical system. Spikes up to 600 volts on a 'car' engine, and over 2000 volts on small diesel engines.
These spikes can and do cause electronics to blow out. You are supposed to disconnect power from all electronics while starting or shutting the engine. That's all it takes.
You can add spike protection, but most devices don't have it because protection wears out, and then the devices can blow anyway.

I'd also check the voltage on the boat, it should never exceed 14.4 volts on a "12" volt outlet. Anything higher means something (regulator, alternator) is failing.

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Old 16-05-2015, 15:13   #18
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Re: 12volt TV broken after starting boat motor

Even at idle???? I must be awfully awfully lucky never to have fried the diodes.

Originally Posted by btrayfors View Post

Yeah, lots of folks have got away with this, even before the make-before-break switches became commonplace.



Don't forget about the OFF position. If you hit that (and maybe linger awhile -- a guest? a distraction?? You can certainly blow the diodes in the alternator.

Why risk this at all, when there are much better ways to avoid the possibility?

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Old 16-05-2015, 15:36   #19
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Re: 12volt TV broken after starting boat motor

Yes, sounds like a voltage spike took out a sensitive semiconductor in the TV. As others have suggested, while must marine electronics/ products designed specifically for marine (and auto) use a 'hardened' against voltage spikes... general consumer electronics products are often more frail. Keeping to house circuit separated rom the starting process is a good idea. I have used the 'Alternator Saver' resistor wire that is available from most marine entities for (?? -$20 maybe). It 'allows' hot switching/ even switching to 'off' w/o incurring any damage. Almost all the charter sailboats employ these (as do I) and I've never heard of any blown alt diodes from those that use the device. I've had my for 20+ years and no issues... I EVEN I have been guilty of making a battery selector SW to off while engine running.

To you original question, if you call/ google Ham Radio Outlet/ and some car stereo shops carry a 5 farad capacitor that will filter spikes out of the 12v line. About $50, as I recall.

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Old 16-05-2015, 15:45   #20
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Re: 12volt TV broken after starting boat motor

As hellosailor and W3GAC have reiterated, voltage spikes from the starter circuit can and do damage sensitive electronics.

But, I guess no matter who says it....again and again...some folks just won't believe it or will draw from their own experience in getting away with it.


Yes, there are "safeguards" ... capacitors and spike spikers and make-before-break battery switches and all the rest.

HOWEVER, why even take a chance when there's absolutely no need to?

Keep the house and start circuits separate. Use an ACR or voltage-follower device like an EchoCharge or DuoCharge to automatically maintain the start battery.

With these devices, operation is TOTALLY AUTOMATIC. NO BATTERY SWITCHING IS NECESSARY. Here's one way to do that.

Click image for larger version

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Whew....I'm done.

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Old 17-05-2015, 07:14   #21

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Re: 12volt TV broken after starting boat motor

Connect the TV to the house battery. Do not combine the batteries to start the boat. Problem solved.

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