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Old 04-04-2014, 08:17   #1
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Connecting voltmeter

I want to connect a voltmeter to a 12-v battery. I connected a small wire (#16) to the starting battery, but before I could connect it to the voltmeter, the wire was too hot to touch. Why? That indicates that too much power is flowing through the wire, but since it was connected only at the battery end, no current should have been flowing.

Do I just use a larger wire? If so, why don't small wires to lights get hot?

Any suggestions would be welcome!

Thanks,
Jack
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Old 04-04-2014, 08:47   #2
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Re: Connecting voltmeter

It makes no sense that a wire connected to the battery and presumably open at the other end should get hot.

The proper way to connect the voltmeter is to use any size wire that you want, but it needs a proper sized fuse installed in the wire near the positive terminal. For 16 gauge, use a 5 amp fuse. Then wire the other terminal on the voltmeter to the ground or minus terminal of the battery.

If this doesn't make sense, get a marine electrician to do this for you.

David
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Old 04-04-2014, 08:55   #3
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Re: Connecting voltmeter

If you meant to say that you connected a wire pair - one wire to each terminal of your battery - and it became hot before connecting the other ends to your voltmeter - then the other end of the wire pair may have had both conductors shorted together at the time the wire pair was cut from the roll.

A single wire, connected only at one end, doesn't carry current and doesn't get hot.

Local help, rather than help from the forum, might be better in this case.
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Old 04-04-2014, 09:32   #4
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Re: Connecting voltmeter

Thanks, dmarchand and bornyesterday,

I agree it doesn't make sense, that's why I'm asking :-)

It was a single wire, to be connected to the voltmeter. Both the meter and the battery were already connected to the common ground.

I forgot about the fuse, will use one next time I try.


Thanks, guys!
Jack
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Old 04-04-2014, 09:40   #5
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Re: Connecting voltmeter

Quote:
Originally Posted by The Way View Post
I agree it doesn't make sense, that's why I'm asking :-)

It was a single wire, to be connected to the voltmeter. Both the meter and the battery were already connected to the common ground.
In that case, I see three possibilities:
  • wiring error
  • it is not a Volt meter but an Ampere meter
  • it is a faulty Volt meter
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Old 04-04-2014, 10:42   #6
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Re: Connecting voltmeter

"I connected a small wire (#16) to the starting battery, but before I could connect it to the voltmeter, the wire was too hot to touch"

A wire, one end of which is connected to battery positive - and which is nowhere connected to anything else - can not become hot because no current flows.

You must have inadvertently connected to something earthy and current must have flowed.

I mean no offence but "Do I just use larger wire?" makes me fear for your safety.

Please pay a qualified person - or at least postpone your installation until you've had time to study the subject enough to stay safe.
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Old 04-04-2014, 10:51   #7
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Re: Connecting voltmeter

Thanks, crm and bornyesterday,

I'll check everything out again.

My first thought was that the wire was too small, then I realized that made no sense. I just mentioned it as the thought-process.

Could be the unconnected end of the wire touched something. It hadn't been stripped yet, but maybe it touched the engine or something.

Should I connect the voltmeter end first?

Don't worry, I'll be careful!

Thanks, and best regards,
Jack
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Old 04-04-2014, 12:13   #8
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Re: Connecting voltmeter

Hello Jack,

Here's a good way to do this:

First connect an inline fuse holder close to the + terminal of the battery, don't put the fuse in yet. Crimp the other fuse holder wire to your 16ga wire, connect the other end of the 16ga wire to the + terminal of the voltmeter. Almost done, next run a wire from the - terminal of the voltmeter to the - terminal of the battery, no fuse needed here.

Now for the moment of truth. Insert a 1 amp fuse in the fuse holder, if the fuse blows then something is wrong with the voltmeter or the wire has chafed and is shorting out. A 1 Amp fuse is more than enough for a voltmeter but a 5 amp fuse will also be safe.

Hope that helps,

Steve
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Old 04-04-2014, 12:19   #9
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Re: Connecting voltmeter

Steve,

Excellent suggestion! Thanks. Sounds like a good way to ensure all the wire-ends are attached to something before there's any juice flowing, instead of waving around in the engine room.

The fuse also protects the wire in case something else is screwy, like a defective voltmeter.

Best regards,
Jack
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Old 04-04-2014, 14:31   #10
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Re: Connecting voltmeter

"Could be the unconnected end of the wire touched something."
This is why the LAST connection you make, every time, should be the connection to the power source. If for some reason you can't do that, you put a wirenut, a piece of tape, something, anything, over the other end so it can't find a way to short out on something.

And whenever you are working on power systems, even 12v batteries, it is a good idea to remove any jewelry, rings, watchbands because yes, you can short things out with them, with rather dramatic and severe consequences. The USN used to have photos [posted on their web site of some poor sailor who got his wedding ring in between a wrench and a common battery terminal. "Traumatic amputation" of the finger resulted. A common "car" battery will put 3000 amps into a crowbar short like that.
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Old 04-04-2014, 14:38   #11
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Re: Connecting voltmeter

Ouch, I bet that hurt!

Thanks for the good advice, hellosailor.

Jack
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Old 08-06-2014, 08:40   #12
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Re: Connecting voltmeter

Got this connected today and working fine. Thanks to everyone for the help!

Fair winds,
Jack
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