not engine question but still need help

[azazzera]

my standard horizon explorer gx1700 radio will not turn on. worked fine up to this season. on own circuit with breaker. fused. when line tested it reads 12.2-12.8 volts. I attached unit direct to stand alone battery at home and also direct to battery on boat and it turns on and off just fine so i know its not a problem with the radio. what could be going on with wire that would produce such results. poor ground? bad connectors? I'm confused that i get 12+ volts on meter but when unit is plugged into wire it dose not turn on. how should i trouble shoot further? looked at specs of radio and its operating voltage is 11 to 13 volts.
thanks for any advice. adam z.

[edwardc]

A corroded connection can introduce a resistance into the circuit. When measuring with the voltmeter, which draws almost no current, a full 12V is read at the wire endss. But as soon as you apply a load that draws more current, the voltage at the wire ends plumets, as most of the voltage gets dropped across the poor connection's resistance.

Try measuring the voltage with the radio attached.

[Dave Neptune]

Just had the same experience Ed described.

Dave Neptune

[azazzera]

Thanks for the reply. I had an inkling that could be. I replaced the connectors at the radio end. Still one more spade set I can examine/replace. Next chance I get on the boat I’ll look at that and report back. I’ll take a look at the entire wire run for defects.
Thanks again.

[ndutton]

This is an excellent example of the difference between voltage and current.

[azazzera]

Was back on the boat this morning. Connected the radio and pressed the power button and it magically turned on. Cycled it on and off a few times and no problems. I connected the same jumper wires I used to connect directly the a battery. While the radio was off I took a voltage reading at the battery side of the jumper wires and got a reading of 5 volts. The gauge of the wire was supper small. Would that have given me the 5 V reading. A little confused as to why I was getting 5 V with the radio off. The reason I used the jumper at all was to give me an exposed part of conductor to take a reading. Explain please. Make me smarter.

[azazzera]

A bit more information on how I took the voltage measurements. There were small alligator clips at the end of the jumper wire that I could clip on to the spade connectors. The positive probe of the volt meter was touched to the speed connector itself. The negative probe I put in the teeth of the alligator clip from the negative side wire. I don’t understand why if the radio was off I was getting any voltage at all.

[ndutton]

Difference between volts and amps

Fluid dynamics are in many ways analogous to electricity. Imagine a bucket with a valve at the bottom.

• When the bucket is filled with water and the valve is closed there is measurable pressure at the valve (= volts).
• When you open the valve water flows out (= current or in electrical terms, amps). Turning on the radio switch translates to opening the valve.

A little confused as to why I was getting 5 V with the radio off. I don’t understand why if the radio was off I was getting any voltage at all.

It's because the electricity was available (pressure/volts) but not flowing (current/amps). If you measure voltage at the battery (the full bucket) with no wires attached at all you'll still measure voltage (pressure).

Now, why did you measure only 5 volts? In your measurement or connection technique you have either a poor, high resistance connection (jumper ends, paint or corrosion on metallic surfaces or meter probe technique) or maybe a meter problem. Are you sure you were switched to read DC volts rather than AC? Then there's this that was unclear to me:

There were small alligator clips at the end of the jumper wire that I could clip on to the spade connectors. The positive probe of the volt meter was touched to the spade connector itself.

WHAT spade connectors? Where? Circuit breaker? Battery? Somewhere else? Pictures would help.

edit: I forgot to address one of your questions:

The gauge of the wire was super small. Would that have given me the 5 V reading?

No, not by itself. The size of the wire has no influence on no-load voltage. Wire size matters immensely when current is flowing however.

[azazzera]

After trying to methodically trouble shoot the problem I believe I have found the connection that is causing the low voltage. Thank you for all the help.