Voltage drop with new radio

Moalex

Recruit
Joined
Jun 20, 2020
Messages
1
Changed the radio in my boat, wired everything up exactly the same as the old one, but now when it's on, the battery gauge jumps. And all of a sudden when I hit the horn, the radio shuts off and the lights dim?
 

dingbat

Supreme Mariner
Joined
Nov 20, 2001
Messages
16,620
Classic under voltage symptoms

When was the last time you had the battery load tested?
 

tpenfield

Moderator
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Jul 18, 2011
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18,452
:welcome: to iBoats . . .

Nice work messing up the electrical system ! :D :rolleyes:

2 thoughts . . .

1) you did not wire everything exactly the same as the old one.

2) defective radio (head unit)


I'd go with #1 for the time being and re-trace all of your steps. When you say the battery gauge (i.e. volt meter) "jumps" . . . does it jump up or down? Does it stay at a different level or return to the previous level after it jumps?
 

Bondo

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Apr 17, 2002
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71,289
Ayuh,...... Clean to shiny metal Clean, all the grounds,...... ya got some corrosion, somewhere,.....
 

gm280

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Jun 26, 2011
Messages
14,605
Any time you experience a voltage drop when you turn something on, you are seeing a situation to where the supply isn't allowing enough current to whatever you just turned on. So the voltage has to drop to try and get the amount of current. So with the above ideas, I would most certain trace the wires and have the battery posts cleaned and shiny. And if it still does it, you could have either a defective radio issue or a battery on it's last leg. If the wires are the same from the older radio you removed, does the new radio have the same current demands (fuse size)? If your new radio demands more current then the wires can carry, your wires will also get hot. Be careful if that is the situation. You will need to go to large diameter wires (lower gauge number). JMHO
 

sam am I

Commander
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Jun 26, 2013
Messages
2,169
Any time you experience a voltage drop when you turn something on, you are seeing a situation to where the supply isn't allowing enough current to whatever you just turned on. So the voltage has to drop

So love this!!!........A man who not only uses ohms law, he truly understands it!! I could only add one small bit to this.....What is limiting the current? And drops the voltage? A increased/ing series resistance of which is as ppl are pointing directly too to reduce by making shiny and cleaning ........"Corrosion/bad connection/loose wires and poor fuse holders" all of which can warm up to the touch.....

More ohms law here!! Power (heat) = V^2/R. At a given current, the heat dissipation at the resistive component exponentially goes up do to a squaring of the voltage drop!!

If the resistive component has a positive temp coefficient(they usually are and exponential as well), then the whole works goes into thermal runaway, hence melted/blackened connectors!! Makes since eh?

Perfect post gents!!
 
Last edited:

gm280

Supreme Mariner
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Jun 26, 2011
Messages
14,605
Sam am i,

I've repaired "black boxes" for military aircraft for decades before switching to computer programming computers to locate any defective part on the boards. Then I moved to reverse engineering older aircraft circuit boards with new modern designs and components. So my entire career has been in electronics. Just some back info. Love making circuits to do what I want them to do...
 
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