Voltage Drop

[CoveDweller]

I need help troubleshooting a power problem. I'm running a 100 yamaha 4 stroke and have a perko battery switch with 3 deep cell marine batteries. Whenever I turn on my docking lights the are very dim and if I rev up the motor they brighten up. If I turn on the interior lighting along with the stereo I get a low voltage alarm and the amp meter buried in the negitive side. I have changed the battery cable ends from the motor to the battery switch and all battery cable ends on all the batteries. I also have run a larger wire directly from the docking light switch to the docking lights, didn't help. Any suggestions would be greatly appreciated!

[Bamaman]

When you're getting a big negative on the amp meter, it indicates you've got a short. You need to start by chasing down that short.

Then, regroup and see how the boat performs.

We seldom see 3 batteries on a pontoon boat. Do you know that the Perko switch is wired properly? There are more than one way to hook numerous batteries up, and all of them are not right. Of course, you want to keep the battery and electrical system for the engine isolated from the other batteries.

Good luck!

[CoveDweller]

Thanks for the input, I will start looking for the short. Could the cables from the motor to the switch possibly be bad? I also get the voltage drop when I hit the trim/tilt button. I have the #1 position on the switch dedicated for starting only, the #2 position has two batteries hooked up for operating the sound system, etc when we are running and anchored.

[HandymanHerb]

Check your grounds too, since that will affect all systems

[jrolin1]

X2 on the ground!

[oldmn19]

I vote for a ground problem too!

[badmoonrising]

I vote for a ground problem too!

Yep !

[tuned]

Hmmm. Good one.
Not totally convinced of ground issue. Ground problems are usually 'opens' or 'intermittant opens' which would not explain the buried amp meter.
I assume that this system ran correctly at some time and was not recently modified?
Also, does it appear to charge properly when running? About 13.5 or 14 Volts? Does this voltage stay up as you add load?

My vote is with Bamaman that you have a partial short as indicated by the amp meter. It could be in your large wiring somewhere or you would likely have blown a fuse or breaker. Your battery switch is a good way to start isolating systems but it can get ugly from there.
This one may take a VOM, if you have one, and some persistance.

A quick and dirty troubleshoot on something like this is to run the motor (so you have some juice to suck down) and turn everything on. Let it run for a few minutes like this and then crawl over every inch of wiring that you can get at and feel for heat. If you find something abnormally warm, track it AWAY from the motor. The farthest point that is still hot is usually where your problem is.
Another trick would be to run one system at a time, very carefully watching your amp meter. You may get an indication that way where to start looking.
Also possible that you have a charging problem, not too likely though, as it should have shown up as low starting power.

If you don't have a good fire extinguisher on board, NOW is the time to buy one. Always good to have around anyway, but very important with this issue.

Good luck mate. Let us know what you find.

There are quite a number of other questions that I would ask if you continue to have problems. If you want to discuss this further, I'll be glad to pm you my phone number.

[CoveDweller]

I ended up replacing the wiring from the switch to the docking lights and also installed LED's instead of the 55w halogen's, problem solved. Thanks all for the assistance with this situation.

[NonHyphenAmerican]

Just an FYI that I'm sure everyone knows but some may have forgotten.

If your terminals are dirty, it can make for voltage irregularities.

If the cables are old and have corrosion built up in them, it can make for voltage irregularities.

So that's always something to double check seasonally and/or whenever you're servicing your boat.

[OK Toon]

This is an interesting thread because I have the same issue the OP mentioned when using the tilt trim. I have 14 volts while running but when I hit the tilt trim switch, the volts drop to below 12. As soon as I release the tilt trim switch the volts go back up to 14.

[teecro]

This is an interesting thread because I have the same issue the OP mentioned when using the tilt trim. I have 14 volts while running but when I hit the tilt trim switch, the volts drop to below 12. As soon as I release the tilt trim switch the volts go back up to 14.

Is this something that you've seen develop over time or has it always been this way? Has something recently changed like the install of the volt meter? LOL

I say that jokingly as the power T&T has got to be your biggest power draw next to your starter motor and trolling motor. Have you also watched the voltage drop on the meter while starting? It likely drops to 12 volts and more than likely drops under 12 volts hopefully no lower than 11 while starting the motor. Dropping to 12.X (?) volts while trimming in itself does not sound like an issue if the voltage pops right back up into the 14.X (?) voltage as soon as your off the T&T

How old is your battery? Is is a sealed battery or one that you are supposed to check and add water too as needed? Does your motor still seem to spin and start with the same vigor as it always did? When is the last time you checked and cleaned your connections to the battery terminals? This is something that you should check monthly and refresh yearly.

On board ship it is an annual for us to take battery connections apart and wire brush or fine emery them back to bright shiny metal wash this down with brake clean and put back together clean and dry then apply a light coating of battery terminal protectant or Vaseline. We then replace batteries at the 4 year mark and also replace the connectors at the same time or sooner if deemed the need for.

[OK Toon]

Is this something that you've seen develop over time or has it always been this way? Has something recently changed like the install of the volt meter? LOL

It has always been that way (new to us boat for 2 years) that's why I didn't think much about it especially since I've never seen anyone else mention it. Nothing has changed and it doesn't seem to affect anything. Just thought it was very strange for the volts to drop that much from the use of the T&T. But if that's one of the biggest power draws, I guess this is normal and I shouldn't worry about it.

I say that jokingly as the power T&T has got to be your biggest power draw next to your starter motor and trolling motor. Have you also watched the voltage drop on the meter while starting? It likely drops to 12 volts and more than likely drops under 12 volts hopefully no lower than 11 while starting the motor. Dropping to 12.X (?) volts while trimming in itself does not sound like an issue if the voltage pops right back up into the 14.X (?) voltage as soon as your off the T&T

I haven't really paid much attention to the volt meter on starting -- when we are pushing off from the sandbar, I'm usually too busy to make sure we don't run over somebody and just want to start the motor and back out safely.


How old is your battery? Is is a sealed battery or one that you are supposed to check and add water too as needed? Does your motor still seem to spin and start with the same vigor as it always did? When is the last time you checked and cleaned your connections to the battery terminals? This is something that you should check monthly and refresh yearly.

Battery is only a couple of years old and I maintain it over the winter on a battery tender to keep it at full charge. But I'll check out the terminals to make sure there is no corrosion and also the connectors.


On board ship it is an annual for us to take battery connections apart and wire brush or fine emery them back to bright shiny metal wash this down with brake clean and put back together clean and dry then apply a light coating of battery terminal protectant or Vaseline. We then replace batteries at the 4 year mark and also replace the connectors at the same time or sooner if deemed the need for.

Thanks again for the great response. That's why I love this site -- lots of great friendly people willing to help another boater out or just to reassure them.