electrical problem

[g0tagrip]

Okay guys, I need help figuring out why when I pull the trigger on my saltwater wash down my Garmin GPS display goes off. Originally I thought I had a bad batteries, they were old and weak and I did replaced them with new Deka's. Alas, still have the same problem. When I turn on the washdown switch on the helm, no issues, just when I pull the trigger on the washdown the washdown pump comes on and the display on the GPS goes off. Interestingly, the GPS when turned back on still holds the waypoint selected. Any one have a similiar issue or have electrical skills? Thanks.

 

[wspitler]

I'd put a voltmeter on the DC source for the GPS (ie.electronics bus) and see if low volts is causing it. The other possibility is a short to ground on the washdown pump. Most likely cause is a high resistance somewhere in your DC system that is causing a high amp load on the system dropping the voltage to the GPS below acceptable limits. Assuming strong batteries look throughout the system for corroded terminals, etc. Good luck!

 

[seasick]

You didn't say if the wash-down pump works. If it does, it is not shorted but there is problem with bad connections, either +12 or ground, a fuse block, fuse holder or breaker. I assume that the breaker or fuse for the pump is on the same main feed and fuse panel that the accessories (GPS) are. Using the wash-down is causing a low voltage condition that is causing the GPS to turn off. This type of issue is fairly common and will take a little detective work to isolate. I would check the voltage at the main feed to the fuse block/panel with no load and with again the pump working. You will probably see a large drop. From there you need to determine the reason. It could be the connection at the fuse panel, the connection at the battery (accessory wire), main breaker ( usually near the battery) and anywhere in between. It could be as mentioned, be a bad ground at any of those points too.

 

[Tuna Man]

I say look for the simple stuff first. Nine out of ten times it will be the negative terminal that feeds the GPS. If that terminal is not the cause, I would look at the positive terminal next. If nether of these, I would look at the panel wires (and the actual fuse) that powers the GPS.

My guess is that the voltage is dropping to the GPS when the heavy draw (washdown) is operating.

Hope this helps.

 

[seasick]

I say look for the simple stuff first. Nine out of ten times it will be the negative terminal that feeds the GPS. If that terminal is not the cause, I would look at the positive terminal next. If nether of these, I would look at the panel wires (and the actual fuse) that powers the GPS.

My guess is that the voltage is dropping to the GPS when the heavy draw (washdown) is operating.

Hope this helps.

Whether it is the ground or the hot, the feed in question has to be common to both devices for the voltage drop to present to both devices. So if the ground to the GPS is separate from the ground to the pump, that is not the cause.
Aft bilge pumps are often connected locally (at the battery) to the ground and the automatic switch circuit is usually connected to a fuse or breaker directly off the battery. If the GPS shuts off when the manual bilge is activated but not when the automatic bilge is, then the problem is the main accessory feed from the batteries to the helm panel. All this assumes that the GPS is not on the same fuse/breaker as the manual bilge.
The manual switch for the aft bilge pump is connected through the battery switch, feed wire and fuse termial block at the helm but still uses the same ground as the auto circuit. That leads me to believe that the problem is in the +12 side of the circuit OR the common ground terminal on the battery.
This should be fairly easy to isolate by measuring voltage at devices under load and not under load and working back from the help panel to the battery switch

 

[g0tagrip]

Thanks for the tips. Soon as the weather clears I will attack it. Still tropical winds and rain today. By the way, It is not the bilge pump that is cutting out the display on the GPS, it is the salt water wash down pump, and yes wash down works fine.

 

[seasick]

Thanks for the tips. Soon as the weather clears I will attack it. Still tropical winds and rain today. By the way, It is not the bilge pump that is cutting out the display on the GPS, it is the salt water wash down pump, and yes wash down works fine.

You did say that earlier. My brain fart!.

Good luck with the testing, let us know what you find.

 

[g0tagrip]

Well I think I got it, ground was crossed at the wash down switch. Moved it to the main ground. Appears that was the issue.