Electrical issue...or not?

[IH82BL8]

When I had the boat hauled in May I began to experience a new electrical problem: when the shore power is plugged into the service on the hard it runs the outlets on the boat, but when I flip on the battery charger, it trips the GFI at the service outlet. I assumed I had an electric issue that would take some professional help to sort out.

However, yesterday, I finally read to sign on the outlet that says it provides only 15 amp service. My battery charger draws 20 amps. Is the amp draw causing the GFI to trip? This would explain why is was never a problem with the 30 amp service at the slip.

I realize that a GFI is designed to trip in the event of a short to ground but it still comes down to a spike in amp draw. Also, a GFI trips in 1/40 of a second. The battery charger will actually run for about a full second before it trips--I can hear the fan start.

If the GFI is tripping due to amp draw, then everything is actually working correctly. Or am I missing something?

Thanks.

 

[JohnShannon]

It is unlikely that your battery charger draws 20A from the 120VAC. It is more likely that your battery charger charges at 20A into 12VDC.

20A on the AC side is about 100A on the DC side quite a battery charger for a 31ft boat.

There are three wires in your AC cord, Hot (120V) Neutral should be zero volts, and ground. The GFI compares the current in the hot and the neutral, if they unbalance by more than a few milliamps the assumption is that the missing current is electrocuting somebody and the GFI trips off.


If your GFI is tripping with the battery charger, it is possible there is a problem with a battery charger. It could be a problem with your GFI.

 

[JoeWhite]

Since you said that you are having this problem when on the hard - I am assuming that you are now using a different AC outlet than the one that you normally use when you are at your slip. My guess is that the boatyards AC outlet is not wired correctly. You can buy a tester for less than $ 10.00 at your favorite hardware store and plug it in and see if it is wired correctly.

 

[rgranger]

$6

 

[Chris Patterson]

That's odd. I had this exact same issue awhile back, and the charger would not run on that 15 amp circuit. Everything else did, but not the Truecharge.
Put 30 amps in the boat, and it charges like new. I don't know..

 

[Chief RA]

I am surprised that "Maine Sail" hasn't addressed this issue for you by now as this is his main area of expertise. It sounds like the battery charger is wired to the ground lead and the hot wire for power rather than the correct way. It should be powered with the common and the hot to operate properly. Chief

 

[kenn]

Some ideas:

- check the wiring as suggested above. The $6 outlet tester would suffice.
- measure the AC current draw of the boat on shore-power before the charger comes on. You might already have loads that, combined with the charger, draw over 15 A.
- try the charger on a number of different 15 A circuits, both GFI and not, using a good extension cord directly to the charger, bypassing the boat AC wiring. If it pops most breakers, GFI or not... it's drawing too much.
- Spit-balling - Many chargers have digitally-controlled DC-DC converters which can present a complex load and put garbage out on the AC line... which some GFI circuits might not like.

The battery charger will actually run for about a full second before it trips--I can hear the fan start.

Digitally controlled chargers come on like that, so this seems to confirm the idea of too much current from the AC outlet.

 

[walt]

Adding a little to the good advice already posted...

It is unlikely that your battery charger draws 20A from the 120VAC. It is more likely that your battery charger charges at 20A into 12VDC.

See the above previously posted, I’m guessing you meant that you had 20 amps on the DC side and not the AC side. If you’re charger has a standard 15 amp plug like this one http://www.homedepot.com/p/U-Socket-15-Amp-AC-Standard-Duplex-Wall-Outlet-White-with-Built-in-USB-Charger-Ports-ACE-7169/203423602 (minus the usb charger) it will normally draw way less than 15 amps on the AC side.

Is the difference between on the water and on the hard that the output on the hard has GFI and that is when the problems started?

As said previously, check the AC polarity first just to make sure this isn’t a variable. Likely you will find its wired correctly - but easy to just check.

GFI wont trip for over current, it will only trip for a ground fault. A seperate set of breakers would be tripping for over current. Assuming the AC from the source is wired correctly (most likely the case), I would run separate AC power cord from the source and only plug it into the battery charger (assume its three wire). Try this with and without a second separate power cord to the rest of the boat. The purpose of the second power cord is to either ground or not ground the rest of the boat that is sitting on the hard.

You may have a true ground fault possibly in your charger. It may not be a dangerous type since it may only be leaking back to the earth ground on the power cord rather than the water but worth tracking down.

And.. it may just be nuisance tripping. I have a space heater that when I turn it on a certain way, it will trip the GFI if there is a long extension cord involved. I have checked to makes sure there is no ground fault on the space heater, its just some transient condition that causes the nuisance trip.