Inverter question: "ground" wire

tenders

tenders

Innocent Bystander
My inverter has three inputs on the DC side: positive, negative, and ground. The manual says:

Connect the Ground Cable to the appropriate location below:
a. If this unit is mounted within a vehicle with a grounded metal chassis, attach the Ground Cable to a nearby location on the chassis.
b. If this unit is mounted in a boat or vehicle with an ungrounded chassis, attach the Ground Cable to the vehicle’s grounding system.
c. Only if this unit is being used outside a vehicle, attach the Ground Cable to the Negative Terminal of the Inverter.

My boat does not have a "grounding system" per se, so I've just cross-connected the ground cable to the negative terminal.

This seems to work OK when I plug stuff directly into the inverter.

What I'd like to do, though, is power all the AC stuff in the boat through the existing AC wiring once in a while. But I'm finding it difficult to connect the output of the inverter to my shore power cables so I can effect this. When I use an extension cord, the inverter beeps and shuts down.

Could this be an issue with the way I've connected the grounding terminal? I'm wondering if there's some sort of inductance set up by the extension cord that trips up the inverter circuitry because of a bad ground. (And clearly I am not an electrical engineer.)

Thanks in advance for any insight on this!
tenders
1969 Ericson 32 #112
Muxie Duxer
City Island, NY
 
M

Mike.Gritten

Member III
I can't speak to your inverter, but we have a 1000 watt Xantrex on our boat. If I switch my AC selector to the Inverter and I have too heavy a load drawing on the AC circuit (electric water heater, electic space heater, etc.), the unit tries to accomodate the load, fails to do so, and then beeps and shuts down. Could this be what's happening in your install?
 
tenders

tenders

Innocent Bystander
Mike.Gritten said:
I can't speak to your inverter, but we have a 1000 watt Xantrex on our boat. If I switch my AC selector to the Inverter and I have too heavy a load drawing on the AC circuit (electric water heater, electic space heater, etc.), the unit tries to accomodate the load, fails to do so, and then beeps and shuts down. Could this be what's happening in your install?
Click to expand...

Although its behavior is like what would occur with an overload, that isn't what's happening. This inverter is rated at 2000 watts continuously and (to my surprise) will run a shopvac and a heat gun at the same time. It's quitting with ANY load through an extension cord--and maybe even no load at all, although I'm not positive of that.

What kind of AC selector do you have? Assuming I can get the inverter working on the built-in wiring that would be a good thing to have.
 
M

Mike.Gritten

Member III
We have a standard Blue Seas 8 position AC panel (I can't remember their part number). The top 2 breakers are the "shore power" main switch, the next 2 breakers are the "inverter" main switch (with a Blue Seas lockout slide to allow only one or the other to be "on" at any one time), and the bottom four are "portside outlets", "starboard side outlets", "water heater" and "battery charger". It all works great for us.
 
EGregerson

EGregerson

Member III
inverted invertor

Hi All; Tenders: If i understand this correctly, you are taking dc voltage to an inverter, and then attempting to run into the AC system. This would be a no no.

Shore power should not be run to an inverter I wouldn't think.

Run your shore power to the AC panel; from there to the load; eg light bulbs. This should already be wired in the boat (note the color codes for Ac and DC are different) (there is a guide on this web site showing which color wires go where and for what).

But unless some alterations of the boat's electrical system have been made, the boat should work fine as is; AC or DC. Just don't try feeding the DC to the AC thru the inverter. I suspect this is what is causing the inverter to 'beep'. I hope this helps. Good sailing.
 
tenders

tenders

Innocent Bystander
What I wrote makes sense to me, kind of I guess, but maybe not to anybody else.

What I'm trying to do is go battery --> inverter --> world's shortest shorepower cable converting a three-prong house plug to a three-prong 30-amp plug --> 30-amp shorepower jack on boat. That will power the boat's AC systems via the inverter and I'm pretty sure that isn't going to blow anything up; there's no actual shorepower involved.

The question is really what, if not the negative terminal, to run the terminal to on the DC/battery side labeled "ground."
 
EGregerson

EGregerson

Member III
re-verter

Ok; You're not actually hooked to shore power; only using the inverter to replace shore power. I can only think then that the beep is caused by overload; the sum of the current or wattage draw exceeds the capacity of the inverter (or the capacity of the house bank batteries).

My little 175 watt inverter simply plugs into the 'cigarette lighter' (now called a power port). One + and one -. No 3rd ground wire so it must be internally grounded to the inverter chassis; which is what you're doing when you hook the ground wire to the chassis, only externally. So everything should be copasetic.

What wattage is your inverter? what amps capacity is your house bank? How many appliances are hooked up when you throw the switch? and what do they draw?
 
Tom Metzger

Tom Metzger

Sustaining Partner
Check the AC wiring

tenders - You have an almost 40 year old boat. There is a good chance that the AC wiring is not wired correctly, and you are putting a ground on the inverter where it does not belong. This shuts down the inverter.

You can check it out with a multimeter if you know how, or you can buy an outlet tester (below) at any hardware store. [SIZE=-1]This device will not only indicate if the outlet has power, it will also indicate if the outlet is grounded and whether the hot and common wires are reversed. You use it with the shore power connected. If you find that the wiring is incorrect fix it before trying the inverter again.[/SIZE]

The inverter AC ground should be tied to the boat's AC ground. There are threads here on how the AC ground should be handled. This generally results in an argument. Search on "galvanic isolator".
 

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footrope

footrope

Contributing Partner
Blogs Author
Isolation transformer in the shore power system?

You may have an isolation transformer in your shore power system. When you connect your inverter output to the main AC system, you might be sending your inverter output into the isolation transformer, which is basically a coil of wire and which would certainly overload the inverter. If I recall the wiring diagram on my boat (and I could be wrong), this might be worth checking while you're poking around (with the power off).

I'll be at the boat Thursday and will check the diagram and let you know.
 
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tenders

tenders

Innocent Bystander
> What wattage is your inverter?
1750 steady, 3000 surge

> What amps capacity is your house bank?
I don't know, but more than enough to handle the next question

> How many appliances are hooked up when you throw the switch? and what do they draw?
Zero and zero. Inverter works fine with any item plugged directly into it. With the extension cord, it poops out before it even gets hooked up to the AC on the boat.

I'm pretty sure the boat is wired reasonably well. It's been through several surveys. The wiring is early '90s vintage, it's all on GFCI outlets, and I have the tester you pictured. It says all outlets are A-OK when plugged into shorepower.

>You may have an isolation transformer in your shore power system
Do not have.

> The inverter AC ground should be tied to the boat's AC ground.
It would be, once everything is hooked up. The inverter AC output is via two three-prong outlets, no direct wiring.

Again, the question really is what the right thing is to do with the "DC ground" terminal. Let it float, bridge to the negative terminal (as the instructions seem to suggest can, though not necessarily should, be done),...? I think it would be a BAD idea to bridge it to the AC ground.

I'm thinking from EGregerson's reminder that plug-in inverters have only two connections that the grounding issue isn't the source of the problem I'm facing. Either there's something wrong with the extension cord (which I think I've ruled out but I'll re-check) or there's something odd about using an extension cord with an inverter.
 
tenders

tenders

Innocent Bystander
I think a different extension cord was the first thing I tried but I'll look at it again.

> For grounding, try Blue Seas http://bluesea.com/viewresource/101

Great link, thank you!

That link shows the DC ground, the DC negative terminal, the AC ground, and the AC neutral all bussed together. My DC negative is connected to my engine, shaft, prop, etc.

Doesn't that represent a potential HUGE galvanic problem?

Or does that arrangement actually MITIGATE the galvanic potential?
 
Randy Rutledge

Randy Rutledge

Sustaining Member
What If

AC ground and AC neutral are common at the service panel of any service entrance. I would think that the Ground and neutral output of the inverter connected would be a functional arrangement.
I frequently use an inverter at work to power a laptop and printer by way of an extension cord and power strip with no problem.
The web site listed mentions AC connection with the DC ground. A broken AC light bulb laying on the engine block (or other shorted AC appliance in contact with DC neutral) or a badly wired boat would have to be the cause of crossover. If the DC and AC never cross paths then I don’t see how AC gets to the DC ground. In the world of what if, if you were to have a floating neutral and a load on the inverter with the green wire to the DC ground/negative then the AC hot would go to the DC ground through the load unchecked.
What happens if you have an onboard battery charger does it isolate or connect AC and DC ground?
This and about $5.00 will get you a fancy cup of coffee.
My head hurts and I need a Margarita, who has the tequila????
 
tenders

tenders

Innocent Bystander
> Yes, but it does eliminate the bodies floating around the boat.

Really? My boat is technically in the Bronx. We should tell the police about this miraculous wiring practice IMMEDIATELY.
 
S

skipper007

Member II
GFI protected? Using a long extension cord can cause a GFI to trip. Could the AC output be GFI protected? Different extension cord check would seem a good check. Broken insulation - long inductive paths - GFI protection. I dunno.
S
 
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