how to block 12v DC battery power and pass AC grid power 120v upto 50 amps?

[sdowney717]

This is on my boat with twin 35 amp shore power
Talking about the shore ground to 12vdc negative junction inside the breaker box.
I have a 3000 watt MSW inverter where the 12vdc side must NEVER connect to the AC side or the inverter will self destruct.
Normally that will not happen. BUT, If a faulty appliance were to be plugged in or a wire failure, conceivably, the 2 power sources would connect with each other.

Is there a way using semiconductors to achieve DC current blocking but pass the higher voltage AC current?

I can use a power relay to disconnect DC ground to AC ground when the inverter is running.

 

[goldsmith]

This is on my boat with twin 35 amp shore power
Talking about the shore ground to 12vdc negative junction inside the breaker box.
I have a 3000 watt MSW inverter where the 12vdc side must NEVER connect to the AC side or the inverter will self destruct.
Normally that will not happen. BUT, If a faulty appliance were to be plugged in or a wire failure, conceivably, the 2 power sources would connect with each other.

Is there a way using semiconductors to achieve DC current blocking but pass the higher voltage AC current?

I can use a power relay to disconnect DC ground to AC ground when the inverter is running.

Hi Sdowney
One of the options that are available for this aim , is using a Gaertz bridge ! ( four diodes ) . it won't allow that incorrect directions go through the forbidden section ! or another way is using a thyristor and a fuse and a comparator !
Best Wishes
Goldsmith

 

[sdowney717]

looking at Gaertz bridge, I found a datasheet for SB107
http://www.datasheetcatalog.org/datasheet2/0/00f6uf95prcd232t9jxlza0cah3y.pdf

It mentions maximum DC voltage blocking. Now this only has a 10 amp rating. Can you show me a part that has a higher rating?
Or can you show me individual diodes?
thanks or I am way off here?

Says surge current of 300 amps but Maximum Average Forward Rectified Current is only 10 meaning on a ground fault it would burn out.

How does Gaertz bridge differ from a normal bridge rectifier?
If using a 50 amp bridge rectifier, the voltage drop is only 1.2v so it will conduct the DC 12 volts not block it?

 

[goldsmith]

It mentions maximum DC voltage blocking. Now this only has a 10 amp rating. Can you show me a part that has a higher rating?
Or can you show me individual diodes?
thanks or I am way off here?

Says surge current of 300 amps but Maximum Average Forward Rectified Current is only 10 meaning on a ground fault it would burn out.

If using a 50 amp bridge rectifier, the voltage drop is only 1.2v so it will conduct the DC 12 volts not block it?

You can find other diodes and make your own gaertz bridge or perhaps integrated circuits for this aim . some years ago i've used a metalized package bridge rectifier with ability of handling 210 Amperes . if you try you can find gang of these rectifiers .
But as i've told you another way is available too . a thyristor or a triac with a fuse and a comparator . when a mistake happened , it will short the power line and then fuse will be burned .
Good luck
Goldsmith

 

[sdowney717]

I took a digital meter and the AC ground is at zero ohms to the negative 12vdc terminal, so maybe my issue is only internet myth.

Unlikely they would design inverter so that an appliance short when attached would destroy it? That would be very poor design.

From manual only says this.

I was concerned the neutral wire would accidently contact ground and blow up inverter, which I have read on some websites can happen.

Do not connect the Inverter to RV or household AC distribution wiring, to an AC load circuit
or where the neutral conductor is connected to the negative terminal of a DC power source.
Connecting to these circuits could cause damage to the Inverter and/or create a spark.

My neutral is not connected anywhere to the ground on the boat with Inverter selected for power source. And when I switch from shore grid power to gen power to inverter power, I am switching both hots and neutrals.
Neutral wire is connected to ground on shore grid power and gen has neutral to ground bond. BUT since I switch both hots and neutrals these never interconnect. I am using 4 pole double throw relays rated 35 amp with 120vac power. I don't believe that a big enough arc would develop to momentarily interconnect these wires.