Curious if this "back-channel" to the inverter could be dangerous

[havesomejoe]

This is kind of complicated to explain so bare with me..

I recently installed an automatic transfer switch into my RV and connected my inverter to it so that now shore power and my inverter can power the same existing set of outlets. Something surprised me when I was testing it.

I forgot that the way the RV was designed, when you are plugged into shore power, the converter powers your DC fuse board instead of your battery.

Somehow I overlooked this "back-channel" of DC power, and because I wired my system together in a circuit that flows through the inverter's terminals, my inverter receives power from shore power (I attached a diagram) and can thusly be turned on in a way that skirts my intended fused route from the battery.

If the inverter is able to turn on, I don't think it's that big a deal because the automatic transfer switch should prioritize shore power, so the inverter wouldn't do anything.

But my fear is that in some rare scenario someone could plug a device directly into one of the inverter's spare outlets and that maybe my system isn't designed for this pathway so something would cause a fire.

If you look at the diagram there is a 50a circuit breaker that I could just disconnect to.. break that circuit... but it's rather inconvenient to remember to do that whenever I have shore power, and it's located underneath a seat that i'd have to lift up to get to.

What do you think, could this play out badly or is it sufficiently protected via fuses and breakers? I'm thinking the latter, but wanted to get a second set of eyes on it.

Looks like the diagram photo is getting compressed too much so here is a link to it in full resolution.

 

[svetz]

... my fear is that in some rare scenario someone could plug a device directly into one of the inverter's spare outlets and that maybe my system isn't designed for this pathway so something would cause a fire.

If the the concern is that while on shore power someone plugging directly into the inverter's socket would cause a problem, you're good. It should even work if the inverter is on. That's because the appliance plugged into the inverter doesn't backfeed the system.

BUT, there is a bigger problem with your setup.... While OFF shorepower and ON inverter, the inverter will draw DC and convert it into AC. The Converter will take the AC and try to recharge the system. The more the inverter drains the batteries the more power the converter will draw to recharge them.

Seems like you need to put the converter on the shore power side of the ATS, or add a relay to turn it off. It might be okay - I did see the bit in the OP about "when on shorepower the converter energizes the DC side", so there might already be some sort of relay that just isn't in your diagram. You can check that by disconnecting the converter from the fuse block, switching to the inverter, and seeing if the converter leads you disconnected are live. If they are, you want to fix that.

 

[havesomejoe]

If the the concern is that while on shore power someone plugging directly into the inverter's socket would cause a problem, you're good. It should even work if the inverter is on. That's because the appliance plugged into the inverter doesn't backfeed the system.

I forgot to add that this fear would play out only if I had my battery switch disconnected. This scenario is probably very rare but I'd prefer it be impossible. So the scenario would be:

1) I disconnect my main battery switch (now my batteries can't power anything and can't be charged).
2) Have both shore power connected and the inverter turned on (now shore power powers a circuit that my inverter is on)
3) Someone plugs a hair dryer into an open inverter outlet and runs it full blast.

Seems like you need to put the converter on the shore power side of the ATS, or add a relay to turn it off.

This is actually how I wired it. When I wired in the transfer switch I disconnected the converter/charger from the main AC breakers and instead put them on a fused line to the same terminals as the incoming shore power line, so it is only powered when shore power is connected. Good call on testing the leads though, I'm going to do this today just to verify I wired that properly so thanks for the tip.

Another issue that may be present (and I just emailed GoPower about it) is that it seems like this transfer switch prioritizes the alternative power source (in my case, the inverter) so it seems that when both inverter and shore power are on and connected, my appliances are being powered by my inverter whilst the connection I mentioned in the last paragraph is allowing my batteries to be charged at the same time (discharging and charging... dumb). Perhaps it was designed only considering generator power, in which case maybe they decided to prioritize that so you wouldn't be wasting fuel...

 

[svetz]

I forgot to add that this fear would play out only if I had my battery switch disconnected. This scenario is probably very rare but I'd prefer it be impossible. So the scenario would be:

1) I disconnect my main battery switch (now my batteries can't power anything and can't be charged).
2) Have both shore power connected and the inverter turned on (now shore power powers a circuit that my inverter is on)
3) Someone plugs a hair dryer into an open inverter outlet and runs it full blast.

Technically that's okay. The inverter is just using shorepower courtesy of the controller converting it to DC.

In practice, if the DC system can't handle the load, a fuse should blow (e.g., it's charging the battery, the hotplate is on, the radio is jamming, and they try to dry their hair). You could always just put a blank face plate over the outlets so no one could ever plug anything in.

Another issue that may be present (and I just emailed GoPower about it) is that it seems like this transfer switch prioritizes the alternative power source (in my case, the inverter) so it seems that when both inverter and shore power are on and connected, my appliances are being powered by my inverter whilst the connection I mentioned in the last paragraph is allowing my batteries to be charged at the same time (discharging and charging... dumb). Perhaps it was designed only considering generator power, in which case maybe they decided to prioritize that so you wouldn't be wasting fuel...

I think it's normal for an ATS to prioritize one set of inputs. If you want it the other way around just switch the ac inputs; then shorepower will have priority.

 

[havesomejoe]

You could always just put a blank face plate over the outlets so no one could ever plug anything in.

That's a good plan, i'll definitely block off those extra outlets just in case.

I think it's normal for an ATS to prioritize one set of inputs. If you want it the other way around just switch the ac inputs; then shorepower will have priority.

Hmm yeah I may do that. GoPower will tell me which set of terminals have priority and then I can decide. I'll at least make sure to point that out in the video I recorded as I set it up

The more I think about it, and after your comments and suggestions, I believe everything is in proper order. I also can't imagine any scenario where I'd disconnect the main battery switch if shore power is connected. That switch is really only for putting the RV into long term storage. And if I were to do that anyway, it's like you pointed out, I've fused the DC system so it would disconnect any excessive use.

Thanks for the help!

 

[havesomejoe]

So I did find out the logic of this particular transfer switch (GoPower TS-30 - which is just a rebranded Progressive Dynamics switch).

From Progressive Dynamics manual:

When the shore power is applied the relay is at rest and power is transferred to the panel.

When Generator (or inverter) power is applied there is a 20-45 second delay and then the relay activates transferring Generator/Inverter power to the panel.

If shore power returns while the Gen/Inv power is present nothing will happen. When the Gen/Inv power is removed the relay will drop out and allow the shore side to supply power.

Generator/Inverter overrides shore power.

That being the case, I would prefer the reverse logic, so I'm going to swap the connections, that way the above mentioned charging+discharging issue won't happen if the inverter is left on while plugged into shore power.