Head scratcher

[foldbak]

I had an interesting thing happen last weekend. I have a 2018 Cougar with a custom generator and inverter install.

• 4KW Onan LPG generator
• 4KW Aims inverter
• Transfer switch #1 switches Shore power and Generator. Shore is priority.
• Transfer switch #2 switches Shore/Gen power and inverter. Shore/Gen is priority.

• Converter is removed and inverter is the battery charger.
• Inverter and generator control panels in house.

Last weekend we were in a river front full hook up site when the power went out. The rig switched perfectly. The only reason I knew the power was out was the dock lights went out. When I attempted to start the generator it just cranked over. I thought the generator had failed and needed repair. We shut off the AC and broke out the cards. About an hour later the dock lights came back on. For whatever reason I decided to try the generator again and low and behold it started.



I was and still am baffled. The only thing I can think of is it has to be on the PG&E side causing preventing the generator from starting.... maybe ground and common shorted? Thoughts?

[LewisB]

I'm not sure I understand your drawing and the placement of the primary transfer switch. Is this a 30A or 50A RV system? What you are saying is that the loss of power in the shore system was somehow preventing the generator from starting? Then when the shore power was restored, the generator would run? So, did you try unplugging the shore power cable then starting the generator? Does the generator normally run with no shore power connected? Does that change if you just plug in the cable to the trailer?

I'm scratching my head too

[LHaven]

Originally Posted by LewisB

I'm not sure I understand your drawing and the placement of the primary transfer switch.

It's even tougher to troubleshoot when the second transfer switch isn't shown.

[foldbak]

The second transfer switch is built into the inverter. It simply allows the inverter to pass inverted power upon loss of shore or generator power.



No I didn't unplug from shore power and try to start the generator but after some giving it some thought the only logical conclusion is a safety feature in the generator preventing it from starting is a wring fault is detected.



In this case it was auto verses power pole that caused the outage. If ground common or ground hot were shorted the back feed from a running generator could be fatal. If ground and hot were shorted it would simple pot the breaker. That's the best I got...

[LHaven]

Originally Posted by foldbak

The second transfer switch is built into the inverter. It simply allows the inverter to pass inverted power upon loss of shore or generator power.

That would be the transfer switch that IS shown on the diagram. What I don't see is a transfer switch that selects between shore power and generator power. Either that, or the house panel is connected to the wrong place.

[LewisB]

Still don't know if it is a 30A or 50A system - makes a huge difference in the wiring.

I assume you are not using an EMS - not just a "surge protector" but a true EMS. A good EMS would protect your rig from the problem you suspect you may have seen. It would isolate your rig from a shore power mis-wire or short circuit plus it would allow the generator to start if your suspected problem is the issue.

Since you should have one anyway, I recommend you get a good EMS and then see if the problem re-occurs. That's about the only advice I can offer. Good Luck.

[LewisB]

Originally Posted by LHaven

That would be the transfer switch that IS shown on the diagram. What I don't see is a transfer switch that selects between shore power and generator power. Either that, or the house panel is connected to the wrong place.

Ken's right. Your "house panel" has to be on the "AC out" side of the transfer switch shown at the bottom of the diagram.

[LHaven]

Clearly this application needs either two transfer switches, or a multi-port prioritized transfer switch that I'm not sure anybody makes. Getting an accurate diagram of where they occur in the circuit and how they are interconnected may make it immediately obvious why your AC power stalled out in this situation. This incomplete diagram may be actively masking the design error.

[foldbak]

• It's a 30 amp circuit
• Transfer switch 1 is clearly marked switching shore and generator.
• Transfer switch 2 is inside the inverter clearly switching from a power source IE. shore or generator to inverted power.

My design and diagram. As built and has preformed perfectly on 3 different trailers since 2005.


No I dont have a EMS.

[LHaven]

Here's my conundrum.
From the Onan installation manual:

A vehicle with provisions for connecting to shore power (utility) must have an approved device to keep the generator set and utility from being interconnected.

If you look at the next page past that link, you'll see the diagram showing that the service panel must feed directly off the transfer switch. That is the only way to give the service panel an exclusive choice of one source or the other but not both.

Your diagram shows a hardwired interconnect between the genset output and the service panel. When shore power is active through your existing transfer switch as shown, shore and generator are shorted together. This is not just a bad idea, but violates Code. (Again, this assumes there are no errors in your diagram.)

Your switch TS1 only has one possible mode of operation: when shore power is out, connect the service panel to the inverter output. Which means your generator is now also cross-connected to your inverter.

I am guessing that your hidden TS2 is not a "transfer switch" at all, but a relay that switches the inverter between "consume AC power and charge the batteries" mode and "consume the batteries and output AC power" mode. It doesn't isolate two inputs, it just reverses inputs and outputs.

Assuming the power-fail operation of the inverter is automatic (not manually controlled), when shore power fails on this circuit, the inverter will energize, provide power to the service panel, and also present power at the generator output.

i am proposing that your generator fails to start because it detects existing power at its output terminal (it might even be designed this way as a safety feature). This would explain your symptoms precisely.

[LewisB]

I'm with ken on this:

Originally Posted by LHaven

Your diagram shows a hardwired interconnect between the genset output and the service panel. When shore power is active through your existing transfer switch as shown, shore and generator are shorted together. This is not just a bad idea, but violates Code. (Again, this assumes there are no errors in your diagram.)

Our last 2 trailers have been set up with 2000W invertors, on-board generator, etc. and were professionally wired. In both cases, the equivalent of your T-1 switch the main transfer switch had 2 inputs (shore or generator) and only 1 output (house panel). There was no way that both the shore and generator circuits could be shorted - it was either/or only.

Our current trailer actually has a second transfer switch that has 2 inputs (shore/gen OR inverter) and 1 output to selected circuits in the house panel. This allows powering selected circuits from the inverter when shore or generator power is not operating. Our prior trailer was set up just as described by Ken in his subsequent paragraph.

So, if your diagram is as installed, I'd say you have been dodging bullets. I know that is true for anyone who operates without an EMS as well.

Best of luck in resolving your issue - be safe.

[foldbak]

OK I see the confusion. The inverter is designed to be the final switch in the circuit. All AC power comes from the inverter as intended and feeds the panel. You see the lone hot wire coming from the inverter to the panel. That is the feed wire.



To make the schematic easy it shows the common and grounds as shared but there are individual romex runs for all.



https://www.aimscorp.net/4000-Watt-1...r-Charger.html

1. Our 4000-watt pure sine wave inverter transforms DC (direct current) power stored by batteries into AC (alternating current) electricity you can use to power tools and appliances.
2. A built-in 40-amp automatic transfer switch lets the product automatically switch from using a battery bank to shore power. This provides protection in the event of a power outage. The switch will automatically detect the outage and redirect power from your backup battery bank, giving you a smooth, seamless transition for your electrical appliances and equipment. With this 4000-watt inverter, pure sine power can run even sensitive electronic equipment and gear efficiently and effectively.
3. This inverter also has a built-in 100 amp battery charger that can use AC power, from the grid or from a fuel-powered generator. It can be used to recharge a battery bank as well. The battery-type selector on the top of the unit lets you adjust the voltage provided to the bank.

After some discussion with a local Onan service tech, the generator has a safety feature that will prevent it from starting if sensing any short on the output side to prevent feed back.


Power pole down, common touching ground.....no start. The common is shared and always present.

[LHaven]

Yup, what is and isn't connected to each other near the service panel was very confusing as this was drawn (no dots or hops).

Sharing grounds like this is fine, but I'd be wary of sharing neutrals haphazardly. It's common for the neutral on a two-leg circuit to float away from 0V in either direction depending on usage patterns elsewhere in a campground, including the use of autotransformers by other campers. This can cause a significant voltage difference between neutral and ground.

You verified that your generator is designed not to start if it detects funny business on its output lines, which is a crucial piece of information. A floating neutral could easily cause a situation that looks like funny business -- for example, in a situation where your shore outage is caused by a hot lead (only) break to your pedestal, which is exactly what would present from from a popped breaker in the CG's common feed box. That would explain your generator's failure to start.

If you could rework the system to feed the service panel neutral only from the inverter and feed the gen neutral only into the transfer box, I think you would have a winner. The necessary design is to create two cascaded classical transfer switches, and any interconnections "around" them are going to introduce instabilities.

[RoadToad]

Unplug shoreline.
Eliminate the external unknowns.
If Gen still won't start, check batterys.

[sonofcy]

Originally Posted by foldbak

I had an interesting thing happen last weekend. I have a 2018 Cougar with a custom generator and inverter install.

• 4KW Onan LPG generator
• 4KW Aims inverter
• Transfer switch #1 switches Shore power and Generator. Shore is priority.
• Transfer switch #2 switches Shore/Gen power and inverter. Shore/Gen is priority.

• Converter is removed and inverter is the battery charger.
• Inverter and generator control panels in house.

Last weekend we were in a river front full hook up site when the power went out. The rig switched perfectly. The only reason I knew the power was out was the dock lights went out. When I attempted to start the generator it just cranked over. I thought the generator had failed and needed repair. We shut off the AC and broke out the cards. About an hour later the dock lights came back on. For whatever reason I decided to try the generator again and low and behold it started.



I was and still am baffled. The only thing I can think of is it has to be on the PG&E side causing preventing the generator from starting.... maybe ground and common shorted? Thoughts?

The diagram makes no sense. It however does explain what happened. If the generator is allowed to turn ON while the transfer switch is set to shore then you would be back feeding the grid which is a huge safety issue.The generator needs it's own transfer switch.

[RoadToad]

Originally Posted by sonofcy

The diagram makes no sense. It however does explain what happened. If the generator is allowed to turn ON while the transfer switch is set to shore then you would be back feeding the grid which is a huge safety issue.The generator needs it's own transfer switch.

Actually there is nothing wrong with the wiring diagram.
One needs to understand that there is a transfer switch built in to the inverter.
There is no backfeed situation, unless there is a component failure.

Peruse the "Class B Forum" and you will discover the identical setup and the expanded drawing diagram that clairifies the unseen Xfer switch of this diagram.

With the sophistication of the modern inverter/charger/manager, such as in this unit, this configuration is becoming increasingly at large.

This is no problem inheirent in this configuration.

Of course component failures and/or faulty wiring are still possibilities.

[RoadToad]

Originally Posted by sonofcy

The diagram makes no sense. It however does explain what happened. If the generator is allowed to turn ON while the transfer switch is set to shore then you would be back feeding the grid which is a huge safety issue.The generator needs it's own transfer switch.

Look closer....
The Gen feeds the Xfer Sw depicted at the bottom of the dwg.
Shore feeds the other input to that Xfer Sw.(Shore & Gen are never connected)(Cannot "backfeed".)
The output is sent to the inverter and feeds one side of the internal Xfer Sw.
The inverter feeds the other input side of the internal Xfer Sw.
the AC output of the inverter is:
> Gen if it is running otherwise Shore if plugged and hot elsewise Inverter if batteries are sufficient.<