Power flow chart

[capnTelescope]

There has to be an easier way

... but it's a little more complicated at first.

Here's the charge while towing / AC transfer system on my tear. I didn't use a PDC or other power center. When I boondock, I'm on DC only. A 115VAC relay acts as an automatic transfer switch.

Most any Double Pole Double Throw (DPDT) relay with a 115VAC coil will do. Connect the inverter output to the Normally Open contacts and the relay coil. Connect the shore power input to the Normally Closed contacts. Finally, connect the "switching" contacts to an outlet. Plug the charger, fridge (and whatever else gets 115VAC while towing) into the outlet. Now, the inverter will supply whatever is connected from the inverter (if it's running) or shore power will take over when the inverter is off. Without shore power or inverter tow power, turn on the inverter in the Power Center, otherwise you're on DC only.

Size your inverter to handle the charger and whatever else gets AC while towing.

All this is thoroughly cussed and discussed in the "Charging While Towing" thread. Refer to the diagram above, rather than the one at the linky.

HTH.

[GuitarPhotog]

60-80 A per day is 720-960W. If your 200W solar system actually puts out 150W, it will take you 6 hours of full sun to replace that charge in a battery rated for at least 120-150 AH.

Camping in the desert, I think 900W capture with a 200W system is reasonable. Shade, or clouds, or high ambient temperatures (panels derate as ambient temps increase), will affect your yield.

And we won't mention that on two of my recent trips, I had 8 or more consecutive days of rain ;-(

<Chas>

[m.glisson003]

There has to be an easier way

... but it's a little more complicated at first.

Here's the charge while towing / AC transfer system on my tear. I didn't use a PDC or other power center. When I boondock, I'm on DC only. A 115VAC relay acts as an automatic transfer switch.

Most any Double Pole Double Throw (DPDT) relay with a 115VAC coil will do. Connect the inverter output to the Normally Open contacts and the relay coil. Connect the shore power input to the Normally Closed contacts. Finally, connect the "switching" contacts to an outlet. Plug the charger, fridge (and whatever else gets 115VAC while towing) into the outlet. Now, the inverter will supply whatever is connected from the inverter (if it's running) or shore power will take over when the inverter is off. Without shore power or inverter tow power, turn on the inverter in the Power Center, otherwise you're on DC only.

Size your inverter to handle the charger and whatever else gets AC while towing.

All this is thoroughly cussed and discussed in the "Charging While Towing" thread. Refer to the diagram above, rather than the one at the linky.

HTH.

Thanks for all of the helpful info! I will reference that thread.

[m.glisson003]

60-80 A per day is 720-960W. If your 200W solar system actually puts out 150W, it will take you 6 hours of full sun to replace that charge in a battery rated for at least 120-150 AH.

Camping in the desert, I think 900W capture with a 200W system is reasonable. Shade, or clouds, or high ambient temperatures (panels derate as ambient temps increase), will affect your yield.

And we won't mention that on two of my recent trips, I had 8 or more consecutive days of rain ;-(

<Chas>

Yeah that's why I'm putting 400W of solar on the roof. Just incase I don't get many hours of sunlight. Worst case I have a generator and can cut back on my usage depending on the weather forecast

[bdosborn]

I don't like to use a relay for switching between 120V sources because it doesn't check the phase between two sources before transferring. The inverter *won't* be in phase with the shore power and out of phase sources act like a fault i.e the fridge motor sees it as a fault if you forget you have the fridge running on the inverter and you switch it to shore power via a relay. It probably won't let the smoke out of anything but it's hard on the fridge motor. I prefer a double pole, double throw manual switches with center off positions. Just make sure and hang out a second of two in the center off position when switching between sources and you don't have any phase difference issues.

Bruce

[capnTelescope]

Bruce, your point is well taken. I considered just exactly what you described, and decided there wasn't anything to worry about. But Dear Readers should note that in my case, things are running off the inverter powered by the TV and I just don't plug into shore power while the inverter (and the TV) is running. That's why I don't worry. Plugging into shore power is one of the last steps when I set up camp.

If there were the two out-of-phase sources of AC, the relay would isolate the two AC sources from each other. Any phase change would happen after a brief (milliseconds) power interruption while the relay changed contacts. I haven't ever tested whether that would have any bad side effects, but AC motors don't require a full stop after a power interruption.

[bdosborn]

If there were the two out-of-phase sources of AC, the relay would isolate the two AC sources from each other. Any phase change would happen after a brief (milliseconds) power interruption while the relay changed contacts. I haven't ever tested whether that would have any bad side effects, but AC motors don't require a full stop after a power interruption.

When the relay disconnects from one source, there is a brief time when the motor acts like a generator and back feeds power. It's also slowing down so the frequency is dropping. Then the connection to the alternate source occurs and it could be 180 degrees out of phase so the motor goes from being a generator to a motor again, during the milliseconds it takes to transfer from one source to the other. Like I said, it probably wouldn't hurt anything but the RV ATS manufacturers (which are just relays) don't recommend switching sources on running motors because of it.

I used something like this from eBay:

eBay Linky

Bruce

[capnTelescope]

... but the RV ATS manufacturers (which are just relays) don't recommend switching sources on running motors because of it.

Well, I'm not going to argue with the folks at Progressive Dynamics. OTOH, how many AC motors are in a teardrop or TTT? Likely none. Dual voltage refrigerators have a DC motor, and convert AC to DC, so there is no phase issue there. If you have an AC-only refrigerator, yes you could have an issue. If you're using a microwave, don't switch AC sources while cooking. But then "they" say you should let a reefer sit until the high pressure refrigerant bleeds down.

I think this whole thing is really a non-issue for anything less than a motorhome, aircraft or spaceship. You pays your money and takes your choice.