Autotransformer

[rv_safetyman]

Nick, my manual would suggest that most of the Trace (and I would assume Xantrex as well) inverters have the capability of 60 amp pass through.  If you only have one inverter (don't have two stacked inverters), you must have some AC circuits that are not protected.  One inverter would pass through the current for one leg but not the second leg. 

I am getting in over my head, but I think that is correct.

Jim

[Nick Badame Refrig/ACC]

Hi Jim,

I have the one 3000w inverter and 60a pass through. I have the option to run anything I want off the inverter if I choose.

The only drawback is I have to flip the brakers of the heavy loads before unplugging from shore power.

If I forget, the inverter will sence the load and shut down with a fault. Not a big deal.

Nick-

[Sean]

Wow, lots to answer here.  Let's see if I can remember it all.

First off, thanks, Jim, for the reference to the other "testing" thread.  Even though that thread is a full year old, I have just posted a response over there -- I found a major safety issue with the way Jim Stewart (and others) are using the three-light testers in parallel.  See http://www.busconversions.com/bbs/index.php?topic=3209.msg68651#msg68651

Regarding my LVCO being so low:  I have not found any problems with 96 volts, however, I am very sensitive to the extra load it places on the air conditioners, and I keep a careful eye on them.  None of our electronics has had a problem.  Oddly, the most sensitive electronic item we have is the coffee maker.  If it's brewing when the air compressor kicks on, it loses it's mind, and we have to reset its clock before it will finish brewing the pot.  Our fridge is 24 VDC, so it can't have this problem.

Regarding the Progressive Industries product:  I had a chance to evaluate one of these a few weeks ago.  It was, I believe, the EMS HW50C.  By evaluate I mean "disassemble."  Basically, it's a microcontroller connected to three voltage monitors and two current transformers, along with a MOV board for surge suppression.  The microcontroller also monitors the MOV board and will alert you that it needs to be replaced, in the event it actually comes into play.  The two hot legs and the neutral run through a three-wire contactor (basically a three-phase motor starter), and the microcontroller gates the operating current to the coil.  It only closes the contactor to pass power through if voltages are within limits, and it will open the contactor on a variety of conditions.

In my opinion, this device has the potential to save the average (non-electrically inclined) RV owner a lot of hassle.  OTOH, you are stuck with its pre-programmed limits.  I was also unimpressed with the construction, as the entire case is plastic (for 240 volts, I prefer grounded metal "dead-front" construction), the MOV board is "mounted" by being tucked behind two plastic stanchions that hold the cover screws, and the cheapo contactor is barely rated for the full 50 amps continuous that you might actually be using.  They did, very cleverly, design the LED digital readout so that it can be horizontal and readable no matter which way you mount the case.

With regard to inverters protecting downstream circuits, be aware that when the inverter is operating in "pass-through" mode, and even the very best inverters do this, any and all power quality problems with the incoming power line are also passed through to the loads, right up to the point where the inverter decides they are completely outside of limits, at which time it disconnects the incoming power and starts inverting.  This means two things:

(1) "Dirty" power will still go through.  Spikes, sags, etc. lasting shorter that the inverter's time threshold will be passed on to the load.  And the inverter will not disconnect until voltage drops below the LVCO or rises above the HVCO.

(2) The inverter can go into what I call "yo-yo mode."  This is where the inverter is running in pass-through mode, and whatever load you have connected comes on (like, say, an air conditioner starts up) and, as the current rises, the incoming line voltage drops.  If you are on the end of a long branch circuit, particularly if it has been wired with undersized conductors, you will see the voltage drop off quite markedly and rapidly.  At some point, the line voltage may drop below the inverter's LVCO, and it then disconnects and starts powering the load by inverting from the batteries.

Well, now there is no load on the incoming line, and the voltage very quickly rises back up to nominal.  The inverter sees this new, higher voltage, and, after some time delay (in my case, 20 seconds), decides the input power is acceptable again, and goes back into pass-through mode.  At which point the running load brings the voltage back down, and the cycle repeats itself ad infinitum.

OK, I think I touched on everything...

-Sean
http://ourodyssey.blogspot.com