Why such a high surge?

[eflyersteve]

Working on setting up a new travel trailer on solar and have had two occasions where I've connected the inverter and had the internal fuses blow and FETs short out.

This is a 1500 watt (3000 surge) pure sine inverter.  The loads in the travel trailer are the converter/charger (no battery load - just the power to run the 12v portion of the fridge) fridge is on propane. microwave and the propane/CO detector.  The first inverter, I got about 2-3 days of use before it popped and the most recent one I've had for a few weeks. 

What could be requiring such a high startup surge that it's popping inverters?  When things are working, I don't run high load appliances (no microwave or a/c) and I make sure things are off when switching on the inverter.  The setup is simple - I have it installed in a shed and am using the shore power cord so I'm confident that the wiring is all good.  Once I am confident that things will work well, I plan to install it in the travel trailer.

Thoughts or suggestions would be greatly appreciated.

 

[B and C]

It is not clear how you are connected. Solar panels, charge controller, batteries and inverter in the garage with the trailer plugged into the inverter?

It more sounds like you have the inverter connected to your house batteries that are being charged by your converter in the trailer that is plugged into the inverter. If this is the case, yes, you will fry something. You may have the solar charge controller and panels connected to the batteries too but won't affect the circular charge circuit above.

Edit to add: You cannot plug the trailer into the inverter if you are wanting the electrical outlets to work Another transfer relay has to be installed that bypasses the charger in the trailer.

 

[eflyersteve]

No house batteries connected. A 4s lifepo4 100ah battery charged from a 60a mppt solar charge controller fed by 600 watts solar. Inverter connected to the battery, shore power plugged into inverter. The converter/charger in the RV isn't connected to batteries.

 

[B and C]

Can you plug your trailer into a kill-a-watt that is plugged into shore power to see if you can isolate the problem? If you have an older used trailer, the converter may be shot.

Edit to add: The converter in the trailer needs a battery to charge. I would not plug the trailer into the inverter. Take a household appliance and plug into the inverter. What you are doing is bad practice.

 

[Trebor English]

No house batteries connected.  A 4s lifepo4 100ah battery charged from a 60a mppt solar charge controller fed by 600 watts solar.  Inverter connected to the battery, shore power plugged into inverter.  The converter/charger in the RV isn't connected to batteries.

If the inverter output is connected to shore power that will blow up the inverter.  The power company equipment is huge and will not be bothered by the inverter.  The inverter output will not beat the power company into submission.

 

[eflyersteve]

Plugging in the RV's shore power (the 120v input) into the inverter. Not connecting 120v to the inverter haha. Yes, I know better.

Short, maybe easier to read version:. Something in my 2019 model travel trailer is causing enough of a power-on surge to fry 2ea 1500 watt inverters (3000 watt peak pure sine, well reviewed units). The inverter is the only thing supplying power to the RV. No external power, no house battery.

B and C:. Do you think it might be the converter causing the surge because it doesn't have a battery connected? If so, the solution would be to separate all the 12v circuits and run them either off the lifepo4 battery or the mppt charge controller load output (mine is equipped with this feature) - correct? Essentially eliminating the converter.

Thanks to all who are taking the time to help.

 

[B and C]

I guess I am trying to figure out why you are plugging the trailer into the the inverter. If it is just to get power to the outlets, the preferred way is to add another relay into the circuit that will bypass the converter in the trailer. A relay like this: https://www.amazon.com/dp/B00MJVSCY...olid=13VYN7BHCGYSP&psc=0&ref_=lv_ov_lig_dp_it

Are you never going to plug into shore power or a generator? Remember, the sun doesn't always shine to recharge from.

You are trying to connect your trailer in a way it never designed for. Put your batteries in the trailer and connected to the trailer system. Add the relay and you can then power your outlets from the inverter. Wire your solar charge controller to the batteries.

 

[highdesertranger]

"The inverter is the only thing supplying power to the RV. No external power, no house battery."

if you have no house battery what is powering the inverter? this is all very confusing on what you are trying to do.

highdesertranger

 

[tx2sturgis]

Actually I understand what he is doing because I have done that me-own-self. Many newer RVs will operate the 12v circuits with no batteries connected, in 'power supply' mode.

OP, double check the inverter operation on a single heating or cooking appliance, not a microwave. Something like a toaster, space heater, electric skillet, electric hot plate. You want a wattage of about 1000 watts more or less, to test the inverter. Let it run for a few minutes to make sure the inverter is OK. If you get any warning lights or beeps, or it shuts down, something is wrong.

Assuming it passes that test, proceed:

Open up the converter panel in the RV and locate your 120v breakers. Turn them all OFF. 

Double check for these breakers: A/C roof air OFF. Outlets OFF, refrigerator 120v heater OFF, microwave OFF, water heater electric element (if equipped) OFF. Converter main, OFF. Everything OFF. If your water heater has an electric element, turn it OFF at the water heater.

I recommend the following test be done with a smaller inverter fuse (or 12v breaker) inline or installed at the inverter...maybe half the normal rating, just for this test. 

Now plug the shore cord into the inverter, and observe it for awhile after you turn on each breaker individually. Turn on the Converter Main FIRST. Check that the 12v items work, such as lights, water pump etc while that converter main is on. Be aware that many of the 'phantom loads' will power up with the converter, such as propane detector, USB ports, fridge electronics, etc...all at the same time.

Then turn on outlets, check those, then the other breakers, and observe the inverter. When you get a warning, overload, blown fuse, etc, you will have found the offending circuit.  

You may have to operate the RV in this test configuration with some of the breakers OFF.

It might be that the surge load with ALL the breakers turned on is a bit too much for that inverter.

Let us know what you find.

 

[eflyersteve]

Sorry - I have the solar components (panels, mppt charge controller, batteries, inverter) all in a shed right now - testing before installation into the RV. I am plugging the RV into the inverter. 120v from the inverter is powering the RV in the same way as you would connected to a 120v 30a RV receptical. To avoid wasting power charging a house battery in this test, I have removed it from the converter charger. It isn't being used. Isn't connected.

The question is: when powering on the inverter with the RV plugged into it (fridge set to propane as described above) what would likely cause a high power-on surge that would exceed the surge capability of a 1500 watt pure sine inverter?

 

[eflyersteve]

And before someone says "solar panels won't work in a shed" - those are actually outside.........

 

[eflyersteve]

Tx2Sturgis - BINGO! Actually, after my first inverter bit the dust, I did exactly that - all breakers off, power inverter on, power inverter off, switch second breaker on, power on inverter. I can leave them all on and it will power everything fine and might do this a dozen times and suddenly 'Pop!'. Note that I don't run the electric water heater, microwave or a/c.

I've tested the inverter with a heater at 800 watts and at 1500 watts directly into the inverter and it worked beautifully. Those lifepo4 100a batteries hardly sagged a bit.

 

[tx2sturgis]

Make sure your fridge is not trying to run on AC power. It might be kicking on and pulling a high surge.

Turn it OFF or run it on propane. Many newer fridges have 'auto' mode where they will switch to AC if they see that AC power is available.

 

[eflyersteve]

You know, I typically run it on propane when running the inverter, but I might have left it in auto mode now that I think back. I plug the RV into the utility mains when I'm not testing the solar and I prefer to run it on auto when doing so. When I got home I might have unplugged the RV from the mains and plugged it into the inverter and powered it on without switching to propane. If the compressor was running and attempted to re-start on the inverter, the surge would have been pretty high. You might be on to something and it might explain why this issue isn't consistent.

I wonder what the locked rotor power requirement for a typical dometic RV fridge is? I wouldn't think it would be too great.

 

[tx2sturgis]

Is your RV fridge one of the newer compressor RV fridges or the classic absorption type? 

If your fridge has vents on the outside it's the absorption type. It will have a 'gas' or 'LP' setting.

If you hear a compressor running, then it's obviously a compressor fridge, with no ability to run on 'gas'. Some newer RVs have those.

Either way, they pull some current on AC, and if yours has an 'auto' mode this might explain it.

 

[eflyersteve]

Fridge appears to be the absorption type - even on A/C, the current draw is relatively low.

For what it's worth, I've been using a 400w MSW inverter that I borrowed from my son and it is holding up fine with no issues even when leaving all the breakers on. I purchased a 750w MSW to keep as a backup and it seems to be working fine. I'll have to investigate further with a watt meter to see if I can see what's happening. I'm a little hesitant to buy another pure sine inverter at this point.

Thanks for all the suggestions so far. Much appreciated.

 

[tx2sturgis]

Hmm...dunno…

As I type this my trailer is plugged in thru the shore power cord to the 700 watt PSW inverter in my pickup truck.

It's running fine.

Of course, it does not power the roof air or the microwave, but it charges the house batteries and runs all the normal 12v systems just fine.

 

[eflyersteve]

Thanks for that info. A couple of things I'm wondering about - does the converter/charger freak out when I power it up with no battery load (maybe I should just install the deep cycle lead acid battery and let the inverter power it to charge that battery). The second thing I wonder about is if neutral/ground bonding in the trailer vs. the inverter could cause issues. One curious incident that occurred frequently with my first inverter (different manufacturer) was the GFCI would trip often when switching it on. Not always, but sometimes. Never happens when connecting to utility power. I wonder if the neutral and ground are bonded in the inverter and this is causing issues with a possible neutral/ground bond in the RV.

Finally, if I can't reproduce this issue, I wonder if I should just go big on the inverter and use one with a much higher surge capability. I've been using 1500/3000 inverters. Perhaps a 3000/6000 would survive whatever is happening. I know, it's just a guess and possibly an expensive one.

 

[tx2sturgis]

It's kinda hard for me to help you troubleshoot 'blind'...I'm not able to see exactly what you're doing.

But some things I would try are:

Install a fully charged house battery in the trailer, plug the trailer into normal shore power, and let it fully charge and top-off the battery. Again, make sure all the big loads are turned off, then plug the trailer into the inverter observing the procedure I outlined earlier.

My inverter also has a GFCI and a grounding point, but I do not use the grounding terminal. GFCIs are very sensitive to tiny amounts of ground currents. If your shore cord is even laying on wet ground, that is sometimes enough to trip the GFCI.

Obviously I'm not telling you to slosh around bare-footed in wet grass and grab the metal parts of the trailer...make sure you observe safety protocols.

I guess its possible you might need a larger inverter, but my trailer pulls around 25 to 150 watts average, from the inverter, with minimal loads. If things are working correctly, it does not take much power to run the trailer in 'standby'.

Of course if the trailer converter was charging a depleted battery, and you had all the lights and fans and radio and other things on, it will pull much more power.

 

[highdesertranger]

"Fridge appears to be the absorption type - even on A/C, the current draw is relatively low."

if the refrigerator is running on electricity then this statement is false. however if you are running on propane then this statement is true. absorption refrigerators are very inefficient(energy hogs) running on electricity.

highdesertranger