Why such a high surge?

[eflyersteve]

Relatively speaking, the fridge, on A/C, doesn't draw enough to pop a 1500watt inverter. I didn't imply, at all, that they were efficient lol.

 

[highdesertranger]

why, what is the draw? 1500 watt is like a hair dryer. highdesertranger

 

[eflyersteve]

Why? Ecause it doesn't draw much power. Looks like about 100 watts on A/C.

I've been running a 750 watt MSW inverter for several days now (and a 400 watt before that) and it's been running great. Maybe I really did just have two bad inverters.

Thanks again for all the replies. Much appreciated.

 

[XERTYX]

I'm not an expert by any stretch of the imagination.

Are you saying that you have a shed connected to shore power as though it were an RV connected to shore power. Then using the inverter in it plugged into a 30 amp RV receptacle on an actual RV as though it were connected to shore power?

That is to say your shed is the power company. Charged from shore power. Then its output is powering an RV?

Sorry to seem stupid but I'm not following your train of thought.

 

[eflyersteve]

I have solar panels connected to an mppt charge controller which charges 12v 200ah lifepo4 battery. An inverter is connected to the battery. This resides in a shed. Think of it as an off grid solar system. My RV is plugged into this inverter, thus powering it (the RV).

I have removed the deep cycle lead acid battery that is normally connected to the RV. Therefore, the RV converter/charger is only providing 12v DC to those systems on the RV that are connected to it. No battery connected to the RV. No power to the RV other than from the inverter. No power to the inverter it her than the lifepo4 battery.

 

[XERTYX]

Ok. I'm with you now. Just an observation.... the RV is connected to the 1500/3000 inverter. Under normal conditions like the testing you've done isolating circuits and removing the refrigerator from the equation shouldn't draw anywhere near 1500w. But yet the inverter has failed twice. The RV is plugged in via a 30A shore power connector. 30A X 120V is 3600W. Now that doesnt mean it's always drawing 3600w. This is true. But is it possible that because there is no battery connected the converter is basically just a 12V power supply that the converter is being tricked into thinking there IS a battery there and it's very very dead. So it is trying to bulk charge the non existent battery and drawing 30A?

If you were to attempt another pure sine wave inverter I would recommend plugging a kill a watt meter in between the inverter and RV. Then look for big fluctuations in wattage.

Its interesting that the smaller non pure sine wave inverters work just fine. Maybe the converter doesnt like pure sine wave for some reason?

Just speculation on my part.

 

[Zoomyn]

. ..had two occasions where I've connected the inverter.. .

When connections are made there can be 'bounce' - where the connection gets strobed once or more times with each new join/part making lightning-like spikes across the connected wiring & devices.  Quite a great deal of care goes into reducing/eliminating mechanical switch bounce, so imagine if you're physically attaching a lug onto the battery, twisting wires together, pushing a lug into a clamp it's maximum 'static pop' time until we've finished borking around.

On inverters when connected the electricity loads up capacitors and coils -- so as soon as the electric 'pressure' is severed all sorts of back flow blooms back out... Now if someone is jittery its 8, 18 or 88 charge/discharge pulses from an unsteady hand doing the connection... that can/will trigger switching logic at just the wrong time to allow the magic smoke to be released.

Anyhow, loads of articles online about DC noise filters and switch/circuit breaker best practices - starting with getting a good grade circuit breaker as the doomsday fuse at battery (Blue Seas or equal) and using it as the entire DC circuit kill switch... then size and fuse legs of circuit accordingly. No manual connect/disconnect allowed more than once or twice for testing and then be extra careful...

 

[tx2sturgis]

On inverters when connected the electricity loads up capacitors and coils -- so as soon as the electric 'pressure' is severed all sorts of back flow blooms back out... Now if someone is jittery its 8, 18 or 88 charge/discharge pulses from an unsteady hand doing the connection... that can/will trigger switching logic at just the wrong time to allow the magic smoke to be released.

The above is all true but most newer high quality, high capacity inverters have some form of delay: 'soft start', time delay, or 'ramp-up-time' before full power and voltage is applied to the output. This helps to reduce the transient inrush current when 12v DC power is applied, whether the inverter is on or off.

 

[eflyersteve]

Fridge uses about 320 watts when in A/C mode as measured with a kil-a-watt meter. Was surprised to see it that high. I'm seeing about 375 watts with all the breakers left on and the fridge on A/C. Switch the fridge to gas and with all the breakers on but nothing running other than the propane alarm and the charger/converter and the power use drops to about 50-55 watts. This is with or without the deep cycle lead acid battery connected to the converter/charger. Definitely not enough to pop a 1500 watt inverter.

Unfortunately the kill-a-watt meter inst quick enough to measure transient spikes, but at least I have an idea of what uses power and how much.

Some more things to note:

Both sine wave inverters had 'soft start' features.
Both popped their fuses and FETs when i powered them on with the RV connected (a 'soft start' scenario)
Both ran the RV for some period of time with no issues before they popped.
I've never connected DC power to the inverter with it connected to the RV and it switched on.

 

[tx2sturgis]

I often power my trailer with my 700w sine wave inverter, which itself is powered by 200w solar and 2 AGMs. I never try to run the 3-way fridge that way, it just gobbles up wattage, around 150 watts on AC (I believe) but I have not actually measured it.

BTW, just for clarity, 'A/C' is often the abbreviation for Air Conditioning, and 'AC' generally means shore power (Alternating Current). By no means is this an exact definition. But 'DC' and 'AC' are usually referring to 12v or 120v power.

Not trying to be picky because I know what you are referring to, but sometimes 'A/C' might be misunderstood depending on context.

 

[XERTYX]

Ok I could Google this but I wont. FET is a transistor is it not? Have you disassembled the popped inverters?

You needn't answer these questions but if you're educated enough to diagnose failure in individual components on a printed circuit board why in the world would you prefer to run an RV without a house battery?

Sorry, but this seems superfluous to me.

 

[wayne49]

Try it with a useful battery (charged before hand) connected to the RV converter/charger.

 

[eflyersteve]

Why would I want to charge a lead acid house battery from an inverter running on a 12v battery? Not super efficient. I also didn't want to waste power from the solar to charge a separate house battery. I'll eventually install an automatic transfer switch and upgrade the converter/charger to a better unit so that the lifepo4 battery is charged from either solar or shore power. Again, this is just a temporary setup to test everything before I install it all into the RV. Note that its not dfficult to diagnose shorted FETs with a meter if you know what you are doing.

Re: AC vs A/C understood - hopefully context is understood. Not sure of an 'air conditioner' mode for an RV fridge. Was just a mistype on my part. I've caused a lot of confusion on this thread obviously.

I'll be happy to let this thread die out as I don't think we will be able to guess at why 2 expensive inverters have went bad while 2 cheap ones continue to work great. I'll just stick with the cheap ones and install the components in the RV.

Thanks again to all who have tried to help. Much appreciated.