inverter protection from surge back EMF etc

[rgormley]

Any idea on a way to protect an inverter from back emf`s surges etc etc

Ie: fluros flickering, motors in Fridges turning on/off

they would be making some nasty stuff going back to the inverter.

i would like to help protect by placing some surge dampening on the inverter output

woould a good quality surge/power board work?

[TomW]

rgormley;

Funny, never saw anyone claim this to be a problem until this post?

My thought is you are over thinking things. Seeing problems where none exist, etc.

I could be wrong but it just doesn't seem like it would be a problem in quality equipment. And, if it is a problem in cheap equipment the fix is probably simply buy good gear.

Maybe you have a link to information about this?

Always curious about new information.

Cheers.

TomW

[veewee77]

My guess, and this is strictly a guess, mind you, is that the manufacturer would have taken that into account when they produced the inverter. With any kind of quality inverter, you'll likely see that they are pretty well protected from that right out of the box.

Now, if you get an inverter made by Ralph's Inverters, you might have a problem.  

Doug

[boB]

A good inverter will be able to sink reactive power as well as source it.

This is why, for instance, a modified square wave inverter has that flat

spot at zero volts in its PWM duty cycle.  It's basically a short circuit

at that time to the AC output.

In a sinewave inverter, the output impedance ~should be~ low for either the

goes-inta' or the goes-outa direction of current.

If an inverter is making AC and gets connected to another AC source, like

the grid or a generator, then it's called "backfeed", which is sometimes

hard to protect from, but again, a good inverter will have "backfeed protection"

and shut off when it sees high current at the wrong time in the AC cycle.

Spikes can be helped by different methods like MOVs and stuff, if that's what

you're talking about.

boB

[rgormley]

err maybee the cheap ass factor here...

the inverter i have bought is a new 24vdc 3kw cont rated  (6kw surge) for only $400 AU. so maybe a elcheapo!

yes maybee i`m looking for problems that simply is not there.

(i have a 12volt 3kw cont rated inverter) and it has ben happy for 3 year running 24/7 onthe fridge-freezer  / fluro lights /PC`s etc)

so yes maybe it`s in my mind

MOV`s yes thought about them acroos the AC but dont they go short cct if overvoltaged (ie spike was absorbed by them?)

dont fluro ballasts produce evil back emf when the balast collaspes?

or should i take a chill pill...

Cheers...Richard

[joestue]

Any current stored in the circuit or load due to inductance should be absorbed by the inverter's output capacitance.

if you really think the voltage spike could damage the inverter, then find an old motor run capacitor and a make a low pass filter from two additional inductors.

[Flux]

Be very careful trying to add any form of filter to a msw inverter, you may do far more damage than the spikes that really are no issue anyway.

Beyond adding a MOV I would do nothing and unless you really know what you are doing the MOV may be best avoided or already incorporated.

Capacitive loading on simple msw inverters will probably tax the protection circuits to the limit or defeat them. Power factor correction capacitors in lamp ballasts are best removed if you must use them on msw. Power factor correction doesn't work on step waveforms as it does on sine waves.

Flux

[hydrosun]

I had a problem with my Outback inverter shutting off when the only load was my Staber washing machine. Outback sent out a tech to put an occiloscope on it. Seems the back emf was causing the inverter to cut voltage output to compensate. But then the inverter would overshoot too low and shut itself off at the 108 volt low voltage cutoff. I noticed that it only occurred when the Staber washing machine was on by itself. Most of our lights are 12 volts. But when we had one 120 volt compact fluorescent light on, the inverter didn't shut off. Outback engeneers theorized that the capacitance of the light counter balanced the inductance of the washing machine motor. They had never had anyone complaining of the same problem. I solved it by mounting a light socket on the washing machine and screwing in a cfl. I tried a 7 watt but it still shut off. So now I have a 15 watt cfl and the inverter never shuts off. I also have a mechanical timer on the machine to totally disconnect it to eliminate it's phantom load.  

So adding a compact fluorescent seems to filter or compensate for emf from a motor that was causing a not so cheap inverter to shut off.

Chris  

[joestue]

Your right, the harmonics generated by the 3 level inverter are insane, I didn't think about that, in which case the capacitor would effectively appear as a short...

[JW]

bump

[joestue]

Why dredge up a 14 year old post?