[SOLVED] qoestions about using power inverters

[obrien136]

I was trying to use a 13.8Vdc to 110VAC power inverter (350 watts) to power a model railroad layout. THe resistance of the tracks was if I recall correctly, when one engine was on, about 12 ohms. There were two turnoffs and a blinking (led) water tower that ran on about 18Vrms. At 17 or 18 VDC the lay out draws a little over 1 amp, I figured a 350 W inverter would allow for surge current that might occur as the engine powers up. But for some reason the power was initially low so that the train engine ran slow and the watertowwer wouldn't blink. I then measure the inverter output at no load and it was 80Vrms This is the second inverter that this has happened with. I am wondering if I am destroying them or is the place where I got them selling defective equipment. Would it put out a low voltage if it was defective or if the 40 amp fuse
blew? Do they have a minimum load requirement like some switching supplies?

 

[obrien136]

I meant to mention that the battery voltage stayed about 13V , no less than 12.7.

 

[BradtheRad]

What shape waveform does your inverter put out?

I had a square wave inverter. It read 90 VAC. But it was not RMS. My meters caused a low reading, due to the fact they are not calibrated for a peak value of square waves.

Instead like most cheap meters they are calibrated for an average value of sine waves.

If your 110VAC inverter is a sine wave type, then it produces peaks of 160-170 V.

However if it is a square wave type, then the peaks will be much lower. This might explain your low voltage to your train layout.

 

[Audioguru]

A very cheap inverter that has a square wave output is designed to provide normal power to a heating electrical product or to an incandescent light bulb that is also a heater. An electronic product including a motor speed control (maybe your train has one) does not work properly from a square wave because it relies on the much higher peak voltage of a sine wave (that produces the same average heating power as a square wave).

 

[chuckey]

If you know how to do it, a large electrolytic across the diode output in the power unit might help. You can try with one on the output side, the only problem is that when you reverse the engine you reverse the polarity on the power unit which will blow up the capacitor (stand clear!!).
Frank

 

[obrien136]

Thanks, that clears it up.