AC inverter...MINIMUM load?

Karl · Posted: Fri Mar 05, 2010 8:00 pm Post subject: AC inverter...MINIMUM load?

I have a Tripp Lite PV375 inverter that I want to use only to power a wireless router, a modem, and a network switch. Total power draw is probably only about 20 watts. The inverter is rated at 375 watts, with 600 watt surge. The inverter is obviously overkill, but I already owned it and it was not being used for anything.

Here's the problem: with all three devices plugged in, the measured voltage output of the inverter is only 99vac (with a battery reading 13.3vdc, deep-cycle, solar charged). None of the devices function, but just have very dim panel LEDs.

If I add extra load, such as a 100 watt light bulb, the inverter output jumps up to where it should be, about 114vac. It appears that the inverter is "expecting" a certain minimum current demand before it delivers standard voltage AC output.

I can't afford to "throw away" 100 watts by running an unnecessary extra load just to fool the inverter.

Do inverters typically need a minimum threshold wattage before they deliver their 115vac output, or, is this a defective unit? (The Tripp Lite knowledgebase was not helpful, BTW) If so, would getting an inverter rated for perhaps 50 watts solve the problem?

journey on · Posted: Fri Mar 05, 2010 8:15 pm Post subject:

First, Tripp is a well known mfg. Second that inverter is a sine wave inverter. Third, it's cheap and probably not the best 375 watt inverter in the world, since it's Tripp's cheapest.

There may be some voltage sag at low PWM pulse width. However, does it run your doo-hickies at that voltage? Remember, those devices convert the AC input down to DC voltages needed to run transistors, etc. So 99 VAC may work. Will it regulate with a 40 watt bulb? If not, try something else, or ask Tripp what's going on. Here's their web site: Tripp Inverter

Please note this is post 1111. Is that an evil sign?

Boris

Salty · Posted: Fri Mar 05, 2010 8:16 pm Post subject:

I probably only know enough to be dangerous on this subject but here are my thoughts - some inverters have an adjustable threshold to turn them on. If you can override the auto turn on feature that should solve this. There is also the issue of square and sine wave output and what you are measuring your voltage with. It is possible that your meter is not giving you an accurate voltage reading on anything coming out of your inverter. Some inverters cannot deliver the right waveform to run every type of load either. I'm sure someone smarter than me can chime in here and explain some of the reasons for these issues. I bought one of those cupholder inverters for about $39 and it runs my laptop just fine, I think it would run the peripherals you mentioned in your post too.

JamesTXSD · Posted: Fri Mar 05, 2010 8:36 pm Post subject:

journey on · Posted: Sat Mar 06, 2010 10:44 am Post subject:

Jim,

Good thought. Rolling Eyes

Boris

thataway · Posted: Sat Mar 06, 2010 10:13 pm Post subject:

I have owned one of these for some time. They are not a true sine wave inverter, but rather Pulse Width Modulation sine wave (or psuedo sine wave), slightly better than a stepped wave inverter. I suspect that the type of devices you are using is what is keeping the voltage from registering a full 115 volts. (they are rated +/- 8 volts).

I also suspect that putting on a full resistive load (the light bulb)--and possibly any light bulb-- is allowing the developement of the PMW sine wave and a higher apparent voltage rating. I probably would keep a small light bulb running, or get a smaller inverter. I try and match the inverter near 80% of anticipated load. This will be effecient.