Inverters - true or modified sine wave?

Re: Inverters - true or modified sine wave?

In general, induction motors draw an extra 20% power, and run hotter. If only run for short time, before they get hot, probably not a big problem except for the extra power consumption. Longer running motors, such as fridge / freezer compressors will have a greatly shortened life. The windings tend to vibrate excessively as well in motors, with the possibility of wearing through their thin insulation.
One other problem is with "capacitor run" motors, which are in better quality items from breadmakers to fans and high efficiency fridge/ freezers etc. On normal pure sinewave power, the capacitors modify and control the currents through certain of the motor windings. However, when run on MSW, the nature of capacitors cause them to "pass" excessive currents, because of the sharp edges and spikes in the MSW supply. This results in excessive buzzing, poor performance and overheating. It is this same characteristic of capacitors that results in the burning out of some electronic items, ranging from breadmakers to some chargers and many other items. The excessive currents "passed" by the capacitors in some power supply designs, (when operated on MSW) result in overheating that burns out components on the circuit boards. In these cases, you MAY detect a hot or burning smell before the item fails, but most times, the smell comes after the fact. How do you know if your item will survive on MSW? Trial and error. Throw the dice and take your chances.
In general, CFL lights work fine on MSW, as do most items with "universal, brush type" motors, such as skillsaws, electric drills, angle grinders and hedge trimmers, as these motors traditionally will operate on anything you feed them, AC, DC, or pulsed. The exceptions may be those with electronic controls, although the variable speed controls on drills and jigsaws tend to work fine.
In general, you will find that battery chargers for cordless items, if they don't burn out, will not properly charge the battery. Probably because of the substantially lower peak voltage from MSW inverters. Yes, the "average" voltage is close to that of pure sine, but the "peak" voltage is much lower.
Microwaves tend to hum loudly, basically sound sick, and have much lower heating power. Again, the electronics in the clock / timer / controls, depending on the design of their power supply may burn out in short order. Roll the dice to find out.
This post isn't BS. I've been there, done that and experienced it all.
Hope this helps.
Wayne

Re: Inverters - true or modified sine wave?

mike90045 wrote: »

For life in your trailer, I'd strongly suggest the Morningstar SureSine, 300watt cont, 600w 5 min surge, High efficiency. Very new design, no bad reports about it.
http://www.morningstarcorp.com/products/SureSine/index.shtml
$300 and a 2 year warranty to boot!

That is a nice little inverter. I like that it manages to do without a cooling fan.

But - I do want an inverter with an integrated transfer switch to pass through AC when I am connected to shore power. I do not want to deal with the complexity of only having certain inverter-powered outlets.

Any recommendations or opinions on something like the PureSine 2.0 or the inverter / chargers from Magnum?

- Chris // www.technomadia.com

Re: Inverters - true or modified sine wave?

I love my 2 Puresine 300's. Very impressed with them.
As to switching to shore power, a simple relay, with it's coil powered from the line from shore, could easily be wired to automatically switch the loads from inverter to shore, whenever shore power presents itself to the relay coil.
When the shore power vanishes for any reason, the relay snaps the loads back to inverter.
Re microwave, if you intend to run that, you will meed a big (at the very least 1500 watt) pure sine inverter. Consider the value of running the microwave vs the extra costs for inverter, as well as the much larger idle current of that larger inverter, if you decide to use it to power small loads. Or have 2 inverters. A small one on 24/7 for lights etc and the big one only on to run the micro.
Wayne