modified sine vs pure sine...

[johnnyb]

Have my GW100 ready to go but am still trying to figure out this back up power. Searched past posts and all I think I am reading about is inverters for pellet stoves using pure sine wave inverters. Will taco 007's and honeywell zone valves work with modified sine units. What do you guys use? I am confused, just got off nightshift and wife wants green monster running! went to outfit that deals with inverters that sells both modified and pure and didn't understand a word he said. Looking at an AIMSCORP UNIT; PWRIC1500W, it is a modified sine unit, any one use one or know anything about them?

how long would a 1500 watt unit run per amp draw, and for how long? is there a formula to determine this?


any info would be great

jb

 

[jebatty]

I use a modified sine on my Tarm without issue. Pure sine wave inverters are very expensive, and a modified sine wave should be fine. A relatively easy approximation of how much battery power you use is this:

Watts used by system at 120 volts: assume 400 watts. Amps = watts / volts = 3.33 amps at 120 volts.

Divide house voltage by battery supply volts to inverter (assume 12): 120 / 12 = 10. Amps drawn from 12 volt battery = 3.33 x 10 = 33.3 amps. If you have a 24 volt inverter, amps will be 1/2; if a 36 volt inverter, amps will be 1/3, etc.

Amp hour capacity of deep cycle (not starting) battery (assume 100 ah). Amp hour capacity divided by amps needed gives you maximum time of output: 100 ah capacity / 33.3 = 3 hours. BUT, divide this by 2 to give actual maximum, as deep cycle batteries should not be drawn down to less than 50% of capacity, and if regularly used and ideally, you do not want to drawn them down more than 70-80% of capacity for longest life.

So, based on assumptions, you have 3 / 2 = 1.5 hours of run time on a 12 volt battery, with 400 watts system draw at 120 volts.

This is an approximation, as watts is not an accurate figure to use in most systems, as there is power factor loss (volt-amps is the accurate figure to use). To get a better approximation, assume a 0.7 power factor. Then the 1.5 hours of estimated run time is reduced to 1.5 x 0.7 = 1.05 hours.

If you put in an inverter backup system, charge the batteries fully, and test the system to make sure it works satisfactorily and how long before the inverter cuts out due to low battery voltage. That will be your maximum run time. Plan on 1/2 of this as the practical maximum. It is possible that as battery voltage drops, output voltage also will drop, and your circ pumps will suffer brown out which may affect their operation or damage them. If you have a more than simple control system, brown out also may affect your controls.

Rather than going with a simple battery inverter backup, you might want to consider a computer-type UPS system, which I believe has better voltage regulation. You may need quite a high capacity system if you are looking for several hours of operation, and this can get expensive.

Alternative: get a small generator to provide backup power for extended periods. Likely to be less expensive by a considerable amount. High capacity deep cycle batteries can get expensive. And you may have other uses for a generator, plus you probably can run some lights, keep the refrig running, etc.