Solar question : LUSENET : TimeBomb 2000 (Y2000) : One Thread

Here a Lizard Ranch we have enough solar stuff for light using 1 to 10 watt panels to charge batteries and lanterns. I would however like to join the rich mans club and have enough solar to run our electric wheat grinder in lieu of the hand crank grinder. If the electric grinder uses 1200 to 1500 watts how much of an inverter do I need. I assume that the grinder uses 1200-1500 watts per hour. Will a 100 watt inverter do thr job or do I need a 1500 watt grinder?

P.S. Can do code but am mechanically challenged.

-- Ed (, March 02, 1999


Hi Ed, If the grinder rating is 1200 to 1500 watts, then you're correct to assume that's per hour. BUT...that's also what the rating of the inverter would need to be as well. So, you've got to plan on 2 things here...first is to size the inverter large enough to do the job, but not so large as to break the bank....1500 watts should do the trick. A Portawattz 1750...$525. Second thing is to replace the battery power used from your storage battery during food grinding. On a 12 volt system, 1500 watts for a 1/4 hour period = 375 watt-hours. 375/12 = 31 amp hours. If you use a 64 watt solar module, with an average of 4 hours of sun per day, you'd get app. 256 watt-hours (21 amp hours)...or app. 10 minutes of grinder time. For more grinder time, add more modules. Or if you only need this much time every other day, then the single module will have time to "catch up" and should work fine with enough sun. Anyway...that's how it works. A Unisolar 64 watt module will set you back app. $350...a small charge controller around $39. Then add battery, stir and power! Good luck there at Lizard Ranch...let me know if I can answer other questions for ya! Roy Four Winds Renewable Energy Co.

-- Roy @ Four Winds (, March 02, 1999.

Are you sure that your grinder draws 1200-1500 watts, that's over 1 HP!

Let's do the math anyway. Motors typically draw 2-4 times as much power to start than they do to run. Inverters "usually" can handle 50-100% overrating for brief spurts. If you are trying to run a 1500 W motor (which is 12.5 Amps) it will pull somewhere between 3000-6000 watts at start up. This means that you'ld need to have a 1500-4000 watt inverter. Now please note the LRA (locked rotor amps) is the max the motor will pull if the motor is completely jambed (locked up). Therefore, your starting watttage will usually be much less than the LRA rating. Your basic formulas are P=IE (P=power=watts, I=Intensity=amps, E=Electromotive force=volts) and E=IR (R=Resistance=ohmage). Technically that's just for totally resistive loads, motors are inductive loads so you have to factor in a L.F. load factor or phasor angle. However for the ballpark stuff we're working with here, this will get you started. Contact the grinder and the inverter manufacturers for the details.

-- Ken Seger (, March 02, 1999.

Hi Ed. Another site to check out is homepower. It looks like You'll need Acrobat to get much info past the home page. <:)=


-- Sysman (, March 02, 1999.

You might consider a hybrid system. We use solar for our tv, radios, satellite dish, computer, scanner, printer, fax...and lighting. We have a modified sine wave inverter...OK if you are not too near neighbors. For the big the washing machine, the wheat grinder (its a Milpa and it needs a 1 horse motor on a shaft with a belt) etc...we use a gasoline generator. I know...where are we going to get the gas if TSHTF? He's working on it.

Sunelco is pretty good in their catalog for explanations of systems. They are really swamped with orders, though. Search the web for photovoltaics...there's other companies out there.

You can look on the backside of your grinder, should tell you watts or amps. Follow the math the other guys gave you.

Mary P.

-- mary p. (, March 02, 1999.

There may be another solution. Use a smaller electric motor on the grinder, and either a smaller pulley on the motor or a bigger pulley on the grinder to require less power and a smaller inverter. For example, double the diameter of the pulley on the grinder and it will run half as fast,require half the power and run twice as long at one half of the wattage required.

-- Tom (, March 02, 1999.

This is a nice site for do-it-your-selfers

Lotsa good stuff

-- CT (ct@no.yr), March 02, 1999.



-- Sysman (, March 02, 1999.

It seems to me that it'd be most efficient to get a DC power motor, and substitute it for the AC one. You lose less power due to inverter inefficiency, and you don't have to spend big bucks for a large inverter.

I'm doing a solar system that will power my well pump, LED lights, radios, etc, and I don't even have an inverter. Don't need one.

Running AC appliances on DC power can be a real pain in the rear if you have motors involved.

-- BIll (, March 03, 1999.

Moderation questions? read the FAQ