AC to DC conversion

[Kyle Vanderbeek]

I am a knuckle head when it comes to solar power. Know just enough about it to get myself into trouble. So I hope that somebody can help me. I have a corn burning stove that uses 5 amps of 120 volt AC power. I would like to run this stove off of a battery and an inverter. Do I need to have enough solar panels to generate 600 watts (5amps x 120volts) in order to keep up with this stove, or are DC watts different than AC watts?

[ghurd]

Watts are watts.

Except solar 'rated watts' and 'output watts' are not the same, it'll take about 900W rated of solar to get the 600W for the motor, and the 900W only happens for a few minutes a day.

How long or often does the motor run?  What does it do?

Seems like a LOT of power 24/7.

Depending on where you live, and if it is 24/7... solar powering that could break 6 figures US$.  I hope it only runs a few minutes per hour!

G-

[scottsAI]

Hello Kyle,

As ghurd says watts are watts,

But V*A = watts on the label are not the watts the unit uses while running normally.

The motor in the corn stove needs enough power to get through the kernel that binds the screw feeder. So it will have spec like 5 amps at 120vac, actual should be much less.

You need to measure the actual power the thing uses.

May I recommend a Kill-O-Watt meter, cost around $30. sometimes less.

KOW will measure the real watts used. This will become what you need to make.

Can measure KwHr just like your power meter. The real story.

I have only seen one corn stove, it had a screw feeder with a timer, would turn so many times in one minute or something like that. Spent most of the time off.

Then we have what are peak watts, like the starting current of a motor.

Average power...what the motor needs to run normally loaded in normal use.

The inverter must be sized to supply the peak watts. Peak is the max of all things that may be started at the same time. By using staggered starting, the peak watts can be much lower.

Solar panels work best when coupled to a battery. The battery can supply the peak current where as the panels supply the overall average power produced.

A 100w solar panel will be rated at 17v at 5.88amps. When the solar panel is connected to a battery the voltage will be the battery voltage times the panels current. This is how to calculate the power going into the battery. To finish the power into battery you need to find the full solar hours per day of your location. It's an average number but can help you determine what to expect. I live in MI, solar hours here are 4.5hr per day. So the actual power into the battery each day will be 13v * 5.88 = 76.5 watts times 4.5 = 343watts. Summer the power in will be more, winter less.

After you read more about this it will make since.

Have fun,

Scott.

[Devo]

This is a topic I have been researching a bit my self but the info is not out there. Funny how the people selling these corn stoves don't know how many amps they draw.

I want to buy one this year but I want to be sure I can sustain the electric part with my wind genny.

I would be interested to know the make of corn stove you have & the finally wattage for a day if you get a killa watt meter.(they are a good investment)

Devin

[drdongle]

You might contact the stove's maker and ask about a DC power option, if you can replace the motor and any electronics ( or modify) with a 12V DC unit that would be the best way to go. Simpler and more efficient. If no such change or mod is available then you might want to investigate making the changes yourself...with our help of course.

[nanotech]

I would have to say that the 5A figure is a little on the high side.  All the indoor cornstoves I've looked at have been in the milliamp range.  Like the St. Croix ones use a walwart and are actually run on 12VDC @ 500mA max.

So I would say yours stating the 5A is a manufacturer's high estimation.

[zap]

Here is the exact wording from the St. Croix "Lancaster" manual: "1. The Lancaster is provided with a grounded electrical power cord that can extend from the rear

of side. This should be connected to a volt AC electrical outlet. The current

requirement is approximately 3 amps. (5 amps with igniter running)"

A Bixby stove's requirements:

Electrical:

120 volt AC (all loads shown are combined)

-Normal Operating Mode: 1.6 Amps

-Ash Dump: 4.6 Amps

-Ignition Mode: 8 Amps

A Magnum "Baby Countryside" and other Magnums can be run on DC but the igniter will not function running on DC. Probably because of the high amperage required for the igniter IMHO... A comment from American Energy Systems,  http://www.hearthdirect.com/downloads/public/Ignitor.pdf

Finally, a 5 page discussion at http://iburncorn.com/ about battery backup in the old fourm http://iburncorn.com/forum/viewmessages.cfm?Forum=9&Topic=873&srow=1&erow=10

[altosack]

Hi Scott,

You have a good explanation that I think will be quite useful to the original poster, so please don't take offense when I nitpick a little.

Power * time = energy:

76.5 watts (power) * 4.5 hours (time) = 343 watt-hours, which is energy, not power.

In general, power in the summer will be less, since the panels will be hotter and voltage will go down (although it probably won't matter unless you are using an MPPT charge controller), but the energy (power * time) stored will be more since the number of sun hours are greater.

Kind Regards,

Dave

[Ungrounded Lightning Rod]

I note that there is at least one pellet(/corn?) stove that not only runs on 12V but has a peltier thermopile in the exhaust that provides run power and keeps its own battery charged to provide startup power.  (I think it's manual start so it just needs to run the fans until it's up to temperature.)  I believe the thermopile is available as an add-on for at least some of their models.

Which doesn't help you, unless you lucked out and got one of their adaptable models, since you already have your stove.  (I've heard there MAY be a  thermopile designed to be hooked into essentially any stove's chimbney piping but haven't seen it...)

(Seems to me adding a thermopile to the stove and hooking it to charge your house batteries would do much the right thing:  When the stove is running it would average more than enough power to make up for its load.)

= = = = =

Given that the high current is mostly for the igniter you might want to consult your manual and see if the stove can be run with the igniter disabled and manually lit.  (Or if it can run with a defective igniter - in which case you could just disconnect it.)  Then you could run it on a lower power alternator and reduce your idling losses.

You might also want to consider a hack like this:

 - Attach a small inverter - enough to power the logic plus the fans and auger in run mode.

 - Disconnect the igniter from the controller.

 - Substitute a 110V relay to turn on 12V to a larger inverter to power the igniter.

 - Hook the second inverter output to the igniter.

I'm presuming that the stove runs most of the time, and you're around to turn it on when necessary, so doing the same thing with yet another inverter for the motors (and perhaps hacking the power supply for the electrinics so it doesn't NEED an inverter) wouldn't make sense.  Of course if it runs only occasionally, DC powering its brains and having separate inverters for the fan/auger and the igniter which only run as needed would save a lot of power.

(My own out-in-the-boonies house uses a propane stove with a miliwatt valve and mechanical stat, so it will light and convection-circulate to keep the house from freezing and the living area comfy in the event of a power failure taking out its fan and the main furnace, or a battery failure taking down the main furnace's stat.)

[scottsAI]

:-)

Yep, you have it right altosack.

I left the hr off the 4.5, and then left it off the result! 343 watt-Hr.

Thanks!

Have fun,

Scott.

[TAH]

I have a St. Croix stove and it would average around 400 watts all the while it was running. Besides that they are really not safe even on grid power since any momentary power outage even a fraction of a second will cause the stove to go into a restart mode which shuts off the exhaust fan, the hot air fan and dump in a pile of fresh pellets. This has the result of filling your house with a huge amount of smoke and making the stove overheat and trip it's thermal switch causing more fun. After many calls to them they admitted that this is the way it is designed and didn't see a problem. They recommended a UPS "big enough to keep the stove running until you can turn it off when the power fails." When I pointed out that this UPS would need to be pretty large to supply 400 watts through the night they said "the stove should never be run unattended".

I reworked a few things in the stove and have the wattage down to about 75 after it lights but even so I would be afraid to trust the thing for regular heat. They also pull a huge amount of inside air to eliminate smoking. The outside air vent is a small tube and the stove won't run very right unless it's damper is closed 95% of the way. (per st.crook tech). The combustion air comes almost entirely from the house. I would have gone with an outdoor corn boiler if I had known more about the pellet stoves to begin with. Every sales guy that I had talked to before I bought the stove claimed that they were 75 watts or less and many stoves do not even list the max AMPs.

 

[jmk]

 I wanted to run my outdoor wood boiler and inside zoning pump. The wood boiler has a Teco water pump that is 1.7 amps ( 210 watts ), and the zoning pump is 60 watts. The wood boilers pump runs non stop 24/7. The zone runs about 1/3 of the time. My wind turbine isn't keeping up. It might once all the leaves come off the trees. What I did is put my sub panel over by the grid panel and wired outlets for the inverter, and outlets that hook to the grid breakers where the wires from the furnaces hooked up. I pulled the wires out of the grid panel that go to the furnaces and put plugs on the ends of them. When they are plugged into the grid and power fails I can plug them into the inverter outlet and it will run for 2.5 hours until I get to 80% of battery power. That's with no wind coming in, so with wind it will last longer. If it's windy I will just plug them into the inverted power to use the power up. If I am home and watching. When the leaves come of the trees it should be close enough to keep it plugged in to the inverted power and also run the charger on the SW 24/40. It will pick up the difference in the load, and keep a charge cycle on the batteries. I love my wood stove. It heats the hot water, and the house for free. I don't even have to cut wood and haul it anymore. The tree services are happy to have a place to dump wood off. Yippie!  The stove cost $8,000 and will have paid for itself half of the way through this season ( 2/ 1/2 years ). I just want to think of it as if it will pay for the turbines system by the end of next year. Then I will just consider them assets!  I think they need to make a corn or wood boiler that makes electricity.