Buying an Inverter
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wsar10
Burning Hunk
Definitely need a pure sine inverter (preferably a digital pure sine inverter). I have seen numbers on here of 700W @ startup (personally I would double or triple this for other possible uses or transient events). To figure out the battery to power the inverter (for just the pellet stove) you have to figure out DC Amp Hours based on your AC Wattage.....
lets say you want 10 hours of run time, (using Ohm's law)
700wAC / 12vDC= 58.33 DC Amp per Hour (we will call it 59Ah)
if you want it to run 10 hours than 59Ah X 10hrs= 590 DC Amps
than read the specs on your inverter to find out its power consumption (efficiency rating)
worst case scenario say 10%
590 X 0.10=59,
590 + 59= 649 DC Amps
that puts you into a 650 Amp battery.
These are just numbers based on the STARTUP power consumption, and are general figures just to show the process.
Also have to pay attention to cable size and length, Fuse size etc. etc when actually assembling this all.
lets say you want 10 hours of run time, (using Ohm's law)
700wAC / 12vDC= 58.33 DC Amp per Hour (we will call it 59Ah)
if you want it to run 10 hours than 59Ah X 10hrs= 590 DC Amps
than read the specs on your inverter to find out its power consumption (efficiency rating)
worst case scenario say 10%
590 X 0.10=59,
590 + 59= 649 DC Amps
that puts you into a 650 Amp battery.
These are just numbers based on the STARTUP power consumption, and are general figures just to show the process.
Also have to pay attention to cable size and length, Fuse size etc. etc when actually assembling this all.
ESPECIALLY pay attention to the wire size from the batteries to the inverter! The bigger the better. I see many people complaining that their inverters keep tripping or won't work and then come to find out that they have 12 gauge wire running to it or alligator clips at the ends! The voltage drop will trip the inverters every time.
Also, if you really did need 650 Ah battery, you would really want TWO in parallel since you don't want to drag the battery all the way down to parade rest. For the life of the battery, you shouldn't drop below 50% even for 'deep cycle' batteries.
Another thing to look for that better rates batteries is the term 'Ah capacity', which is how many minutes the battery can discharge at 20 amps. A similar rating system gives you the minutes it will last at 25 amps. It helps compare batteries. Golf cart batteries are your best bet even though they are 6 volt and you have to hook two in series for your 12 volts.
Woody1911a1
Feeling the Heat
My stoves use max 193 watts WITHOUT the ignitor. In an emergency where you need the inverter, I would disconnect the igniter and start the fire manually with hand sanitizer and a torch. Then run it continuously just adjusting heat levels as needed. Even doubling or tripling the required wattage means a 500 or 600 watt pure sine wave inverter. You're in the $150 - $200 range. Then you need the batteries, a disconnect, a LARGE fuse around 75 amps or so, heavy wire around 4 gauge and suitable sturdy connectors, AND some forethought on how to wire it all safely.
Mr Spock said :
<
Some electronics boards will malfunction using modified sine and motors typical draw more amperage making them hotter and working harder
>
I would like him ( or anybody else ) to say a bit more !
The electronic board is working on DC - the supply will be rectified so it can be sin or pseudo sin - I can't see how it can tell the difference.
However the triacs controlling the motors are another matter !
On paper I can't see why they should be unhappy with pseudo sin but I would like to know more.
My problem is more with 5 minute outages and an invertor could solve that problem without a big battery.
<
Some electronics boards will malfunction using modified sine and motors typical draw more amperage making them hotter and working harder
>
I would like him ( or anybody else ) to say a bit more !
The electronic board is working on DC - the supply will be rectified so it can be sin or pseudo sin - I can't see how it can tell the difference.
However the triacs controlling the motors are another matter !
On paper I can't see why they should be unhappy with pseudo sin but I would like to know more.
My problem is more with 5 minute outages and an invertor could solve that problem without a big battery.
I have a Xantrex PROwatt SW600 pure sine wave..
http://www.donrowe.com/Xantrex-806-1206-PROwatt-SW-600-p/806-1206.htm
http://www.donrowe.com/Xantrex-806-1206-PROwatt-SW-600-p/806-1206.htm
I was going to put on of these in my camper.
(broken link removed to http://invertersupply.com/index.php?main_page=product_info&products_id=427&cPath=13&gclid=CIWon96Pl7kCFZCe4Aodym8A3g)
(broken link removed to http://invertersupply.com/index.php?main_page=product_info&products_id=427&cPath=13&gclid=CIWon96Pl7kCFZCe4Aodym8A3g)
Many DC power supplies need a "clean" smooth sine wave input to provide a good DC output. "Noisy" inputs can cause momentary voltage drops or voltage spikes, either of which could cause the DC control board to reset or shut down.
wsar10
Burning Hunk
I am new to pellet stove's but definitely nor electronics........ So based on my understanding of similar products I would say,
No, there is an AC side of that board and a DC. your motors are controlled by a DC (coil side) AC (switch side) relay. Your motors are AC powered but DC controlled.
I have a hard time explaining something like this with out my "dry erase" board in front of me so that I can illustrate......BUT,
draw a sine wave on a piece of paper (large) than take lego blocks and try to mimic the shape.........done yet ! point is YOU CANT.
that being said, a square wave (bit) is on or off or at a SPECIFIC voltage level (I/O or low/hi) this is how ALL digital electronics work....ANALOG sine waves have curves rather than fixed levels. Therefore while your digital signal is stuck at a specific voltage until it STEPS upto the next voltage (top of the next lego block) your inductive load is falling short on voltage, whereas a sine wave steadily increases rather than abruptly steps (hence "it has curves" instead of straight lines). this is OK if you have a resistive load but not if you have an inductive load.
I'm not sure about specific specs on modified wave inverters, but if your insistent on one than it would have to be a ridiculous number bits (steps) per wave (or whatever the logic is called in this application), maybe 64 bits per wave would work for a motor this small ?????? I would just pony up the money for the correct equipment and then you have it for other uses (refrigerator etc.etc.)
hope this helps some..........
wsar10
Burning Hunk
this is generally correct, ALL mains voltage is unstable and noisy............
but this why we build filtering circuits and voltage regulators. A power supply is going to have transformer, a bridge rectifying diode setup, smoothing and filtering caps than voltage regulation (generically).
transformer AC > bridge rectifier (to rectify + and - voltage, you now have DC) > smoothing cap (to get rid of bulk of the noise, transients between wave peeks)> filtering caps (fine tune any left over noise) > voltage regulation.
And that transformer depends on its input (normally mains power) being a sine wave. When fed from a square-wave inverter, the voltage "corners" will cause very large current spikes in a transformer. It can be beyond the capability of the filters in common inexpensive power supplies.
It comes down to the amount of filtering in the stove's DC power supply versus the amount of distortion (% THD) in the inverter's output voltage.
One assumption you made is incorrect, at least for Quadrafires. The motors are not controlled by DC coils pulling in the AC side of a relay. They are controlled by Variacs, which are turned on and off by the DC logic. So you are really pulsing the motors at the slower speeds. Still, you and others are correct IMHO about the ill effects of feeding modified sine waves to the control box, although twice I've run my stoves on the old generator in a pinch. KNOCK ON WOOD. Now I have a Xantrex 2000 watt PSW inverter for when AHBL DAY comes.
wsar10
Burning Hunk
Non sine inverters simulate a sine wave using square waves. As others have mentioned common consumer grade solid state electronic devices have an AC to DC converter (power supply) that rectifies and filters the power. However they are engineered with the power grid in mind. A 60hz sine wave usually not exceeding 5% harmonic distortion. Modifed sine inverters generate much higher harmonic distortions because they generate a stepped sine waveform. These harmonics can get through the power supply circuits and interfere with operation. Microprocessor devices are the most susceptible. Modifed sine are best for restive type loads such heating elements and incadesant lighting. AC motors can loose up to 20% effecieny due to the lower RMS voltage and therefore must draw more amperage to maintain tourqe.
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A big <Thank you > to Mr Spock and others.
This was a problem that had worried me for a while now and it is good to understand at last why ( and where ) you need to be careful.
My future 'rule of thumb' will be
< if its not a power switching input ( as with all computers ) use pure sine >
One last worry..
Is it possible to have a pure sine inverter which cannot support an inductive load ?
When running , a pellet stove is surely just that ?
This was a problem that had worried me for a while now and it is good to understand at last why ( and where ) you need to be careful.
My future 'rule of thumb' will be
< if its not a power switching input ( as with all computers ) use pure sine >
One last worry..
Is it possible to have a pure sine inverter which cannot support an inductive load ?
When running , a pellet stove is surely just that ?
You and me both, haven't seen a Variac since some microwave repeating station (HvH) build in the late 50's!Showed my age on that one
ha ha ha. Let's try TRIAC...............
ha ha ha. I think I actually still have one up in the attic along with a big isolation transformer!
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