Alternative electric source for blower fans

So I used my insert for the first time last winter and it occurred to me that relying on the public utility for electricity was fine most of the time, but for power outages I was SOL. So I started looking at the possibilities for backup power, none of them very good. The blower fans for my Jotul 550 Rockland each use just under 90 watts. The small APC backup I have it attached to is good for only about 15 minutes. I had it left over from an aquarium I sold, so I re-purposed it.

Then I was reminded about thermoelectric generators. These seem perfect not just for backup power but for primary power for the blower fans, The down side seems to be cost. But when you compare it to the cost of a backup system, it seems the cost may not bee too bad. But if a wood stove manufacturer were to develop a regular product and include it with the stoves, the price would come down.

Provided the temperature difference between hot and cold sides of the generator are maintained, as the stove gets hotter, the generator just produces more power. So you get stove-powered electric blower fans. So long as you burn, you have power.

Of course, using more efficient fans that did not require 90 watts each would help. That power consumption surprised me when I calculated it. I would think Jotul would use more efficient fans, but I do not know all their design considerations and budget either.

I am not talking about powering my house from the stove, just the blower fans.

So are there any electrical engineers here that have looked at something like this?

are any manufacturers looking at this that we know of?

Thermoelectric generator WIKI

I've been thinking about it for awhile but can't seem to find a good solution to get over the cost. This is the only 'solution' I've seen: http://www.tegpower.com/products.html

why not get yourself some DC powered fans...can be run on just a few volts...some aa batteries even.

Yeah, I looked there. But those retail prices are high. I kind of figured if a stove maker, like Jotul, Harman, P.E., etc were to come out with some they would be in a better price range.

If I had any electrical engineering skills I would take a shot at it just for fun. But I do not want to mess up my stove, or do something stupid with electricity. Shocking, I know

Not for the main blower fans. I run them off an APC ES 750, which is considerably larger than AA batteries, and they drain that in about 15 minutes. Enough for a brief outage, which is what we get around here. The grid is pretty good.

But I am thinking more along the lines of completely unhooking from the wall socket and powering the fans with the stove heat alone. The products at tegpower look close to the mark, but not knowing how to properly size them, I would not know what to get or how to rig it up.

I was wondering why the fans were AC and not DC, but I guess that eliminates the need for an inverter to swap the AC you get from a wall socket to DC. It would be nice if there was a DC option for the blower fans, I suspect there are a few folks that would like to use power right off some off-grid home system, whether solar, hydro, wind, whatever. But just being able to keep the fans going during a mid-winter blackout would be a good thing.

I'm sure the stove makers could bring prices down a bit but they would still be starting with some very high numbers. Just look at the eco-fan. I suspect that has a single TEG with a small 'hobby' sized motor and runs ~$120. For what we want, you'd need 3 or 4 of the highest rated TEG units (http://www.customthermoelectric.com/powergen.html?gclid=CMXDzPHkgKcCFQYnbAodChKbfQ) then a more standard motor, switch, housing, etc. At these costs, I suspect the market for this is much smaller than the manufacture's would be interested in. I wonder if it could be made eligible for some subsidy?

I don't think you'd do any permanent damage to the stove and electrical danger is limited because we're not dealing with high currents here but, even a minor experiment would cost $300-$500 dollars.

Well, think about it as an option. You can choose the standard fans or TEG powered fans. If you do not care about power outages then standard fans are fine.

But if power outages are a problem for you, or you are off the grid and use expensive generator power, then this might be a good choice.

Compare to a backup supply: the es 750 I use costs about $70-80 and lasts about 15 minutes. a 1500 equivalent is about $225-$250 and would last about 30 minutes. Yet for $3-500 you might get permanent power. Sounds like a good deal in comparison.

So yeah, compared to regular fans they are pricey. Bu compared to a backup system they seem like a very good alternative,

Have you hooked up a kill a watt to the fan to measure the 90 watt usage? Also have you changed the batteries in your APC backup lately?

I went off the ratings on each motor. So far as the APC goes, no, it's a couple years old, so that 15 minutes of run time for the fans is based on a somewhat degraded battery. I usually wait until the things start issuing the warning beep and then use APC's battery exchange to buy a new battery and dispose of the old one. Doing that, these things last nearly forever.

FWIW a kill-a-watt thingy measured the single fan on my Regency I-2400 insert at more like half that 90 watt draw. More efficient fans would seem to be the low-hanging fruit to start finding an economical way to do it. I would love to unplug that wall cord and have a fire-powered woodstove! ;-)

My Jotul Rockland only pulls 75 watts with both fans running

I've used some deep cycle batteries through a 1500 watt Harbor freight 12VDC to 120VAC inverter to power my insert fans for 12+ hours at a time. I've also taken an old APC 2200 ups and removed the dead batteries and hooked up 4 external 12V deep cycle batteries in series to get the 48 volts the APC needed to run. Both setups have powered my insert fans, plus my TV and internet for hours at a time. I lived for 2.5 weeks like that last winter when my utility pole went down by taking batteries to work each day and charging them up.

What about something similar to a diesel motor turbo. the draft air turns a fan which then turns a fan that moves air through the insert. Seems that would be easier on a free standing unit and may cause some issue with the heat, moving parts, and unclean environment. I like the inverter idea. The other option that I have heard of folks using is hooking up a deep cycle battery in their vehicle then monitoring the remaining voltage using an inverter to power a tv, satellite, laptop, etc. and starting the vehicle periodically. That would seem to be the cheapest option in my mind.

A turbo in the stack wouldn't work, our stoves fdon't produce anywhere near the exhaust pressure and volume to spin one... and if we did it would act as a big restriction and make the stove run funny.

Computer UPS are never going to be an idea situation to run blowers because they are optimized to run computer loads not motor loads... and you loose a lot of efficiency in the interter. I think seriously run a blower on battery the best runtimes would be had if you could find a a DC blower.. ideally a high efficiency one (anyone know - do they make DC brushless motor blowers??). You would need a DC power supply to run it on line power when the power is on but That shouldn't be hard to find.

Ive said it in other threads but I would be cautious with any setup trying to run off your cars battery... First off you need to know its charging system will maintain a deep cycle properly... second a deep cycle usually wont put out the kind of cranking amps a starter battery does, could be an issue in cold... and third using the car to recharge uses much much much more gas vs. a small dedicated generator.

I don't think a UPS cares what it's running as long as the load is within it's power rating. Sure there will be some efficiency loss in the conversion but fans don't draw all that much power anyway. The UPS also has the nice feature of keeping output voltage steady and should shut down if the batteries get too low. You could get 12VDC fans if you wanted, a 7 inch Pro Comp radiator fan draws just under 5 amps and moves a lot of air, might be overkill. A 100 amp hour deep cycle battery would let you run it for 16 hours to 80% depth of discharge.

Hmmm, could be - Im not a double E. I do know that APC has a tech article on this subject and they specifically recommend against using inductive motor loads on their UPS's. I guess the main concern is that the stepped square wave output of their inexpensive models doesn't work well with an AC motor.

Might depend on the motor. Some "AC" motors are universal motors and can actually run on AC or DC. I've run an electric chainsaw from my APC: