Battery Size Required to Run a Blower?

Mass Solar · September 2008

This might be a little off topic - so I apologize on what board to post on.
Not being an engineer, I was looking to find some information on what size battery one would need to power a small blower fan on a wood insert? Unfortunately, the blower itself did not have any stampings on it as far as power draw, but its a fairly simple device of 2 small "cage" type fans that force air in on the bottom of the insert, and then circulates the warm air out of the top of the unit. I was looking at buying a battery backup device to run the fan for perhaps 24 hours when the power is out. Was looking at ones that can be used for computer systems, but got a bit confused on the "sinewave" do's and don'ts. Thanks.

mike95490 · September 2008

Re: Battery Size Required to Run a Blower?

I'll assume your "wood insert" is some sort of wood fired heater stove, that has rigged onto it, a blower, to force air thru some passages, to heat the air, and therefore the room ?

It doesn't matter if it's a heater or an air conditioner. The fan motor will still draw the same. 2 small squirrel cage fans will take quite a bit of power, I'd guess at 1/5HP on the shaft, and with losses, about 1/4Hp consumed. 1hp = 750W, so your motor may burn close to 200W.

In 24 hours, that's 4.8KWH.

for a motor, you WANT/NEED a pure sinewave. (Moringstar Suresine 300W)

Next step, get a power meter of some sort, and measure power draw of your fan. for 5KWH of storage, you should just wear a jacket. It's THAT expensive, unless it's a very attractive fan.

BB. · September 2008

Re: Battery Size Required to Run a Blower?

If it an AC motor--then get a Kill-A-Watt AC Power Monitor Meter.

For solar, and energy conservation in general--you need to know how much power you are using, how much you can save with conservation (smaller/more efficient/only on when you need it)--then after you have "conserved"--figure out how much energy (watt*hours or kWatt*Hours) you loads will need.

Pure or True Sine Wave vs Modified Sine (or Square) Wave inverters... The "Cheap" inverters are all MSQ--basically AC Square Waves... Works well for filament lamps--not so well in motors and some electronics.

Pure Sine inverter copy your utility power. Everything runs fine on them (although, you have to have a large enough inverter to start/run your loads). Much more expensive though...

To run a light, portable TV, electric drill off of your car battery--a MSW inverter is OK... If you want a permenant installation, running motors (fridge) and such--really recommended to buy a true sine wave inverter.

All About Inverters (FAQ)

-Bill

crewzer · September 2008

Re: Battery Size Required to Run a Blower?

The blower fan in my wood burning stove insert draws 60 W in the "low" position. Assuming 90% inverter efficiency, that's 1,600 Wh/day. Limiting discharge to ~50%, it would require a size 8D battery (12 V x ~250 Ah.)

HTH,
Jim / crewzer

Mass Solar · September 2008

Re: Battery Size Required to Run a Blower?

Thanks Jim. Was looking at purchasing one of these?

Any recommendations?

http://www.blackanddecker.com/productguide/product-details.aspx?productid=16896&toolview=4#details

mike95490 · September 2008

Re: Battery Size Required to Run a Blower?

Mass Solar wrote: »

Thanks Jim. Was looking at purchasing one of these?

Any recommendations?

http://www.blackanddecker.com/productguide/product-details.aspx?productid=16896&toolview=4#details

NOT that one, unless you are getting a great deal on a hundred of them:
Class 2 Power Unit Battery - 12V, 19 Amp hr, sealed lead-acid

8D is a big honking battery, about 2x the size of one on a full size pickup truck. You sometimes see them in an external battery tray on an 18 wheeler.

Or you could parallel two or 3, 'box store' deep cycle batteries.

Mass Solar · September 2008

Re: Battery Size Required to Run a Blower?

Thanks for the info...sorry I am such an idiot when it comes to these type things.
Most times the power is only out 2-3 hours or so, so I guess I was thinking that I would go big and get something for 24 hours...not realizing the cost.
Could you recommend a batter/inverter combo that might provide enough power for 2-3 hours? (I have contacted the mfg for the blower to determine the amps/watts of the fan motor)
Thanks!

BB. · September 2008

Re: Battery Size Required to Run a Blower?

Highly recommend getting the Kill-A-Watt meter I recommended earlier... Besides measuring the real power required by your fan--you can use the k-a-w for measuring usage all over your home (how much does that old fridge take, or that extra one in the garage for holding "drinks").

Also, for a point application, I would look at getting a used UPS (from an old computer center) with a large battery (or add an external battery).

But--in the end, this is probably not a good use of money (UPS for wood stove fan). UPS batteries typically last only a couple years, and you might be better off--if you justify a replacement stove--looking for a stove that does not need electrical power for efficient heating.

Yes, you can buy/build your own inverter+charge controller+battery system... But buy the time you get all of the components, wire it up, and such--it probably would not be worth the time/money for the occasional 2 hour failure vs just buying a used UPS (and, typically, a new set of batteries). And, lead acid storage batteries do not like to be discharged below 50%--so you have to either manual watch your system when the power goes down (and turn it off manually) or get/make some sort of battery monitor to turn off the inverter before the battery is fully drained (and ruined).

And, if you have longer power outages--the UPS (unless you get/make a big one), is still going to need a generator for backup.

If, however, you need more power than just for the stove (lights, fridge, radio, TV) and you have frequent and/or long outages--then a larger system + generator backup (natural gas or propane--depending on local fuels available) may make very good sense.

-Bill

Mass Solar · September 2008

Re: Battery Size Required to Run a Blower?

Hi Bill, Thanks for the input. I was holding off on getting a Kill O watt meter, as we already are very frugal on electric use, and we average about 300-350 KW hours on a monthly basis for a 1800 ft house with a family of 5. Newer applicances, all light bulbs are CFL's (wife dislikes

..but they save a lot of $$$'s)
points well taken on the battery thoughts.
Thanks,

BB. · September 2008

Re: Battery Size Required to Run a Blower?

Sounds like you have the conservation side down pretty good--especially for a cold location like Mass.

-Bill

westbranch · September 2008

Re: Battery Size Required to Run a Blower?

if you want to stay away from the battery during outages look at the Eco Fan, it uses a bimetal strip and ?? to run itself, there are 2 sizes. Made in CANADA
but also lots of US sellers...

They work great. If a in a large room go for the larger one, the small one works well in 2 -300 sq. ft. room

see here : http://www.caframo.com/ecofans.htm

HTH
Eric

BB. · September 2008

Re: Battery Size Required to Run a Blower?

There are also Stirling Fans for wood stoves... I have no idea if this is better or worst than the Thermal Pile fans of the previous post--or if the vendor in my link is any good or not.

Wood stoves tend to get very hot--and it is certainly possible that any of these fans can be "cooked" by overheated stoves (or blocked air flow).

-Bill

westbranch · September 2008

Re: Battery Size Required to Run a Blower?

You are right about the heat part Bill, the manufacturer has placed a bimetal strip on the bottom to 'lift' the unit slightly to keep its temp down. We use ours right over the firebox of our large wood cookstove. In the winter it can get the oven over 600 F so don't know just how hot the top gets? 4 winter seasons so far and still going strong...

Eric

Mass Solar · September 2008

Re: Battery Size Required to Run a Blower?

Thanks for the info West Branch. I was actually at looking at one of the fans, but I have a small insert vs a free standing stove. Any Idea how it would work on a small insert?

BB. · September 2008

Re: Battery Size Required to Run a Blower?

Generally, squirrel cage blowers (look like pet rat exercise wheels) work better against "back pressure" --- like that you would need when trying to "pump" air around a stove insert.

An open "fan" would not work very well at moving air against back pressure of ducting/stove if you tried to hook it up.

Also, your fan probably takes 40 to several hundred watts--I would guess that those stove top fans would only generate a few watts at best--so there is not near the same amount of energy available to move the air either.

-Bill

westbranch · September 2008

Re: Battery Size Required to Run a Blower?

I doubt that it would work on an insert unless there was at least 6 - 8 inches protruding into the room and then not that well.
They don't create a truly measurable air movement, just slow and gentle , that you do notice if you remove the fan, they seem to 'mix' the air more than a regular fan.

Eric

icarus · September 2008

Re: Battery Size Required to Run a Blower?

Both of the thermal electric fans work quite well. I have had a smaller one that has been in continuos service for at least five years. It doesn't stop turning from early October until sometime in April. I have a neighbor who has the larger one, and it too has been going 24/7 for 5 years or so. The really do move a lot of air (relatively) without any noise or fuss. You do have to be careful not to overheat them however.

I have seen the Sterling engine variety, but don't have any real knowlege of them, but it seems like it too would move a lot of air.

Tony

PS to add to Eric's note. The thermal electrics work best (sort of only) when they can draw cooler air. Thermal electric works with temperature differential, so they rely on cooler air. It is suggested that you put the fan on the back of a stove. Ergo: it won't work well on an insert very well.

Battery Size Required to Run a Blower?

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