Max From A Squirrel Cage Blower

The RPM maxes out when the the motor reaches it's max amp draw.

Remember that as the air is passing something warm it's "picking up heat". If you try and pass too much air you're not allowing enough time for the air to pick up the heat. Think of how you can run a lighter past your hand quickly and not get burned. Slow your hand down enough and you're feeling more heat until you actually are burning.

The RPM maxes out when the the motor reaches it's max amp draw.

The motor is still loafing along. it isn't even above ambient temperature yet.

Remember that as the air is passing something warm it's "picking up heat". If you try and pass too much air you're not allowing enough time for the air to pick up the heat.

I deal with Solar heat too, and youre thinking "Temperature" Temp and heat are two different things.

With a faster airflow, the temp may not be as high, but the BTU's pulled from the metal heat exchanger is greater because of the greater temp difference.

Seems to me you're not testing the right parameter here. You should be monitoring the duct output temperature as a function of blower amp draw/air flow, etc.

So, stick a thermometer in the pipe and start running different pulley combination till the hottest air comes out the stack, and the load doesn't over amp the motor.

Nice job on the box!

Lyn Said:

Seems to me you're not testing the right parameter here. You should be monitoring the duct output temperature as a function of blower amp draw/air flow, etc.

So, stick a thermometer in the pipe and start running different pulley combination till the hottest air comes out the stack, and the load doesn't over amp the motor.

Nice job on the box!

Tghe only trouble with that is unlike a LP fire or natural Gas one. the fire being wood the BTU input is constantly changing ya know? And this thing is a tank too. it doesn't look very big, and it isn't really roughly a 24" cube. But it weighs like 300 pounds. So temp changes are very slow. and the delay between the slow response and the varying amounts of heat from the wood. without changing anything blower wise the heated air can vary anywhere from 100 to well over 200 even, so that would be very hard to do.

And Thanks for the comment of the nice fix up.

Joe

GA

For the same reason I program the blower on my pellets oven to a higher air speed.

I get similar heat output with a lower exhaust temperature and less pellets.

try a little restriction on the inlet. You may have some turbulence there.

Will Try That

Why do you choose to increase the pulley size, if you already found a designed sizes in your LPG furnace. as I Understand that must be the optimum value.

A blower do not offer constant load with all speed, you can google fan laws to find the impact of speed on the load-line of a blower. But surly increasing pulley size is not going to give an increased speed always. In fact you may find it lower than of previous values. and motor may operate in the unstable range of torque speed curve,

Blower load line should always intersect the torque speed curve in stable speed zone.

It's obviously spinning faster you can both visually and hear that it's faster, and the huge difference in airflow as well.

The motor should contain an electrical info plate, on it find FLA or RLA rating, your amp draw should be around 3/4 of this rating, (probably around 2 amps@240v)...The amp draw should be tested with cabinet sealed....The air turbulence you are hearing(buffeting) is due to supply side duct design, lack of smooth aerodynamic quality..This can be eliminated by slowing air flow or redesigning supply air duct/plenum....The motor should be rated continuous duty and have overload protection...If your motor is overloaded it will overheat and ruin bearings...Rule of thumb, you should be able to hold your hand on the motor at operating temperature....

There is no intake ductwork just the opening to the blower it looks similar to this.

maybe add a tube to it so it is like a old hot rod carb intake?

I was referring to the discharge side, where the air exits the blower...sorry for the miscommunication...Usually there is what's called a plenum attached to the discharge which then connects to the duct distribution....What is your discharge configuration?

I have to take exception to, "Rule of thumb, you should be able to hold your hand on the motor at operating temperature".

This may be the case with this particular blower motor, but many very efficient motors run at temperatures much too hot to touch. Motor manufacturers claim it's better to get the heat to the outside of the motor than to keep it inside, and I agree.

I know, picky, picky, picky.

At anyrate I havent checked the current draw. but temp wise the motor itself is barely if any at all above ambient temp. It to the touch feels cool. and the air exiting from it is also this way so the motor itself is running quite cool.

I was referring to this application....and stand by my thumb....What particular application were you referring to? And IC motors don't count...

I've used a lot of Baldor pump motors 3-10HP TEFC at many different voltages and they are always too hot to touch.

This is from their manual:

"WARNING:

Surface temperatures of motor enclosures may reach temperatures which can cause discomfort or injury to personnel accidentally coming into contact with hot surfaces.

When installing, protection should be provided by the user to protect against accidental contact with hot surfaces.

Failure to observe this precaution could result in bodily injury."

Yes case and point...As a long time resident of the land of sprinkler systems and pools I am quite familiar with water pump operating temperatures, they do operate at a temperature that will burn the hand and it is normal operating temperature for them....I guess I was fixated on fractional hp air movers...oh well, I guess that's what happens when you get old...what was the question again?

You know...almost everything has it's limitations. I suspect that the rate at which the blower is operating has exceeded it's capability. In other words it can't suck any more air in or can't discharge it at the speed you are now running it. Plus, you are running the risk of over heating the bearings. If you want the thing to keep working, providing you with nice warm air flow, I would keep the speed more reasonable, and be satisfied.

How long is the air flow path (both inlet and outlet counts) and how mechanically rigid and balanced is the blade-pulley assembly on it's axis? Does it mechanically vibrate also? S.M.

Inlet is nothing as seen in the above image. it is open on both sides like that image also,

outlet it goes directly under the Stove. as seen in this image before i cleaned the beast up. Some of you may have remembered about be looking for rust advice. before and after shot here.

The air passes through a wrap around jacket. It's like a stove inside of a metal box. the air goes in the bottom and passes all around between the two boxes and out the top a 7" diameter ductwork.

I'm running it right now without the decorative brick trim.

Can't help you out on the blower but that is a sweet looking restoration

The fact that you are pushing air instead of pulling it, is the cause of the air turbulence...You'll have to reduce the air flow...

Solar Eagle gets a GA for the above statement. You have already exceeded the fan's capabilities. Back off until the turbulence (puffing) goes away, and you are probably at the max the fan will put out, given the discharge "obstruction". You probably will be (and maybe were?) moving more air after you back off than you are now - it just feels stronger when the air does come. However if you go 60 mph 50% of the time, and 20 mph 50% of the time you are going slower than if you set the cruise at 45 or 50 mph. The same principle works here - the turbulence will slow you way down. If you want to push the air further or mix it better in the room, get another additional fan...

That being said, you could try the intake pipe suggested earlier - but don't spend a lot of money. I am not well versed in the squirrel cage fans, but have dealt with more than my share of industrial cent. fans. Anything is worth a try, but I suspect that you will not be happy with the intake for a couple reasons: (1) I have never seen one on a squirrel cage, and suspect that it won't pull enough suction to work properly (this type of fan is likely a low suction pressure fan), (2) it could very well be noisy, (3) it will stick out the side of your "stove" an make it look ridiculous. On the other hand, if the intake pipe "fixes" the turbulence, you might be able to push a little more air (at the cost of noise).

Furthermore, I suspect with this set-up you are already maxing out (or nearly so) your heat transfer. If you have a constant air flow, you will not move appreciably more heat by increasing air flow by a couple mph. If this is simply not enough to keep the shop warm, you need another wood stove...

Finally, I would suggest you keep the brick decorative pieces for the summer time. They will drastically reduce the availability of air to the intake when in place. Back to the low suction pressure fan, if you can't get a lot of static pressure from the fan design, then you won't get a lot of air to push.

As for the discussion on overworking the motor, you guys are all thinking about most applications for most motors. A fan is different and actually in the inverse to logical thought. If a fan does not have the ability to push (or pull) air, it does not work as hard as if you give it the air to move. If the fan is turning "too fast" to actually move the air it is given, it will actually pull less amps than it will if the damper is open and the ducts are non-restrictive. Maybe a squirrel fan is different (though I doubt it), but a cent. fan is that way. If you want more air or more push than the restrictions allow, you need a different rotor design or a redesign of the system. There are some funky things that happen related to turbulence (which MAY be going on here), but by-and-large the motor works hardest when you give it the designed amount of air and the proper amount of restriction (or lack thereof) in the duct system. Read a fan curve and this makes sense, put an amp meter on a fan motor and open/close the damper and you will see it in action.

Often, fan manufacturers will publish the max RPM on the catalog info for the fan. Since your unit is salvage, I doubt you could find this info. I would SWAG that the max RPM is in the 1500 to 2000 RPM range. (Scientific Wild Arse Guess)

The fact that the air flow is buffeting, you are operating in the "stall" reagion of the fan curve. The fan wheel is in an area of unstable operation and cannot move any more air. Even though the motor is not overloaded, the fan wheel is overloaded. You will need to slow down the wheel speed for stable operation.

At the low airflow and pressure you are working with, this instability is not dangerous, but it is not an efficient operating point. The buffeting air flow will induce vibrations into the fan structure and bearings causing shorter bearing life.

You may not have reached the limitation of the blower.

That puffing is a resonance and you you can either slow down out of the resonance, speed up through the resonance or dampen the resonance.

Have you tried going even faster yet?

You can dampen by tuning out the resonance with an empirically determined length of duct at the inlet or outlet or by introducing some partial feedback from the hi pressure (outlet) to the lower pressure (inlet) side.

Try faster first.

You will know when you've reached the blower's speed limitation when airflow starts to slow (or fails to increase) with increased blower speed.

You will also know it is too fast if the blower flings apart.