AHS S130 Brushless blower motor

 
mac48370
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Post by mac48370 » Sun. Mar. 07, 2021 5:47 pm

Currently have the direct mount motor and for a second time over the years the motor bearing needs replacement so I want to build the belt drive to save the motor bearings and at the same time I wanted to convert the standard motor to a brushless servo motor with a amp to drive it the a equivalent one is almost half the size of the current ac motor and more efficient my question is with the servo I can get alot higher RPMs would the output of the boiler be more if I run it at say 5k vs 3.4k on the current motor?


 
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lsayre
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Post by lsayre » Sun. Mar. 07, 2021 7:09 pm

Whatever any relationship between fan speed and max BTUH output may potentially be, it is likely highly fallacious to presume a 1:1 relationship between fan speed and BTUH input/output. From what I can tell by looking at mine the pulleys on the motor and fan sides for the belt drive version are exactly the same in diameter, and the belt drive versions fan is rated at 1725 RPM, and AHS sells this "premium" version as a 130K BTU boiler just the same as they sell the "budget" one with a direct drive fan running at twice that speed as a 130K BTUH boiler.

Pressure drop is an exponential function, and the more you attempt to draw air through a bed of coal the harder this exponent bites you and drastically thwarts your hope for a 1:1 gain. That plus chimney draft plays a major part here, and it is not affected by fan speed. There are likely multiples of complex relationships fighting against the presumption of a 1:1 relationship. Heat transfer into the water through the boiler walls may be a big factor.

In the end the aforementioned heat transfer may prove to be a lot like the BTUH output for a hot water baseboard. For HWB's, the BTUH radiating from the HWB is hardly changed when the water flow through the radiator is quadrupled from 1 GPM to 4 GPM. The gain for this example may be on the real world order of about 10% as opposed to an intuitively presumed 400%.

 
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lsayre
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Post by lsayre » Mon. Mar. 08, 2021 6:54 am

Another way to look at this is that more conventionally designed stoking coal boilers efficiency ratings are only perhaps on the order of 5 to 10 percent below the "fan on" cycle efficiency rating/presumption of AA or AHS boilers with their massive diameter and high RPM fan induced "swirl" chambers driven by huge 1/3 to 1/2 HP motors. And the same goes for hand fed boilers, which can easily meet or even exceed the BTUH output of an AHS or AA without any swirl chamber or fan (albeit at even less efficiency than for a conventional stoker design). The chimney draft and firebox size plus exchange sq-ft are likely far and away more important overall than the fan diameter or fan RPM's.

In the end the only significant long term advantage and benefit of a huge and high RPM fan combined with a swirl chamber design is in its measure of greater "peak operating" efficiency, combined with a smaller firebox size and reduced heat exchange sq-ft size demand. The BTU's are in the coal. The boiler merely extracts them at some measure of efficiency. To presume a 100% gain in BTUH output from the doubling of fan speed (or a 50% reduction in BTUH output for halving the fan speed) is clearly wrong thinking.

Intuition makes for bad science.

 
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Post by Freddy » Mon. Mar. 08, 2021 8:32 am

"Heat transfer into the water through the boiler walls may be a big factor."

That's my knee jerk reaction also.

Along with: Axeman Anderson designed this boiler. They spent three years developing the original, and in the 77 years since then, neither Axeman Anderson nor AHS (who "borrowed" the design... legally I might add) has seen a need to redesign the air flow.

But... if you make a change...and it would be fun to do so... let us know how it works out!

 
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Post by lzaharis » Mon. Mar. 08, 2021 8:43 am

Please listen to Larry,

He is trying to help you, not hinder you and your coal burning.

You should purchase the factory supplied replacement motor, pulleys, V belt, V belt guard and motor bracket for your stoker as it is properly designed to operate correctly at the correct speed for the combustion of the pea sized coal and at the same time provide you with the proper fan speed.

 
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lsayre
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Post by lsayre » Mon. Mar. 08, 2021 9:16 am

I wouldn't personally want to stress my fan shafts two pillow block bearings at much more than 1,725 RPM. Let alone 5,000 RPM. YMMV

 
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Post by Rob R. » Mon. Mar. 08, 2021 10:02 am

mac48370 wrote:
Sun. Mar. 07, 2021 5:47 pm
Currently have the direct mount motor and for a second time over the years the motor bearing needs replacement so I want to build the belt drive to save the motor bearings and at the same time I wanted to convert the standard motor to a brushless servo motor with a amp to drive it the a equivalent one is almost half the size of the current ac motor and more efficient my question is with the servo I can get alot higher RPMs would the output of the boiler be more if I run it at say 5k vs 3.4k on the current motor?
Yes, the output would be more. How much more I am not sure. At some point you will have problems with clinkers. I would stick with the factory fan speed.


 
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Post by Scottscoaled » Mon. Mar. 08, 2021 5:14 pm

Sure, your output will increase. More air equals higher burning temps. But just like any other coal boiler, your stack temperatures rise and you end up dumping all the excess heat outside. Your efficiency goes way down.

 
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Post by StokerDon » Tue. Mar. 09, 2021 9:27 am

mac48370 wrote:
Sun. Mar. 07, 2021 5:47 pm
my question is with the servo I can get alot higher RPMs? would the output of the boiler be more if I run it at say 5k vs 3.4k on the current motor?
First we would have to unravel one of the great mysteries of the AHS S130. The fan.

What we know:
1) The direct drive S130 has a 3450 RPM motor. Therefore the fan spins at 3450 RPM.
2) The belt drive S130 has a 1725 RPM motor with a 3" drive pulley and a 3" driven pulley. Therefore the fan spins at 1725 RPM.

What we don't know is the fan design. I would think that they would use a different fan for these two different fan speeds. Otherwise the boiler would have two vastly different output BTU ratings. The fan speed is what determines the BTU output on one of these boilers.

In short, If you want to keep the boiler output the same, keep the fan RPM the same. Maybe call AHS and ask them if the 1725 RPM fan is different?

-Don

 
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Post by lsayre » Tue. Mar. 09, 2021 11:49 am

If flue gas temperature precisely doubles as fan speed also precisely doubles then one might be able to make a legitimate case for BTU output doubling. I'm more inclined to believe that the gain will be far more moderate and also potentially even non-linear with respect to fan RPM's (as per my hot water baseboard example which I tossed out as a potential corollary).

McGiever has had a 3-Phase variable speed fan motor on his AA for at least a few years (if not a gaggle of years) now, so likely he has the greatest level of hands on experience here.

 
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Post by StokerDon » Tue. Mar. 09, 2021 12:32 pm

Larry, I'm not saying that the BTU output would double, just the fan speed. The BTU output would increase but as the fan speed increases above the factory design, I suspect efficiency will decrease.

-Don

 
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Post by mac48370 » Mon. Mar. 15, 2021 12:39 pm

So I contacted AHS and they said more RPMs will get me more BTU and quicker reheat. The direct mount has an 8" impellor vs a 10" one on the indirect mount however the direct mount does run at double the speed and pushes more air according to AHS. My plan is to use a brushless servo motor with an amplifier I can control the RPMs all the way out to 5000. The equivalent brush less motor is much smaller vs a traditional brush and can be run faster with much less power. I'm sure at some point efficiently my drop off but at the time these were designed they were limited to the motor technology of the time 3400/1750 is a standard for all these older motors.

 
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Post by Rob R. » Mon. Mar. 15, 2021 12:54 pm

mac48370 wrote:
Mon. Mar. 15, 2021 12:39 pm
So I contacted AHS and they said more RPMs will get me more BTU and quicker reheat.
Do you think you need extra output?

 
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lsayre
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Post by lsayre » Mon. Mar. 15, 2021 12:57 pm

CFM 1/CFM 2 = RPM 1/RPM 2 x (D1/D2)^3
CFM 1/CFM 2 = 3450/1725 x (8/10)^3
CFM 1/CFM 2 = 2 x 0.512
CFM 1/CFM 2 = 1.024

2.4% more CFM at the cost of 3,450 vs. 1,725 RPM's and exposure to far more heat and a much shorter life expectancy.

Is it worth it?

 
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Post by StokerDon » Mon. Mar. 15, 2021 7:35 pm

mac48370 wrote:
Mon. Mar. 15, 2021 12:39 pm
The direct mount has an 8" impellor vs a 10" one on the indirect mount
Wow, thanks for clearing that up. I always wondered what was different about the fans.

Once you get this thing running I think you will find that it is better for a coal boiler to satisfy heat calls slowly rather than quickly.

-Don


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