Leemade DC issues

[hermit]

Attention Lee, Ryan, Dave if you're still around, or anyone else that has embarked on the homemade DC road. I did a big Boo-Boo, and its gonna end up costing me $$, so I need some advice.

A couple years ago, if anyone remembers, I made a blower using Lee's plans and used it on the WOOD Mag cyclone. Worked great in the basement shop, and even works good in my new roomy shop, but of course it wasn't as powerful at the end of the long runs as I would have liked. So I decided to upgrade. I originally used a 1HP 1725 rpm motor on the blower. I thought I'd give a 1.5 HP 3450 rpm a shot and see how it did. Well its been so long since I built the thing, I forgot about measuring the amperage. To make a long story short I think the large impeller (19") caused the thing to burn up, cause it won't turn on again. It only ran about 10 seconds. I've checked the obvious stuff, and have pretty much determined I blew the thing up.

So, I've decided to go back to 1725 rpm. I would just use the old one, but I screwed the bearings and housing around the shaft up removing it (don't ask). As this was an old rebuilt one to begin with, I don't think I'll look into repairing, but just buy another one. My question is this .... should I stick with the 1 HP rating that worked, or should I move up to a 1.5 HP but with the slower rpm? Would this make any difference in performance and would I run the risk of burning this one up too?

Thanks,
Todd

[Stytooner]

With an impeller that size, it really moves a lot of air at 1750 rpm's. I'm not sure about the numbers on HP if you double the speed. Loring?
One of the guys built one with a motor like this, but he reduced the speed some with pulleys. IIRC when I tested my 1 HP 1750 motor, it drew 13 amps at start up and fell down to about 6.5 amps when it was up to full speed. I have moved it a few times but none of my runs are more than about 12 feet or so.

I think it would be okay to increase the speed some with a bigger motor, but not sure double the speed is advisable. Most of the impellers on store bout units that run this fast are 13" and smaller. The impeller on mine is 19". It was Randy in Indiana that used pulleys on his.

[hermit]

Thanks Lee,
I made mine a 19" too, copying yours. I've basically learned the hard way that double speed is too much, thats why I'm going back to 1725. What I'm wondering is, since I probably have to buy a new motor, would the extra 0.5 hp help at all, or would I just waste extra money on the motor and extra electricity. I have some long runs. One is down the length of my shop; 32 ft. I thought going from 1 hp 1725 rpm to 1.5 hp 1725 might work better (I dunno something along the lines of being able to maintain speed better with reduced airflow, i.e. dirty filters etc.), but I'm a little gunshy with the episode yesterday.

Saddened by DC loss,
Todd

[LCHIEN]

my two cents:
Blower CFMs vs power is a sort of counterintuitive thing.
Fact #1 If you have a 1 HP motor working and drawing 1 HP and moving 1000 CFM,
Increasing the motor rated HP will not increase the CFMs any.
A 2 HP motor just will draw 1 HP of power and not move a bit more air unless you lower the restriction or otherwise improve the flow conditions.
If the 1 HP motor was underpowered before, then it would have tripped the circuit breaker or burned up the windings.

Fact no. 2, Blocking off the ductwork partially makes a lot more noise with the turbulent airflow, you think its working harder but the amperage and hence motor power actually drops. The motor works the hardest moving more air CFMs, less CFMs = less power. Decreasing restriction will increase amperage.

Commercial DC manufacturers most probably carefully check their systems to make sure that with all ducts open (max airflow) that the motor draws no more than rated amps. If it does, they go to a bigger motor or reduce impellor performance (e,g, smaller or less effective vanes).

So at twice the speed, you were trying to move twice the air volume/minute and that's probably why the motor burned up because it wasn't rated twice as high.

In answer to the last question, the extra 0.5 HP rating at the same speed would be totally wasted. But you would not waste electricity, it would still draw the same HP that the 1 HP motor ran at successfully. Don't confuse motor rated HP and work done. The motor only limits the maximum work it can do (rating) the work done is defind by the restriction and airflow design.

If you increase the size of your ducting and reduce the restriction on long runs, then a 1 HP motor @ 1725 may be too little power, in which case a 1.5 HP motor may be required. Its difficult because you have to buy and install it first, but you have to check the amps under the most flowing operating conditions to verify you have the correct motor size.

[hermit]

Thanks a million Loring. Thats what I was wondering. Like I said, I knew a lot more when I was building this thing, as I was reading all kinds of info. Increased static pressure was what I was trying to convey in my last message about the extra 0.5 hp.

I think I'll go back to the 1 hP. Then see if I can get my BRAND NEW 1.5 hp 3450 rpm motor fixed ........ and experiment with making a smaller impeller.

Thanks again guys
Todd

[Stytooner]

The other option you have is to keep the 1.5 motor and the 19" impeller and use pulleys intead of direct drive. In theory you could increase the pipe size some and reach a point with this motor and pulleys that would be optimal for this motor. It wouldn't be near double speed, but possibly at 2000 RPM.
It might require a bit of testing with different pulleys, but I expect there would be a sweet spot setup with 6" pipe and the 19" impeller.
You may want to PM Randy in In.
http://www.bt3central.com/showthread...078#post121078

[hermit]

Neat seeing my old posts here! Thanks Lee. If I do get the larger one fixed, any ideas how to support the fan in the housing to run a pulley system? Remember mine is above a cyclone so its inverted not on its side like yours.

[Stytooner]

It would actually take up less room to run a pulley system. You could have the motor to the side. You would need some shaft stock the same size as what was on the motor. You can get pulleys and pillow block bearings with locking colars from Surplus Center.

You would need to move or make a motor mount on the side. If you had the motor mounted on a box like I do, then you can move it to accept the pillow blocks. Two good cast iron pillow blocks will easily carry the impeller. Don't get the cheap ones.
They have a selection of pulleys as well.

[hermit]

Update:

Well, I seemed to have lucked out! First, I opened up my old motor and found that all I needed was a new bearing. Luckily I found one in stock for 12 bucks at a local supplier, so I got the old 1HP fixed. Then I found that I didn't ruin the new motor after all, so I was able to return it for a refund. I had to assemble/disassemble/install/remove the blower assembly about six times all told to get it working correctly. The fan wasn't running true and keep rubbing. I had to rebalance the impeller again. It took me all weekend to get the thing running right, but all in all I am very happy now. So what I thought was going cost me about $400 ended up costing $12, and now my curiosity has been satisfied. Actually the cyclone is running great again, since I gave the filters a GOOD cleaning while off. MDF dust really clogs them up. Thanks for the pillow bearing info LEE. I didn't know they made those. IF I decide to experiment again, I'll keep them in mind.

Thanks again for your time guys,
Todd

[Ryan F]

Blowing Up DC Motors

I cant believe I finally checked back on this forum after 1 1/2 years and the same stupid thing happened to me..... kind of......

At my new shop I moved the cyclone outside. Worked great. Couldn’t even hear the thing running. Then it happened. The moisture finally got to the plywood impeller base and it started to warp.... then BANG!!! MMMmmmmmmmmmmmmmmmmmmmm....... CLICK! (breaker tripping) no more fan.

Since I'm going to have everything outside you guys have any suggestions. Since time is really hard to come by these days, I’m thinking of “Eeeek”... buying a fan / DC / Cyclone..... Feel free to beat on me. I have been gone a long time....

[Stytooner]

Hey there, Ryan. Good to hear from you. I have been wondering how you were fairing. Sounds like you are doing better than your DC.

My unit is outside as well. It's out of the rain under a shed, but still in contact with plenty of humidity. I did initially paint a couple coats of oil based enamel on the inside and outside of my unit. I think this is the barrier against humidity thats keeping mine in top form. My motor is also a TEFC (totally enclosed fan cooled) type which is not open to humidity.

I will suggest that you could use treated plywood and paint it. What might be better is sheet metal with angle iron for bracing. Was your impeller made out of plywood as well? I can't recall.

Since you are short on time, a store bought unit of about 2HP may give you close to the same performance. Not sure how well the motor would hold up depending on what type of moisture you are getting, but it might save you some time.

[hermit]

Hi Ryan, sorry to hear about your issues. I guess I'm not the only one that has been absent either. I don't have any recommendations over what Lee said. It seems it boils down to keeping the weather away. I would say it shouldn't be too hard to make a new housing and paint it if your motor is still good.

BTW, mine is down AGAIN too. It was running beautifully then the other day I heard thump, thump, thump. Mine is down in the garage, shop upstairs so it took something to hear it too. It sounded like the fan was hitting the housing but it wasn't. Turns out my motor failed again bad. I think the switch is burned up. It makes a heck of a racket when turned on. So I either need to get this one fixed or buy another.

Good luck,
Todd