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DC PM Motor Output


By coldspot, Section Mechanical
Posted on Thu Jan 26, 2006 at 09:25:37 PM MST
Wind

Thinking OutLoud or On-Lineso to say.
First off, I understand this is theory and in "True" use they will porbebly be proportional.
 Take a DC motor rated 120 VDC, 18 Amps @ 7100 RPM.
  1. X 18 = 2160
  2. / 7100 = 0.30
 So every rotation = 0.3 Watt

 Or a 24 VDC, 3.1A @ 1630 RPM.

  1. X 3.1 = 74.40
  2. 40 / 1630 = 0.05
 Each R = 0.05 Watt

So am I thinking along the right lines hear or am I off track, (as per "PAR"), lol?????
DC PM Motor Output | 12 comments (12 topical)

Re: DC PM Motor Output (3.00 / 0) (#1)
by wpowokal on Fri Jan 27, 2006 at 05:02:29 PM MST

Coldspot I (like many I suspect) don't understand your point, are you thinking of using this motor as a generator or motor?

If its a PM motor then the field strength  basically remains the same(the magnet strength). If its a compound wound motor then it changes with output current(applying KISS here).

120v at 7100 rpm is 60 rpm/volt (7100/120)

Your motor type will affect what current you may get at lower revs. Then watts is amps x volts.

alan down under

"Dream as if you'll live forever, live as if you'll die today." James Dean



Re: DC PM Motor Output (3.00 / 0) (#2)
by coldspot on Fri Jan 27, 2006 at 05:22:25 PM MST

Yes- As the Title states "DC PM Motor"
120 VDC 18 Amps 2.5HP @7100 RPm

[ Parent ]


Re: DC PM Motor Output (3.00 / 0) (#3)
by wpowokal on Fri Jan 27, 2006 at 10:37:48 PM MST

OK DC PM motor, so the answer to your question at the bottom of your post is no.

allan down under
"Dream as if you'll live forever, live as if you'll die today." James Dean
[ Parent ]



Re: DC PM Motor Output (3.00 / 0) (#4)
by coldspot on Sat Jan 28, 2006 at 09:28:33 AM MST

Alen downunder-
THANKS,
But
"So am I thinking along the right lines hear"
" or am I off track"
It was a two part question I quess.
  1. Rpm = 1 Volt
  2. RPM's to get to 12 Volts then. ouch, thats going to be tuff.
And for the other PM DC Motor
(67.92), 68Rpm=1volt
815 RPM's to get to 12 Volts, ouch again, but 815x.05=40.75 Watts, and 720 x .5 = 360   Watts.
Boy, it looks like I'll never get to charging voltage, (untill snow melts and I climb a tree by cabin and top it for a windmill mount){I borrowed some "Linemans spikes" a couple years back and really didn't want to test them but looking like I will have to,  if this was only 20 something years ago, would be easy}.
 O-well back to trying to build hubs, (to mnt blades to these PM Motors).  


Re: DC PM Motor Output (3.00 / 0) (#5)
by ghurd on Sat Jan 28, 2006 at 09:46:23 AM MST

I suggest spining the motors with a drill to check the open circuit volts. Then connect a battery and check the amps. I don't trust the reverse math any more.

My attempts with small general purpose (auto, fan, etc) 12V motors had less than good results. Very bad actually.  Most would not get to 12V, or only charged at a few dozen ma at a very high speed.  My little VCR windmill would do more 12V charging here than most 12V motors I tested, no kidding.

The larger motors do a lot better, but some stlll have the same problems.

Nando knows a guy using 24V truck fan motors with good results. I haven't found one yet.
G-
Ghurd.info
[ Parent ]



Re: DC PM Motor Output (3.00 / 0) (#6)
by wpowokal on Sat Jan 28, 2006 at 09:53:38 PM MST

Coldspot I disagree with your logic on watts, revs are correct.

For a PM motor the field strength is fixed, therefore you should have reasonable amps at all speeds/volts.

Yes it is not realy a suitable motor for wind, a simple tape drive motor (TDM) will give much better results at much lower speed. You could expect 10-15 amps into a 12v system.

Even rewinding your motor would be an option.

allan down under
"Dream as if you'll live forever, live as if you'll die today." James Dean
[ Parent ]



Re: DC PM Motor Output (3.00 / 0) (#7)
by coldspot on Mon Jan 30, 2006 at 12:44:01 AM MST

Allen-
"(TDM) will give much better results at much lower speed"
I have a Ametek 30 VDC up and running now, but do to control box build slowness,(lack of cash)(Hate to think I wish for snow to make some pocket money shoveling the chit)LOL!
All my Ametek is doing is lighting two trailer tail lights, untill tomorrow, thats when I run the cord out to the tower and hook up control box to battery banks.
Today I also got a hub half finished for the 3/8th" servo motor shaft, will finish with either zub-woofer blade scraps, (the leftover parts of tube), or some trimblades I'm doing. The hub will be a 4-Blade unit.
 You'd think I could find a "Motor Arbor" in town. Fat chance, most retail places needed a picture to understand what I was asking for, geeeeezzzzzzz!
I'll order a couple someday, need a couple 5/8th and one 1/2.
Anybody have any idea on blade size for a Ametek 30 VDC, (3-BLade), I'll listen!

 So far what I've found about my building scrounging is the blades to motor are what i stall against, I've made a bunch of blades, my own idea "Trim Blades", Zub-Woofer's and some 3 and 4 sets from scrap's from the tubes. But, I'm still a newby and will learn and get better as i grow with my interest in "RE"!  :)


[ Parent ]



Re: DC PM Motor Output (3.00 / 0) (#8)
by wpowokal on Mon Jan 30, 2006 at 05:23:17 AM MST

Coldspot,
         I have a 30v TDM flying using a set of these;http://www.tlgwindpower.com/quad_mm.htm.

It charges my spare batteries, or should I say keeps them topped up.

The are made for the job, a 5/8" centre for TDM's so it's a simple job.

allan down under
"Dream as if you'll live forever, live as if you'll die today." James Dean
[ Parent ]



Re: DC PM Motor Output (3.00 / 0) (#9)
by coldspot on Mon Jan 30, 2006 at 10:34:46 AM MST

Yes Allen
Those are great looking but @ $99. To much for me.
My scrap blades are just like that also.
That site also had some "Motor Arbors", @ 6 times HarborFreight prices.
For $12. HomeDepot has ceiling fan blade kits, up to 5 blades.
My Ametek has a 3 blade ceiling fan blade, I'm looking into adding to these for more power. Thinking about 2-liter pop bottle straight area, halfs added to leading edge.
Thanks
But I need hubs for other PM Motors right now, and I need furl. Local windMill farm folder up two out of 43 MONSTER blades acouple weeks ago. We get on a 1-5 scale, (1=low, 5=high), 3 normal and 4 to 5 sometimes.
 thats why I'm inventing "TrimBlades", (cheap like free) but still stalled on hub for these. Motor Arbors would help, if I can find localy.

[ Parent ]


Re: DC PM Motor Output (3.00 / 0) (#10)
by ghurd on Mon Jan 30, 2006 at 11:21:47 AM MST

Arbors.  Now thats what I'm talkin'bout!
Everybody thinks $250 for magnets is sooo much.
Try $10 for magnets and $100 for a plate, bearing & hub.
Costs that much even with go-cart parts.

Jerry has some great posts about speaker plates.
Drill the center, add a set screw, true them up in a lathe.
Could work for blade mounting or magnet disks.

Grainger has cheap a 'hex hub' if you can find/make something it mates with.
http://www.grainger.com/Grainger/searchresults.jsp?search_type=keywordandcatmfgindx&QueryString= hex+hub&catindx1=&catindx2=&xi=xi

G-
Ghurd.info
[ Parent ]



Re: DC PM Motor Output (3.00 / 0) (#11)
by coldspot on Wed Feb 01, 2006 at 07:31:01 PM MST

GHURD-
Thanks again for the tip!
SWEET looking hex hub,
But closest grainger is still 2.5-3 hour away.
maybe when I get some cash I'll order but can ask for in a new word/phrase localy! lol
You'r the man!!!!!

Thanks

[ Parent ]



Re: DC PM Motor Output (3.00 / 0) (#12)
by nothing to lose on Fri Feb 03, 2006 at 08:14:11 AM MST

What about a cheap pulley? Might even find a used one free from some junk.

Get one for the type motor shaft you have that is flat on the face. Drill a few holes to mount your blade hubs bolted to the pulley. I try to use a slightly large puley so that I have a solid area to drill through for the mounting bolts, not through the V groove as that would cause problems.

What about the center from a metal fan blade like from an old junk airconditionare. I have used just the center hub and sometimes the arms that hold the blades also to mount plastic blades. The arms are easy enough to cut off with a hack saw or such.

Could use my favorite if smaller lighter blades, drill a hole into solid wood or 3/4" plywood that is smaller than the shaft then hammer it on for a pressed fit. Be carefull about damaging your motor. I've done this for testing alot of light blades like Zubbly PVC and barrel blades. Surprised me how well it actually worked. I was able to use wood screws then anywhere real easy to mount blades. My problem was I chewed them up with screws changing stuff so much.  I think I preffer plywood if you try this, solid wood may split along the grain. Though I did use a small length of 2x4 for a 2 blader this way just fine. Mostly I preffer about 6" round though.
Weather proof the wood and keep an eye on it if you use a press fit. I flew mine for along time just changing out the blades but the same hub without problems. It only got loose for me after I took down the mill and bounced it around here and there.
.
nothing to lose

Spelin and tpying are my strong points, not electronics.



DC PM Motor Output | 12 comments (12 topical)
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