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Author Topic: Will this power supply power this motor (needing verification)  (Read 3536 times)

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Offline jayfehrTopic starter

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Will this power supply power this motor (needing verification)
« on: July 13, 2015, 04:53:58 pm »
My plan is to build this bandsaw: http://woodgears.ca/bandsaw/homemade.html

Using this old treadmill motor:


however they guy that saved the motor for me didn't pull the motor driver out. So I need a power supply/driver to power it. I found the one linked below on ebay, but I'm not sure if it'll work. In fact the low price kind of scares me. But from what I can tell it handles the proper voltages (90v) and since the motor pulls 8A the driver needs at least 720W and the supply is rated for 800W. To me it seems safe, but a second opinion, or some additional advice would be nice to have.

http://www.ebay.ca/itm/DC-9-90V-10A-800W-Rectangle-PWM-Motor-Speed-Controller-w-B10K-Potentiometer-/310987278653?pt=LH_DefaultDomain_0&hash=item486849493d

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Offline leblanc

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Re: Will this power supply power this motor (needing verification)
« Reply #1 on: July 13, 2015, 05:05:06 pm »
Remember that the torque is roughly proportional to the current (and the speed is roughly proportional to the voltage).

The PWM will control the average voltage and therefore speed.

The amount of torque you put on the motor will determine how much current is drawn. I have not seen numbers on torque for bandsaws, but I would imagine it is quite a bit smaller than a treadmill, depending on gear ratio. You'll probably only be drawing a fraction of that 8A rating. I would recommend putting a ~5A fuse to protect the motor, in case there is a large torque applied.

Don't forget that there will temporarily higher torque when accelerating.

You could also take a look at power ratings on off-the-shelf bandsaws if you want a ballpark figure.
« Last Edit: July 13, 2015, 05:31:26 pm by leblanc »
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Offline PSR B1257

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Re: Will this power supply power this motor (needing verification)
« Reply #2 on: July 13, 2015, 05:23:04 pm »
You know, that you need a suited power supply first of, don't you?

Quote
In fact the low price kind of scares me.
Me too. I wouldn't trust this thing any further I can throw it ;D

A simple way to drive the motor would be a variac and a diode bridge (the motor doesn't need any filter caps)
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Offline jayfehrTopic starter

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Re: Will this power supply power this motor (needing verification)
« Reply #3 on: July 13, 2015, 05:28:06 pm »
I forgot to include the power supply I'm looking at. It's this one here:

http://www.ebay.ca/itm/CNC-Switching-Power-Supply-800W-Ajustable-70-90V-11-4A-with-Cooling-Fan-/181251671363?pt=LH_DefaultDomain_0&hash=item2a33710543

Outside of the 24V range I'm a little nervous about homebrewed solutions. My confidence just isn't there yet, and I do really like living.
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Offline PSR B1257

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Re: Will this power supply power this motor (needing verification)
« Reply #4 on: July 13, 2015, 06:11:03 pm »
Quote
Outside of the 24V range I'm a little nervous about homebrewed solutions.
Always a good idea to be precautious at higher voltages.

For reasonable money you can get a variac with enclosure.
http://www.ebay.ca/itm/POWERSTAT-116CU-10A-0-140V-OUTPUT-VARIABLE-1-4KVA-120V-AUTOTRANSFORMER-B224696-/301584871818?pt=LH_DefaultDomain_0&hash=item4637dbf18a
There is also room for a diode bridge.
Just saying... :)

Hang on, what do you think of http://www.ebay.ca/itm/Dart-Controls-510-100C-36M-DC-Drive-for-90VDC-Motors-120VAC-Input-/331450078184?pt=LH_DefaultDomain_0&hash=item4d2bf6d3e8
Hmm... can't see a power rating...but I guess it's worth asking the seller.
« Last Edit: July 13, 2015, 06:15:47 pm by PSR B1257 »
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Offline Deathwish

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Re: Will this power supply power this motor (needing verification)
« Reply #5 on: July 13, 2015, 06:37:04 pm »
another good place to ask is in here

http://www.ukworkshop.co.uk/forums/
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Offline Zero999

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Re: Will this power supply power this motor (needing verification)
« Reply #6 on: July 14, 2015, 10:20:14 am »
Quote from: PSR B1257 on July 13, 2015, 06:11:03 pm
Quote
Outside of the 24V range I'm a little nervous about homebrewed solutions.
Always a good idea to be precautious at higher voltages.

For reasonable money you can get a variac with enclosure.
http://www.ebay.ca/itm/POWERSTAT-116CU-10A-0-140V-OUTPUT-VARIABLE-1-4KVA-120V-AUTOTRANSFORMER-B224696-/301584871818?pt=LH_DefaultDomain_0&hash=item4637dbf18a
There is also room for a diode bridge.
Just saying... :)

Hang on, what do you think of http://www.ebay.ca/itm/Dart-Controls-510-100C-36M-DC-Drive-for-90VDC-Motors-120VAC-Input-/331450078184?pt=LH_DefaultDomain_0&hash=item4d2bf6d3e8
Hmm... can't see a power rating...but I guess it's worth asking the seller.
A decent quality, properly built 90VDC switched mode power supply should be safer than a Variac. It will be isolated from the mains and will output smooth DC, rather than 90VAC which has a peak voltage of 127V and can more easily disrupt the heart's rhythm than steady 90VDC.

Voltages under 120VDC are still considered to be SELV, although above 60VDC there's a considerable shock risk so basic insulation from the user is mandatory.

The motor may not be designed for direct connection to the mains so whilst a Variac will properly work, it's not a good idea.
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Offline flynwill

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Re: Will this power supply power this motor (needing verification)
« Reply #7 on: July 14, 2015, 02:19:56 pm »
I would recommend a bit more research.  There are supplies out there designed as speed controllers for DC motors.  They sense the motor speed from brush switching and adjust the motor current for constant speed.  Sherline uses such a controller on their lathes (but that controller doesn't have enough oomph for your motor).
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Offline flynwill

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Re: Will this power supply power this motor (needing verification)
« Reply #8 on: July 14, 2015, 03:07:20 pm »
This looks like it might do what you want:
http://www.kbelectronics.com/data_sheets/kbic.pdf

Available from Amazon.
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Offline PSR B1257

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Re: Will this power supply power this motor (needing verification)
« Reply #9 on: July 14, 2015, 03:28:37 pm »
Quote
It will be isolated from the mains
Yes, but a usual AC-motor isn't isolated from mains either, if memory serves me correctly  8)
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Offline Zero999

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Re: Will this power supply power this motor (needing verification)
« Reply #10 on: July 14, 2015, 05:09:08 pm »
Quote from: PSR B1257 on July 14, 2015, 03:28:37 pm
Quote
It will be isolated from the mains
Yes, but a usual AC-motor isn't isolated from mains either, if memory serves me correctly  8)
The difference is an AC motor will be designed for direct connection to the mains.
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