[gerryv]

Hi,

I recently bought an older D&M 4 CNC enclosed "trainer" with a Sherline Mill off eBay. It arrived with a different drive motor than pictured. The one in the picture was a larger diameter black one like you see on the Sherline web page.

The motor I received was a smaller diameter silver coloured marked 40v DC (however it looks like a number was scraped off to the left of the 40 - perhaps a 2 or a 4??, or maybe just something else? Also one of brush connectors is broken and there is a slight grinding sound when the shaft is rotated (likely a bad bearing being that it's not an enclosed motor). Not too exciting all-in-all especially because I know nothing about motors or how to fix them.

The fellow tells me that the motor he sent is better because it is matched to a 40v controller in the back of the unit. I'm wondering why it would have had a 90v motor on it for the pic. then?

Q. Is there any easy way to tell what voltage the controller actually is as there was no documentation with the unit?

Besides the fact that this motor smells suspiciously like toast, my gut is
telling me that a 90V DC motor probably offers more umpfh (torque?) than a 40v does anyway.

Q. Is this correct or not?

He's offered to send me the 90v motor if I return the 40v one first (more cost) but says it would run at only 4/9ths of its potential (seems logical) with the 40v controller, if that's what it really is.

Assuming there is no desire to get into a protracted disagreement here and also recognizing that my budget is very tight (I'm on a small disability income):

Q. In terms of the motor, what are my best options and what would you do under these circumstances (besides taking him to task) if your primary objective is to get it up and running well without throwing lots of money at it?

Thanks kindly,
- Gerry

[Stepper Monkey]

With a DC motor, its not just about voltage, but about total current draw as well. It is very possible that a given 40v motor with a matched 40v controller could give more oomph than the 90v with a matching 90v controller depending on the amps (and therefore total watts) they draw. With the 90v motor and 40v controller you could really lose out both ways, probably particularly in speed depending how it is set up.
You would have to post the stats of the 40v motor and the power supply rating to know for sure whether its better to fix the motor, replace it with another 40v, or to trade for the 90v motor and just buy a new controller (which for 90v is not hard or expensive to find at least).
Just too little info to go on right now, sorry.

[gth629e]

Hello Gerry,

Sorry to hear you are having problems.

So I did some quick research and this is what I found.

First of all I agree with stepper monkey that an optimal system would have a DC motor and controller to match its specifications. More volts does not mean more torque if the amps are limited.

I looked at Sherline's website and found this information on the motors that installed on the system here http://www.sherline.com/dimen.htm.

Just scroll to the bottom and it gives the specs.

Usually when you talk about a DC motor you would use Watts to rate the power rating.

Watts= Amps x Volts

Firstly Sherline does sell their systems with a 90 VDC motor on their systems which brings up the question, why would they use a 90 VDC motor if some other motor would be more efficient to work with the 40VDC controller.

Using the graph and the given information and running some basic calculations it is safe to say that the controller that is originally on the system is supplying 85-90 VDC and probably maxes out at around 45 AMPS.

So he must have changed the motor and the controller and not just the motor. If he says that the controller is only rated to 40 VDC then that is not the controller that is originally on the system. Or either Sherline is giving false numbers on all machines, unlikely.

Oh and not to mention at the bottom of that page Sherline outright says the controller is rated at 90 VDC

From Sherline's page

"NOTE: Electronic circuitry built into the speed control supplies a constant 90 VDC output to the motor regardless of the input current .."


So take from this what you will. I would personally ask for what was promised. I know that many other small milling machines made in china come with a 40 VDC motor and controller that could easily be bolted to the Sherline mills and lathes. (not saying that is the case)

Anyway, hope this offers some in site and let us know what you decide.

Please feel free to check out my website www.cncroutersource.com. Its a few weeks old and I'm trying to get it up and running and would appreciate any feedback.

I still have many pages I need to upload.

I ask one of my coworkers if I can look at his Sherline. Then I will be able to tell you for sure the actual controller and motor specs.

Brian

[email protected]