are these steppers a good deal?

[johnny v]

I just saw these steppers on kijiji online classified STEP MOTOR, LIN ENGINEERING - BRAND NEW -Reduced - Mississauga / Peel Region Tools & Hardware For Sale - Kijiji Mississauga / Peel Region Canada.

I noticed that they are 3.2 volts (3.2 amps). Im used to seeing higher voltages on the steppers people seem to use around here. My question is can you figure out the oz-in rating from just the volts and amps? Must be a formula

Thanks!

[doorknob]

According to the web page at Lin Engineering - Step Motor Specialists these are 8-wire NEMA 34 motors with a rated holding torque of 434 oz-in.

The stepper motor drivers that are used by DIY CNCers typically apply a higher voltage to the motor than the motor's nameplate voltage in order to achieve adequate torque while running at a higher speed (because the drivers have built-in current limiting to prevent exceeding the motor's ultimate ratings).

According to a widely-used rule of thumb for determining the voltage to use based on the motor's winding inductance, with this particular motor you would use up to 39 volts if you wire the motor for bipolar parallel operation, or up to 79 volts if wired with a bipolar series hookup.

[johnny v]

Thanks doorknob for the link. I picked up four brand new steppers for $50!

Can anyone point me to a good source (thread, link, book) of info that explains inductance, resistors and power supplies and bipolar series vs bipolar parallel hookup? My steppers are only four wire so I am not clear how to wire series vs parallel (although I do understand how to wire a set of speakers in series vs parallel).

I have my first cnc toys (my new steppers) and want to make sure I make optimal choices (gecko g540, 48v power supply and 3.5 k ohm resistors???????) is my "not quite educated/in over my head still" guess.

Thanks very much.

Here are the motors again (please note mine are the same serial number but are only 4 wire): Lin Engineering - Step Motor Specialists

[keebler303]

Only 4 wires means you cannot choose between series or parallel. It is one or the other. If your motors are rated 3.2A then you want 3.2K resistors. Other than that your shopping list looks good.

Matt

[doorknob]

You might find this document useful:

http://www.hossmachine.info/Gecko%20...r%20basics.pdf

Since your motor only has 4 wires, it's not clear from the spec what their rated winding inductance would be. Presumably your motors could have been wired internally for either bipolar parallel or bipolar series hookup. It's even remotely possible that it's a custom version and the specs for your motor are completely different from the published specs for the 8-wire version that motor. However judging by the nameplate max current rating, it's more likely that the internal wiring is set up as bipolar series, and therefore you will be OK with the 48 volt power supply.

One way to help confirm that guess is to measure the resistance of one of the windings (using a digital multimeter). If it measures approximately 1 ohm, then that probably confirms that the windings are wired internally in a series arrangement. If, instead, it shows up as something like 0.15 ohms then it has been wired internally in parallel.

[johnny v]

They read 1.2 ohm's...so it seems they are wired internally for series ( according to doorknob's previous post, I can use up to 79v). Does this new information change the resistor rating of 3.2K? I am going with a simple gantry design like TulsaTurbo's "Shopdroids" designs: ShopDroids CNC Machines .
I have priced out the PBC linear rails and am ready to go for it. I think I might buy a big ol' monster of a variable power supply. Some extra $ now might ensure it's usefulness as I fall further down the CNC rabbit hole.

P.S. I can't believe how helpful everyone is, makes me smile every time I log on! Thanks very much.

[keebler303]

Amps = Kilo ohms for the G540 so if they are rated for 3.2A then yes.

What type of power supply are you referring to? The most durable and reliable is a linear, non regulated supply. Most folks are using ones from Antek. They are available on ebay or from his website: https://www.antekinc.com/

Matt