I have a box of stepper motors and I can't remember where I got them from, nor can I find the datasheet for them.
They are named: 16HY0417N (or possibly H instead of N at the end). I think they are from MOON (we usually buy stepper motors from them). They might have been customized for us (connector mounted), but maybe it's possible to read out the current from the model number?
I need to know the max. current and rated voltage.
As @Andy aka said, If you want to be professional, buy new ones.
If you still want to try and use the ones you have, you can check the resistance on the windings, note the size of the stepper, to have a reference of the resistance there, and check for similar size stepper motor's datasheets.
If you manage to find similar datasheet of the motor you already have, and their internal resistance is the same/similar to yours, just use the same current and voltage rating that the datasheet suggests.
Operate your stepper on this suggested current and check its temperature. If it is cold while you operate it, you can increase the current. Steppers can get hot, so hot that you cant touch them.
You can also check similar datasheet's maximum temperature
Your choices for small-ish stepper motors will likely be 5V or 12V coil drive.
Measure the coil DC resistance, and budget about 1W max for the coil as an initial guess. This will tell you, roughly, the current and voltage the motor is designed for.
If possible, design your drive so that it can use a lower ‘hold’ current when the motor isn’t in motion. This will help keep the motor cooler.
MORE: On Moon's site, they have a range of hybrid stepper motors, here: https://www.moonsindustries.com/series/nema-16-standard-hybrid-stepper-motors-b020104
Based on that part number (HY160417N), I'd infer that it's a NEMA16 hybrid, with a either 170mA (most likely) or 1.7A coil rating. You could contact them through the link above and confirm for sure, and also measure the coil resistance as above.
Measure the dimensions of your stepper motor and the diameter of the rod.
Measure the resistance of one of the 2 windings.
Go to Sonceboz, NMB and Digikey web sites.
Compare your dimensions and resistance with their products.
You can get a rough idea of what you got in hands.
The max current can be determined by electrical tests.
You could perhaps get a rough estimate of the DC current level that makes the windings magnetically saturate.
Immobilize the rotor, or give it lots of friction-damping. Test with one winding. Test signal (I + i), where I is DC and varies for the test, i is small fixed amplitude sine wave, maybe 1kHz. Observe the resulting (V+v), and look for the DC level I at which the AC voltage component v changes significantly in its response.
