Thread: PSU Assistance

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  1. #11
    Quote Originally Posted by CNCStudent View Post
    transformer rated at 50v ac, once rectified will provide ~70v DC (with no load), is this not a little high given the geckodrive guidance is 32 x SQRT (L), where L is in mH.... [32xSQRT(3.2) = 57v]
    This is the problem I referred to. OTOH I didn't quite get that this thing was designed for an AC input, so maybe I should have kept my wug shut

    The problem with rectifying and smoothing a transformer is that you get peak volts at no load and a square wave as you start pulling power. If you try to smooth it the capacitors quickly become bucket sized and hideously expensive.

    A switchmode PSU uses the bottom end of the rectified wave form where the low voltage gaps are so much narrower and you can keep the power flow using inductors.

  2. #12
    Any comments are much appreciated, here to learn, just not been impressed by the occasional squeal from my switch mode PSU (given the drives and motors are near silent.... Drives do have fans on them, but no unusual noises, been brilliant drives since recommended on here), did consider the use of a TDK lambda 48v 1000w (FPS1000) PSU as they could be got on fleebay for not a lot and there is also no minimum load requirement, but kind of thought a smooth ac rectified power supply is probably better than a switched mode PSU.

  3. #13
    Neale's Avatar
    Lives in Plymouth, United Kingdom. Last Activity: 9 Hours Ago Has been a member for 3-4 years. Has a total post count of 591. Received thanks 79 times, giving thanks to others 5 times.
    I wouldn't get too hung up on ripple, within reason. Apart from anything else, Leadshine recommend transformer/rectifier/capacitor supplies rather than switchmode. Ripple isn't too good if you are talking audio amplifiers, but motors aren't that fussy. We are already over-driving the motors from a volts point of view and relying on the drivers to "lose" excess volts. The drivers will have internal regulation (must have, given their wide working voltages) so the internal clever electronics are fine. They have current limiting on the motor drive side and while I don't know what kind of frequency they use for the PWM, I doubt if it will worry about a bit of input ripple at a lower frequency. The downside is that linear PSUs are bigger, heavier, and probably cost more than a cheap Chinese SMPS. But the "soft" current limiting might cause fewer problems with peak pulse loads?

  4. #14
    I don't think the problem is in the motors so much as the breakdown voltage of your H bridges

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