[SOLVED] Given, a 24v DC motor: can I use 24v and ground AND/OR, +12v and -12v ?

[jmarks6205]

'Tho I am 62 years old, I JUST became aware of how incredibly interesting electronics truly is. I have watched many hours of YouTube in the past couple months, and have purchased a "training book with a matching kit" - so having a lot of fun learning very basic things. I have a basic question about DC electricity for which I can't seem to be able to Google an answer: given a two-wire 24v DC motor, will it "care", if I provide +24V and ground, OR if I provide +12V and -12V. Given both provide a 24v difference in "potential", is there really a difference - in the simplest model? Thanks - Jon

 

[thylacine1975]

Welcome to a truly fascinating + addictive subject area (electronics and all things electrical) Jon!

Your intuition is certainly correct - nope, the motor won't care. As you say, all it "sees" from either source is a 24V potential difference. The 'absolute' voltage is (generally) irrelevant

 

[jmarks6205]

thylacine1975: Thanks for getting back to me so quickly. I'm feeling much better about "modeling" the problem I am currently trying to fix. The "problem" I'm trying to fix: I have a massage chair, which I can no longer live without - and after 7 years, it is broken electronically, and has several 24v DC motors. High-level symptom: hand-held controller indicates power up, and responds to inputs (via visual display) - but the chair makes no movement. I pulled out the power supply/controller for examination and see the unit has two transformers: 1.> 115v to 12v AC (relatively small), and 2.> 115v to 21v/16A (relatively much larger toroidal). While I could measure the output of transformer #1, I could NOT get a voltage reading from the toroidal. It turns out the primary winding on that transformer is "open", so I believe I truly have root cause. But since I have not YET been able to locate a replacement (and since I am now FASCINATED by what I am seeing/learning), I decided to hook up a variac, in place of the toroidal and see what I could learn. Here is where the model I was building started to go "sideways". With the variac providing 21v, I expected I would see +24v and -24v DC after the bridge rectifier - mostly because the of the silk-screening in MANY places on the board, AND because I know all the motors are labeled 24V DC. But I am only getting +12v and -12v (roughly) from the rectifier (KBPC3506, which the data sheet tells me is a "half-wave" rectifier, BTW). So this "scared" me a bit, in terms of me thinking, either: 1.> something ELSE is wrong, or 2.> I had not wired in the variac properly (al'tho it seems incredibly straightforward). But then when I measured the voltage in the two supporting 50v 3300microfarad capacitors, I got a reading of roughly 29.5v. Which I can make sense out of mathematically, if I take 21v rms and apply the 1.4 factor for "peak voltage" - I could understand the caps charging to that voltage (<--is that a fantasy from watching too may YouTube videos?). Now coupled with YOUR answer, that the motors COULD run on +-12v supply, I'm starting to think that the only "problem" I probably have, is the toroidal went belly up - and the fact that the primary went bad is really a good thing, since the primary is electrically isolated from the rest of the electronics, completely - right? Does that model sound, at least, "in the ballpark" to you - or are you just LYAO right about now? No worries, I know I don't have much of a clue, but I am enjoying this. THANKS !! - Jon