Power supply with positive and negative voltages 12 and 24v where to buy ?

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03 Aug 2022 03:19 #248895 by smc.collins
as title states looking for a dc psu for 12 & 24  with positive and negative voltages. just a CYA in case this spindle drive gets fussy about input voltages

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03 Aug 2022 07:46 #248907 by tommylight
Does it have to be switch mode?
You can always do that with two power supplies but leave one not grounded, ground the one with the minus side used as the 0.

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03 Aug 2022 11:37 #248919 by smc.collins
i doubt this old drive cares if it's SMPS or not, got a schematic for using a standard PSU that way ? not very familiar with that method

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03 Aug 2022 12:59 #248928 by andypugh
How much current do you need on the -12? Perhaps an isolated DC-DC converte connected to the 24V main supply would work?

My mill has just one big 24V supply and then a bunch of DC-Converters for the other voltages:

photos.app.goo.gl/EqX6ExZZ1fR2yzEM7

To get -12V you would need to connect input negative to output positive. I don't know how much they like that, in general.
(I just checked my drawer and found that all three types I have use a common GND, so won't work)

However, ebay has lots of +/- 12V step-down converters, and you can always ignore the +12.

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03 Aug 2022 18:44 #248959 by smc.collins
I'm not sure if this diagram is showing a 12v 10ma output or input, the arrow is ambiguous, so, i ordered a dc dc buck bost 12v converter that has negative and positive rails and 20w per rail.

i know the older atx psu with isa slots had the -12v for the isa bus, but those are crazy hard to find

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03 Aug 2022 20:59 #248970 by tommylight
Every PC power supply should have a -12V, it is used for audio.

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06 Aug 2022 01:03 #249169 by smc.collins
many many many new PSU's do not have the -12v rail

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06 Aug 2022 08:34 #249186 by tommylight

many many many new PSU's do not have the -12v rail

They do, is this new enough:
www.google.com/search?q=asus+rog+thor+12...ges&aqs=heirloom-srp..
It is an ATX standard, so till they move to the new 12V only standard, they will have -12V.
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06 Aug 2022 14:42 - 06 Aug 2022 14:43 #249204 by smc.collins
I'll have to recheck pc power supplies, i have a few laying around that do not have the -12v
i didn't think to search atx standard, and that may be why I'm not getting the results i was looking for, thanks for the lead, I'll chase one down
Last edit: 06 Aug 2022 14:43 by smc.collins.
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06 Aug 2022 16:27 #249212 by tommylight
Reading this back it came to my attention i never mentioned that -12V rail on PC power supplies is very low current, usually 0.2 to 0.3A.
Sorry for the omission. :(
--
I think i still have some very old AT power supplies, the ones with a mechanical toggling switch, pretty sure they also have -12V, but i would not bet on it.
Also have anything in between till the one i linked above and some more of those monstrosities, thinking of using two of those 1200W for welding, or 10 of them for plasma cutting! :)
At the very least, they are much, much more efficient, but expensive.

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