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Chinese Ebay PSU's?

Posted: Thu Jul 02, 2015 5:43 pm
by ZakRabbit
I'm looking for a psu, and the information is sparse and even conflicting about PSU's in general. If I go ATX, I'm thinking it SHOULD be modular and at least 750W, if I go with an LED psu, I need to find a power switch, and those are rated in ams, so I'm guessing 20-25 ought to be good for single hot end, heated board, three positioning and one extruder stepper. I can get said 25 amp psu for less than $30... is this a bad idea?

Re: Chinese Ebay PSU's?

Posted: Fri Jul 03, 2015 7:17 am
by Eric
The relationship between power and amps is Watts = Volts * Amps. So a 12 Volt 25 Amp supply is a 12V 300 Watt supply.

However, an ATX supply is not a single-voltage supply, so that wattage rating (e.g. 750) represents the power capacities of several different voltage supplies added together. You need to look at the label on the side of the power supply (usually shown in pictures on ebay) to see what the 12V rating is. Those labels are usually given in Amps, but if it's Watts, you now know how to convert.

Re: Chinese Ebay PSU's?

Posted: Fri Jul 03, 2015 7:31 am
by Tincho85
Hi, I'm using generics PSU for both heated bed and hotend/electronics. They are working fine.
600w ATX 12vdc for hotend, steppers and electronics (today I would buy a switching PSU or use a stepdown and only use the 24vdc psu).
720w Switching 24vdc for the bed only.

If you can afford it, get a Meanwell.

Re: Chinese Ebay PSU's?

Posted: Fri Jul 03, 2015 1:12 pm
by Polygonhell
I have Chinese generic PSU's on a couple of printers here, I prefer them to any ATX solution, just because I've had issues with ATX power supplies in the past, they are designed for a very specific job, and often there are safeties in them that prevent them hitting 12V without a load on the 5V line.
The generic PSU's are much simpler, but you have to be comfortable with mains wiring, if you wire it wrong it's possible to electrify the case.

Re: Chinese Ebay PSU's?

Posted: Fri Jul 03, 2015 3:50 pm
by ZakRabbit
Polygonhell wrote:I have Chinese generic PSU's on a couple of printers here, I prefer them to any ATX solution, just because I've had issues with ATX power supplies in the past, they are designed for a very specific job, and often there are safeties in them that prevent them hitting 12V without a load on the 5V line.
The generic PSU's are much simpler, but you have to be comfortable with mains wiring, if you wire it wrong it's possible to electrify the case.


Now, that's something I hadn't even considered... I come from an automotive background so I'm comfortable with wiring, but not too familiar with the 110V aspect. I know you've been around since the beginning, and I just finished reading all 30 pages of mchackney's build where I know he uses one each a 12 and 24V. I'm thinking of starting with a 12V source. I've seen where a 25Amp unit can be had for $30, but can I trust it?

Re: Chinese Ebay PSU's?

Posted: Fri Jul 03, 2015 4:40 pm
by Polygonhell
25A is what I have 3 of here. I've yet to have one fail, but the build quality isn't stellar, so I assume failures do happen. I have a spare one I keep meaning to use on the Max, but the original PSU hasn't been an issue and swapping it is more work than I can be bothered with.

One of the nice things is most of the Chinese PSU's come with trim pots, and the 12V ones will usually hit 15V, which is probably enough to make the heated bed reach 100+C reliably.

The wiring Isn't complex, but you'll want to verify it with a meter before you get excited and turn everything on.

Re: Chinese Ebay PSU's?

Posted: Fri Jul 03, 2015 4:59 pm
by ZakRabbit
Polygonhell wrote:25A is what I have 3 of here. I've yet to have one fail, but the build quality isn't stellar, so I assume failures do happen. I have a spare one I keep meaning to use on the Max, but the original PSU hasn't been an issue and swapping it is more work than I can be bothered with.

One of the nice things is most of the Chinese PSU's come with trim pots, and the 12V ones will usually hit 15V, which is probably enough to make the heated bed reach 100+C reliably.

The wiring Isn't complex, but you'll want to verify it with a meter before you get excited and turn everything on.


I bet. Is there something like a diagram I can use? I'm guessing you don't really want to cut a lamp cord and just hook up the input willy nilly... It is my first build, and while I'm confident I have the capability, I've been using the time for the parts to arrive to read everything I can by you, mchacker, and a few others that seem to have their stuff together to keep my ego in check and make sure I do this right.

Re: Chinese Ebay PSU's?

Posted: Fri Jul 03, 2015 5:49 pm
by Eric
Lamp cord is a bit light for this purpose and usually is only two conductors. Make, buy, or cut a cord that has a 3-prong plug. North American outlets wired correctly have the neutral on the wide prong, hot on the narrow prong, and safety ground on the round peg. Match those up to the right connectors on the power supply and you should be good for AC input. If you get hot and neutral swapped (or the outlet is wired wrong), it will probably still work, but you may have 120V where you don't expect it, a shock hazard.

If you want a power switch, route the hot lead to the switch first and then back to the power supply input.

Re: Chinese Ebay PSU's?

Posted: Sat Jul 04, 2015 12:26 am
by ZakRabbit
Eric wrote:Lamp cord is a bit light for this purpose and usually is only two conductors. Make, buy, or cut a cord that has a 3-prong plug. North American outlets wired correctly have the neutral on the wide prong, hot on the narrow prong, and safety ground on the round peg. Match those up to the right connectors on the power supply and you should be good for AC input. If you get hot and neutral swapped (or the outlet is wired wrong), it will probably still work, but you may have 120V where you don't expect it, a shock hazard.

If you want a power switch, route the hot lead to the switch first and then back to the power supply input.

Exactly what I was looking for, thank you! Now, I just have to keep calm and not buy both a 12v and 24v supply... hee hee hee. I will be going with a smoothieboard with 626pilots's firmware.