Dual power supplies



  • I think the risk is too great. I will alter to a heated bed with its own power supply (120v). Then, I could get a pad rated at 700+ watts. So I will just have a spare ps laying around.


  • Moderator

    Probably best. Take caution with the 120v heater as well.



  • A 320W power supply will definitely shut down if you connect a 400W load. It's not a "this is risky" it's a "this don't work"
    Another word of caution ... there are many many virtually indistinguishable from the real thing Meanwell power supplies around. The only way to tell is if you know what specifically to look for (or open up the supply and see if the PCB has Meanwell markings on it). I had just such a supply sold to me as a brand name Meanwell supply. It had an issue, the supplier said I could open it up to check (so he likely didn't know) and it turned out to be a clone.



  • @Weevil said in Dual power supplies:

    I thought the image above is Duet 3.

    Yes, it is. You specified a Duet 3 in your original post, and were given instructions for a Duet 2 in the next post. Assuming you actually have a 3, the post with the image is correct.


  • Moderator

    @jens55 said in Dual power supplies:

    A 320W power supply will definitely shut down if you connect a 400W load. It's not a "this is risky" it's a "this don't work"
    Another word of caution ... there are many many virtually indistinguishable from the real thing Meanwell power supplies around. The only way to tell is if you know what specifically to look for (or open up the supply and see if the PCB has Meanwell markings on it). I had just such a supply sold to me as a brand name Meanwell supply. It had an issue, the supplier said I could open it up to check (so he likely didn't know) and it turned out to be a clone.

    Best to buy something like a power supply from a reputable reseller of such things like Mouser or digikey. They've got a wide selection too so you can get exactly what you need and you know you're getting what you pay for.



  • Fair cop, didn't spot the 3.

    What's not been mentioned so far as far as I can see is that if you are going to the trouble of splitting up power suppies then you should carefully consider using additional interlocking to isolate the power supply to the heaters in fault conditions, either risen by the duet or external means such as fuses, thermal snap switches, etc.



  • This Mean Well should be able to handle 400W Bed. https://www.amazon.com/gp/product/B00UWCD22O

    If you want to offload the high current from the Duet board you can use a SSR such as this one https://www.auberins.com/index.php?main_page=product_info&products_id=288

    If you feel comfortable with high voltages you can run the bed on mains AC and a smaller and fan-less 24V power supply for the rest.



  • @jens55 I took apart the ps. circuit board had the Meanwell logo cleanly printed and well as a label on the large transformer. There is also the name Kerwin printed nearby on the board. Circuitry looks clean except for the white pasty stuff on some components. If this is a clone it's a damn good job. I did get it off ebay but the seller had sold over 1000 items with 100% rating if that's worth a hill of beans. I have compared photos with other sites. The only difference I noticed is the output adjust screw is white in some, blue in others but Meanwell carries both. My gut tells me they are legit. I like to think I have a good eye for it. Here's to hoping.



  • I think it is likely that you have the genuine article. My clone had only a tiny mention of Meanwell on the pcb but the real thing has very prominent markings.
    The only way of telling fro the outside is peeking into the ventilation slots and looking for the big Meanwell name in the middle of the pcb. You can make out a small section of it on the real supply from the outside.



  • After a few hours thinking I realised that standard duet advice of tying earth and negative terminals on the PSU and both having posative and negative tied to the board from both PSUs could be bad news.

    When you chain them like I originally suggested if one of the negative legs fail you completely loose one or both circuits. If you tie both individually to the posative and negative terminals on the board (bearing in mind the labelling implies the ground is common) and tie the earth and negative poles on the board if one negative leg fails then all current could be conducted through the mains earth wiring, which is unlikely to be rated for more than 13 or 15A.



  • @zapta I think I'll go with a heated bed with its own 120v power. That way, I can get the 700watt heater.



  • I have an idea. Please confirm the logic is sound. Couldn't I combine my 2 power supplies of 320watts to make 640watts as shown in the diagram? This should satisfy the 400watt heated pad, right?wiring2.JPG



  • Yes, this would work. One of several caveats: If a power supply ever fails, or is just turned off somehow, while the bed is running, the 'other' power supply will be overloaded and either thermal shutdown or fail.



  • I think this is a bad idea .... you can't guarantee that the load will be shared equally. In theory it will work but IMHO it is poor design.
    Go with your 120V bed heater, that will be the optimal configuration.


  • administrators

    @jens55 said in Dual power supplies:

    I think this is a bad idea .... you can't guarantee that the load will be shared equally. In theory it will work but IMHO it is poor design.

    Exactly so. The two PSUs won't share the load equally.

    Meanwell sells a 24v 480W PSU. You could use one of those for the 400W bed heater.



  • @dc42 Thanks guys for letting me bug you with ideas. I will go with the heated bed with its own 120v power. It is the most sensible route and costs less.😁



  • @Weevil mains powered heaters are usually cheapest BUT, BUT, BUT, BUT !!!!! pay attention ... especially with high power ones!!!

    normally printers come with underpower bed heaters intentionally, they size them so that if they are "always-on" they can't overheat the bed (usually they reach equilibrium around 100-120C) but they take age to reach set temp... now when you put a "properly sized" heater that will reach set temp in 20-30sec that heater will reach equilibrium around 400 or 700C and can cause fire if it goes into "always-on" mode ... and triak can easily die in "conductive dead" contrary to what we'd like (open-dead) setting heater to "always-on" leading to fire!!!

    There are 2 general solutions for this

    1. dual triak, so if one is dead the other will not be
    2. thermal fuse

    I don't go the first way as, while ppl calculate the odds are crazy low it happened to me few times on non 3d printer machines, especially with triak's from non reputable sources so I don't trust that solution... (note, all those ssr's you find for under 40-50$ they are with PRC made low cost triaks)

    So, I go with thermal fuse solution... they work like a charm and they solved me call to firefighters more than once 😄

    talking about this: https://www.aliexpress.com/item/32884513591.html
    26cbe7b2-3098-46c3-8b93-c741e51eb6f1-image.png

    there is a type with spring
    eeb1968f-e994-485d-a327-f88bf3201460-image.png

    and without spring
    959593a5-c340-4398-9115-dc884d587a21-image.png

    both should get the work done ...

    you attach it to your bed and you power your whole printer trough it, or you only power your bed trough it, depending on what you like better .. when the fuse gets melted the power is cut, you can't reset it, you have to replace it .


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