Dual power supplies



  • Hello,

    I have 2, 24v, 320watt power supplies I plan to use for my Duet 3. One will be dedicated for a 24v, 300 watt heated pad. I cannot find a wiring diagram to set it up. Any suggestions would be appreciated



  • Feed the posative side of the heatbed to the posative side of the heatbed psu. Run the other PSUs posative to the duet board. Run a negative wire capable of taking full current of both PSU from the duet to the duet PSU, then add a jumper from the same gauge wire to tie the negatives on noth PSUs together.



  • If you are running a cheap no-name PSU keep a close eye on it. Pulling 300W from a 320W PSU maybe a bit much for it, but in your defense so long as the heat bed isn't underpowered it will only be pulling 300W while it is warming up.



  • It is much simpler than that.

       A      B     C      D      E      F      
    

    97fb741e-f681-4f95-a5d7-50b364e6a799-image.png

    Duet PS to A and B (observe polarity)

    Heatbed PS to C and D (observe polarity)

    Heatbed itself to E and F. (no polarity)


  • Moderator

    @DocTrucker said in Dual power supplies:

    Feed the posative side of the heatbed to the posative side of the heatbed psu. Run the other PSUs posative to the duet board. Run a negative wire capable of taking full current of both PSU from the duet to the duet PSU, then add a jumper from the same gauge wire to tie the negatives on noth PSUs together.

    This would be correct for the Duet 2. The Duet 3 has separate power in for bed heater.



  • @Danal Thanks, I'll cautiously give it a shot.



  • @Phaedrux said in Dual power supplies:

    @DocTrucker said in Dual power supplies:

    Feed the posative side of the heatbed to the posative side of the heatbed psu. Run the other PSUs posative to the duet board. Run a negative wire capable of taking full current of both PSU from the duet to the duet PSU, then add a jumper from the same gauge wire to tie the negatives on noth PSUs together.

    This would be correct for the Duet 2. The Duet 3 has separate power in for bed heater.

    The OP specified 3.

    And... is it not true that those instructions leave out a wire? The second heatbed wire needs to go to the BED- on the Duet 2, correct?



  • I thought the image above is Duet 3.



  • @DocTrucker I am using 2 Mean Well's RSP-320-24 which from what I read is pretty good.



  • Correction, the heated pad is 400watts. Will this be too much a strain for a 320 watt ps?



  • 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.


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