Blowing power supplies
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@opentoideas said in Blowing power supplies:
well there are a few things. did you buy your duet from an authorised reseller or could it be clone? the clones are similar but can be slightly different eg. printing may say "based on v1.03 design"
He got it from Duet3D, this is apparent from his original post in which he refers to the "on special batch".
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I saw that but the supplier is not mentioned and likewise I made the same assumption as I considered that special when I bought mine last week but it could also be the special sale on Aliexpress for example which is why I wanted to clarify as the description sounds more like these with the fuse issue.
these are the only way i can see having a fuse on a 1.03 board
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Just a quick reply to a few things. My original Duet Wifi (from the late beta batch) was from Duet3D. The Duet 1.03 is also from Duet3D. I do have a 0.6 Duet from Replikeo, but I don't use it anymore. Happy to provide screenshots of my receipts for proof if it's still being questioned.
I do have a multi-meter. I've been focused on power supply repair since, so that's why I haven't gotten around to checking the bed. I'll be attempting to replace the parts that I identified above.
All my other hardware either comes from e3d, or Robotdigg, except the 400 & 800w supplies.
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LOL I am as confused as you then about your fuse on a 1.03 board.
just noticed @elmoret mention the photo is on the website is not a 1.03 board so I guess they did have a fuse then???
either way hope you have some good luck with repairing the blown PSU's and get up and running again soon.
I can sympathise, I was just getting to grips with Duet and broke my hotend so stuck waiting on parts myself
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In theory, this COULD be multiple good PSUs failing due to a shorted load, but I’m leaning against that because good PSUs should have short protection that kicks in on overload before they fry. Not saying that always works, but it ought to. I’ve hard-shorted a Meanwell before with a big ol’ spark and it just went into protection mode until I power cycled it.
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The input fuse in a switched mode PSU should only blow if the PSU develops an internal fault, such as a blown switching transistor or capacitor. It will also blow if you exceed the rated input voltage by a sufficient margin, e.g. because the PSU has a 100V/220V switch and you feed it 220V with the switch in the 110V position. It shouldn't blow otherwise, even if you short the output of the PSU.
A continuous small overload might cause one of the switching transistors to overheat, resulting in eventual failure and the fuse blowing. Cheap PSUs do seem to have short-circuit protection, but I don't believe they monitor output current to detect lesser types of overload. With a low-quality PSU the transistors may even be running too hot even at or a little below rated output. That's why an output power safety margin of 20% or so is often recommended.
Failure of the PSU cooling fan could have a similar effect.
You haven't told us the resistance of your bed heater, so we can't work out the total load on the PSU. But 800W should be more than adequate.
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I just measured the resistance of my bed heater, but I'm really unsure I'm doing it right. My multi-meter gets a resistance of 7.5 between it's pins, and the heater returns a resistance of 8.5ohm.
I am about to find the method for calculating wattage, but I really feel like 1ohm is odd.
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@dc42 said in Blowing power supplies:
The input fuse in a switched mode PSU should only blow if the PSU develops an internal fault, such as a blown switching transistor or capacitor.
Given that the 400w power supply first blew the fuse on the IEC plug, then turned on briefly before it's input fuse died, I believe there must've been an internal fault? My assumption is still with over draw.
I've also since seen that 1ohm is in the ballpark of other heaters.
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I found some alligator clips, to get a better hold on the heater crimps. 1-1.1ohms.
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@mortarart said in Blowing power supplies:
I found some alligator clips, to get a better hold on the heater crimps. 1-1.1ohms.
If this is true then you bed needs at 12V a 144W but at 24V it need already 576W. So the 800W supply should get the job done, but the question what quality it was. And at 24V this would over-current the Duet any way since it is rated at 15A and at 24V you bed drivers 24A.
My personal opinion is - if you bed draws alone over 500W, go with mains power bed (I know they are many safety doubts but handling over 20A isn't really safe to - burning connectors, blowing power supplies). -
If it’s really 1 ohm, then yes, that’s a bit of a concern at 24v. Problem is, many multimeters don’t measure accurately at very low resistances. So it could be 1.1 or 1.4 or 0.8 or whatever, we don’t necessarily know.
I would personally not put more than 10A or so on any circuit not wired by an electrician. It’s just an unreasonable amount of amperage for a hobbyist to be dealing with. Typical low voltage terminals and connectors aren’t intended to go that high. Particularly when you factor in de-rating requirements due to adjacent terminals carrying power, or higher ambient temps. There’s a reason heatbed connectors burn up all over the place in the 3D printing world. Yeah, the Duet is good to 18A, but that’s still a LOT of current. And 24v at 1 ohm is more than 18A...
Is the 800w PSU intended to be run with full load on one output? For example, a lot of ATX PSUs have multiple 12v rails and each can only handle a portion of the total rating. Don’t know if that applies here.
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I was running on two rails on the 800w and 350w supplies. How viable is it for me to run the bed off of a massively turned down power supply, via an SSR? If I run it at 18v, it should only draw 324w...
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@mortarart said in Blowing power supplies:
I was running on two rails on the 800w and 350w supplies. How viable is it for me to run the bed off of a massively turned down power supply, via an SSR? If I run it at 18v, it should only draw 324w...
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Also seriously look to get a quality supply.
A good second hand PSU will likely set you back less than a rubbish new one.(and be FAR superior and last longer)
This just cost me £20 on fleabay and was local!
0_1536054740525_1536054706811947497414.jpg
600W with modules for 12V and 24v
Protected against overload thermal trips etc and remote switchable.
There are loads of quality industrial supplies out there for a fraction of what they would cost new and all this one needed was a new £1 fan I already had lying around
p.s. please excuse the mess this is only a temporary testbed as the bits just arrived! first prints will be a case for the duet and a tidy up of all the wiring!
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and yes lowering the voltage on the bed will reduce the power. thats why I got the PSU I am using. I have one 200W 24V module that is dedicated to the Duet and a pair of 200W 12V modules I can link for the bed heater (mine is 12V).
if and when I can upgrade the heater to 24V and have a 360W 24V module I can use - its an unusual PSU!
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@mortarart said in Blowing power supplies:
I was running on two rails on the 800w and 350w supplies. How viable is it for me to run the bed off of a massively turned down power supply, via an SSR? If I run it at 18v, it should only draw 324w...
This will work but be sure to get a good SSR for DC! SSR for AC won't work with DC (it will just turn on and never turn off if you don't cut the power). Don't buy DC SSR from China, I already seen situations where a DC SSR from China turn out to be for AC ;).
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@opentoideas said in Blowing power supplies:
and yes lowering the voltage on the bed will reduce the power. thats why I got the PSU I am using. I have one 200W 24V module that is dedicated to the Duet and a pair of 200W 12V modules I can link for the bed heater (mine is 12V).
Ha, I didn't realise you could do that, until you mentioned it. I could even use something like a 48v heater in future, with an SSR. Just didn't occur to me.
I'm on the verge of buying a Meanwell SE600 from Mouser. They're not super expensive compared to the $200 of Chinese power supplies I just junked, and I figure that for the time being I can down volt that power supply, use my SSR, and separate rails for the bed heater, so as to not overload the Duet.
Though, I'm planning on using e3d's tool changers and a Duex at some stage in the future, so that will probably require another supply.
I'm still finding out quite a bit about self-sourcing...
Grounding my motors for example. I haven't seen that mentioned once in D-bot discussions, despite most mount designs being plastic, and belt driven.
@dragonn said in Blowing power supplies:
@mortarart said in Blowing power supplies:
I was running on two rails on the 800w and 350w supplies. How viable is it for me to run the bed off of a massively turned down power supply, via an SSR? If I run it at 18v, it should only draw 324w...
This will work but be sure to get a good SSR for DC! SSR for AC won't work with DC (it will just turn on and never turn off if you don't cut the power). Don't buy DC SSR from China, I already seen situations where a DC SSR from China turn out to be for AC ;).I'm fairly confident in the SSR I got. It's from the same supply as the 350w supply. After opening each of the supplies up, to see what failed, that one is clearly of a higher standard of construction and components.
Thanks everyone for your help.
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Doubling up two PSU rails, hmm... my gut says that will cause issues with load balancing, where the regulator with a higher set voltage tries to raise the voltage while the regulator with lower set voltage tries to lower the voltage. I’m not positive about this but I don’t think you’re supposed to just tie rails together to drive big loads.
I’m still not sold on motor grounding; the theory behind it makes sense (belts transferring static to the motor) but it’s only really mentioned as an issue in belt drive literature for hazardous atmosphere equipment where spark discharges will cause a fire/explosion. Then you are recommended to use a conductive belt! I would reckon that there are a minimum of several hundred thousand 3D printers in the world with non-conductive motor mounts and no motor grounding. Where are all the failures?
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I am not following precisely what you're talking about with 'doubling up two PSU rails'. What I had previously was a 14awg wire with two screw terminals fixed to the PSU. What I plan to do in future is one rail out of the supply going to the Duet, and two to the SSR->bed.
I would set the voltage for the whole supply (it only has one adjuster) to a lower amount to reduce total watt output, to below 600w.
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Oh, ok, I think we are meaning different things when we say PSU rail. An ATX PSU for example typically has 3v3, 5v, and multiple separate 12v regulators, each of which is only rated for a portion of the total load and has separate wires, connectors, etc. If there are two 12v rails then there are two separate sets of 12v power equipment that are independent of each other. The ATX PSU is nominally rated for the total load across all rails but no single circuit can provide that much power.
Simple industrial power supplies like a Meanwell LRS-xxx-24 have one 24v rail with multiple output terminals to hook up loads to the single shared power supply.
