Blowing power supplies
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on the not blowing the fuse you need to understand the a fuse rating is not absolute. there are time factors involved that are not quoted as this falls into the design and gets complex.
to give a rough idea (overly simplified and generalised before anyone pokes holes
)....a 15A fuse in general will blow at 30A ( I know weird huh)
the point is protection against faults e.g. short circuit.
in that case the current will theoretically rise to infinity and the fuse will blow "instantly"
however if it truly blew at 15A then you would have all sorts of problems as a 15A motor for example draws on average 6x current to start and most devices have an inrush current slightly higher when turned on. so in reality there has to be some headroom.
most times a fuse will handle up to about 2x the rated load for an extended duration but at over twice the load will always blow
you cant rely of a fuse for protection from slight overload, thats not what they are there for.
I hope this massive simplification makes some sense and helps going forward
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@opentoideas said in Blowing power supplies:
in the computing world you were meant to size the PSU based on generic max values for each item in the computer and the numbers often came out 3 or 4 times higher than you needed so our friendly manufacturers realised people were looking for 750W or 1200W power supplies when in reality not everything runs at the same time and a 300W PSU was all that was really needed....... result? 300W PSU badged as 1000w LOL
Actually I'm familiar with this phenomenon. I used to work in the Animation and Games field, and we blew a lot of generic power supplies, rendering scenes and textures. I would buy the more reputable brands, for my workstations when I was contracting, because I didn't want the interruptions to my work. Unfortunately this lesson hasn't carried across. Ironically, the 350w supply, which lasted the longest of the three, actually is branded as WEHO, which turns out to be still around, and seemingly a bit more reputable.
@opentoideas said in Blowing power supplies:
I hope this massive simplification makes some sense and helps going forward
Nono, this has all been very helpful. I'll be using an SSR from here on out, and if I'm lucky I'll be able to repair the 800w supply to use that as a dedicated brick for the heater, though I will take your advice first and figure out the rating for the heater. Another thing I found advised, is to lower the voltage on the power supply, to reduce it's total amps. My thinking was stupidly the other way around. More voltage, meant watts * higher voltage = more capacity. But the capacity of the power supply is fixed by it's hardware, and if you can reduce the amount of amps it has to push through, then it's not going to fail as often!
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glad it helped. on the SSR front be aware that they are different for AC and DC and again China made ones have a spec that is at best misleading and at worst a crappy mosfet unable to cope with 1% of the rated power!
sorry but its another and in some ways worse minefield.
I would think something like https://www.th3dstudio.com/product/high-amp-12v-24v-mosfet-heated-bed-or-hotend/ would be more than sufficient and little different in cost to possibly fake SSR's you could end up with
not affiliated with them in any way was just the first one I found on google that would fit the bill.
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yes lower voltage can help "tune" to what you have available.
good old ohms law - V=IxR
R is the resistance of the heater and is fixed (ish)
I = V/R so for the same resistance lowering V lowers I
at a guess your heater will have a resistance of about 1 ohm which makes the calculations simple as V~I
so 24V will be about 24A or 576W
20V will be about 20A or 400W
please check though as your hater could be wildly different LOL
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v1.03 doesn't have a bed heater fuse.
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@elmoret LOL well it wouldn't blow then. well spotted
very lucky not to damage the Duet in that case!
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But there is a blade fuse on this board? And I bought it from the recent special?
My other Duet doesn't have one. What's the fuse for?
The SSR I have is from RobotDigg; and given their 350w supply performed better than the 'rated' 400w and 800w supplies, I'm a bit trusting. But I'll be doing extensive research before wiring all of this up again. And again; your advice is very helpful.
I wonder how low you can set a 24v Power Supply? I was able to heat the bed on this printer in a surprisingly amount of time.
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@mortarart its possible that they ran out of the 1.03 and you got lucky and have the 1.04
Compare them here www.duet3d.com/DuetWifi
As for power supplies it depends some have no adjustment and even if they do its only a couple of volts either way. Just be sure to check with a meter before connecting up.
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Just checking the obvious... did you set the power supplies to the right voltage? Not putting 220v on a 110v supply or something?
800w is an amount of power that you should notice if you’re actually drawing that. It’s a small space heater worth of heat going somewhere. I would expect smoking connectors and hot wiring and such to help you track down where the energy is going.
Or, stop buying crap power supplies
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@rcarlyle said in Blowing power supplies:
Just checking the obvious... did you set the power supplies to the right voltage? Not putting 220v on a 110v supply or something?
Yes. Definitely set to 220v, on the two that are selectable. The other was sold as a 240v model.
800w is an amount of power that you should notice if you’re actually drawing that. It’s a small space heater worth of heat going somewhere. I would expect smoking connectors and hot wiring and such to help you track down where the energy is going.
Yeah, this is the bit that's weird for me. I was using 14AWG wire, and it was warm after powering the heater. But definitely not hot to the touch. 33c at the highest at the screw terminals via IR gun. And the heater wire, was cold. Room temperature.
I really don't want to be plugging in new power supplies, to blow them, considering that.
Or, stop buying crap power supplies
I'm now less convinced it was due to quality. They'd all lasted for a substantial amount of time on my other large printers.
@opentoideas said in Blowing power supplies:
@mortarart its possible that they ran out of the 1.03 and you got lucky and have the 1.04
Compare them here www.duet3d.com/DuetWifi
As for power supplies it depends some have no adjustment and even if they do its only a couple of volts either way. Just be sure to check with a meter before connecting up.Now I'm very confused. Mine has one large fuse. That image clearly has two fuses. The Duet 1.03 image has zero. I'm hoping I don't have some experimental model that is frying power supplies.
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Definitely says 1.03 on the board.
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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"
you also really need to measure the resistance of the heater. if you have for example a 12V heater then at 24V it will be 4x the power but in that case I think the Duet would have been unlikely to survive but without numbers its difficult as anything could be going on.
do you have a multimeter?
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@mortarart said in Blowing power supplies:
Now I'm very confused. Mine has one large fuse. That image clearly has two fuses. The Duet 1.03 image has zero. I'm hoping I don't have some experimental model that is frying power supplies.
The v1.04 image has 3 fuses, not 2.
The Duet v1.03 image is actually an image of a Duet v1.0.
You don't have anything experimental, you're just using generic Chinese power supplies, and they're failing because they are poor quality, plus you're running a higher load than most.
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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.
