Considering a 12v to 24v upgrade? DO IT!
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@jens55 said in Considering a 12v to 24v upgrade? DO IT!:
@DocTrucker , what makes you think that cartridge heaters or bed heaters are 'passively safe' ?
I wasn't making a statement. More that some people advocate and aim for what they describe as a passively safe system whereby the heaters are incapable of reaching an unsafe temperature if ran at 100% duty.
In reality these aren't that 'passively' safe as two faults could easily render them unsafe, such aa the hotend fan could fail which in some systems would lead to the cold end of the heatsink exceeding safe temperatures for what it is mounted in. Likewise my question was relating to the safety of the cartridges. A system maybe safe if the cartridge remained in the heater block, but I was curious if the temperature of the cartridge would exceed max safe temps if it was at 100% duty at 12V and on free air.
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@DocTrucker said in Considering a 12v to 24v upgrade? DO IT!:
I was curious if the temperature of the cartridge would exceed max safe temps if it was at 100% duty at 12V and on free air.
I guess it all depends on what you would consider a 'safe' temperature. You can expect several hundred degrees before the heat dissipation of the bare cartridge equalizes the electrical generated power (ie equilibrium).
I would suspect well over 500C which is definitively not safe when in contact with everyday substances such as paper/wood/fabric etc. On the other hand, if the cartridge is suspended in mid air, well clear of any combustible material, it will be just fine until the internal heating wire fails. -
@jens55 I'd concur that 500C would be beyond what I would call safe. I was curious if running in free air would cause them to effectively self destruct, and if that failure would be fail safe like a fuse generally holding together or if the failure would be more catastrophic, causing a potential hazard in itself.
Anyway I digress from the original posters topic.
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Fans will fail when overdriven like this, typically rather nosily. You should certainly take care of them with either replacements or a buck converter. If replacing you can go for all 5V fans everywhere and use the inbuilt 5V on the Duet for them
Heaters are not necessarily a blocker. But you MUST re-calibrate them at the least. Basically you will be getting double the power from them and if you cannot sink the extra heat fast enough the heater will burn out,.
Most heaters on powerful machines can get too hot, this is why we have thermistors, feedback and failure modes. For a printbed you can start setting things on fire etc, with hotends you can hit the melting point of the heatblock. Properly tuning them and calibrating heat sensors is your defence against this.
Heatbeds are often relatively easy, you can run most 12V heatbeds off 24V with no issues, Match the PSU to twice the stated 12V current rating, tune and calibrate, and enjoyed the fast warm up.
Hot-end Cartridges are different, they are rated for a certain power (eg 30W hotend cartridges may fail to sink 60W of heat energy and burn out internally). I'd always recommend fitting a cartridge with the correct voltage rating, I'd also recommend the 50/60W cartridge heaters over the usual 30W units, they are very responsive and allow higher flow rates.
Disaster? The original Printeye is dying with RRF 3.5 (M208 depreciated).
PrintPy2024 to the rescue!
MicroPython based; with simple wiring and and no custom PCB. -
@EasyTarget said in Considering a 12v to 24v upgrade? DO IT!:
Heaters are not necessarily a blocker. But you MUST re-calibrate them at the least. Basically you will be getting double the power from them and if you cannot sink the extra heat fast enough the heater will burn out,.
Actually they heaters receive double the current, resulting in the power squared given P = I^2 *R. Your point is still very much valid though, even more so.
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@EasyTarget said in Considering a 12v to 24v upgrade? DO IT!:
Heaters are not necessarily a blocker. But you MUST re-calibrate them at the least. Basically you will be getting double the power from them and if you cannot sink the extra heat fast enough the heater will burn out,.
Actually you will get 4 times the power out of them when you double the voltage !
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@jens55 @Nxt-1 Oops; yep. Thanks for catching that.
I forgot that in pure resistive DC circuits twice the voltage=twice the current too, Increasing Power by voltage squared. For the PSU you only need to consider the Current part of that (It's usual to spec PSU's to maximum current, not 'power', for exactly the reasons seen in my error..)That said; what I said still stands, just more so. A heavy aluminium bed like mine takes 24V despite being sold and marked as a 12V bed. With PCB beds etc you may have more problems.
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Now, everybody has got it? Doubling the voltage means to send 4 times the rated power through a component. This is clearly irresponsible. Simply DON’T DO THAT.
Under normal conditions, you can control the temperatures of the heaters with the Duet, as far as possible, it even provides one or more fallback levels. However, a single system, safe in itself, can still fail, and most of our printers have no independent backup control systems to catch a catastrophic fault.
Think of a thermistor which fails or drops out, which means the Duet can no longer monitor the associated heater - your hot end, rated for 30 watts, can go wild with 120 watts… definitely enough heat to weaken or even to melt the printed parts of the print head. Near the hot end, the deconstructed parts can easily catch fire…
@EasyTarget Still, the bed heater is laminated to the aluminium, which means the conductive path is isolated by plastic. Due to irregularities, the resistance of the path is not evenly distributed, you risk local hot spots. These can - locally - delaminate from the aluminium, are then no longer cooled and will eventually burn through, wrecking the heater. With four times the rated wattage, you are no longer on the safe side.
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Well, for me, I am converting to 24v. But ALL my components will be 24v.
The nozzle heater and fans... the print bed is relayed at 110v.
Looking forward to getting it done.
I'm also converting to MGN12 bearings so its pretty much a complete redesign and has been a slow go...I also agree what everyone else says here. Don't run 12v equipment with 24v's. Your looking for trouble.
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Well he did say he got a device to convert 24v to 12v so I would assume he powered the 12v parts from that.
Maybe not.
Frederick
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@dirtybirdnj said in Considering a 12v to 24v upgrade? DO IT!:
Hello! I recently started having issues where my printer would brown out only when using the heated bed.
A "brownout" would be an indication that your 12v power supply wasn't able to supply the required current.
This could happen with a 24v power supply as well.
Frederick
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@infiniteloop said in Considering a 12v to 24v upgrade? DO IT!:
@EasyTarget Still, the bed heater is laminated to the aluminium, which means the conductive path is isolated by plastic. Due to irregularities, the resistance of the path is not evenly distributed, you risk local hot spots. These can - locally - delaminate from the aluminium, are then no longer cooled and will eventually burn through, wrecking the heater. With four times the rated wattage, you are no longer on the safe side.
Two years in, still going strong. But your point is valid, I shouldn't be so flippant with such advice just because it worked for me. And if mine wasn't a well made unit I might well have had a burn out by now.
I still, however, consider the PSU to be the biggest fire risk in this printer, and most others.Disaster? The original Printeye is dying with RRF 3.5 (M208 depreciated).
PrintPy2024 to the rescue!
MicroPython based; with simple wiring and and no custom PCB. -
@EasyTarget said in Considering a 12v to 24v upgrade? DO IT!:
I still, however, consider the PSU to be the biggest fire risk in this printer, and most others.
Why do you think that?
The various heaters are a source of much higher temperatures.
Thanks.
Frederick
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While the heaters get hotter, they are designed to run hot.
They have temperature sensors and control circuits that monitor their heat and keep it in bounds, most PSUs just have a 'thermal fuse' that melts at a set temperature.
Heaters are unlikely to be full of dust and fluff because they are not out of sight.
Heaters don't have large electrolytic capacitors in them, don't have inductors, transformers, power IC's, and a whole bunch of circuitry that runs hot and add risks.Plus, if you think about it; all the energy that goes into the heaters has to first go through the PSU, and it is a high energy device in it's own right. It is also plugged directly into a high voltage, high current supply with no protection beyond whatever RCB/fuse that provides.
Add cheap mass manufacture and a 'pass it' attitude to Quality Control and I think I can justify this statement, somewhat
Certainly if anyone is going to fly the safety banner to advocate 'maximum caution at all times' with heaters I'd tell them to look at the wider picture and re-double their panic.Of course; the safe solution for PSU's is the same as for heaters, pay attention, don't follow my advice, Always stay in spec and never leave your machine unattended!
Disaster? The original Printeye is dying with RRF 3.5 (M208 depreciated).
PrintPy2024 to the rescue!
MicroPython based; with simple wiring and and no custom PCB. -
I still, however, consider the PSU to be the biggest fire risk in this printer
Well, that’s where the power is, but each PSU has a fuse (or more of them) and a metal case with enough distance to its components who might blow up. Our responsibility begins where the PSU ends: there is no instance to certify the correctness of our installation.
What about the cabling? Have we put a fuse on every line which might be overpowered? Are we sure of every single crimp we made? Are we on the safe side with all connectors or may they get hot? And then: we all print lots of parts for our printers. As we intentionally operate with heat - do we consider the fire load density we build into our machines?
Always consider the risk that a single heater at the hot end might go wild, reaching more than 500 C if fully powered. Out on thingiverse, you can find dozens of print head designs and fan ducts whose PLA would not withstand such temperatures because some parts come too close to the source of the heat.
At unexpected temperatures, the heater cartridge can even come loose and drop from its block: what if it induces 500 C to the plastic object it just tried to print underneath? This can well happen at the rated voltage - would you really like to go with four times the power, instead?
And worst: some of us do not even know about the risks. That stood at the origin of this thread, followed by a bold request not to hesitate any longer. Even if i’m wrong and @dirtybirdnj knows what he’s talking about - what I doubt as he exposes his poor fans to 24 V without a sign of insight -, he really should have found some words for those who take his advice for granted.
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In the past 3 or 4 decades I can count on one finger the number of power supplies that have failed on me.
But I do not buy no-name power supplies.
I will continue to have a lot more faith in name brand power supplies than in the inexpensive printers on the market.
YMMV.
Frederick
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@fcwilt said in Considering a 12v to 24v upgrade? DO IT!:
In the past 3 or 4 decades I can count on one finger the number of power supplies that have failed on me.
Having hung around in the IT industry I've actually seen plenty of well made but stressed PSU's go woof in hot server rooms. Branding is no mark of quality, and I stand by what I say; with higher voltages and energies floating around in them, and with peoples habit of putting them somewhere and then forgetting about them, they are the biggest hazard on the average 3d printer, not the hotend or bed.
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It's another occasion where I thank someone for raising a risk I had not considered, but I do doubt if well considered it poses a greater risk than the heater related risks on my systems. However, mine aren't your a typical 'cheap ones' so I've probably missed the point.
If you crowbar the PSU most units detect short circuit and shutdown faster than a fuse will blow.
Here's my checklist:
- Make sure the rating of the PSU is at most around 80% of the max expected draw.
- Wire from PSU rated to take full current of PSU upto lower rated fuses or devices.
- Fuse on mains input to PSU as close as practical to the stated draw.
- Ensure good airflow around PSU.
- Periodically check PSU for fowling and voltage output. Vacuum over vents.
- Use earth fault breakers and spike suppression on supply.
I'd say the chance of a serious PSU fault not failing the fuses on input or output or earth fault detector and becoming a fire is small.
