Choosing a suitable power supply

[pedromelim]

I have been researching a lot about this as i dont to buy something not suitable and only find that its not enough for my needs.
Im planing my build of a coreXY printer (V-Core from RatRig) and to use it with a Duet 2 Maestro.
Originally the plan was to use an AC silicone heater but due to the dangerous of working directly with it, i want to settle with 24v, and this is where it gets a bit tricky.

Now i calculate +/- the power usage from the components and have got it rounded up to 75w, plus 360w from a 24v silicone heated bed. That sums up to 435w.
Adding 20% headroom gives me 522w.

My problem is getting a suitable and reliable power supply for this.

I got 2 ways of doing this and i would want peoples opinion to help me decide, and see if it makes sense.

Powering everything with 1 power supply using one of the power supplys bellow:

RSP-500-24 (would 504w be enough?) - https://www.mouser.com/ProductDetail/MEAN-WELL/RSP-500-24?qs=%2Fha2pyFaduiVs6X1Nelm9kKSIbOuTXswMRLDgce%2ByWC%2FKcvhXTMfqQ%3D%3D

https://www.filafarm.de/collections/elektronik/products/netzteil-ip45?variant=37225080206

Or going with a 300w silicone heated bed and using 2 power supply and this:

https://www.reprap.me/power-expander.html

Im open to suggestions on other routes i can take.

[dc42]

IMO the 504W Meanwell one you referenced will be adequate. If you are worried about running it within 20% of its maximum power output, you can always turn the output voltage down a little.

[Phaedrux]

Also keep in mind that the high wattage PSUs tend to have quite loud cooling fans.

[pedromelim]

@dc42 never tought about turning down the voltage a bit, tks for that appreciate it.
And about the 600w from filafarm? Any opinion on that?

@Phaedrux printer will remain in the office, so probably wont be a problem.

[snoozer]

@pedromelim

I would not dismiss the mains power heated bed. Sure I would stay away from no-name cheap types but as long as you use proper rated flexible cable and ground the print bed I think the mains heated bed is a great option. E3D does them in 3 different sizes, you only need a solid state relay to drive it.

BTW, I am waiting for my V-Core mechanical kit, how long ago have you ordered ? Did you order it from Rat Rig ?

Have FuN!
Jan

PS: To make the mains wiring for a AC bed heater real safe you could use industrial control cable, they are available with flexible cores in various sizes and shielding. That way if a wire inside develops a fault the shielding will cause the RCD to trip if grounded properly. In my opinion actually safer than 24V DC at high currents.

[deckingman]

Most people when upgrading to Duet boards notice how quiet the motors are. This means that noise from things like fans tends to become intrusive and people then look to install quieter fans. So I'd always go for a fan less PSU which is silent. These are reasonably priced at up to 200 Watts but tend to be expensive over that sort of power. Therefore, I'd always go for small fan less PSU and use a mains bed heater driven by an SSR.

[pedromelim]

@snoozer Yes it comes from RatRig, should be shipped next week i think hehe.
Could you link me to those cables?

@deckingman i have researched, and besides the dangerous bit on working with 220v its the part that if the SSR fails closed it will not have a way to stop that worries me the most.
I know that we can order silicone heaters with bimetallic switch to stop this but i dont like the idea of it being built in the heated bed.
I would prefer something that i could exchange if it goes "kaput" (dont know the life span on them) instead of exchanging all the heated bed.

I do have a way of doing it with a different method of cutting the power to the bed, but dont know anyone that has used it.

https://www.tindie.com/products/JasonKits/3d-printer-guard-protect-your-printer-from-fire/

In short, its a standalone circuit that shuts off the printer (or whatever is connected to it) to prevent a fire hazzard.
It can monitor 2 hot ends and 1 heated bed.

As anyone tried something similar?

As i understand i would need a SSR and a heavy duty relay NC.

[Phaedrux]

@pedromelim said in Choosing a suitable power supply:

if the SSR fails closed it will not have a way to stop that worries me the most.

A single use thermal fuse is the typical solution. Attached physically to the bed or heater pad and rated to a reasonable level.

Something like this:
https://www.be-electronics.com/searchresults.asp?Search=thermal+cut+off&Submit=

A good quality SSR certainly helps ease the conscience.
Something like this:
https://www.auberins.com/index.php?main_page=product_info&products_id=288
Or this:
https://e3d-online.com/omron-ssr

Here's a good example bed build from @mrehorstdmd
https://drmrehorst.blogspot.com/2017/07/ultra-megamax-dominator-3d-printer-bed.html

And E3D sells a ready made bed that seems very well made. https://e3d-online.com/high-temperature-heated-beds

[snoozer]

@pedromelim

Re Cable i would look at this if you can isolate it thermally from the actual bed. For example put strain relieve on the frame of the Z axix platform.

https://ie.rs-online.com/web/p/cy-cable/1762362/

or

https://ie.rs-online.com/web/p/multicore-industrial-cable/7142299/

if it touches the heated bed. For the latter I would try to find a metal braided sock/sleeve as screen. The screen would not be for interference but to have a conductive connection to earth so that if the cable breaks it will trip the RCD. The cross section depends on the heated bed ofc, keep in mind you only have a very short cable, its not like a house or industrial installation of many meters.

With the open failing SSR you have the same problem with the 24V bed, a switch in the mains supply will keep you safe from that and the thermal fuse also seems to be a good way.

My picks re cable are quick pick as idea only, I would actually go hands on in a wholesale place to feel the flexibility of it and they usually sell you a short piece instead of a 50m reel.

Jan

[deckingman]

@pedromelim In addition to what others have said about thermal fuses, be aware that MOSFETs which are on the board itself, can fail the same way as SSRs. That is to say, they can also fail in such a way that full power would be supplied to the heater.
Duet firmware does a good job of detecting heater faults but of course, it should not be relied on.
Having said all that, if you aren't comfortable about using a 220v heater then don't. But the risk of electrocution is probably higher than the risk of fire (but both can be mitigated).🙂

[snoozer]

Just to add, heater pads with adhesive may not hold up as well as factory bonded heaters. I have read in a number of places that the adhesive can be an issue at higher temperatures. So for a 24V bed I would try to get a PCB heater type, for a mains powered bed a factory vulcanised heater on aluminium.

Jan.

[snoozer]

@pedromelim

Just out of curiosity, what Hotend are you planning to use ? I am just interested in anything regarding the V-Core. I have a topic here that I extend as it go along.

https://forum.duet3d.com/topic/9465/core-xy-based-on-rat-rig-v-core-and-duet-2-ethernet

THX
Jan

[mrehorstdmd]

@phaedrux said in Choosing a suitable power supply:

Here's a good example bed build from @mrehorstdmd
https://drmrehorst.blogspot.com/2017/07/ultra-megamax-dominator-3d-printer-bed.html

I don't recommend mounting the TCO on the bed plate as I did in the page you linked. The adhesive that holds the heater on the bed is starting to let go after about 2 years. If the heater ever falls away from the bed plate the TCO won't do its job. I'll be moving the TCO soon...

I recently put a kinematic mount and new bed in SoM and mounted the TCO on the heater using a blob of high temperature silicone. That's the safer way to do it, I think. When I rework the heater in UMMD I'll probably stick the heater to the plate using the same high temperature silicone.

[wilriker]

@mrehorstdmd said in Choosing a suitable power supply:

I recently put a kinematic mount and new bed in SoM and mounted the TCO on the heater using a blob of high temperature silicone. That's the safer way to do it, I think.

That's also the way how Keenovo does it if you order the heater with a TCO. Or actually they put it under another layer of silicone but that's essentially the same.

[Phaedrux]

@mrehorstdmd Right. Good warning. Was that with the 3M adhesive sheets or was it bonded with RTV silicone? I can't remember. I've bonded my heater pad with RTV silicone, that should last a lot longer than a sticker sheet. I remember seeing your post about the PEI sheet lifting when the 3M sheet lost it's bond.

[snoozer]

@phaedrux

Hi, could you elaborate regarding RTV Silicone ? I am suspicious about adhesives and would be interested to know more. Do you by any chance have a link to a product ?

Thanks
Jan

[Phaedrux]

I used this: https://www.amazon.ca/Rutland-600-Degree-Silicone-2-7-Ounce-Super/dp/B004YEBWTG/ref=sr_1_34?crid=1ESRUA3CQI4NP&keywords=rtv+silicone&qid=1552499348&s=gateway&sprefix=rtv+sil%2Caps%2C171&sr=8-34

But there are many options and types. It's also called gasket maker.

I cleaned both the aluminum and heating pad thoroughly, then applied a thin layer of the silicone, then used a rolling pin to slowly roll on the pad. Added a bead around the edges of the pad to seal them in, and then placed it on a flat surface with a flat board over it and several rolls of filament on top to press it down. Left it to cure for a day. It's been going fine for about a year of daily use.

You can see pictures of it in the link in my signature.

[mrehorstdmd]

@phaedrux I used the adhesive that came on the Keenovo heater- it's 3M 468MP. It holds with temperature cycling for about 2 years then seems to dry out and let go.

@snoozer You can get high temperature silicone at auto parts stores for about $5-6 for a tube.

[snoozer]

I figured out by now RTV is an abbreviation lol, I thought its a brand so. Have found a number of brands and types...... Thanks for the responses however !

Jan

[Phaedrux]

@snoozer room temperature vulcanization is a mouthful.