[resolved] Running 12V HBP at 24V for Better Performance?

[Solved: Putting 24V on the build plate is okay. Using a light dimmer and SSR could also be a solution if it's wired properly. A transformer would work, but isn't a good option.]

I recently got my Folger Tech FT-5 assembled and vaguely functioning (still need to tune), and I noticed that the 300x300mm aluminum build plate/heater takes forever to heat up. I have a 1/8" thick mirror on top as a build surface. The ambient temperature is 17C, and at 12V, it takes 23 minutes to heat to 60C! I read a little bit about this online, and I turned up the voltage on the PSU to 14V (which is the max the MKS Gen 1.4 Controller can handle) and the time was reduced to 13 minutes, but the printbed cannot reach more than 72C even with the increase in voltage. BTW, it took 45 minutes to get that hot.

Everyone seemed to be talking about replacing the bed with a silicone heater and solid-state relay, but wouldn't it be just as effective to run the build plate at 24V and drive it with a SSR instead? I would keep the current build plate, and all I would be adding is a secondary 24V PSU and a SSR that's controlled by the MKS Gen 1.4 controller. The total cost of this upgrade would be $30 for both components, when compared to ~$60 for a silicone heater alone. Is this a valid solution to my problem, or am I overlooking something serious here? Below, I've listed some specs/calculations that could be useful.

Resistance of heater: 1.8 ohms
Voltage drop from PSU to HBP @ 12V: 0.3V
Calculated power at 14V: 109W
Calculated power at 24V: 320W, which seems reasonable.

The printer is an open frame cartesian-style printer, and the heater is built into a 3mm thick aluminum plate. I currently have no thermal insulation underneath the heater, but I've read that insulation doesn't have much of an impact.

Edited 3 time(s). Last edit at 11/19/2016 08:02PM by Lazerlord.

1.8 Ohms seems very high for a 300mm² 12V bed. It's not by any chance a dual 12/24V design that you've accidentally hooked up to the 24V connections?

[edit for wrong V]

Edited 1 time(s). Last edit at 11/19/2016 11:54AM by JamesK.

Nope, there are only two pads for power (and some smaller ones for LED, etc.) and yes, it's only 1.8 ohm. My guess would be that having it be lower resistance would be a bit too much power draw for the power supply they provide, which is 12V @ ~320W.

I actually thought of a cheaper solution: A 24V transformer and a SSR, because why do I need DC anyway if it's just for the HBP?

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power supply they provide, which is 12V @ ~320W.

Wow, that's stingy. The 'standard' mk2 pcb for 200mm² is typically around 120W and is considered by most people to be under-powered. If you scale that up for 300mm² you'd want 270W just for the bed, which doesn't leave much lee-way on a 320W supply.

These days a transformer can cost more than than a switched mode power supply. I used to build linear power supplies for all my projects in "the good old days".

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JamesK

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power supply they provide, which is 12V @ ~320W.

Wow, that's stingy. The 'standard' mk2 pcb for 200mm² is typically around 120W and is considered by most people to be under-powered. If you scale that up for 300mm² you'd want 270W just for the bed, which doesn't leave much lee-way on a 320W supply.

These days a transformer can cost more than than a switched mode power supply. I used to build linear power supplies for all my projects in "the good old days".

Yeah, after looking on ebay for a 24V transformer, I see what you mean. I do realize that it's a bit stingy, but as far as being a starting point, this kit is actually pretty good for the price. So going for a separate 24V power supply and controlling the HBP with a SSR is all okay to do? I'm pretty sure it will work just fine, as the increase in thermal output is controlled by the thermister, but are there going to be any issues with hooking up 24V to this build plate? It seems rugged enough to handle it.

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but are there going to be any issues with hooking up 24V to this build plate?

I haven't tried anything like that, but I don't see any problems. With the resistance you measured I make that 320W at 24V which on a 900cm² bed should be fairly safe even if it got stuck at full power. I believe you have to be fairly careful in your choice of SSR, some of the cheaper ones have quite high resistance and will generate a lot of heat at the 13+ amps it's going to be passing. There are some notes about this (and recommendations) on the duet wiki: [duet3d.com]

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Lazerlord
Nope, there are only two pads for power (and some smaller ones for LED, etc.) and yes, it's only 1.8 ohm. My guess would be that having it be lower resistance would be a bit too much power draw for the power supply they provide, which is 12V @ ~320W.

I actually thought of a cheaper solution: A 24V transformer and a SSR, because why do I need DC anyway if it's just for the HBP?

You don't need regulated DC to power a bed heater, AC is fine. The problem is a transformer that can handle that much power is big and very heavy. I ran my printer with a 24v heated bed, transformer, and SSR for a couple years. You could try running the heater using an SSR and a lamp dimmer instead of a transformer, but may need some extra stuff to ensure safety.

320W is pretty low for a 300 x 300 mm bed. My 450W heater gets the aluminum bed up to 105C in about 6 minutes, and that's almost too long to wait. I don't further handicap it by putting a piece of glass on top that guarantees that the surface temperature is always lower than the set temperature and that you're going to be waiting longer to get to print temperature.

In the end it comes down to this: like the heaters provided in most kits, your heater is under powered. Get a 500-600W line powered heater and wire it carefully. Everything else is just band-aids that don't address the real problem.

Edited 1 time(s). Last edit at 11/19/2016 06:21PM by the_digital_dentist.

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