Using same PSU for printer and heated bed?

[tommyph1208 55]

So...

Just to revive the never dying dscussion on heated bed upgrades for the UM1 I wanted to ask a few questions in relation to this...

First of all, I am no big expert when it comes to electronics, so bear with me if something is way off...

I have this heated alu bed lying around: http://reprap.me/front-page-show/alu-reprap-heater-board-mk3.html

And I was talking to a friend of mine about doing a heated bed upgrade for my UM1, and the possibility of using the same PSU for both printer and the heated bed...

I've read enough on different forums and websites to come to the conclusion that I should not attempt to connect the heated bed directly to the UM Electronics, but instead use the heated bed output of those to control a relay sitting in between the heated bed and a 12/24V power supply...

I'm not a big fan of adding more cables, weight etc. to the printer and would therefore really like to make do with just one Power supply...

So I guess my qustion boils down to:

Is it possible/recommendable to eg. get a 20V power supply with enough watts to run both printer and heated bed, but connect them seperately to the PSU?

(UM electronics directly, Heated bed through relay)

My friend was worried about voltage fluctuations when the relay kicks the heated bed on and off, and how these would affect the rest of the printer... Any input on that? Has anyone done something similar?

 

[owen 19]

As long as the PS has enough watts. Allow 70W for UM. Add the HB Watts and go at least 50W more than that to be sure and you should be right. 24V is more common for HB's though and if you go to 24V for UM you may need a better 12V reg inside UM or at least provide better cooling for the current one.

 

[tommyph1208 55]

As long as the PS has enough watts. Allow 70W for UM. Add the HB Watts and go at least 50W more than that to be sure and you should be right. 24V is more common for HB's though and if you go to 24V for UM you may need a better 12V reg inside UM or at least provide better cooling for the current one.

 

Thank you for the insight Owen

I read somewhere that the alu heatbed I have should really function anywhere in between 12 and 24V (it has points for those two levels of current to be soldered onto it)

I think I would be most comfortable with not feeding more than the default current into the Ultimaker PCB, having to replace/heat manage a bunch of components that might or might not cope with that...

Any idea what would happen by powering the 24V port of the HB with just 20V?

And what about the voltage fluctuations I mentioned? I read somewhere that someone had measure a 24V PSU dropping to 21-22 V when the relay kicks on the heated bed (rising again afterwards), If I got, say a 20V PSU, it would perhaps momentarily drop to 17-18V, maybe even lower... How would that effect the printing UM?

 

[am001 0]

I use a 24v 400W PSU from China cia eBay. It adjusts down to 19v, same as the UM power supply, and can drive a 12v reprap heated bed PCB very nicely direct from the existing MOSFET. Draws around 350W during warm up with everything on full. Very neat, no relays, fast warm up and dead stable temperature if you make Marlin use PWM for the bed.

Andrew

 

[tommyph1208 55]

I use a 24v 400W PSU from China cia eBay. It adjusts down to 19v, same as the UM power supply, and can drive a 12v reprap heated bed PCB very nicely direct from the existing MOSFET. Draws around 350W during warm up with everything on full. Very neat, no relays, fast warm up and dead stable temperature if you make Marlin use PWM for the bed.

Andrew

 

So you can turn your 24V China PSU down to run only 19V?

But how come the UM wiki specifically state that you should not run a heated bed directly from the UM PCB? Are you not worried about that?

All these contradicting information get me seriously confused...

 

[owen 19]

So you can turn your 24V China PSU down to run only 19V?

But how come the UM wiki specifically state that you should not run a heated bed directly from the UM PCB? Are you not worried about that?

All these contradicting information get me seriously confused...

 

Myself and a few others have blown up the on board MOSFET like this. I don't know how but some people have gotten lucky. Mine only took about a minute to blow.

The trouble with running a 24V HB at 20V it will heat up much slower. Change in power is proportional to the square of the change in voltage.

So if you halved the voltage the power will be a quarter of the original.

The upper limit of voltage is about 30+ I believe. Limited by what the stepper drivers can take and the 12V reg. (which will heat up much more with higher voltage)

 

[tommyph1208 55]

Myself and a few others have blown up the on board MOSFET like this. I don't know how but some people have gotten lucky. Mine only took about a minute to blow.

The trouble with running a 24V HB at 20V it will heat up much slower. Change in power is proportional to the square of the change in voltage.

So if you halved the voltage the power will be a quarter of the original.

The upper limit of voltage is about 30+ I believe. Limited by what the stepper drivers can take and the 12V reg. (which will heat up much more with higher voltage)

 

Yes I heard horror stories about that and definately don't feel like trying out my luck ith direct 24V to the UM... I have no problem withusing a relay...

Regarding the curret used to power the heatbed; I have this quote from the RepRap wiki (http://reprap.org/wiki/PCB_Heatbed):

"It has dual power mode optimized for 12 or 24V but you can also use everything in between (16V, 19V what have you) (Your printer controller will regulate the power to the heatbed in order to get your preset temperature.)"

Does this basically refer to PWM mode of heating? Which is not what I will be using with a relay...? Or am I completely off?

The wiki also mentions all sorts of other options, like:

 

"With 15V on the 12V terminals will maintain approx. 115 degree Celsius without regulation"

and

"Running 24V on the 12V terminals will heatup the heatbed to 100 degree in only 2 minutes

(Your printer controller will regulate the power to the heatbed in order to get your preset temperature.)"

 

[owen 19]

Using the relay your temp will be regulated and you can apply 24V to the 12V terminals to get fast heating.

You will get double the current running through the cables and relay though and 4 times the power into the HB.

Your power supply will obviously need to supply 4 times the power as well.

It's all a balancing act. Voltage of PS chosen. Connecting to which terminals on the HB(12V and 24V). Trading of power required to speed of heating and cables required and if you want to run the UM off the same PS then that adds to the mix. Going lower voltage to the UM is possible down to about 15V but you can get slightly less performance from your stepper motors.

If you could find a high powered 19V PS or 24V adjustable PS (Common I think, mine is adjustable but only puts out 360W), you could try running the 12V HB circuit from the 19V. It will be quick but you'll need fairly high power, I don't know how much and reasonable cables and relay. It would be good if you could find someone who's done this to find out the current and power required.

 

[tommyph1208 55]

Using the relay your temp will be regulated and you can apply 24V to the 12V terminals to get fast heating.

You will get double the current running through the cables and relay though and 4 times the power into the HB.

Your power supply will obviously need to supply 4 times the power as well.

It's all a balancing act. Voltage of PS chosen. Connecting to which terminals on the HB(12V and 24V). Trading of power required to speed of heating and cables required and if you want to run the UM off the same PS then that adds to the mix. Going lower voltage to the UM is possible down to about 15V but you can get slightly less performance from your stepper motors.

If you could find a high powered 19V PS or 24V adjustable PS (Common I think, mine is adjustable but only puts out 360W), you could try running the 12V HB circuit from the 19V. It will be quick but you'll need fairly high power, I don't know how much and reasonable cables and relay. It would be good if you could find someone who's done this to find out the current and power required.

 

Hoping that someone stumbles upon this thread

 

[jonnybischof 60]

It's definetly better to use 2 PSUs.

I don't know about the UM warranty policy, but I think that if you decide to use a different PSU than the one supplied (absolutely no matter whether it's almost the same or something completely different), you will void your warranty for the electronics, which is 200 Euros if you have to replace them.

-> I may be off with that policy thingy, but that's the standard.

Also, if I'm allowed to say that, the UM1 electronics board is not really suited to drive a high current heated bed, even if there were a sufficiently powerful PSU. I'll take the standard low-power switch which is used to switch the DC supply on the electronics on and off as an example. This thing already sparks enough as it is when flipping.

So, the best way to go is using a relay (or even better: a MosFET switch, maybe tonight I get around to posting something about that) and a second PSU.

A standard 200W industrial PSU that you can get on Ebay or a more decent electronics shop is usually small enough to fit under the printer (print some extended feet for the UM if necessary) and is pretty cheap.

 

[tommyph1208 55]

It's definetly better to use 2 PSUs.

I don't know about the UM warranty policy, but I think that if you decide to use a different PSU than the one supplied (absolutely no matter whether it's almost the same or something completely different), you will void your warranty for the electronics, which is 200 Euros if you have to replace them.

-> I may be off with that policy thingy, but that's the standard.

Also, if I'm allowed to say that, the UM1 electronics board is not really suited to drive a high current heated bed, even if there were a sufficiently powerful PSU. I'll take the standard low-power switch which is used to switch the DC supply on the electronics on and off as an example. This thing already sparks enough as it is when flipping.

So, the best way to go is using a relay (or even better: a MosFET switch, maybe tonight I get around to posting something about that) and a second PSU.

A standard 200W industrial PSU that you can get on Ebay or a more decent electronics shop is usually small enough to fit under the printer (print some extended feet for the UM if necessary) and is pretty cheap.

 

I bought my printer second hand, have no warranty whatsoever...

I absolutely agree about driving the HB through a relay rather than directly through the UM board, but as I see it this really shouldn't have anything to do with whether you could ALSO drive the UM from that same PSU?

As Ownen mentions; As long as the PSU current is somewhere close to the standard UM one (19-20V) and has enough power that you can drive both units from it, it should work right?

Question sort of remains though about exactly how many watts the HB will draw from the PSU if 20V is supplied to its 12 or 24V port, and what will this off value mean for its performance, (heat up time, likelihood-of blowing-up etc.)

Also, I am still uncertain about the possibility of the PSU momentarily dropping from the 20V to something lower when the relay kicks on the HB... like: How much of a drop, how long to recover, and what will this do to the printer mid print?

 

[jonnybischof 60]

Yes, it should work. If you supply the UM with 20V, this will also increase the printhead heater power a little bit. I guess this won't matter much, though.

You can easily calculate how much power the HBP will draw at whatever voltage:

U = R * I

means: Voltage (U) equals Resistance (R ) * Current (I). Units are Volt (voltage), Ohms (resistance) and Amperes (current).

And, second formula:

P = U * I

means: Power (P) equals Voltage (U) * Current (I). Units are Watts (power), Volts (voltage) and Ampere (current).

Example 1: A 12V, 200W power supply can deliver 16.7 Amps of current.

Example 2: A heated bed which says "12V, 100W" will draw 8.3 Amps of current and have around 1.5 Ohms resistance.

----------------------------------------------------------------------------------------------

The MK3 heated bed says "1.4 to 1.6 Ohms for 12V" -> that makes 8 Amps of current = 96 Watts

It also says "5.0 to 5.4 Ohms for 24V". That makes 4.6 Amps of current = 110 Watts.

So I guess the target power of the MK3 heatbed is 100 Watts. You shouldn't go much higher than that.

If you take a 20 V PSU and use the 24V configuration, than you get 20V divided by 5.2 Ohms = 3.8 Amps. That makes 20V times 3.8 Amps = 77 Watts.

So you lose almost 30% of power.

If you take the 12V configuration with a 20V PSU, you get 13 Amps = 260 Watts -> this will most probably make the MK3 go up in smoke...

As Owen already said: Always leave some headroom for the PSU. If you take a 200 Watts PSU and draw 200W from it, it will run hot and possibly not live as long as it should.

It depends on the PSU, but usually the ideal load for a switching PSU is 65 - 80%. Go for that range and you shouldn't have any problems with that.

/edit

corrected a calculation error on the second example...

 

[tommyph1208 55]

Yes, it should work. If you supply the UM with 20V, this will also increase the printhead heater power a little bit. I guess this won't matter much, though.

You can easily calculate how much power the HBP will draw at whatever voltage:

U = R * I

means: Voltage (U) equals Resistance (R ) * Current (I). Units are Volt (voltage), Ohms (resistance) and Amperes (current).

And, second formula:

P = U * I

means: Power (P) equals Voltage (U) * Current (I). Units are Watts (power), Volts (voltage) and Ampere (current).

Example 1: A 12V, 200W power supply can deliver 16.7 Amps of current.

Example 2: A heated bed which says "12V, 100W" will draw 8.3 Amps of current and have around 1.5 Ohms resistance.

----------------------------------------------------------------------------------------------

The MK3 heated bed says "1.4 to 1.6 Ohms for 12V" -> that makes 8 Amps of current = 96 Watts

It also says "5.0 to 5.4 Ohms for 24V". That makes 4.6 Amps of current = 110 Watts.

So I guess the target power of the MK3 heatbed is 100 Watts. You shouldn't go much higher than that.

If you take a 20 V PSU and use the 24V configuration, than you get 20V divided by 5.2 Ohms = 3.8 Amps. That makes 20V times 3.8 Amps = 77 Watts.

So you lose almost 30% of power.

If you take the 12V configuration with a 20V PSU, you get 13 Amps = 260 Watts -> this will most probably make the MK3 go up in smoke...

As Owen already said: Always leave some headroom for the PSU. If you take a 200 Watts PSU and draw 200W from it, it will run hot and possibly not live as long as it should.

It depends on the PSU, but usually the ideal load for a switching PSU is 65 - 80%. Go for that range and you shouldn't have any problems with that.

/edit

corrected a calculation error on the second example...

 

Thank you for that little recap of Ohms law

The wiki actually says:

"Running 24V on the 12V terminals will heatup the heatbed to 100 degree in only 2 minutes (Your printer controller will regulate the power to the heatbed in order to get your preset temperature.)"

But nothing about it going up in smoke though... So it might actually be worth a try if the 30% loss makes it too slow?

Just had a quick look at my standard UM PSU and its rated at 120W... that + the 260W for the heated bed and then overshooting to land somewhere around the 65-80% of total PSU capacity gives me at a 20V PSU between 475 and ~585W

 

[jonnybischof 60]

I'm quite good at recapping stuff, am I not?

The 120W PSU for the Ultimaker is already oversized - Owen mentioned the UM draws about 70W.

If the MK3 can cope with 260W, it's a pretty good build... It is generally possible, being an aluminum-core PCB which is technology made exactly for that purpose. So I guess they did a pretty good job on that one - didn't expect it.

It's definetly not going to work with any normal PCB

Having less than 100W would probably suck - better to have 260W if that works.

I'm using an ~180W silicone heater for my Basalt stone bed which takes ages to heat up to 100°C (past 65°C it gets really slow), but that thing has 2kg of material that needs to be heated up...

You might need to put some effort into the heater controller configuration (PID settings). If it changes the temperature very quickly, the regulation may oscillate.

 

[drayson 75]

Hi! Had the same idea (1PSU) a while ago but where told that the main board and the plugs might not make it.

There is a description @ the wikimanual of the UM1.

If you try it with a single PSU and have success I would be happy to hear about!!

[owen 19]

You definitely don't want to use the current plug/socket and switch to supply everything.

 

[tommyph1208 55]

You definitely don't want to use the current plug/socket and switch to supply everything.

 

Naturally I would exchange the plug and switch with the one of the PSU I'm buying, and then connect the UM board directly to that PSU...

I still don't know whether or not I would like seperate on/off switches for printer and heatbed... Probably not since the heated is only drawing power when switched on by a relay anyways....

Does anyone know of any PSU suppliers in Europe that might have what I'm looking for? Buying from outside EU add some VAT, Taxes and fees that I would prefarably like to avoid, though buying from china might very well end up being the cheapest solution regardless of the mentioned fees.

Any experience with chinese PSUs of any type? Do they live up to their specs and your user requirements?

 

[am001 0]

I have to disagree with:

"It's definetly not going to work with any normal PCB"

It works fine with the normal 12v reprap pcb heater at 19v. I have mine sandwiched between a 3mm alu plate below, profiled same as the acrylic bed so it uses the UM leveling method, and a 5mm alu plate on top, the size of the PCB, which has been milled flat.

Works Perfectly and has done for over a year. Very neat solution, and it heats to 100deg for ABS in about 4 mins. No where near smoke temperature, the solder resist on the PCB isn't even discoloured.

I imagine that the ALU reprap beds would be very similar to what I have.

PSU I got from China is fine, and they are so cheap that if you found a reseller in EU, it would likely be a Chinese one they are reselling anyway!

If you are worried about blowing the MOSFET because of overheating, replace it (for about £4) with a modern very low Ron version. There are ones now that are rated at over 600W in a TO220 package. Alternativly put a small heatsink on it!

Personally I would not give up the simplicity, stability and control of the PWM via the MOSFET by introducing a relay.

You must bypass the 5A DC connector though. I soldered leads direct to the PCB behind the connector.

 

[drayson 75]

Guys, as I read your postings, I really started again to think about my initial idea to build a HB too...

I took a look at the spec for the MK3 alu HB at the page likned above and I hope that someone can help me understand the connections...

With a MK2 it´s more or less fine (for a mechanical guy like me) but with this pattern I´m a bit screwed...

The big pads are for 12/24V and ground - that´s clear.

But for what are two the small pads near by?

The NTC pads are for connecting the termistor - but where to place it - as usual in the middle of the plate or as on some picures shown as SMD directly at those pads?

Additionally I can´t find a hint if or where I could mount a LED for status...

I would be very happy if someone could point this out for me....

 

[tommyph1208 55]

Guys, as I read your postings, I really started again to think about my initial idea to build a HB too...

I took a look at the spec for the MK3 alu HB at the page likned above and I hope that someone can help me understand the connections...

With a MK2 it´s more or less fine (for a mechanical guy like me) but with this pattern I´m a bit screwed...

The big pads are for 12/24V and ground - that´s clear.

But for what are two the small pads near by?

The NTC pads are for connecting the termistor - but where to place it - as usual in the middle of the plate or as on some picures shown as SMD directly at those pads?

Additionally I can´t find a hint if or where I could mount a LED for status...

I would be very happy if someone could point this out for me....

 

As I understand it the thermistor can be placed pretty much anywhere as the Alu plate has a very even heat distribution so maybe directly at the connectors is fine.

On my MK3 there are two connector pads just below the NTC (I think those are the same drayson is referring to... they are smaller than the 12/24V connectors and larger than the NTC)... as far as I have understood it, these for mounting the LED....

 

[Wrangler 0]

Guys, as I read your postings, I really started again to think about my initial idea to build a HB too...

I took a look at the spec for the MK3 alu HB at the page likned above and I hope that someone can help me understand the connections...

With a MK2 it´s more or less fine (for a mechanical guy like me) but with this pattern I´m a bit screwed...

The big pads are for 12/24V and ground - that´s clear.

But for what are two the small pads near by?

The NTC pads are for connecting the termistor - but where to place it - as usual in the middle of the plate or as on some picures shown as SMD directly at those pads?

Additionally I can´t find a hint if or where I could mount a LED for status...

I would be very happy if someone could point this out for me....

 

I put the HB on the original terminals too and put a heatsink on the mosfet, yust to make sure. works flawlessly for over 3 mnd.