Discussion and Recommendations for a 24V Power Supply?

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gestalt73
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Discussion and Recommendations for a 24V Power Supply?

Postby gestalt73 » Mon May 19, 2014 7:11 pm

So, after noticing that the Smoothieboard supports 24V power for everything, steppers, heated bed, hot end, I started looking for a good 24V PSU.

For power budgeting I'm assuming (does this sound right?):
  • 10A for the heated bed
  • 3A for extruder 1
  • 3A for extruder 2
  • 4A for all 5 steppers

Here is the best one that I've come across so far, it's a Meanwell SE-600-24
http://www.jameco.com/Jameco/Products/ProdDS/295902.pdf

They're selling it for $89.95
http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_295902_-1

I'm pretty sure that this one won't entirely fit into the space that the current PSU sits in, but I think I'll be ok with that. Or I'll hack the base to make it fit. ;-)

Also, just in case anyone else is thinking about doing this, everything needs to support 24 volt power, including all hotend fans, part cooling fans, etc.

What is everyone else using, and what would you recommend?

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby nitewatchman » Tue May 20, 2014 9:15 am

You may be a little low on your bed running at 24 volts. The Rostock bed is in the 17A to 20A range @ 24VDC. You should do you own math however to assure that you have capacity. Most P/S will just shut down in an overload situation.

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby bdjohns1 » Tue May 20, 2014 10:48 am

I've got the Meanwell 750-24 750watt supply, which gives me 31.x amps to play with. Right now, I'm only running the bed off it, and everything else on the old 12v supply, with an SSR driving the output.

Instead of converting everything to 24V, I actually got a couple of small DC-DC converters off eBay I'm going to try sometime. Each one's rated to 10A on the 12V side. I figure I'll put the hot end and electronics on 1, the steppers on the other. In theory, my 750W supply should be ok with that plus the bed. Conversion losses on the DC-DC is supposed to be ~90% or so.

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby gestalt73 » Tue May 20, 2014 12:50 pm

Oh, what a bummer, I totally forgot about ohms law and power.

Double the volts, means doubling the amps, which means quadrupling the power.

So, I I just wired everything up to 24v without setting a max_pwm or current values, my power consumption would be in the 40amp range, or somewhere around 960watts. That's alotta watts. And I'm also guessing, that except for the heated bed maybe, running the hotends and steppers at 24v all out would be a bad idea.

And if I limited each hotend and stepper to half it's available amps at 24v, using a max_current 25% or max_pwm value of 64/256, there'd be no difference than running the whole shebang at 12v, right?

So, it looks like it doesn't make alot of sense to run a 500w 24v supply for everything, but if I ever needed a boost for the heated bed, that power supply might fit the bill.

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby nitewatchman » Tue May 20, 2014 5:03 pm

Correct logic - math may be off. I think that you would be at 20A or 480W on the bed.

There is nothing wrong with the concept of running the bed at 24VDC. You would wire the SSR to the Rambo output as if it was the bed. This will cause the SSR to switch on and off very quickly, talking milliseconds here as the Rambo calls for power controlled by the PID Loop. The bed is then connect to the 24VDC power supply with the SSR output in the circuit as a switch. The Rambo controls the bed power by switching the output rapidly with amounts of dwell time or Pulse Width Modulation. On the output side of the SSR the circuit is just a brute force circuit juicing the hot bed.


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Re: Discussion and Recommendations for a 24V Power Supply?

Postby snoman002 » Tue May 20, 2014 6:39 pm

I think that's backwards. 480 watts into a heated bed would turn it into a cooking plate! You only need so much power to achieve a certain effect, double the volts and you should be able to half the current needed for any par ocular effect.

In effect, your only going to need a certain amount of watts to make the bed put out a set amount of heat. At 12 volts it would take XX amps, at 24 volts it would take half as many amps.

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby Eric » Tue May 20, 2014 7:22 pm

snoman002 wrote:I think that's backwards. 480 watts into a heated bed would turn it into a cooking plate! You only need so much power to achieve a certain effect, double the volts and you should be able to half the current needed for any par ocular effect.

In effect, your only going to need a certain amount of watts to make the bed put out a set amount of heat. At 12 volts it would take XX amps, at 24 volts it would take half as many amps.


You're correct on what you "need", but that doesn't change the realities of what happens when you increase the voltage without making any other changes to a resistive circuit.
Assuming the circuit doesn't fail entirely, the math is easy:

Amps = Volts / Resistance
Power = Volts * Amps
Power = Volts * Volts / Resistance

The variable in this dicussion is Volts, not Resistance. To change Resistance would mean replacing the heat bed itself.

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby snoman002 » Tue May 20, 2014 8:47 pm

That would imply the bed was on full power at all times, but how do you change the temp of the bed now?

Your trying to maintain a temp, that temp takes a certain amount of power and that doesn't change. To change that temp you vary the circuit to maintain the same amount of power being consumed to heat the bed.

Point being, in operation, 24 volts will consume less amps to maintain a set temperature.

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby ZakRabbit » Wed Jul 22, 2015 12:01 am

snoman002 wrote:That would imply the bed was on full power at all times, but how do you change the temp of the bed now?

Your trying to maintain a temp, that temp takes a certain amount of power and that doesn't change. To change that temp you vary the circuit to maintain the same amount of power being consumed to heat the bed.

Point being, in operation, 24 volts will consume less amps to maintain a set temperature.


Somewhat along these lines, I bought a 24V power supply, but it is rated at 20A. By my calculations, with the Onyx at 1.1 ohms I'll be right on that limit. I see two options: try to sell this one and buy one with a higher amperage rating, or install a power resistor in series with the bed. If the second option is feasible, any recommendations on such a resistor? 1 ohm should be good, but would one of those huge aluminum bodied units be required?

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby Tincho85 » Wed Jul 22, 2015 12:07 am

ZakRabbit wrote:
snoman002 wrote:That would imply the bed was on full power at all times, but how do you change the temp of the bed now?

Your trying to maintain a temp, that temp takes a certain amount of power and that doesn't change. To change that temp you vary the circuit to maintain the same amount of power being consumed to heat the bed.

Point being, in operation, 24 volts will consume less amps to maintain a set temperature.


Somewhat along these lines, I bought a 24V power supply, but it is rated at 20A. By my calculations, with the Onyx at 1.1 ohms I'll be right on that limit. I see two options: try to sell this one and buy one with a higher amperage rating, or install a power resistor in series with the bed. If the second option is feasible, any recommendations on such a resistor? 1 ohm should be good, but would one of those huge aluminum bodied units be required?


or dialed it down to 20vDC
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Re: Discussion and Recommendations for a 24V Power Supply?

Postby ZakRabbit » Wed Jul 22, 2015 12:27 am

Tincho85 wrote:
ZakRabbit wrote:
snoman002 wrote:That would imply the bed was on full power at all times, but how do you change the temp of the bed now?

Your trying to maintain a temp, that temp takes a certain amount of power and that doesn't change. To change that temp you vary the circuit to maintain the same amount of power being consumed to heat the bed.

Point being, in operation, 24 volts will consume less amps to maintain a set temperature.


Somewhat along these lines, I bought a 24V power supply, but it is rated at 20A. By my calculations, with the Onyx at 1.1 ohms I'll be right on that limit. I see two options: try to sell this one and buy one with a higher amperage rating, or install a power resistor in series with the bed. If the second option is feasible, any recommendations on such a resistor? 1 ohm should be good, but would one of those huge aluminum bodied units be required?


or dialed it down to 20vDC


That came to mind, I was just worried that would still be too close to max output even if just during initial warming. I do have an ssr, and I made sure to get the brand that is less likely to be a knockoff.

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby teoman » Wed Jul 22, 2015 1:59 am

While the bed is heating up, that is effectively the only circuit in the system. The motors are not running and the hotend can be setup to start heating up after the bed is up to temp.
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Re: Discussion and Recommendations for a 24V Power Supply?

Postby Jimustanguitar » Wed Jul 22, 2015 8:31 am

I'm pleased with my Mean Well SP-500. It was surplus though, I'd hate to pay for it new.

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby JFettig » Wed Jul 22, 2015 10:20 am

Here are a few good ones to search ebay for:
SP-500-24
SP-750-24 - I have one in my custom delta, its kind of loud
SE-600-24


Jim - is your SP-500-24 fan really loud?

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby Jimustanguitar » Wed Jul 22, 2015 10:56 am

JFettig wrote:Jim - is your SP-500-24 fan really loud?


It's definitely louder than an ATX supply, and I have the covers off of my machine so the sound isn't muffled by being enclosed in the base, but I wouldn't call it "really" loud, no. The main difference is that the fan switches on and off with a thermostat instead of just being on all the time. You notice when it turns on, but probably wouldn't think about it at all if it were on constantly.

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Re: Discussion and Recommendations for a 24V Power Supply?

Postby stonewater » Wed Jul 22, 2015 7:25 pm

my 30 amp 24 volt meanwell is LOUD... so loud I cannot use it in the house, so I am back to 12 volts and gonna get me a corvair 750 watt psu. I will sell it if someone wants it, along with the SSR..... check amazon pricing, that's where I got it .

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