Max output voltage of PSU?

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Tincho85
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Max output voltage of PSU?

Post by Tincho85 »

Sorry, I didn't know where to start this thread.

I have a 12v 30a PSU and was wondering up to how much I can (safely) increase its voltage output.
13v? 14v? more?

One more thing, if lets say, the output voltage is set to 13v. The maximum amperage will decrease to 27.7? or it will remain of 30a?
The other way... if the output voltage is set to 11v. Will it deliver 30a or 32.7a?
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Re: Max output voltage of PSU?

Post by Qdeathstar »

it won't deliver 32 Amps unless you load pulls that much...

the more load you have, the more voltage drop you'll experience up to the point where the psu fails.


How safely you can increase the voltage depends on how sensitive to voltage differences your load is.

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Re: Max output voltage of PSU?

Post by Tincho85 »

I was scared of turning the screw down too much and break the power supply. But still did it and found out that the max output voltage is 14.98vDC and the minimum 10,48vDC.
Now I wonder what are the drawbacks of powering the whole printer with 14,5vDC...

The bed would appreciate the higher voltage. Would it be too risky for the rambo mosfets?
Fans, I think they could be protected via eeprom (Extr. 1 extruder cooler speed?).
Motors, something needs to be changed in the firmware?
40w Heater cartridge, can it handle it?
What else?
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Re: Max output voltage of PSU?

Post by Polygonhell »

The only real issue running at >12v is that anything that takes 12V is getting the increased voltage.
The Rambo is fine, you'll get increased power draw from the bed/hotend, but those are probably fine assuming the wiring is good. Running 15V through the fans will likely shorten their lives.
FWIW I commonly turn those sort of power supplies up and have had few problems on other printers.

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Re: Max output voltage of PSU?

Post by IMBoring25 »

You'll be working everything harder, pushing almost 50% more power through all the circuits.

If you haven't moved the bed current off the board with a relay, the heat bed terminal on the board is a likely candidate for spectacular failure. Several here have melted the terminal down WITHOUT messing with the voltage (myself included, though mine were Melzis on a RepRapPro Mendel).

That will probably also, in some usage scenarios, come close to rated current at well above rated voltage, so the PSU itself may go into protection (or, absent protection, do something more spectacular).

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Re: Max output voltage of PSU?

Post by Tincho85 »

Actually, I did have the bed with a SSR+24v setup combo, but my fotek failed recently (worked fine for almost 2 years). An Auber one is on it's way, but in the meantime I was considering bumping up the voltage of the 12v psu. It's taking forever for the bed to heat now :/

Thanks for the heads up guys, I'm not going to mess with the voltage, this is my only board.
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Re: Max output voltage of PSU?

Post by Eric »

To answer the original question, a 350W supply has a cooling system designed to function at 350W or less. If you increase the voltage, assume the available current has been reduced appropriately. At the same time, as you increase voltage your loads current requirements may be going up.

Nothing on the Rambo should break from raising the voltage a few volts, as that's still well short of the boards specified limits. Its the stuff that's connected to the Rambo that you need to evaluate, along with any increased current requirements as mentioned above.

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Re: Max output voltage of PSU?

Post by tylurker »

Im running my cheap 350W 24V China PSU at 30.59V steady with the v adjustment pot up all the way. the steppers like it.

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Re: Max output voltage of PSU?

Post by Mac The Knife »

I've been running my RM V2 at 14.8 volts for a while now, with no issues. The only fans I've had to replace are the peek fan, and the RamBo fan, and they were replaced while I was still using the stock ATX power supply.
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Re: Max output voltage of PSU?

Post by Tincho85 »

You are correct Eric, the best thing is not to pull more than 80% of their maximum power. Either way, yes. I also think a 30a psu can handle the load at 14,5v.

If anyone is interested, regarding this:
Tincho85 wrote:the output voltage is set to 13v. The maximum amperage will decrease to 27.7? or it will remain of 30a?

Yes it will decrease.

Tincho85 wrote:if the output voltage is set to 11v. Will it deliver 30a or 32.7a?

It will still deliver 30a.

Source: http://nz.wellforces.com/resources/how-to-calculate-maximum-output-currentpower/319/#.V-bjiIWcG9I

@tylurker wow that's a lot! why that much?
@Mac, 24v fans? or with 12v ones?

Now I'm baffled, mixed opinions. To do or not do to... :D
Silly question, would I have to tweak the motor current in the firmware if the psu is bumped to 14,5v?
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Re: Max output voltage of PSU?

Post by Mac The Knife »

No. Leave the motor current the same.
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Re: Max output voltage of PSU?

Post by Qdeathstar »

It's crazy how much difference a few volts make.. i was able to turn the dial from 12v to 15v on the stock PSU and now my bed heats up to 100c in about 10-15 minutes vs 30-35minutes... Won't have to do the 24v upgrade now, as im happy with the 10-15 minutes :D

Now, if i could just get this other issue i'm dealing with solved :D

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Re: Max output voltage of PSU?

Post by Eric »

Qdeathstar wrote:It's crazy how much difference a few volts make.. i was able to turn the dial from 12v to 15v on the stock PSU and now my bed heats up to 100c in about 10-15 minutes vs 30-35minutes... Won't have to do the 24v upgrade now, as im happy with the 10-15 minutes :D


Not crazy at all, if you look at the math: Power = E*E/R
If E = 12V and R = 1.1Ω, E*E/R = 130.9 Watts
If E = 15V and R = 1.1Ω, E*E/R = 204.5 Watts
204.5/130.9 = 1.56
That's at 56% improvement in heating power for the bed. Also in power demanded from the power supply.

The people that upgrade to 24V with a new power supply and stuff are getting a 400% improvement...which is WAY more than they needed in most cases.

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Re: Max output voltage of PSU?

Post by Tincho85 »

I just increased the voltage of the PSU to 14vDC and measured the bed mosfet of the Rambo.
Be warned, it does get hot.

While heating (from 0º to 60º) it got to 54ºc
Now that it's just regulating, it went down to 35ºc
All other mosfets (hotend, fans, etc) 23ºc

I guess that when printing ABS, with a bed temp of +/-100ºc, the mosfet temperature would increase even more.
I'm going to monitor it for a while.

PS: is it safe 54ºc? when would it become dangerous to the point of melting it?
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Re: Max output voltage of PSU?

Post by Eric »

Tincho85 wrote:I just increased the voltage of the PSU to 14vDC and measured the bed mosfet of the Rambo.
Be warned, it does get hot.

While heating (from 0º to 60º) it got to 54ºc
Now that it's just regulating, it went down to 35ºc
All other mosfets (hotend, fans, etc) 23ºc

I guess that when printing ABS, with a bed temp of +/-100ºc, the mosfet temperature would increase even more.
I'm going to monitor it for a while.

PS: is it safe 54ºc? when would it become dangerous to the point of melting it?


23C is probably your ambient temperature, or close (25C = 77F)
35C is less than your body temperature. (98.6F = 37C)
54C (129F) isn't hot enough to burn your finger.
In general, if electronics don't get too hot to touch, you're in great shape.
In the case of power mosfets, you're probably still good up to about 150C. Check the data sheet to be sure.

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Re: Max output voltage of PSU?

Post by dc42 »

The bed heater mosfet used on RAMBO according to the schematic at http://reprap.org/mediawiki/images/d/d0 ... c-note.png is a PSMN7R0-60YS. This is a terrible choice, because it's not suited to a gate drive voltage as low as 5V. No sane electronics engineer would choose it. That's why it gets hot. How hot will depend on how lucky you are with the particular mosfet on your board, and on the exact voltage on the +5V rail. The mosfet should preferably be replaced by a more suitable one, which would run cooler and reduce the voltage drop - thereby increasing the bed power a little. Have you measured the voltage drop across it when the bed is operating at full power?

That said, 54C or a little higher for the temperature of the *tab* of the mosfet (not the plastic case) should not be a problem - although it will heat up other components in the vicinity. The maximum allowed junction temperature for that mosfet is 175C.

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Re: Max output voltage of PSU?

Post by Qdeathstar »

So, one of the side affects of doing this (which i expected) was that my led strips are burning out because of the higher voltage (and because i have them inside the heated enclosure)...

are there better choices for LEDS? ones that maybe run at 15v? I know there are 24 strips, but i think the light they'd put out at 15v would be too small.

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Re: Max output voltage of PSU?

Post by Tincho85 »

I use a cheap 2a power supply to power up my lightning. They cost like u$3.
Add a switch and you are done.
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Re: Max output voltage of PSU?

Post by Qdeathstar »

yeah, I hear you its just extra wires... plus I was hoping for some suggestions besides the strips.... I don't think they are holding up to well to the heated enclosures either...

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Re: Max output voltage of PSU?

Post by dc42 »

Qdeathstar wrote:So, one of the side affects of doing this (which i expected) was that my led strips are burning out because of the higher voltage (and because i have them inside the heated enclosure)...

are there better choices for LEDS? ones that maybe run at 15v? I know there are 24 strips, but i think the light they'd put out at 15v would be too small.

You could put put a few 1N4001 or similar silicon diodes in series with your LED strips to reduce the voltage back to 12V.

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Re: Max output voltage of PSU?

Post by rurwin »

dc42 wrote:You could put put a few 1N4001 or similar silicon diodes in series with your LED strips to reduce the voltage back to 12V.


+1
around 0.7V drop for each diode, forward biased, of course.
Depending on how the LED strips work, you might get more life out of them by running them under-voltage. LEDs used to have infinite life but the new ultra-bright ones are used so close to their limit that they don't.

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