Power supply advice please

dc42

As Ryan and others have said, the switching frequency of the drivers is around 30kHz. That's a cycle time of about 33us. If the motor needs 4V and you use a 24V supply, then the on-time of the motors will only be a little higher than 4/24 * 33 = 5.5us at standstill. Meanwhile, your SMPS also probably has a switching frequency around 30kHz, so the feedback time constant in the SMPS must be a lot greater than 33us to prevent the SMPS being confused by its own ripple voltage. So the SMPS won't see the peaks at all, even if all the stepper drivers happen to take their peak current in sync, and will respond to the average stepper driver current.

cap

i think i am having power issues i have a 12v 25amp PSU i turn bed and hot end on and can here my hot end fan slow down just a little
now i tuned my hot end with just hot end turned on so now i get error heating to slow if i try and heat the bed and hotend at the same time
so i believe my PSU is two week would you agree
also if it is i read some where about running two PSU 1 to run the heated bed and anther to run the duetwifi is it safe and a viable option are am i just splitting hairs and need to re-tune my machine with everything turned on

dc42

I run a dual extrusion printer with an approx. 120W bed heater from a cheap 12V 25A LED PSU, with no problems. The fan slow down when the bed turns on is barely noticeable. So I suspect that either you have too much resistance in the wires and connections to the power supply, or it is indeed too weak - perhaps because you have a more powerful bed heater than I do.

Try measuring the voltage at both the power supply output terminals and on the Duet VIN terminals, with and without the bed heater turned on, to see if the power supply voltage really is dropping significantly or the problem lies in the wiring.

cap

do you know i did not even consider the amount of power draw from my heater bed i got a 12V 280W 300x300 SILICONE HEATED BED
so i would need a12v 300w 15 amp psu to run the bed alone

and in the mean time can i reduce the power consumption of my bed and wait longer for it to heat up

cap

i just looked and i got a 300w 25amp 12v pwu

cap

anyone like to recomend a good 12v psu needs to run 280w hotbed e3d hotend 2 fans and 5 motors running at 800mw each

dc42

See https://duet3d.com/wiki/Choosing_the_power_supply. But consider whether an upgrade to 24V would be beneficial, see https://duet3d.com/wiki/Choosing_stepper_motors#How_to_work_out_the_power_supply_voltage_you_need. Of course, if you do switch to 24V then you also need 24V heaters and fans.

dc42

@cap:

do you know i did not even consider the amount of power draw from my heater bed i got a 12V 280W 300x300 SILICONE HEATED BED
so i would need a12v 300w 15 amp psu to run the bed alone

and in the mean time can i reduce the power consumption of my bed and wait longer for it to heat up

You could turn down the power supply voltage a little if it has a voltage adjustment potentiometer.

cap

well if my math is right i need 350w now add 20% extra 470w that was rounded up never down
i want to stick with 12 volt i no it means things take longer to heat up but i have a stock pile of fans heater cartage

so if i get a 500w PSU that is going to out put about 40amps is that not going to kill the duetwifi board
i mean thats some power supply also what size wire do i need for that

dc42

Yes 450 or 500W sounds about right for your printer.

Can you confirm that you are using a SSR to control the bed heater? The Duet WiFi is rated at 15A bed heater current, but your heater will draw 23.3A.

cap

no im not whats a ssr

edit

ok i did say im no engineer but i do love this guy i think if you sent this guy a board asking him to do full review and setup blog it would help your sale to low tech peeps like me and boost your sales
https://www.youtube.com/watch?v=TiEwNf1H_Tc
https://www.youtube.com/watch?v=TiEwNf1H_Tc

thanks for the help good job ive only got low hours with my prnter plugged in ill get this sorted with out going stupid money what would be a good ssr to get

DjDemonD

A solid state relay - a device to switch a large current using a small one. Used when you power your heatbed from mains power with a DC-AC SSR, or if you buy a DC-DC SSR from a second DC power supply. Usually they isolate the low current and high current side optically. A good idea if your print bed is larger than the usual 200x200mm as to achieve the desired 0.5W/cm2 requires a larger heater which draws more current than most controller boards can handle.

They can handle low frequency PWM for more precise control of bed temperature.

It is also possible to use a mechanical relay, but without PWM using bang bang mode.

cap

thanks for this info i must off edited my above statement as you replyed

cap

ok so had a look at ssr WOW how many there a lost here
can you recommend a good one with out killing my pocket
are am i looking for a

ssr 40a dc ??

iDevelo

@cap:

no im not whats a ssr

edit

ok i did say im no engineer but i do love this guy i think if you sent this guy a board asking him to do full review and setup blog it would help your sale to low tech peeps like me and boost your sales
https://www.youtube.com/watch?v=TiEwNf1H_Tc
https://www.youtube.com/watch?v=TiEwNf1H_Tc

thanks for the help good job ive only got low hours with my prnter plugged in ill get this sorted with out going stupid money what would be a good ssr to get

I think you sent Tom one not long ago didn't you Tony?