Peak AC current consumption of MK2S
Hi all
I was trying to determine MK2S' peak current consumption at 220Vac side by enabling the "Preheat" (both heat bed and nozzle were heated), and I got up to 1.8A r.m.s at AC side. Please see the attached test diagram. However, according to MK2S' specification label (behind the Z frame) it should be 1A at 180-264Vac. To me there is a safety concern since the 1.8A during preheat is not just a transient state. It could last up to 5 minutes before reaching the target temperature.
I asked Prusa's support team why my measurement is different than the product specification, and they replied their measurement did show only 1A at 230Vac during preheat. It looks like either I'm not measuring the current right or my MK2S is not performaning correctly,
I would be appreciated if anyone can share their current measurement result at AC side while enabling "Preheat", so that I can compare the result and identify the root cause.
Re: Peak AC current consumption of MK2S
on my Prusa I3
I used my multimeter on 10 amp AC mode, to bridge the fuse holder (Yes there was another fuse to the live side of the test point, and my fingers were well out of the way),
I turned the printer on, and recorded 0.11 Amps AC
I selected preheat PETG, and saw the current rise to 1.17 amp AC... which is nowhere near your test current...
as the temperature rose, the input current began to diminish. within 1 minute it had gone down to 1.11 amps...
I suspect this was because heaters are often non linear resistors, which increase in resistance as temperature increases....
then I turned it off.
My mk3 prusa printer gives an indicative 1.17 amp initial input when heating bed and extruder... which is nowhere near your 1.8 amps.... and it's nowhere near to an i3 Mk2... 😳
so I did the same test on my mk2...
Initial current 0.08amps, on start up,
engaged heater and heatbed and saw 1.01 amps, which dropped to 0.96 amps at about 50 centigrade on extruder when the hot end fan kicked in.... heatbed led still solid
my mk2 has the Mk 42 heatbed,
I am in the UK,
even factoring nominal 240 volts to 220 volts, the current would be bobbing along, around 1 amp
hope this helps,
regards Joan
I try to make safe suggestions,You should understand the context and ensure you are happy that they are safe before attempting to apply my suggestions, what you do, is YOUR responsibility. Location Halifax UK
Re: Peak AC current consumption of MK2S
Just add up the wattage of the various components:
Heatbed: 160W (absolute maximum, with 12V supply; if the voltage has been tweaked, then it could be higher)
Extruder heater: 40W (but these are generally over-rated)
Electronics: 20W (with just the extruder fan running; no motors)
So about 220W which is 1.0A at 220V; if you give the PSU a 75% efficiency rating, then 1.33A would be maximum RMS current draw.
Peter
Please note: I do not have any affiliation with Prusa Research. Any advices given are offered in good faith. It is your responsibility to ensure that by following my advice you do not suffer or cause injury, damage…
Re: Peak AC current consumption of MK2S
Thanks to Joan for the measuring result and to PJR for your information.
Acutally I didn't measure just one MK2S. I'm building a print farm with 20xMK2S, and I've got the same result (1.8A@220V) on all of them.
The only difference about our poewr supply is probably that I have 60Hz AC power in Taiwan rather than 50Hz. However I supposed the frequency has nothing to do with the current consumption.
I can't help but wonder if power factor could be a factor here. If I undertand right the PSU of MK2S doesn't have PFC (Power Factor Correction), and therefore its power factor cannot be as good as close to 1. With 220W consumption at DC side, I assume there should be more than 300VA apparent power at AC side if the power factor is around 0.7 (usually worse).
Unless the building you tested the printers are equipped with APFC (Automatic Power Factor Correction) device and therefore cover the poor power factor of the PSU. I'm pretty sure the building I'm located has no APFC. Any thought on this?