Low heating element current

Esteban

Hello everyone,

I'm experiencing a slight problem with the output current of my bed and hotend. Nothing alarming in the sense that they work and to my knowledge have always worked like that, but in the need to heat my machine much faster, I checked my amperages:

For the hotend = ~1.75A but connect to “out 1”.
For the bed = ~6.85A but connect to “out 0”.

*to the current clamp

My board is a Duet 3 Mini 5+, so I should be able to get 15Afor the board and 5A for the hotend. However, this is not the case. There's no limitation on my power supply (LRS-350-24 MeanWell), whether the elements are switched on separately or not, the values remain approximately the same.

Where could the limitation come from? I don't have PWM limitation for my M307 controllers.

M950 H0 C"out1" T0 ; create heater #0
M143 H0 P0 T0 C0 S285 A0 ; configure heater monitor #0 for heater #0
M307 H0 R2.43 D5.5 E1.35 K0.56 B0 ; configure model of heater #0
M950 H1 C"out0" T1 ; create heater #1
M143 H1 P0 T1 C0 S115 A0 ; configure heater monitor #0 for heater #1
M307 H1 R2.43 D5.5 E1.35 K0.56 B1 ; configure model of heater #1

jay_s_uk

@Esteban maybe the rating of the bed and the hotend heater?

Esteban

@jay_s_uk said in Low heating element current:

maybe the rating of the bed and the hotend heater?

For the trays, no, it's a 320W. As for the hotend, I confess I haven't tested it with more powerful heaters, but I'm pretty sure I have a 60W (Chinese, but normally not the cheapest of all).

infiniteloop

@Esteban

There's no limitation on my power supply (LRS-350-24 MeanWell)

It should provide up to 350W at 24V.

For the trays, no, it's a 320W. As for the hotend, I confess I haven't tested it with more powerful heaters, but I'm pretty sure I have a 60W

320W + 60W = what? More than the PSU is rated for. Steppers, MCU etc. come on top. "No limitations"? Think again.

I checked my amperages:
For the hotend = ~1.75A but connect to “out 1”.
For the bed = ~6.85A but connect to “out 0”.
to the current clamp

There is no way to measure these properly with a multimeter. Improperly done, you even risk your board. Heaters are not fed with a static current. Instead, they have to be tuned to follow an optimised curve. Your M307 lines from the config don’t reflect any tuning - maybe that’s stored in the config-override.g though. To understand how tuning works, study Tuning the heater temperature control.

Esteban

@infiniteloop
No, everything has always gone smoothly. But if I max out at 6.8 * 24 = +/-160W and 1.7 * 24 = +/-40W, could that explain why there's no voltage drop?

achrn

@Esteban I would focus on whether your measurements are actually valid. In what situation did you take the measurement? Your H0 has no Q value, so at anything less than 100% duty (i.e. heater cold and on at full power) it's PWM at 250 Hz. Does your clamp meter measure accurately if it's a square wave at 250Hz? Even if it does, have you corrected for the less-than-100% duty?

If you really want to measure the current personally I'd put the heater into bang-bang mode (B1 in the M307), connect an ammeter in series, and take the readings quickly as the heater element first heats up.

dc42

@Esteban how does the size of the opening in your current clamp compared to the size of the wire you are clamping it round? Current clamp meters rely on the clamp capturing almost all of the magnetic field surrounding the wire. If the clamp opening is much larger than the wire then only some of the magnetic field from the wire will be captured by the clamp and it will under-read.

I suggest you use a multimeter to measure the resistance of the heaters (with power off of course), then apply power with full PWM and measure the voltage across each heater. From that you can calculate the current.

Bear in mind that some heater elements have positive temperature coefficients, so their resistance will rise and the current drop as they heat up.

Esteban

@achrn
Non je n’ai changer aucun autre paramètre.
Pour ma pince, c'est une pince professionnel mais je ne trouve pas ses caractéristiques.
Je vais tacher de voir en contactant directement mon lit momentanément a l’alimentation pour vérifier mes résultats.
Et de modifier mon Gcode

Esteban

@dc42
C'est une pince relativement grand, environ 50mm de diamètre.
Je vais tacher de faire ces meusures

infiniteloop

@Esteban

if I max out at 6.8 * 24 = +/-160W and 1.7 * 24 = +/-40W, could that explain why there's no voltage drop?

Sure, but I doubt the measured values. Both @achrn and @dc42 have pointed out how to improve accuracy, but in the end, the Duet has to apply PWM to fine-tune the temperature of a heater, which might be the reason why your PSU can handle the load.

As soon as heaters arrive in PWM mode to regulate the current, they draw less power - on average. Cheap PSUs might be unable to deal with the spikes (that’s why ”Chinese Watts“ tend to deliver less ”bang” than you’d expect), but thanks to beefy capacitors and maybe some over-engineering, you are on the lucky side:

everything has always gone smoothly.

According to my static calculation (addition of nominal power requirements of all components), you are a bit over the limits, but as long as the voltage remains stable, there’s no reason to worry.