Is this safe??? (power x carriage stuff)

Mangy_Dog · 9 Sept 2018, 15:37

So I'm currently designing my corexy machine. And right now I've nearly finished designing the x carriage.

Im Using te micro Mate-N-lock connectors, theyre like miniture ATX power connectors.
http://www.te.com/usa-en/product-4-794682-4.html#pdp-docs-features

According to the spec sheet each inner pin can take 5a continuous power.

Now, have I got my maths right and is this safe to do with the duet...?

On the x carriage Im doing dual extrude, 2x 24v 40w cartridges if running at full whack draw 1.6a each.

So 3.12A for those, then a negligible 1 always on fan at 25 ma and a pwm controlled fan at 25ma when at full power. plus 6 leds.... each at 20ma....

3.12
0.025
0.120=
3.265A potential total

This is well within the 5a spec, So to save on cabling and taking up connector pins, I should be able to run a full 24v cable to the x carraige and run the heat carts and other little bits off that one line?

And I guess a 20AWG cable running all that power from the board to the X carriage.

Am I assuming correctly that the heat carts run by gating the ground rather than gating the 24v?

Is this a sound idea? Or am i designing a very expensive fire?

Mangy_Dog · 9 Sept 2018, 20:27

Also to add, Using the BL touch on this as well. And ive noticed that on the bltouch the 2 gnd pins are common... But the gnd on the duet doesnt appear to be... At least the gnd pin on the end stops dont appear to have a continuity to gnd when i just checked.

Which brings me to a second question... Is all GND common? Or is it isolated for the different rails, and devices?

LHelge · 10 Sept 2018, 09:18

I run my BL-Touch (the newest version) with 4 leads through a Molex Micro-Fit. The two GND-leads are internally connected in the BL-Touch. No need to connect both to the Duet board.

dc42 · 11 Sept 2018, 11:47

@mangy_dog said in Is this safe??? (power x carriage stuff):

At least the gnd pin on the end stops dont appear to have a continuity to gnd when i just checked.

Check again - there should be continuity.

Mangy_Dog · 9 Nov 2018, 19:30

Yeah, your right i also read that the endstop plugs are wired differently to protect against reverse polarity issues or something....... I was checking continuity of the IO pins

So the other big question... Is all Ground common? or is it zoned off? So say if on my print carriage I put some 24v LEDs and put their ground on the same ground as the 5V parts (bl touch) would that cause an issue? or can the 24v rails and the 5/3/12(?) rails share the same ground?

Or is there any kind of fly back protection between 5v zone gnd and 24v zone gnd before it goes to the PSU - ,that i would be undoing by sharing the ground like this?

dc42 · 12 Sept 2018, 07:50

Always use different signal and power grounds. The main reason is that if the ground wire breaks, then 24V will feed through the power stuff (e.g. always on fans, LEDs) to the broken common ground, and from there through the "signal" devices (e.g. bltouch or other Z probe) into the signal inputs.

Mangy_Dog · 13 Sept 2018, 19:13

in that case maybe ill forgo the LED lights on the print carriage... ran out of pins on my micro matnlok plug...
Pins
1, 24v (for both heat carts, and 24v fans)
2, Heat Cart 1 Return
3, Heat Cart 2 Return
4, Part Cooling Fan return
5, Direct extruder motor lead 1
6, Direct extruder motor lead 2
7, Direct extruder motor lead 3
8, Direct extruder motor Lead 4
9, 5V (for thermometers and Bl Touch)
10, Therm 1 return
11, Therm 2 Return
12,Bl Touch Signal
13, Bl Touch Z
14, GND (likely for just Bl touch)

dc42 · 13 Sept 2018, 22:32

On the Smart Effector we connect the LED string in parallel with the hot end fan.

You need 3 wires to connect 2 thermistors: the signal line for each thermistor, and they can share a common VSSA line. You also appear to be missing the return for the hot end fan.

I prefer to use separate connectors for the 24V items (heaters, fans, LEDs) and the low voltage connections (thermistors, bltouch). Otherwise you could easily wreck the Duet by accidentally shorting the 5V connection to one of the heater or fan connections.

Mangy_Dog · 14 Sept 2018, 15:37

@dc42 said in Is this safe??? (power x carriage stuff):

On the Smart Effector we connect the LED string in parallel with the hot end fan.

You need 3 wires to connect 2 thermistors: the signal line for each thermistor, and they can share a common VSSA line. You also appear to be missing the return for the hot end fan.

I prefer to use separate connectors for the 24V items (heaters, fans, LEDs) and the low voltage connections (thermistors, bltouch). Otherwise you could easily wreck the Duet by accidentally shorting the 5V connection to one of the heater or fan connections.

Damn, thanks for catching that... I missed the ground for 24v fans, I think what happened before was I was in the mindset of sharing the common ground with the leds and fans, and simply forgot when i posted my last post

I have 4 pin connectors too... I guess I can just add another 4 pin to the design. And like you said, put the 24v power stuff on that.

And keep the 14 pin for 5v, signals and motor stuff.

So I guess, 2 connectors 1x14, 1x4;

On the 4 pin put my 24v stuff
1, 24v (power hotends, leds and fans)
2, 24v GND (hot end fan and LED power gnd)
3, Heat Cart 1 Return
4, Heat Cart 2 Return

14 pin
1, 5v
2, 5v GND
3, Therm 1 Return
4, Therm 2 Return
5, BL Sig
6, BL Z
7, Step 1
8, Step 2
9, Step 3
10, Step 4
11,
12,
13,
14, Part Cooler Fan Return (this is still going to be powered by 24v so its way over this end of the plug)

Hows that look?

dc42 · 14 Sept 2018, 20:28

Better would be one connector for the thermistors and bltouch (minimum 7 pins), and another for the heaters, fans, motors and LEDs.

Mangy_Dog · 14 Sept 2018, 21:06

Ive only got 14 or 4 pin connectors Ill have to work with that... Anyway the pin gap shouldnt cause any issues... Also these plugs cant fit the wrong way round...