Hot End Light - electronics help please [SOLVED]

Hi Guys,

First of all know that I have only newbie basic electronics knowledge, so don't judge me too harshly

I'm trying to wire up a strip of LED lights under the hot end, physically it looks great electronically ...not so much. I tried wiring it up as i would expect but it failed miserably with the Hot end fan randomly stopping and starting while printing. I also have a Thermal switch wired in to start the fan when the hot end heats up.

Any assistance would be greatly received.

Thanks Matt




Edited 1 time(s). Last edit at 02/08/2014 11:49AM by iamburny.

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How big is that resistor Matt, and is it getting hot? I reckon you'd want to have the diodes in parallel with the fan, but move the resistor to the 12V rail and have it in series between the fan and the diodes - it'll then drop the voltage and limit the current going to the diodes, without shorting out the fan (as it is at present).

also the forward voltage of the diodes is likely to be about 3 volts, so you could probably just have three diodes in series with the dropping resistor (this would mean the resistor drops less voltage and needs a lower power rating),

Ray

Hi Matt,

What is the specification of the thermal switch [EDIT: forget that, I have just followed the link you provided], what have you physically attached it to, and how?

Your schematic of the LEDs and resistor is wrong, they should all be in series - but that is taken care of for you on the LED strip anyway.

Edited 2 time(s). Last edit at 02/08/2014 10:15AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Hi Matt,

I think I've worked out what the problem is. Judging from your photo, I think you have attached the thermal switch to the heatsink. However, in normal operation with the fan on, the heatsink doesn't get as hot as 50C. So that thermal switch is not suitable, it will cut in and out as you describe. It would be suitable if you attached it to the heater block instead, except that it is only rated for 130C.

You've given me an idea for the pcb I am designing to go on the hot end and include the modulated IR sensor (see [forums.reprap.org] and other posts in that thread). It could also monitor the voltage across the hot end thermistor, and use it to control the fan.

Edited 1 time(s). Last edit at 02/08/2014 10:25AM by dc42.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

@rayhicks - I've know idea what rating the resistor is as its embedded in side the strip, i cant find a data sheet anywhere, this is the ebay link (not much use!) ebay

@dc42 - I had the thermal switch fitted before i installed the LED's and it was working fine, cutting in about 60c and off at about 45c - the contact surface of the switch is touching the heater block and not the heatsink, right above the heater cartridge with a little heat paste between them for good measure. I'm thinking the cutting in and out is more to do with the LED's and resistor but not sure.

Matt

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Limited Edition Red RS Ormerod 1 #144 of 200 - RRP 1.09fw
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The LED and resistors (given that they are cut from a strip and designed to work from 12V) should not be affecting the fan, unless something is shorting against the LED strip. If the on/off switching appears random, then it sounds to me that you have a bad connection. If it is a regular on/off cycling, then the thermal switch is probably no longer in such good thermal contact with the heater block.

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Large delta printer [miscsolutions.wordpress.com], E3D tool changer, Robotdigg SCARA printer, Crane Quad and Ormerod

Disclosure: I design Duet electronics and work on RepRapFirmware, [duet3d.com].

Fixed =)

Thanks for your help, i think i had a positive and negative mixed up somewhere, and Dc you were right about the LED's in series i found this on a similar datasheet.



So my circuit now look more like this.



Next mod is a redesigned air duct, the air flow from the holes directed at the nozzle is pitiful from such a powerful fan,

Matt

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Limited Edition Red RS Ormerod 1 #144 of 200 - RRP 1.09fw
iamburnys Ormerod Upgrades Github
Follow me on ThingiVerse My Designs