Slow getting to 110C bed target on 10" i3v

[TechMasterJoe]

V0.3.jpg
OK guys here is the finial PCB i will send out to the fab house
opto-iso + 500ma PNP driver for main mosfets makes sure both are in full saturation
made a foot print for the XT60's and put them on board
made it as simple as i can power on one end, hotbed on other..

if anyone is interested in whats really just a ground switch with a crazy low volt drop just PM me
i can safely say this will take 60 amps all day without fail.
at 60amps total resistance comes up a tad to .00091ohms (.052vd) or about 3.5watts lost (mosfets rated for 200watts dissipation each)
this the size of the board and traces i think 60amps is a safe rating with spikes up to 100 amps the
board and connectors are really more of the weak point. i expect the copper to go long before the mosfets
i will Tin the power traces (silver solder) to help with power limits.
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official price is 20$ shipped and includes 6feet of 10ga silicone ultra flex cable
the two things will increase hotbed power by
20% over 14ga speaker wire and stock relay
16% over 12ga and stock relay
37% over 14ga wire and ramps built in mosfet (yes ramps really eats that much power)

[printbus]

Looks like something with potential!

...includes 6feet of 10ga silicone ultra flex cable...

IIRC, you don't have your printer yet. What is the concept for connecting 10ga wires to the smallish pads on the heat beds? Some people are going to need guidance on that.

...37% over 14ga wire and ramps built in mosfet (yes ramps really eats that much power)

I'm curious - did the analysis factor the voltage drop through the 11-amp polyfuse on the RAMPS heat bed circuit? I think that alone adds 0.1 ohm of resistance.

[JimG]

at 60amps total resistance comes up a tad to .00091ohms (.052vd) or about 3.5watts lost (mosfets rated for 200watts dissipation each)

I'll admit to not having thought this all the way through, but .....

Can you arrange the new PCB in a way that would permit using conductive epoxy to bond the new PCB to the heater PCB? If the portion of the new PCB that is bonded coincides with the copper pads for the MOSFET heat sinks, then you would not lose even the 3.5W. I understand that there is a big loss in efficiency when trying to cool the MOSFETs with a heat sink that is already at 110C, but I am thinking it might still work OK?

Jim

[TechMasterJoe]

questions and answers

1. as far as attaching 10ga to the hot bed i will have to try a few things and see how it works
2. yes that loss is with a unmodified RAMPS 1.4 board with a poly fuse that get damn hot with out a fan
3. i will look in to it driving mosfets at or near 110c will shorten the expected life but of the 2watts lost at the mosfets 5.8 watts is lost in 6ft 10ga cable

i can talk to my board house and maybe make a few hotbeds with everything on the hotbed but that can be drastically more expensive.
the piggyback option will work but it will take up apx 1/4in under the hotbed so some people might have to raise it up a bit.
the mosfets are really big compared to the Dpaks on most control boards .131 tall and .6in wide .575 long monster mosfets i like to call them
i use them on a dual channel mixing speed controller i made for 15lbs combat robotics wight class. 4 mosfets form a H-Bridge and a AVR dose the talking
the board for that is 1.8in by 4.2in has 8 mosfets i have never burned one up and take them to 100 amps at 48volts with peeks over 400amps driving unfiltered DC motors.
the reason for using them is simple i have 2 full reels (1854) on hand and a mini pick and place machine to do the job + a DIY reflow oven that works

[JimG]

as far as attaching 10ga to the hot bed i will have to try a few things and see how it works

One of the main advantages to locating the MOSFET PCB on or near the heater PCB is that you could use the light gauge OEM wires for a very short run from the heater to your new PCB. This would avoid the need to desolder the OEM leads, and replace them with heavier gauge leads.

BTW, I am very jealous about the pick and place machine

Jim

[TechMasterJoe]

One of the main advantages to locating the MOSFET PCB on or near the heater PCB is that you could use the light gauge OEM wires for a very short run from the heater to your new PCB. This would avoid the need to desolder the OEM leads, and replace them with heavier gauge leads.

BTW, I am very jealous about the pick and place machine

Jim

i have FW and a program that will pull placement from eagle you just need a vacume pump, servo,and a small solenoid valve to make a 3d Printer into one
fw is for RAMPs (i do think you will need to change Z to a belted system)
i will need to clean up the code a little before i go handing it out
it will export files as a CSV and will work with the cheep china units as well

if you want to put the mosfet driver under the wood Y bed to isolate it from the heat and use the stock cable i don't see why not just keep it under 6in to take full advantage of it
i will still include the 10ga to run back to the psu but i guess twisted pair bell wire can be added of equal length to send control signal.
i can add a bright led to

i used a diy for a long time
but now own a used MC-385V2V this thing is fast......