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Dual heaters not working

Posted by makinit42 
Dual heaters not working
February 03, 2013 06:49PM
Hello reprapers,
I have been pounding my head agains the keyboard for a few weeks now and finally decided it was time to ask for help. I recently built a Prusa Mendel kit from A2Aprinter.com. First off let me suggest you look elsewhere before ordering from these guys. After a half dozen request for information from them I have never recieved a single email back. So here is my issue. The kit comes with RAMPS 1.4 and a dual heater element for the extruder. I can not find directions on how to wire up two heat resistors on one extruder to the RAMPS though. I have tried both in parralel and in series. In both cases the temp will rise to 180ish and stop. I can not get it to go up to the 230 required for ABS. I am using sprinter for my firmware and pronterface for the computer side software. Things I have tried.

1) running one heater (The same temp was achieved)
2) running the heaters in parralel (No change)
3) running the heaters in series. (No Change)
4) review that the thermistor is correct. (it appears to be working ok)
5) review the settings in sprinter (I can not find anything that appear to be wrong)
6) replace the power supply. (I got annoyed with the ATX power supply so I replaced it with a 12v 20amp supply from ebay.
Re: Dual heaters not working
February 03, 2013 07:02PM
Check the resistance of the resistors. If they are too high you could struggle to get high temps. I think 5.6 - 6.8 are recommended for j-heads. I'm sure the same will be true for most others.
Re: Dual heaters not working
February 03, 2013 11:27PM
They are 6.8 each. Is that ok? Do I run them in parallel or serial?
Re: Dual heaters not working
February 04, 2013 01:37AM
Parallel: I suppose you'd want dual heaters for a capability of about 40W. Wiring them in serial would get you only about 10W. You should be able to measure about 2*12V/6.8ohm=3.4A through the pair while heating up from cold.

Check your temperatures with something other than the thermistor readings themselves.
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