Electronic Problems!

I'm using RAMPS 1.4, and the Q3 Mosfet was melting the stepper motor drivers. I separated the wires, so they wouldn't touch. Then the mosfet started melting the terminal block. I'm pretty sure this shouldn't heat up that much. Any help is appreciated.

Not quite sure what you're saying but...

Has Q3 got a heat sink on it? If not, you must put one on.
Have you got a fan blowing over the Ramps board? If not, you must fit one.
Are the wires going into D8 nice and tight and not showing burn marks? If they are, re-cut the wires, strip the insulation back and re-fit them

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Waitaki 3D Printer

Ok, sorry... now that I read it again, I realize it makes no sense...

The Mosfet that is closest to the D8 connector is over heating. If I let the power on for a few moments, the plastic from the D8 and D9 terminals start to melt! I don't have a heatsink on. The Mosfet looks like it is burnt. Do I have to change the Ramps Board? How can I make sure this doesn't happen again? Is there too much current passing?

I had my mosfet burn out last week on two different ramps 1.4 boards due to trying to run a heater bed that draws alot of Amps. I installed a new heater relay from makerfarm $ 15 and replaced mosfets was like $6 for 5 on ebay and added some 10*10 aluminum heatsink( dont remember cost) to it also can be found on ebay. Running now. Just so you know you can just replace the mosfet itself not the whole ramps.

Quote
luillo1
Ok, sorry... now that I read it again, I realize it makes no sense...

The Mosfet that is closest to the D8 connector is over heating. If I let the power on for a few moments, the plastic from the D8 and D9 terminals start to melt! I don't have a heatsink on. The Mosfet looks like it is burnt. Do I have to change the Ramps Board? How can I make sure this doesn't happen again? Is there too much current passing?

You will still need to do what I stated earlier.
Also, check your heat bed resistance and post a pic of it if you can. If the bed is shorting, you will draw too much current.

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Waitaki 3D Printer

Here are some photos of the Resistance of the of the Heat Bed, and of the Mosfet of the RAMPS. Also, should I add a heater relay? Is it necesary? Recomended?

cant read your photo... resistance should be about 1.1 ohm.

But in general don't get cheap arse Chinese ramps... the standard mosfet barely copes, the Chinese knockoff doesnt.

or if you do, first thing, replace Q3 with a real MOSFET

"mosfet is Best mosfets for driving your heated bed: IRLB3813, IRLB8743, FDP8870, AOT240L, CSD18502KCS. These mosfets will run merely warm with NO heatsink and a load current of 10A. They should be good to over 15A with no heatsink according to the worst-case numbers in their datasheets and is also see also [reprap.org]"

Edited 2 time(s). Last edit at 04/18/2014 11:23AM by Dust.

My apology, I've missed the MOSFET research page at the end of the sentence in your last reply post.

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Hi Dust

Thanks for the recommandations with the MOSFET replacement, I've burnt 3 ramps 1.4 already with small 4cm fan blowing directly on to the 3 MOSFET on the board.

All 3 boards are burnt in exactly the sample place, not only burnt the MOSFET, also burnt my middle pin of the Heatbed MOSFET on the PCB board.

I'm not familar with electronics, can you recommend which of the following MOSFET has the highest handling current for replacement please.

IRLB3813,
IRLB8743,
FDP8870,
AOT240L,
CSD18502KCS

Many Thanks

Edited 2 time(s). Last edit at 04/18/2014 02:21PM by duckfriedrice.

Hello all,
I am having the RAMPS 1.4 and Arduino 2560 running with the reprap discount smart controler. After several days experimental the thing works, hurray!
There is only one minor thing, the BED is not heating. even when I give the order to preheat ABS. The BED is still cold. In pins.h there are several BED commands.
Any body who nows about the commands to heat the BED or what are the Volts on pins 8+ and 8-?
Thanks a lot whatever your message is.

Is your bed thermistor reading room temp?
Does the bed Mosfet LED illuminate when switching the bed on?
Have you got 12v to both power connectors?
What voltage do you read between the two terminals on D8?
Do you read 12v between the power input ground terminal and the positive terminal on D8?

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Waitaki 3D Printer