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2nd ramps board this week

Ben.folkes

2nd ramps board this week
January 23, 2015 06:24PM

Registered: 9 years ago
Posts: 49

Hi, I've just got my reprap up and running this week and after one day the Mosfet for the heatbed has got extremely hot and burnt out and I've just bought a new board and the exact same thing has happened. Could it be that the top of Mosfets have contacted with each other or is there a problem with my heatbed?
Thanks
Ben

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Ben.folkes

Re: 2nd ramps board this week
January 23, 2015 09:00PM

Registered: 9 years ago
Posts: 49

Could this be that I need to get a heat sink for this mosfet?

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Ben.folkes

Re: 2nd ramps board this week
January 23, 2015 09:48PM

Registered: 9 years ago
Posts: 49

Another thing is that my local shop only has tip42 transistors. Would these be able to replace the heatbed mosfet?
Thanks

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tmorris9

Re: 2nd ramps board this week
January 23, 2015 11:04PM

Registered: 11 years ago
Posts: 1,171

No I am pretty sure a TIP42 is not mosfet. Absolutely you need a heatsync and possibly a fan to blow on the heatsync.

Search the forum for mosfet as there have been suggestions for better replacement #'s than the originals so they can withstand more current.

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tmorris9

Re: 2nd ramps board this week
January 23, 2015 11:11PM

Registered: 11 years ago
Posts: 1,171

Don't know if you are in the U.S. but here is one that was suggested on a 3D forum (not this forum) [www.mouser.com] it shows 2 different ones but they are just from different makers.

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SteveRoy

Re: 2nd ramps board this week
January 23, 2015 11:21PM

Registered: 10 years ago
Posts: 477

Repalce it with a IRLB8743PBF
Use a heatsink on it.

Steve

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Ben.folkes

Re: 2nd ramps board this week
January 24, 2015 10:25AM

Registered: 9 years ago
Posts: 49

Thanks, I've just ordered a new mosfet and heatsink. I might have to get a new ramps as I made a mess with the soldering iron when removing the old one so I don't know if the terminals will be ok. Could there be a short in my heatbed or will it just be cheap mosfets?

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SteveRoy

Re: 2nd ramps board this week
January 24, 2015 01:26PM

Registered: 10 years ago
Posts: 477

Quote
Ben.folkes
Thanks, I've just ordered a new mosfet and heatsink. I might have to get a new ramps as I made a mess with the soldering iron when removing the old one so I don't know if the terminals will be ok. Could there be a short in my heatbed or will it just be cheap mosfets?

Probably cheap mosfets. I have found some RAMPS are better than others when buying from China suppliers.
And yes they can be hard to de-solder/remove.

Measure the resistance of the heatbed, it should be around 1.2 ohms

Steve

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cozmicray

Re: 2nd ramps board this week
January 24, 2015 02:46PM

Registered: 11 years ago
Posts: 1,049

Perhaps your 10KW or shorted heater
is drawing too much current for the MOSFET to handle?

confused smiley

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Ben.folkes

Re: 2nd ramps board this week
January 24, 2015 03:39PM

Registered: 9 years ago
Posts: 49

How would I use a multimeter to check this?

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Ben.folkes

Re: 2nd ramps board this week
January 24, 2015 03:48PM

Registered: 9 years ago
Posts: 49

And should I replace the other 2?

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SteveRoy

Re: 2nd ramps board this week
January 24, 2015 06:50PM

Registered: 10 years ago
Posts: 477

Quote
Ben.folkes
How would I use a multimeter to check this?

Undo the leads off D8 and measure across them with the multimeter set to ohms (on a low setting).
As to changing the mosfets on the old RAMPS, sure I think it's worth a try, though from experience they are hard to remove cleanly.

Steve