Burned power FET on Ramps 1.4 Board

[Remo400]

Hi,
i want to share my experience with this.
Still in the test Phase of my i3-R Printer the power Fet for the headted bed burned. I was heating only to 70 Degrees.
Before i decided to order a new board, i browsed the web and found the following site
http://forums.reprap.org/read.php?219,792911
The important lines are "And replacing a mosfet in a TO220 package by a better one isn't difficult. Typical good choices are IRLB8743 and IRLB3036. "
I ordered the IRLB3036 from Conrad Electronis.
https://www.conrad.at/de/Search.html?se ... 1Fc1202469

Not only did i put the new FET but i also put a second one on the other side of the board in parallel. Insolating material has to be put to make sure that no short can happen.
Now the bed is heating to 100 Degress withot Problems, the FETs not even getting warm

cheers
Ernst

[RoMaker]

It is true that lately, I noticed a big drop in quality of 1.4 ramps.
I thank you for the trick of the new mosfet

[Kachidoki]

Hi, glad to hear that you recovered your ramps. I think that putting two fet in parallel is useless for two reasons.
First, because one can drain enough current to supply more than a dozen heated bed while dissipating less than a quarter of a watt. So I let you imagine when supplying only one heated bed.
Second, because the two fet may have a slightly different Rds(on). So without doing any load balancing, the current will flow mainly through the lowest impedance.
At least, there is no risk to let them in parallel. [emoji5]

[Remo400]

Hi, glad to hear that you recovered your ramps. I think that putting two fet in parallel is useless for two reasons.
First, because one can drain enough current to supply more than a dozen heated bed while dissipating less than a quarter of a watt. So I let you imagine when supplying only one heated bed.

I assume you are absolutely right. After i finished my repair I measure the current drawn by the heated bed it turned out to be only 7 Amps.

Second, because the two fet may have a slightly different Rds(on). So without doing any load balancing, the current will flow mainly through the lowest impedance.

I thought the same too, but i learned that the FETs have change their impeadance when getting warm. This will balance the current between the two.

At least, there is no risk to let them in parallel. [emoji5]

Right, so lets leave it like that.

Cheers
Ernst