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F2 - MFR1100 Fuse / Bed Heater

Posted by Dennis Mc 
F2 - MFR1100 Fuse / Bed Heater
June 15, 2016 12:29PM
Recently added heated bed to my RepRap I2. Generally works well but frequently the bed shuts down prior to reaching the set temperature. If it reaches the set temp it will maintain temperature throughout the print. Noticed today that F2 was quite hot (could not hold finger on surface) just as the bed heater shut down. It seems that F2 is overheating as the bed is heating up. There is good voltage to the heater (12.75vdc) as it is heating.

Any suggestions?

Thx, Dennis.
Re: F2 - MFR1100 Fuse / Bed Heater
June 15, 2016 01:04PM
Either replace it with a real fuse or use a fan to cool it.
Re: F2 - MFR1100 Fuse / Bed Heater
June 16, 2016 12:15AM
Its a poly fuse, that's how they work, they heat up and disconnect, when they cool down they reconnect

Its rated at 11amp at 12v, are you drawing more than that? If so you need to replace with an appropriate fuse
NB it is voltage dependent, 16v max on most of them.
If your drawing less than 11amp the fuse is probably damaged and needed replaced
Re: F2 - MFR1100 Fuse / Bed Heater
June 17, 2016 11:40AM
Thanks for the feedback.

I hooked up an ammeter which indicated that the bed is drawing ~9 amps @ 12.75 vdc. Probably as you suggested, the poly fuse is just tripping early. Think I'll try a small in-line resistance. 0.1 ohm should drop the current by 0.5 amp. Maybe just enough to prevent the fuse from tripping.

Re: F2 - MFR1100 Fuse / Bed Heater
June 28, 2016 07:00PM
Just had another idea. Is there a way to change the rate at which the bed heats up in the software? Am currently using Sprinter. (Yes I am trying to avoid replacing the poly fuse). Thanks. Dennis.
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