Polly fuses.
Is the general consensus that they can be bypassed or eliminated on a RAMPS 1.4?
It keeps kicking the heat off for the hotbed.
Yes. Replace with those replaceable car fuses.
Ok great. I am going by a parts house here anyway in a bit. What amps would be good.
Depends on your heat bed and the quality of your ramps, 15 to 20.
The terminals are not rated for much more than your polyfuse, but many electronics boards go over double the current rating on the HBP connector anyway. Take care.
It depends on your MOSFET too. Too much current and the MOSFET will die (if your bed resistance is too low). Sometimes the bed getting cold mid print may be a sign of a too-low resistance bed. That can be fight against by lowering the power applied to the bed. In Marlin you can do that by lowering MAX_BED_POWER value.
I changed out the original mossfet for 150A one. The red bed does have .8 ohms resistance. I have seen some max bed stuff in there but never really checked it out. Thanks for bringing it up i will investigate it. Maybe if i can turn it down the POLY fuses might be ok.
Or you can completely bypass the board and use an ssr, using the ramps hbp output to simply trip the ssr. That’s the safest method, just adds a component, but they’re cheap on Amazon
Ya i do something similar with my Printrboard except i am using a MOSSFET. I was trying to keep this on all contained if possible. Cuts down on the rats nest.
If you can get an SSR Thats good. I went through 3 that either burnt up blew up or were stuck shut before I gave up and went with a higher quality ramps
A value around 170 might do it. You want to keep power around 120w. P=V^2/R so your bed is 180W now (at 12V). You can keep the power down by properly cycling it on and off. You want a fraction 120/180 of ON time. So because 100% on time == 255, a value of 180 might be a good starting point delivering 120W to your bed. This hopefully will keep your polyfuse and MOSFET happy. But be warned your bed heating time will increase too.
Wouldn’t it be preferable to have a fan over replacing the poly fuses? My screw terminals were getting hot before my poly fuses cut out.
thats what I have done…
Ya your correct. I should have a fan on there.