Replacing the PTC Polyfuses November 17, 2014 06:44PM |
Registered: 11 years ago Posts: 363 |
Re: Replacing the PTC Polyfuses November 17, 2014 07:33PM |
Registered: 12 years ago Posts: 1,320 |
Re: Replacing the PTC Polyfuses November 18, 2014 02:39AM |
Registered: 12 years ago Posts: 1,592 |
Re: Replacing the PTC Polyfuses November 18, 2014 03:19AM |
Registered: 14 years ago Posts: 1,092 |
Re: Replacing the PTC Polyfuses November 18, 2014 09:13AM |
Registered: 11 years ago Posts: 869 |
They do what they were designed to do. The amount of time it takes for them to trip is based on the amount of current being drawn through them at what voltage. If you are looking for overcurrent or complete short protection, then get a fast burning fuse. They are designed to protect from running excessive current than what the downstream circuit was designed to handle over time, much like a circuit breaker for a home would do. The 11 amp fuse for instance is designed to hold at 11 amps, meaning you can run 11 amps through it all day and it won't complain. When you run more than 11 amps, then the fuse will start to heat, increasing resistance and lowering current. As time progresses, if it continues to heat then resistance continues to increase until the circuit eventually opens, or current is sufficiently reduced to prevent overheating. But just like many other safety devices, there's limits to what it was designed to protect.Quote
Cefiar
1. They don't really protect anything, since they take ~20 secs to trip. If your PSU doesn't shut down, other things are more likely to be damaged in that 20 secs. If you have a fairly capable PSU and a short, this can actually lead to the Polyfuse catching fire as there is too much energy to dissipate, even if they've got a fan pointing at them.
Sure they are available at higher voltages, just usually with lower current ratings. Polyfuses operate by the power (voltage * current) being drawn through them so you can't really keep them the same size while increasing the voltage without lowering the current rating. But there are options. If you're going to run 24v, your current needs are halved for the same power, so this one should be more than suitable.Quote
2. The 11A fuse for the heatbed is only rated to 16V (you can't get them at higher voltage ratings). This affects you a lot if you run 24V for the heatbed (or all your electronics).
It's not a design flaw. It's operating as design. My Honda can't tow a semi trailer. That doesn't make my car a flawed design, it makes it not designed for what you're asking it to do.Quote
3. The 11A fuse is VERY CLOSE to the limit for many heatbeds, and can unnecessarily trip (IMO this is a design flaw with RAMPS in general caused by using Polyfuses).
Again, you're asking more than what it was designed for.Quote
4. Now that we're getting new designs and people running multiple hot ends, the 5A Polyfuse is also very close to the limit, leading to people having weird issues
Re: Replacing the PTC Polyfuses November 18, 2014 05:04PM |
Registered: 10 years ago Posts: 590 |
Re: Replacing the PTC Polyfuses November 19, 2014 02:29AM |
Registered: 14 years ago Posts: 1,092 |