I’m struggling to find the correct PPTC (through hole) device simple 24VDC 2A fast trip, with a holding current of 1.2-1.5A. We ordered JK30-200s as suggested by someone and when tested at room temperature (21-22°c) they pass over 5 Amps (for over 30 seconds-Huge) with no trip at 2A when tested.
Is there a selector form by any of the manufacturers to aid in selecting the best device for an application?
Everything I am finding in the smaller voltage like 24V are surface mount.
I’d suggest taking a critical look at what the application needs are, and whether or not PTC fuse technology can offer what’s being asked for. They’re inherently slow and sloppy in their characteristics, and would likely not be used at all were it not for that handy self-resetting behavior.
It’s entirely expected that a PTC fuse with a rated hold current of 2A would not trip at room temperature when passing 2A, because that’s pretty much the definition of the hold current spec; the maximum current that can be passed without expectation of the device opening. The “trip current” on the other hand is the minimum current flow required to cause the device to open at some future point. The two usually differ by roughly a factor of two. Given that P=I2R, that’s actually a typical gray area of 4x between “will trip” and “won’t trip.”
Per the datasheet excerpt above, it’s not at all unreasonable that the device would take 30 seconds to trip with a current of 5A, considering that its specification permits a delay of to 11 seconds with a 10A current. Assuming for simplicity a constant energy input required to trip, at 5A one could expect delays of up to 44 seconds by rough estimate.
Hi Sid1,
As Rick describes, PTC fuses are not capable of doing what you require. In addition to the large difference between hold and trip currents at room temperature, these characteristics shift dramatically with temperature as well.
Even standard fuses are going to have trouble meeting your requirements. If you really need the characteristics that you describe, including resetability, then you might want to consider a solid-state solution. This would be significantly more expensive, and would require the use of several surface-mount components, but they are more likely to give you the kind of performance you are looking for.
Here are a few different types of parts which might be suitable for you, depending on the specifics of your particular application:
“Electronic fuses” and “Current Switches”
“Hot Swap Controllers”
“Power Distribution Switches”
Some of these parts will also attempt to limit current before turning off the circuit as well as allow for a controlled rise in current at power-up. Additionally, some of them will automatically attempt to reset continuously until the over-current condition clears, whereas others require power to be cycled off and on again before they will again allow current to flow. You would need to read datasheets carefully to be sure a particular part is suitable, based on allowable voltage range and other relevant characteristics.
