1
\$\begingroup\$

I have a bunch of COB LEDs that I am going to wire in series using an LED driver. The driver gives off between 40-75V and 0.5A max. The circuit should run around 70V and 0.5A.

Due to space requirements, I need to locate the driver away from the light casing. Thus, the 70V 0.5A line is the only thing that will be running into the case to the LEDs. I would like to put a thermal cutoff (triggered at around ~85°C) in the case, but it seems most cutoffs are either AC or DC (but rated for much lower voltage).

I've searched Digikey and Mouser but can't find any cutoff that would work. I'm guessing there must be some solution but I don't know enough about various electronics.

\$\endgroup\$
  • \$\begingroup\$ Welcome to EE.SE. \$\endgroup\$ – Sparky256 Oct 12 '18 at 0:28
  • \$\begingroup\$ What you want is a thermal disc, which resets when cool enough. A thermal cut-off is like a fuse, once open it must be replaced. \$\endgroup\$ – Sparky256 Oct 12 '18 at 0:40
  • \$\begingroup\$ cantherm.com/wp-content/uploads/2017/05/SDF_JUNE_2016.pdf 250V -10A rated on digikey \$\endgroup\$ – sstobbe Oct 12 '18 at 1:21
  • \$\begingroup\$ @sstobbe. I found the same, but the OP wants re-settable thermal disc or polyfuses. The ones you show do not reset. \$\endgroup\$ – Sparky256 Oct 12 '18 at 1:58
  • \$\begingroup\$ @Sparky256 Fair enough, wasn't clear on OP requirements, those are indented to prevent total meltdown and ignition. \$\endgroup\$ – sstobbe Oct 12 '18 at 2:24
0
\$\begingroup\$

If it is a signal or LED driver it is still AC or DC based current, enough for a thermal disc to pass through if contacts are closed. Voltage is not an issue here as 70 volts is not that much at all, as the cutoff will likely have a 250 VAC rating to cover most any common use.

You want one with N.C. contacts that open when too hot. You should be able to find one close to the cutoff point you want. Once OFF they have to cool by about 5 deg F to reset.

This was the best list I was able to find. It seems they are not as common as in the past. I suspect adjustable electronic types have replaced them. As it is mostly what I find and becoming more popular are solid-state resettable polyfuses. Not designed for high voltage or high current they can drive an AC or DC relay that has the right voltage / current ratings. An exception would be in the link below which leads to high current 250 volt PTC's that reset when cooled off.

Link to a better solution

\$\endgroup\$
  • \$\begingroup\$ Would am AC thermal disc work if I am using DC? If so, all I need to do is spec it for the current and temp, and make sure the 70V is below the voltage listed correct? \$\endgroup\$ – Ethan Oct 12 '18 at 1:04
  • \$\begingroup\$ Yes. Most disc have a 250 VAC rating just so they can be used most anywhere. Look at the link I posted in my answer and you may find something at least close to what you want. \$\endgroup\$ – Sparky256 Oct 12 '18 at 1:09
  • \$\begingroup\$ @BeB00. Looks like the OP may need a boost relay as these are rated no more than 60 VDC, and my list had them at 9 VDC as a polyfuse. The mechanical disc had too low of temperature ratings. \$\endgroup\$ – Sparky256 Oct 12 '18 at 1:15
  • \$\begingroup\$ thanks for all the info. this would be perfect for my application but I'm still confused by the fact that it says 'Current Rating - DC 30A (9V), 80A (5V)'. I assume I can't use this with 70V DC? I was just looking up polyfuses. Would those be applicable as away to protect against high temperatures, or would that be considered miss-use, since they are made for current protection not temp protection? I would be open to anything that gives me temp protection and is resettable \$\endgroup\$ – Ethan Oct 12 '18 at 2:53
  • \$\begingroup\$ Don't get caught in the play-on-words. Current or not they will still have a very high resistance above the rated upper threshold, and if driving a booster relay would cut it OFF. When cool enough it will allow current to flow again and the relay is back ON. Remember that all breakers and re-settable fuses have a limited number of times they can open and close normally. This usually is a few hundred times at most, but a good design and cooling of the load should prevent overheating to begin with. \$\endgroup\$ – Sparky256 Oct 12 '18 at 3:00

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.