Re: SSRs for 12-volt automotive use?

by ModemJunki on Wed Apr 10, 2013 8:53 pm

Zener wrote:You can get Pico fuses that are smaller than Polyswitches. I would use a fuse. Polyswitches seem like a neat idea, but in practice a fuse is usually a better choice. That's the short answer. Personally I would use a bigger fuse like an amp or 2. I think he most likely cause of a blown fuse in your circuit is from a voltage spike that causes the MOV to conduct. I would want a clamping voltage that is just a little lower than the Vin max of the regulator.


Zener, I am sorry but I can't figure out what you mean by clamping voltage. All the references I find talk about varistors and not fuses.

What I'm using is a buck converter sold here. The datasheet says it's short circuit protected, I am assuming that means on the Vout side. I went with this as it's a simple and compact way to get switching power into the project. http://www.adafruit.com/products/1065.

The max Vin of the buck is 36V. So am I looking for a fuse that is rated for (example) 32V 1A or 1.5A? And a plain old fast-acting glass fuse with the correct rating should be OK for the low power project, correct?

Originally I was going to use a board from a USB phone charger. The board from the phone charger has a surface mount fuse marked as "150". Since the charger is rated at 5V 1A I assumed the fuse was rated for 1.5A.

Semi-related, trying to identify fuses I found I have some scrap in my pile that appears to have SMD resettable fuses but cant find references (most of the stuff is old). A firewire card has green fuses marked "P" then 150 and 075. I recall that FireWire could have 30V unregulated provided on the bus. But the 150 and 075 doesn't mean a lot to me - milliamps? Amps? - and the part is old so searching yields no answers.
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Re: SSRs for 12-volt automotive use?

by Zener on Wed Apr 10, 2013 9:45 pm

Yes, I was talking about the MOV. The one EasternStarGeek picked out will be good. Yes most glass fuses are rated at 125v as I recall so that should be good.
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Re: SSRs for 12-volt automotive use?

by ModemJunki on Thu Apr 11, 2013 3:04 pm

Zener wrote:Yes, I was talking about the MOV. The one EasternStarGeek picked out will be good. Yes most glass fuses are rated at 125v as I recall so that should be good.


Thanks for the clarification. One of the engineers at work opened up the prototyping parts cabinet to me, so I now have access to a variety of picofuses.

Also I got some aluminum screw-together chassis parts of some sort out of the rubbish bin, now I have the makings of a home-brew chassis for my project.
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Re: SSRs for 12-volt automotive use?

by ModemJunki on Sat Sep 07, 2013 11:34 pm

If anyone is still watching - thanks for all the help, I finally got this project done!
http://forums.adafruit.com/viewtopic.php?f=25&t=37662#p216017
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