Component Identification - Page 1
Forum section: electronics / projects

author: Twistedsnail
author_rank: Contributor
timestamp: March 13, 2016, 03:29:09 am
content: My friend was having a problem with the central locking mechanism on one of the doors on his car.We took it apart and observed that whenever the lock was supposed to be triggered, the red component would heat up and smoke.It needs replacing (it wasn't working and has now destroyed itself), but I don't know what it is.As can be seen in the attached images it is a red disk shaped passive component that was in series with the DC motor.At first I thought it was just a cap, then a MOV or other protection device, but really I have no idea.It had no markings other than a production or batch number, no part number or unit value.I'm really hoping to just replace this part which will be much cheaper than the $80 the mechanic wanted to replace the whole thing.Does anyone know what it could be?

author: wraper
author_rank: Unknown
timestamp: March 13, 2016, 03:32:07 am
content: Most likely resettable fuse. I think that DC motor is either dead or stalled.

author: wraper
author_rank: Unknown
timestamp: March 13, 2016, 03:34:03 am
content: Quote from: Twistedsnail on March 13, 2016, 03:29:09 amThat is a part number, but your photo is not clear enough to see what is written. Seems like muRata logo on it but not sure because of the crappy image. Don't use a flash while making the photos of the components.

author: Twistedsnail
author_rank: Contributor
timestamp: March 13, 2016, 03:44:24 am
content: Quote from: wraper on March 13, 2016, 03:34:03 amThere is no logo, top line is "CQ8R5", bottom line is "@12v"I can't find any information about a CQ8R5Sorry about the photos, they were taken about a month ago at night. And I don't have the part anymore to take new photos.

author: DivineChaos
author_rank: Regular Contributor
timestamp: March 13, 2016, 03:53:17 am
content: If it is a fuse, hook that lead directly up to the motor and supply it with power and see what happens. If the motor does not move, then the motor needs replacement (or in this case, to be taken apart and rewound, bearings replaced, magnets replaced etc...)

author: wraper
author_rank: Unknown
timestamp: March 13, 2016, 03:53:25 am
content: Don't think it is "@"

author: Twistedsnail
author_rank: Contributor
timestamp: March 13, 2016, 04:08:53 am
content: Quote from: wraper on March 13, 2016, 03:53:25 amYou're right, that makes sense.Strange that it doesn't seem to have a valid part number, is it just too old to be listed anymore?

author: JSnyder
author_rank: Contributor
timestamp: March 13, 2016, 04:17:14 am
content: looks like it might be a PTC being used for over-current/inrush protection seeing as it's in series with the motor. "8R5" might refer to an 8.5ohm PTC, just a guess.

author: Twistedsnail
author_rank: Contributor
timestamp: March 13, 2016, 04:29:43 am
content: Quote from: JSnyder on March 13, 2016, 04:17:14 amThat's a reasonable guess.I don't want to put the wrong spec fuse in someones car, so hopefully others will confirm this.Quote from: wraper on March 13, 2016, 03:32:07 amJust did a quick test, the motor works fine, I'm able to "lock" the mechanism with a direct 3v across the inputs. Reversing the connection successfully unlocks.Just need to sort this polyfuse now.

author: SeanB
author_rank: Super Contributor
timestamp: March 13, 2016, 07:50:48 am
content: 8R5 PTC thermistor used as inrush and stall protection, so it likely just failed from the repeated cycles of cooking in the door actuator. Replace with an 8R one the same diameter ( that is the major determinator of current rating and power handling) and it should be fine. Just ordered 10 of them coincidentally as replacement inrush limiters on a transformer, the one in there cracked after a decade of use, but still works, so is scheduled for replacement on the next cycle. Cost is under $1 each.