How to protect from surges - Page 1
Forum section: electronics / beginners

author: ceamiclover
author_rank: Contributor
timestamp: January 22, 2015, 02:50:59 pm
content: Motion triggered light switch.Problem: apparent surges cause battery to immediately discharge.I made 2 circuit boards with HC-SR501 Ir motion detectors to trigger opto-triac MOC363 to trigger Triac BTA16 to jumper a light switch.I replaced the batteries and they worked again. I had been flipping off a power strip that provided the 120vac constant when I didn't want the lights turning on. I flipped the power strip on. the lights flicked on for an instant, and went out. The battery went from 9v to 1v suddenly.This seems like the issue caused by a "brown-out" or surge. I am wondering how I should protect my projects from this. Do I need capacitors? Diodes?In automotive, we use a clamping diode between the power and ground sides of a relay. No idea whether that is applicable here, though.Any help appreciated.I mad the project a few months ago, and can come up with a schematic or diagram if necessary. Haven't learned fritzing yet, but maybe I need to.

author: katzohki
author_rank: Frequent Contributor
timestamp: January 22, 2015, 03:34:07 pm
content: Surge and brown-out and not nearly the same thing. You will see a current spike when first turning on an incandescent bulb. Definitely post a schematic.

author: ceamiclover
author_rank: Contributor
timestamp: January 23, 2015, 01:59:16 pm
content: what programs do you guys use for schematics?

author: ceamiclover
author_rank: Contributor
timestamp: January 25, 2015, 10:46:32 pm
content: Here is my "schematic." I found an error and am wondering if that could have caused the problems. Instead of R1 being 1k, I did 100 ohms.Would this make my project susceptible to spikes? Or would it just be using more current in general?Struggling to get a current reading from the project. It might be fried, or the fuses in my meter might be open.

author: Rerouter
author_rank: Super Contributor
timestamp: January 26, 2015, 02:11:27 am
content: at a guess you need to double check all your wiring, the fact that it is isolated means that any crap or similar that occurs on the output should not effect the input,First and foremost your problem will be no resistor on the base of the NPN transistor, when the motion detector switched on, it will short the battery across about 1V of silicon, (1xBE + 1xCE) try fitting a 1.2K or something sensible in its place

author: katzohki
author_rank: Frequent Contributor
timestamp: January 26, 2015, 10:14:29 pm
content: 100 ohms instead of 1k means that current into pin 1 could be 10x what you meant it to be. Not sure if that's a problem, you'd have to look at the datasheet.There are tons of free schematic capture programs out there. I use Orcad Lite because it has good SPICE modeling.

author: Rerouter
author_rank: Super Contributor
timestamp: January 28, 2015, 06:47:33 am
content: To make clearer what i mean

author: mij59
author_rank: Frequent Contributor
timestamp: January 28, 2015, 07:14:24 am
content: Maybe its a latch up of the motion detector.The voltage regulator of the motion detector has no filter cap on Vin, try 10 uF or so between Vin and gnd.

author: Timmay
author_rank: Contributor
timestamp: January 28, 2015, 10:30:24 am
content: What are you trying to do?

author: ceamiclover
author_rank: Contributor
timestamp: February 20, 2015, 08:51:51 pm
content: Not sure how I missed the last couple of posts.I added a resistor to the base of the transistor and it has been stable for weeks. I will add a capacitor on the next iteration.Thanks