Dim bulb tester / powersupply ? - Page 1
Forum section: electronics / general

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: January 26, 2022, 09:54:57 pm
content: One of the bench projects has been to put together a dim-bulb-tester .My variac is lower power than I would prefer for this project - so spending money there , and elsewhere to build .Most of my variable power supplies are DC .Another piece of equipment for the bench [ future ] variable AC .A friend gave me a Kepco M36-15 , volts 0-36 volts , amps 15 , it has a crowbar system [ not sure what it can do etc. ] but the idea of connecting to shielding on boards - heat up as little as possible to remove , vs. using hot-air station & disturbing other components etc.Not sure if a powersupply with " crowbar " is capable to repeatedly performing this ?If the crowbar in powersupplies could be used as part of a dim-bulb-tester ?I have limited space , so getting as much as possible out of as little [ space ] as possible ?Mostly as a hobby , and retirement supplementing income

author: Benta
author_rank: Super Contributor
timestamp: January 26, 2022, 11:25:34 pm
content: First, you'll need to explain what a "dim-bulb-tester" is.I've never heard of such a thing before.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: January 26, 2022, 11:32:39 pm
content: May not get all the details , but basically using a variac to slowly bring up power on a device [ either unknown history , in for repair or older electrolytics etc. ] and power goes through an incandescent light bulb - dim if no high draw / shorts and bright if high current draw .

author: BrokenYugo
author_rank: Super Contributor
timestamp: January 26, 2022, 11:38:16 pm
content: "Crowbar" is a fairly broad term, more detail about the equipment and intent is needed. Dim bulb is usually used just because it's cheap and fit for purpose.Quote from: Benta on January 26, 2022, 11:25:34 pmA dim bulb tester is just an ordinary lamp socket in series with mains, and a collection of tungsten lamps to screw in. Used a quick and dirty way of powering up electronics when you have concerns of things going short and doing damage. Bulb is sized to at most dimly light (minimal voltage drop) under normal operation of the DUT, hence the name. Good for tube gear, SMPS repair, etc.

author: Benta
author_rank: Super Contributor
timestamp: January 26, 2022, 11:52:12 pm
content: Quote from: BrokenYugo on January 26, 2022, 11:38:16 pmAh. Thank You.

author: edpalmer42
author_rank: Super Contributor
timestamp: January 27, 2022, 12:05:17 am
content: Most crowbars are voltage-based so that if the voltage goes too high, the crowbar shorts the power supply to protect the load. The name comes from the idea of throwing a crowbar across the power supply terminals to absolutely guarantee that the load will be protected. I don't see how this would work with the idea of a dim-bulb tester.BrokenYugo's description of a dim-bulb tester is the same as mine. I don't normally think of including a variac with a dim-bulb tester. It's usually one or the other.Ed

author: tautech
author_rank: Super Contributor
timestamp: January 27, 2022, 08:42:03 am
content: A DBT is so simple and can be knocked together from junk lying around as mine is:Text from this old post:https://www.eevblog.com/forum/repair/suggested-for-a-sticky-part-one-comments-or-additions-please/msg470686/#msg470686Just a incandescent bulb wired in series with the DUT, and good to have a small range of bulbs.This one is switched SPST, but in countries without a polarized main plug I would recommend a double pole switch.As is evident it was knocked together at no cost in a dead PC ATX case, using the existing IEC mains socket and a few "bits and bobs".On power-on the bulb should momentarily flash bright, then dim after inrush currents subside.(if all is well).If the bulb remains bright and the bulb wattage is appropriate for the DUT then "Houston, we have/still have a problem.If you have a DUT that has emitted the magic smoke or continually blows fuses this can be indispensable.

author: basinstreetdesign
author_rank: Frequent Contributor
timestamp: January 29, 2022, 12:38:39 am
content: Like tautech said it can be knocked together from stuff at hand:https://imgur.com/gallery/JSZVOaB

author: rcjoy
author_rank: Regular Contributor
timestamp: January 30, 2022, 02:10:07 am
content: Here's one with an isolation transformer and Variac.

author: KD0CAC John
author_rank: Frequent Contributor
timestamp: January 30, 2022, 02:22:10 am
content: That's what I was talking about .Looks store-bought , wish I still had a shop , to build as niceOnly thing I'm missing is a bigger variac .

author: tggzzz
author_rank: Super Contributor
timestamp: January 30, 2022, 09:44:52 am
content: Be careful of such techniques with SMPS power supplies.When the equipment is workign normally, SMPS power supplies regulateoutputpower.Therefore if you reduce input voltage, they will (attempt to) increase input current - and semiconductors might have a hissy fit.

author: tautech
author_rank: Super Contributor
timestamp: January 30, 2022, 10:10:06 am
content: Quote from: rcjoy on January 30, 2022, 02:10:07 amIf really serious about a decent test bench mains supply a mains test block is a nice addition:https://nz.rs-online.com/web/p/mains-test-blocks/1994813