01621 Make or Mend Monday #1. A New Dim Bulb Current Limiter

[@mikesradiorepair]

I love the chassis you found to make your dim bulb tester. I created something very similar years ago but had to start from scratch. I have to say though, I about pissed myself laughing at one point in the video. The drill bit you used in the hand drill to make the center hole is NOT, I say again NOT a metal bit. It's a wood working Forstner type drill bit. It is in no way, shape or form designed to drill holes in metal. I have dozens of them and they are great for making tear out free holes in wood but the key word there is wood. Anyhow, I wish I had run across one of those chassis when I made mine. Would have saved a lot of work. Mike KC3OSD

[@byterock]

Yep it is a Forstner (a very cheap chinesium one ) and it was 100% trashed from hitting a nail some time ago. I have found that there are very useful for cutting though metal (thin) no good for wood anymore. I have a hole press now so I now use that instead. Cheers.

[@tecnisdaimondm.g9321]

Excelente

[@computerlen]

Mine has one 100 watt bulb which limits the series current to approximateky 1 amp. I feel that that is enough current for the series light to do its job. Any larger bulb would void the protection this project creates.

[@byterock]

I guess it all depends on what you are working on. I had a 30A PS on it the other day I had to use 2 100s and 2 60s to even get it to start up. but that is extraordinary ;)

[@SkylosSobaka]

Nice. You didn't mention how the amount of limiting changes with more or less bulbs specifically, though?

[@byterock]

It is what ever you put in line. In my case I think it is 40/60/40/60 then 60+40 so any combination from 40 to 300 max. The other day when I was working on a large tube amp I had to swap out a 40 for a 300 to get it to fire up.

[@SkylosSobaka]

@@byterock Does adding more bulbs in parallel increase or decrease the effect? How do you calculate the effect? How does choosing different bulbs change it? What about the inrush current - don't bulbs have momentary inrush current themselves as they heat up? I

[@byterock]

@@SkylosSobaka This is an AC circuit so you have to figure out 'Parallel Impedance' I would have to use an impedance calculator for that and still the maths are way above my pay grade. www.electricaltechnology.org/2018/09/which-bulb-glows-brighter-connected-in-series-parallel.html for the long explanation for the .25 reason with AC they all draw their rated wattage in both || and series. In series the lower wattage glow brighter and in || the higher wattage glow brighter. In the end we are trying to limit the 'Current' so if it glows bright you turn it off. I guess I have my subject for my next 'Workbench Safety 101' How does a Dim Bulb work ;) For you last question 'Yes' the current increases as the bulbs heat up and one can see with the 'drill' test.

[@Onkel.Moetrik]

Hi It does not matter if you can't se the difference between live and neutral. It is Alternating Current, so when the circuit is connected the live position changes 50 times per second...

[@byterock]

Yeah that is true but you do not want to mix them up, as neutral in NA is connected directly to ground while live is not. Don't want a grounding error.

[@Atelierul29]

@@byterock yes, but it doesn't matter. If you insert the plug the other way around, your neutral will become live, no matter how you wired them inside. There are some appliances that won't work if you insert the plug the other way around, but we are talking about 0,5% from all electronics. Also, a ground lift button is needed, if you want to take measurements safely, without blowing up your DSO. Those dim bulb testers without a ground wire, are actually better.

[@byterock]

@@Atelierul29 Well it does use a three prong plug, and of course it is only as good (ground wise) as the socket it is plugged into. ;) I am not sure you would ever want to float a DSO. but that is a good subject for a video