Hi all,
I’ve been using a simple dim bulb tester for a while now, just a single bulb in line with a socket and a switch to get instant 230V (I’m in Europe). But, I want to add in a variac and an isolation transformer.
Now, I did find the old Big Dim Bulb tester video ( removed link ) But I’m wondering:
– What is the proper sequence of elements here. What I found online seems to suggest Mains –> Isolation –> Variac –> Limiting
but the video goes Mains –> Limiting –> Variac –> Isolation.
Also Why are there two bulbs in series. Other than for aesthetic effect I don’t see the benefit. Wouldn’t one bulb be more than sufficient? I have 40W, 60W, 80W, 150W and even a 200W bulb here, and a small stockpile left of each. Could wire the thing with a rotary switch to select the wattage/bulb even… but that might be a bit overkill. :’)
My plan is to build a single all-inclusive unit where I can switch each element in and out, and add on a few panel meters for amps and AC voltage. Also a few indicator lights to know what state I’m in, and obviously proper fusing and careful consideration of which states should, and which should NOT be connected to ground as well. (Basically disconnect ground if and only if the isolation transformer is in the loop.)
Any help with the proper sequence and number of bulbs would be much appreciated.
To me, the following would make the most sense, using a single bulb, or a selectible bulb. Bulbs in series drop the max wattage, which I can manage using a smaller bulb. Probably for almost all applications a 60W bulb is enough. (0.261A at 230V mains.)
[Wall Outlet]
│
(230V AC)
│
[Variac]
│
Adjustable AC Output
│
[Isolation Transformer]
│
Isolated AC Output
│
[Lightbulb Current Limiter]
│
[Ammeter] ←─── measures current **to DUT**
│
├────────────┐
│ │
[DUT] [Voltmeter] ←─── measures voltage **across DUT**
│ │
└────────────┘
Hi, below is my setup idea. The number of Light bulbs are either for aesthetics or you can say if you ever troubleshoot units that are a huge power hogs such as for instance a 1KW audio (power amp) or things like that. so you can add or substract as you wish.
@ovi4 This is about the setup I have in place. In my situation, the variac is placed behind the isolation transformer, but I don’t think the respective order of variac and isolation transformer is very relevant.
To keep the setup simple, I also use just one socket and if necessary, I just fit a different wattage light bulb. Mostly I use a 60W light bulb.
As most of the time, say after the initial testing of the old receiver, and there appears to be no abnormal internal power loss, the variac could be bridged using an additional switch. But that is just an option to prevent the variac from consuming continuous power when not ‘activated’.
The only thing is that I have added an extra differential switch of 30mA that is located at the entry point of the power line going to my entire test bench.
You could also provide a power-on switch in series with the fuse. Yes or no combined with the differential switch. I have one integrated in the power distribution socket block on my desk.
Paul
Mine is setup: input, bulbs, isolation, variac, output. I figured it was more efficient to have the isolation transformer fully powered to reduce losses (if any). However, they all work the same as long as each piece is used.
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Hi All – I’ve got a similar set up, but without the isolation transformer. Until now, I’ve not messed around in my home shop with anything that would need the precaution. But I do want to add one in soon. Although I’ve used them before, I’ve not wired one up.
Interesting, Ovi4 – is it common for isolation transformers to have a connection to the core? Makes a lot of sense. I need to crack open my variac to see if the cheap, Chinese knock off even has one. The case, LOL, at least is grounded.
thanks for your time!
– H
That’s corrent the case has to be grounded for protection (just in case).
@ovi4 thanks – does that mean these iso xformers have their cores tied to the chassis? Via a pigtail I assume.
@howardp, from what I’ve seen so far, this is up to the manufacturer. and the electrical code (in each particular country), but as a general idea, yes, the core is (or at least it should) be grounded.