Hi I’m from the United Kingdom and I enjoy electronics and trying to restore radios and anything that can be fixed, I’m still a learner and want to progress and gain a lot of knowledge in this field.
I’ve an old working Berco 10a Variac and have done some mods to it for making it safer, like fitting LED voltmeter fuse switch and a 13amp socket.
My question is I want a 240v 1:1 240v isolation transformer, I want to build it into a bulb limiter. I do have little knowledge what an isolating transformer will do.
All I’m asking is can someone please recommend one for me because they combine several formats and with a KVA range, can someone explain what this means in amp rating for that transformer. I want plug load into my bulb limiter with isolation transformer so I know that load has some protection when I switch it on for the first time. I just want a transformer that has enough amp rating to cover most electronic equipment, I won’t be playing with 1000 volts stuff just domestic.
Any help would be appreciated
Apachepk29
1KVA is equal to 0.8 or 0.75KW (0.8 is usual). So, to calculate other values just do a simple math. Most electronics are rated in KW (or W), but some other ones have Amps written on the label alongside other info. Obviously to convert one over the other a little bit of basic |OHMS LAW (learning) is a good starting point. Transformer recommendation is highly dependent on what kind of equipment you’ll be using it for. Just note that it is always best to oversize/overestimate your needs to avoid burning the transformer. for TV and radio, CD players, basic tuners, and most basic small-size receivers a transformer of about 600-800W (2-3Amps) should do the trick but if you ever get across more “power-hungry” electronics such as High Power Audio Amps of old but very powerful receivers (in the range of hundreds of Watts) then the situation drastically changes.
@ovi4 Many thanks for the information.
If you have or can fabricate a box for a transformer, I can fully recommend this one 1kVA. https://www.tme.eu/gb/details/tst1000w_230v/toroidal-transformers/indel/tst-1000-003/ It too, is in the UK.
Woodb180
One problem you may have with the dim bulb portion of your isolation/current limiter is that in the US we have 120 VAC and use 230 VAC tungsten filament bulbs. I doubt you have 430 VAC tungsten filament bulbs. This is important because the resistance changes with filament temperature so the cool filament allows the dim bulb stay dim under a normal load, but it lights brightly if there is excessively high current. You could probably deal with this by wiring two bulb sockets in series and using two 230 VAC bulbs of the same wattage. BTW, I’ve been at this for 6 decades and I’m still a learner. We all are, some just don’t admit it.
@ovi4 Note that the difference between volt-amps and watts depends on the power factor, which in most cases is inductive (such as transformers), thus the 0.8 correction, though that’s really a rule-of-thumb. For purely resistive loads, volt-amps and watts are equal.
Power factor is a measure of how far out-of-phase the voltage and current swings are, and is affected by the types of reactive loads present. Usually the loads tend to be inductive (motors, transformers, etc.), which causes the voltage cycle to lead the current. Capacitive loads cause the current to lead the voltage, so are often added to an electrical system to bring the power factor closer to unity.
@pauleisenberg Good luck finding regular incandescent bulbs here in America now, as their retail sale has been banned. Some specialty bulbs for appliances are still available, but generally are low-wattage and might need to be used in series to get the same effect. Would be nice if Paul could make a video or two on alternative current limiting devices that don’t need light bulbs.
@dtidrow 100% right. I should have underlined it in my post but… 😏
Is it proper to ask a question about an isolation transformer that I would like to make here or should I start a new thread?