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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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16th Jul 2017, 2:36 pm | #1 |
Hexode
Join Date: Oct 2016
Location: Darlington, County Durham, UK.
Posts: 343
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Those heavy yellow 110v site transformers
Hello
I have managed to collect three French radios which are all 110v but as yet I have not made enough effort to find a suitable power supply, then I thought about those heavy yellow ones for power tools! But I have some recollection of reading that they were not suitable, but I can't remember why or where I read it? Views? Thoughts? Philip |
16th Jul 2017, 2:46 pm | #2 |
Banned
Join Date: Dec 2013
Location: Middlewich, Cheshire, UK. & Winter in the Philippines.
Posts: 3,897
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Re: Those heavy yellow 110v site transformers
They are centre tapped earthed secondaries. They will get hot if run for a long while but otherwise I can't see why they would not do. The regulation may be a bit scatty though.
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16th Jul 2017, 2:49 pm | #3 |
Dekatron
Join Date: May 2008
Location: Derby, UK.
Posts: 7,735
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Re: Those heavy yellow 110v site transformers
The 110V power tool transformers have a centre-tapped secondary (55-0-55V) so might not work so well with any appliance that relies on one side of the mains being much closer to Earth than the other. However, this is highly unlikely to be an issue with a domestic radio set. Ionisation flame sensors and some kinds of touch switch would be affected, though!
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16th Jul 2017, 4:49 pm | #4 |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
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Re: Those heavy yellow 110v site transformers
I've used these extensively; as others have mentioned there's a centre-tap on the secondary which is either tied to the supply-earth or brought out to a separate terminal allowing the user to decide-what-to-do.
I untie the centre-tap and present it as an external connection so I can choose what to do with it [generally leave it floating and instead tie one of the transformer-ends to ground] They're generally well-built, happy to handle the rough-and-ready power-factor-distortion of inductive loads like the motors in power-tools. |
16th Jul 2017, 4:50 pm | #5 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,188
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Re: Those heavy yellow 110v site transformers
Most of those power-tool transformers are potted in resin inside. So while in principle you could disconnect the centre tap from mains earth and say earth one side of the secondary, this would probably result in the core being 55V AC wrt. earth (as it was originally earthed to the centre tap). You can't get to the individual connections to separate the winding tap from the core connection due to the potting.
The transformer I have (for power tools, mainly) claims to be rated at 3kVA for 20 minutes, then let it cool for the same time (or something like that). What is stated nowhere that I can find is the maximum continuous load. I assume it's non-zero, since on building sites, etc, the transformers are left plugged into the mains all day and the load (power tool) is switched and AFAIK the transformers don't overheat like that. So there's enough copper and iron to withstand mains input continuously. Given they are rated at 3kVA and most radios are under 100VA I would be surprised if the transformer couldn't run it continuously. |
16th Jul 2017, 5:12 pm | #6 |
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Re: Those heavy yellow 110v site transformers
I have never known or heard of one blowing up, worst case is either quite smelly and hot or the thermal fuse (if fitted) trips (most seem to have self resetting ones). We have one at work to power USA destined equipment it is powered on 24/7 and usually for a soak test left with a few hundred watts of load for days. It doesn't even get warm.
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16th Jul 2017, 5:54 pm | #7 | |
Heptode
Join Date: Apr 2011
Location: Edinburgh, UK.
Posts: 805
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Re: Those heavy yellow 110v site transformers
Quote:
Continuous load: 2/3rds of rated. Maximum lighting load: 1000 W Continuous rating: 1500VA, intermittent rating: 3000VA You can get smaller ones (but they're not necessarily cheaper) http://www.screwfix.com/p/portable-t...p-1-2kva/30758 600VA continuous, and one of the reviews described it as "a little camp" |
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16th Jul 2017, 7:31 pm | #8 |
Hexode
Join Date: Oct 2016
Location: Darlington, County Durham, UK.
Posts: 343
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Re: Those heavy yellow 110v site transformers
Thank you everyone
So in summary, it will be adequate for me to use as a power supply to get these things working. That gives me a start, as I know I can borrow one from my brother in law on a long term basis However it does remove one of my excuses for tackling them! Thanks again Philip |
16th Jul 2017, 8:10 pm | #9 |
Heptode
Join Date: May 2015
Location: Bradford, West Yorkshire, UK.
Posts: 510
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Re: Those heavy yellow 110v site transformers
Before it became the "norm" to pot these transformers, it was easy to strip off the secondary winding and rewind it to needs.
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17th Jul 2017, 9:51 am | #10 |
Octode
Join Date: Jan 2014
Location: Oban, Scotland, UK.
Posts: 1,118
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Re: Those heavy yellow 110v site transformers
I think I'd rather stump up for a dedicated 230/115 transformer and case-it-up than have such a 'lump' somewhere it could take a chunk out of my shin!
A toroidal rated at 100W (or so) costs........ what? |
17th Jul 2017, 6:02 pm | #11 |
Dekatron
Join Date: Feb 2007
Location: Leominster, Herefordshire, UK.
Posts: 16,526
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Re: Those heavy yellow 110v site transformers
If you already have a 1:1 iso TX get a cheap auto TX of the right ratio and rating to use between the mains and the iso TX primary.
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17th Jul 2017, 6:38 pm | #12 |
Dekatron
Join Date: Jun 2015
Location: Biggin Hill, London, UK.
Posts: 5,188
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Re: Those heavy yellow 110v site transformers
I found it surprisingly difficult to get a small isolating transformer. I was looking for something with a mains primary and 2 half-mains secondaries (so 230V in, 2 off 115V out), the idea being I could connect the secondaries in parallel to run 115V stuff or in series to run 230V stuff. If anyone knows an inexpensive-ish source of such a transrormer (torroidal or conventional core) let us know.
RS do/did a nice 200VA transformer with a primary tapped 0-230-415V and 2 off 55-0-55 secondaries, but it was not cheap. I do have one somewhere I must get round to boxing it up. |
17th Jul 2017, 6:51 pm | #13 | |
Dekatron
Join Date: Apr 2012
Location: Wiltshire, UK.
Posts: 13,951
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Re: Those heavy yellow 110v site transformers
Quote:
Industrial process-control/instrument-panels are stuffed full of situations where you have something crazy like a 415V 3-phase supply and need 110V single-phase, or you have single-phase 110V-with-one-side-grounded and need 220V 2-phase floating... And the "Panel transformer" world is full of interesting solutions! In the past I've stacked a pair of 240-to-415V transformers and wired the secondaries in series so I can full-wave-rectify the result and get nearly a Kilovolt at a healthy amp or so to power one of my HF/low-VHF RF linear-amplifiers. |
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17th Jul 2017, 7:52 pm | #14 |
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Re: Those heavy yellow 110v site transformers
55-0-55 (more like 55 and 55) transformers are readily available, two should fit most needs.
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18th Jul 2017, 9:58 am | #15 |
Heptode
Join Date: Apr 2011
Location: Edinburgh, UK.
Posts: 805
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Re: Those heavy yellow 110v site transformers
Nothing to stop you putting it somewhere inconspicuous and wiring in a 110V mains circuit to suitable sockets around the house -- MK make USA 110V sockets in UK faceplate style, or you could use 2A round pin if not used for other purposes already.
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18th Jul 2017, 10:27 am | #16 |
Nonode
Join Date: Aug 2010
Location: Resolfen, Wales; and Bristol, England
Posts: 2,588
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Re: Those heavy yellow 110v site transformers
Just to keep the record straight, they are not all 3kVA - I have one in the workshop which is only 750VA. It is still in a yellow box with a handle on top, but much lighter to carry!
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22nd Jul 2017, 12:51 am | #17 |
Heptode
Join Date: May 2015
Location: Bradford, West Yorkshire, UK.
Posts: 510
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Re: Those heavy yellow 110v site transformers
Since the advent of "disposable" microwave ovens, even doing that has become an obsolete art. Apart from that 813's are happier with 2KV
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worried about the electrons entering the circuit and the smoke leaving Andrew |
22nd Jul 2017, 11:32 am | #18 |
Pentode
Join Date: Mar 2013
Location: Leeds, West Yorkshire, UK.
Posts: 246
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Re: Those heavy yellow 110v site transformers
Hi Philip is the French system 50Hz or 60 Hz, if your radios have a transformer fitted it might get warm?.If it is built like an AA5 it should be ok.
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22nd Jul 2017, 12:21 pm | #19 |
Dekatron
Join Date: Jun 2009
Location: Staffordshire Moorlands, UK.
Posts: 5,263
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Re: Those heavy yellow 110v site transformers
AS a rule the plastic bodied ones tend to be potted and the metal ones aren't. None of ours are encapsulated and all can have the centre tap disconnected if necessary. One of ours in the welding shop is (despite my objections) left switched on 24/7 and it doesn't get even warm. Modern ones usually have thermal breakers and the older ones internal fuses. They're a good general purpose workhorse and more than a match for any old radio!
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Kevin |
22nd Jul 2017, 3:54 pm | #20 |
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Re: Those heavy yellow 110v site transformers
I had a close look at the works one, it has a resetable thermal trip (those clear 'rubber' button things).
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