Safety kit

[Martin Bush]

Hello all

I have already had some great advice from you all re starting out and I wanted to ask another question. I've started a new thread, which I hope is the right thing to do.

I am looking for the right kind of oitems kit and already have the usual tools (irons, meter, drivers etc), but I know I need to sort things like a lamp limiter and isolating transformer.

So, is there a specific transformer I should get or a good supplier to go to? What sort of rating am I looking for? As this is a vital piece of safety kit I’m not going to go down the second hand ebay route (unless anyone recommends otherwise) but don’t want to pay big money either.

The good news is, I think I understand the lamp limiter, so I won’t bother you with a question on that 

[Radio Wrangler]

Mine came from RS, as I suspect a lot of other people's did.

Having a Megger high voltage insulation tester is a good thing, and you can also check your own isolating transformer with it.

An RCD for just your workshop is another idea in case the whole house hasn't one.

Good parctice is to have a prominent shutoff switch for everything on your workshop or bench just in case the worst happens and someone has to rescue you.

One other test worth doing on equipment is a heavy current test to make sure earth connections between the plug pin and the chassis of earthed equipment is beefy enough to pull a fuse. 25A is the accepted test current.

The high voltage insulation test and the high current earthing integrity tests are combined in a portable appliance tester if you're feeling rich.

The most important safety item is YOU. developing good habits and not taking short cuts with them is important. A lot of people who get shocks had the gear to have prevented the shock, but didn't use it.

David

[paulsherwin]

I agree with David.

Opinions do differ about this, but my view is that an isolation transformer should be some way down your list of priorities. They are most useful if you need to connect earthed test equipment like oscilloscopes to AC/DC sets, but there are other ways of doing this. A transformer can give a false sense of security, as you can still get quite a nasty belt while using one. Conversely you are very unlikely to receive a fatal shock from an AC/DC set if you are in otherwise good health and observe basic precautions.

A lamp limiter is the single most cost effective piece of test gear you can have. You can make it as fancy and 'industrial' as you like, but all you really need is a mains socket, a mains plug, a lampholder, a choc block connector and some cable.

[Nickthedentist]

Isolation transformers turn up secondhand regularly though if you determined to have one, though naturally, the postage cost will be high.

£30 for an unused one here (probably sans case): http://www.stewart-of-reading.co.uk/...20Supplies.htm

[Martin Bush]

Thank you Paul and Nick.

The lamp limiter is on the list and will be a project in itself before I start anything else electrical. It won't be a big project, but it will be an excuse to spend some time in the "workshop" (the back bedroom!).

By the way, I have been given a Cossor Melody Maker 501u via the forum, which I will be reading up on in due course.

[paulsherwin]

You should be aware that the 501u is a live chassis set. Handsome radios though.

[Martin Bush]

Yes, the donor told me that too.

I had been scared off a little by comments made on here about the live chassis on some radios - all good safety advice of course. But I like the look of the set and I also think anything is dangerous if you are not careful.

I've been watching the videos on the Radio Workshop and will continue to look things up/ ask advice on here as long as people will put up with me

[broadgage]

I would add a self contained emergency light to desirable safety precautions, these are widely sold by electrical wholesalers and on ebay.

An unexpected power failure could leave you exposed to danger from rotating power tools, HT supplies, or hot soldering irons.
Also in the event of any serious accident, a well meaning person might turn of the electricity at the fuse box, thereby extinguishing the room lighting.

Put an emergency light over the working area, and if you have an extensive work shop, a second one by the exit.

[Martin Bush]

I don't have an extensive work area, but the the idea of some sort of non-mains light is a good one. I do a bit of kit making, so have the iron on the go and anti-static band on etc... it would be interesting trying to navigate my way out in the dark if the lights or electric tripped.

[Boater Sam]

Never heard of anyone wearing an anti static band whilst working on valve radios, but suppose it takes all sorts!
Not being cynical, my attempt at humour.
Emergency light is a good idea, I use a magnifier lamp with LED running off a car battery.
Cossor 501U is a simple and easy radio to work on, I have several 500 series of various vintages and valve line ups but never seen a 501U, what valve line up is used?
If you need any help and advice or a bit of hand holding, just ask, we are here to help.
Please check as a priority that the mains neutral is to the chassis and that the on/off switch is in the live pole or is in both poles if it is double pole ---AND THAT IT WORKS .--- ( Check with a meter or bulb and battery with set unplugged ) It may not have been made that way.
Golden rule, one hand in pocket whenever working with power on.

[Martin Bush]

Cheers Sam. The band is just for when I am messing with kits with ICs and that sort of thing. I read that you needed one and decided it was a good idea given the amount of static some of my clothes generate! I like to make them simply to practice soldering.

I will see if the donor mentioned the valve line up in his message. He did mention about the live and neutral issue and I may seek aditional advice on here from you guys before I do any plugging in of anything.

[PsychMan]

Don't mean to hijack the thread, but along the lines of an isolation transformer, would the large portable type typically for power tools with a commando socket be suitable?

I have one gathering dust as I inherited my fathers tools and equipment, sadly I never found the sds drill he used with it. I suppose I can answer this myself with a multimeter but would be nice to see if anyone else had done this. To my knowledge it's a 1:1 transformer so I don't see why not, I would imagine theyre used with power tools for safety. I have a live chassis device at the moment, and want to be as safe as I can

[paulsherwin]

It's difficult to say without more info. Most site transformers are autotransformers giving 110V - they can be useful for running American sets (though a bit bulky) but don't provide electrical isolation. I suggest you investigate a bit more before using it.

The key things about working on a live chassis set:

1. Always, always check that the chassis is connected to mains neutral. Check each time you move to a different socket and before powering up after any work. In fact, it's a good habit to check with a (known good) testing screwdriver each time you power up with metal exposed, even if nothing has changed. It only takes a second.

2. Use a plugin RCD breaker in the power socket, the sort sold for use with electric lawnmowers.

3. Keep one hand in your pocket whenever the set is powered up. If you decide to break this rule (and we all do) never touch anything metal with it, either the radio chassis or anything that might be earthed. Never ever steady the chassis with one hand while working with the other.

The one-hand-in-pocket rule is good practice when working on anything that may contain high voltages, not only AC/DC radios. I once managed to touch mains live in a cassette deck that I hadn't isolated properly - it was very unpleasant and I won't be forgetting it, but no lasting harm was done because there was no earth path through the body.

[PsychMan]

Originally Posted by paulsherwin

It's difficult to say without more info. Most site transformers are autotransformers giving 110V - they can be useful for running American sets (though a bit bulky) but don't provide electrical isolation. I suggest you investigate a bit more before using it.

Ah, OK. Now you say that 110v it does sound familiar, I've had little exposure to tools that needed them you see. I'll test the voltages and look for continuity, as you say it could still be useful for American kit

[ex 2 Base]

Would a bathroom shaver socket transformer be adequate for test purposes, I'm not sure of the current rating. Alternatively use two identical transformers back to back, say 2 X 240/15 volts which will be isolating. I am about to connect two transformers back to back, are there any down sides which I'm missing when do this ? Ted

[broadgage]

Building site transformers are indeed almost always 110 volt centre tap output and therefore not suitable for UK 230/240 volt equipment.

Shaver transformers provide the required isolation, but not enough load capacity. The smallest likely loading of an AC/DC live chassis set is about 0.11 amp or about 25 watts (think 100ma series heater chain plus HT current) shaver transformers are often only 10 watts.

A pair of "back to back" mains transformers will work to an extent but the voltage tends to be a bit low and also to vary excessively with changes in load.

One thing about some (most?) AC/DC sets is the mains switch is in the neutral line (stops having loads of volts next to the sensitive volume control), the set is 'safe' (assuming neutral to chassis) when on but when you turn it off the chassis goes up to mains live.

As mentioned before, the best safety is knowledge and applying same, experience can make it an easier job. An example is no one making an atomic bomb got killed by it (directly).

BTW the 'hand in the pocket' trick is to stop you grabbing something else with the pocketed hand if you get a small shock, that could lead to a big one.

[G6Tanuki]

Originally Posted by paulsherwin

It's difficult to say without more info. Most site transformers are autotransformers giving 110V - they can be useful for running American sets (though a bit bulky) but don't provide electrical isolation. I suggest you investigate a bit more before using it.

Yellow 110V site transformers *are* isolating transformers - the whole point about them is that they provide isolation from mains live/neutral so allowing the use of power-tools in a non-supply-ground referenced environment.

[The one I've got here specifies 5Kv isolation between primary and secondary].

If they were autotransformers then the loss-of-neutral on the supply side would put the entire '110V' side at +240V WRT earth. Which would be naughty.

[paulsherwin]

I stand corrected.

[AC/HL]

But I believe most, if not all have an earthed centre tap giving 55-0-55, so would need a slight mod to correct that. Not difficult, but the transformer would need to be clearly labelled, or the output socket changed to prevent accidental future mis-use.