Game on!

Quote:

---

Originally Posted by Kitwn

Y

The problem arises when one side of the supply is connected to exposed metalwork either deliberately or by accident such as touching a metal bench or via another piece of equipment plugged into a dis board fed from the transformer. This creates the risk of you contacting both sides of the supply at once.

---

......That's why SMPS engineers tend to work with one hand behind their back I guess!

Seriously though, the danger isn't that great as to get a shock off an isolated supply you'd basically need to be touching something live with one hand and something neutral with the other, which is likely a smaller risk than touching something live and leakage to earth via feet etc.. And of course as part of the procedure I've always gone through when working in such a way, you do a check that there's mains earth continuity through the iso. transformer, so that in this case the machine chassis is properly earthed.

Quote:

---

Originally Posted by Voicecoil

......That's why SMPS engineers tend to work with one hand behind their back I guess!

Seriously though, the danger isn't that great as to get a shock off an isolated supply you'd basically need to be touching something live with one hand and something neutral with the other, which is likely a smaller risk than touching something live and leakage to earth via feet etc.. And of course as part of the procedure I've always gone through when working in such a way, you do a check that there's mains earth continuity through the iso. transformer, so that in this case the machine chassis is properly earthed.

---

I could have misunderstood but I think kitwin was making the point that, even with a good chassis earth, you will not notice if you have a short from line or neutral to the chassis. So, if you then touch chassis and live you will get a belt the RCD might not protect you from.

.

.

OK, I see what you mean, I must have read it wrong. But I guess in an industrial setup you're not going to have a 30mA RCD, so similarly it's going to be a matter of working carefully.Anyway it's a lot less scary than 370V DC on the primary side of a power supply (or on the braking terminals of a VFD for that matter :upset: )
Interesting to hear you work on PMSM drives, what sort of power? I've only ever come across quite small PMSM's

Quote:

---

Originally Posted by brman

I could have misunderstood but I think kitwin was making the point that, even with a good chassis earth, you will not notice if you have a short from line or neutral to the chassis.

---

It's not beyond the wit of man to make a circuit that detects that, if I have a spare moment I might just add one to my isolation transformer. Not that the current arrangement is anything more than temporary until the workshop electrics get sorted out (type F RCCB maybe?), but I can see it might have other uses.

Quote:

---

Originally Posted by Voicecoil

OK, I see what you mean, I must have read it wrong. But I guess in an industrial setup you're not going to have a 30mA RCD, so similarly it's going to be a matter of working carefully.Anyway it's a lot less scary than 370V DC on the primary side of a power supply (or on the braking terminals of a VFD for that matter :upset: )
Interesting to hear you work on PMSM drives, what sort of power? I've only ever come across quite small PMSM's



It's not beyond the wit of man to make a circuit that detects that, if I have a spare moment I might just add one to my isolation transformer. Not that the current arrangement is anything more than temporary until the workshop electrics get sorted out (type F RCCB maybe?), but I can see it might have other uses.

---

up to about 1kW motors. It is not our main business though so I don't claim to be any sort of expert.

edit to add: yes, I agree. I am much more worried about being zapped by me putting my finger somewhere it should not be than worried about the possibility of a secondary fault invalidating the protection. But I think Kitwin is right with his warning. It is all to easy to forget that not everyone understands the consequences of what might happen and so might think that an isolation transformer is a guaranteed safe solution.

You may be overthinking or misunderstanding this. Having spent most of my career designing and developing mains powered SMPS products, I would endorse the use of an isolation transformer. It's true that the RCD no longer protects you against accidental contact with an HV circuit - but when it's floating, by definition one such point of contact isn't in itself an issue. On the other hand, if it's non-isolated mains, you can get a lethal (deadly) belt just by touching a live node unless you are fully enclosed in a heavy duty rubber gimp suit. Unfortunately these are expensive, uncomfortable and can get you arrested.

Most professional labs use an mains isolation transformer and a variable source, either a variac (variable autotransformer) or a modern switchmode AC source. There is generally an e-stop to completely kill the power remotely in case you observe anything untoward. And you don't let anyone near the stuff without full and formal training.

There's no protecting against complete idiocy and at some point you need to learn the importance of NOT touching 2 different nodes, particularly with different hands. I once did that across 415Vac and somehow live to tell the tale. It hurt like f*ck and I never did it again but might not have been so lucky. For that reason, only using one hand to attach probes etc, combined with an isolation transformer is an <almost> foolproof way to avoid unnecessary bouts of death. Nowadays, we are trained in CPR and have access to defibrillators but those are the ambulance at the bottom of the cliff rather than the fence at the top.

Quote:

---

Originally Posted by Muzzer

On the other hand, if it's non-isolated mains, you can get a lethal (deadly) belt just by touching a live node unless you are fully enclosed in a heavy duty rubber gimp suit. Unfortunately these are expensive, uncomfortable and can get you arrested.

---

PMSL :hysterical: :hysterical:

Got the machine up and running, then realised I needed to get some coolant sorted before cutting anything much in the metal department. Rather than reinvent the wheel from scratch I thought I'd start with one of these off the Bay of fleas:
Attachment 27426
Trying it out it seemed to deliver coolant without too much fog, but was rather feeble in the chip clearing department running off my rather low pressure air supply..Dis-assembling the thing it is made of 4 parts like so:
Attachment 27427
the inner coolant nozzle has the same pitch thread as the outer collar, so threads into the collar when it's put on. The lack of puff looked like it was being caused by the very small apertures:
Attachment 27428
Then I noticed the internal diameter of the yellow plastic end bit looked like it would fit a bit of 6mm AF hex bar, and that the collar and final guide had the same M10 x 1 threads. So I turned and slotted a bit of 6mm AF hex brass to make an alternative inner piece:
Attachment 27429
This push fits firmly inside the end of the yellow bit thus:
Attachment 27430
Screw the conical end guide back on and hey presto there was a good blow & coolant, quite a decently narrow stream too, about 10mm diameter at 100mm distance. And the bits cost less than a fiver :beer:

Nice one! Looks great!

Don't suppose you'd knock off another insert for those of us without a lathe handy?

(Technically the lathe is just a few hundred miles away covered in a mountain of crap, but I've never used it, and plan to eventually start gently...)