Member postings for Mark Rand

Sorry, but the 7.5 hp Teco that is used has a rated output of 10.1kVA. with a 50% overload capacity for one minute on top of that. If you assume a 3 times rated current starting current, then you end up with the 7.5hp unit being happy to start 6.75hp motor.

That's my last post in this thread...

Whatever. The voice of hypothesis obviously trumps the voice of experience...

3 times load with a 50% overload capability gives a 2 times de-rating for the drive, which is what they specified. No one using this sort of drive is going to be driving a Lumsden grinder or similar.

Edited By Mark Rand on 04/10/2023 01:24:06

Yes, but the difference is that our users (or their bosses) were paying us!

Edited By Mark Rand on 04/10/2023 00:52:56

The relevant article is in Guy's (first) machinist's bedside reader.

Where are you getting the 3-4 times unde-rating from??? The Teco VFDs that DD use have a 150% for 1 minute overload rating. DOL Starting a 4hp motor from a 7.5 hp rated VFD is no problem. The 'extra work' that DD do is to modify them to use a voltage doubler rather than a three phase bridge rectifier. I don't know whether they uprate the smoothing capacitors, but they might.

I do use a sine wave filter and delta/star grounded neutral generating transformer with mine, because I was already using them with a second hand Danfoss 23kVA VFD that I had used in the same role. That one was fed from a single phase step up transformer. But, in fact, very few three phase machines need the neutral, just a ground connection.

I have also re-programmed mine slightly and connected a time delay relay to the run signal contacts. This is so that it can live happily in the electronics/computer cupboard in the shed and automatically start when powered up from the switch on the wall. The VFD which gives variable speed for the dust extractor is similarly connected, but with control via a switched potentiometer.

I think that Clive and my experience of using the things trumps scare stories made from whole cloth...

Edit to add:-
I do wish that I had gone with Western Power Distribution's 2005 quote of £1.400 to replace the house's single phase supply with three phase. Trouble is that building the shed had already put me deeply in debt (it cost more than the bl***y house did!). Had I done that, I could plan for more solar panel/inverter capacity than now and for a fast charger for if we live long enough to get an EV. I did run 3ph cable from the breaker at the supply entrance to the shed, so that bit's done.

I might still do it at some time in the future, but only for the latter needs. The shed doesn't absolutely need it now.

Edited By Mark Rand on 03/10/2023 09:13:13

With 45Amps, you aren't going to get more than about 7hp. Drives Direct are egregiously overpriced, but they do source and modify a suitable device to make it do the job in a plug and play fashion. There aren't at all many 240-415V drives about because it's a tiny market segment. They seem to have almost given up selling off their own web site and do it all via fleabay nowadays.

This is what I've got and it does the job with my workshop. Max individual load for me is 2 1/2hp, but I do end up running a couple out of the five machines 3ph at a time reasonably often.

Edited By Mark Rand on 02/10/2023 17:46:12

Bangs head against wall

Yes, I was misreading the original post.

Bangs head against wall again for good measure...

Examples would be these:-

**LINK**

**LINK**

Should be a fairly simple bit of coding. The Centronics interface is/was pretty simple minded. Enough so that I emulated it woth oneof our HP computers in the early '90s in order to drive a printer that had been bought in mistake by the department.

Rugby, Warwickshire. Also a tenner on the lidl.co.uk site. Where is your one?

Edited By Mark Rand on 29/09/2023 11:45:41

The condensing driers normally recirculate the internal air. They do have the disadvantage that they don't work at all well at low ambient temperatures, such as an external garage or utility room. But they are a bloody sight more efficient than any other varieties which don't rely on string, wind and sunshine

Edited By Mark Rand on 28/09/2023 19:48:51

Thy're a tenner here. Still picked up another one, they don't get treated with quite as much repect as the 'real' metrology gear in the shed.

Is the library still the Passmore Edwards one? Went to Newton Abbot Grammar (Knowles Hill now) from 1969 to 1976 and was a/the junior member of the defunct Torbay MES from it's founding until I left in '76.

To be fair, the distance from Southend or Brighton to the Midland exhibition is about the same as the distance from me in Rugby (12 miles away from the Midland one) to Harrogate or The Bristol one and I visited those regularly.

Likewise. late '60s onwards. Spoke to Prof Chaddock about his wonderful gas turbine there. Lovely chap .

Wait a minute. Is this the neighbour's tree?

If so, talk to them (after getting better advice than you are likely to get from a public forum). They are liable for damage to your property caused by the tree...

The irritating thing is that an 11kW air source heat pump costs £2,400 retail and can be installed with two 22mm pipes and two cables. If I didn't bother to tell the council, it would cost me less than £3,000 complete with changes to valve gear and control systems. One theoretically needs to be F-gas certified to install it, but it's a sealed, pre-gassed unit!!!

I personally don't need larger radiators. I replaced all the radiators with larger, louvred ones so they could run at lower temperatures than the previous owner's ones in order not to burn adults and children in the house.

Note that many colonials incorrectly refer to grub screws as set screws...

But yes, it it's got a (parallel) shank that's the same or larger size than the thread, for shear loading and location, it's a bolt. Including woodspoiling coach bolts.

Edited By Mark Rand on 26/09/2023 20:51:46

Just a thought :- the etch primers tend to have a surprisingly short shelf life. Is it possible that some of the primer has plated out on the bottom of the tin and is blocking the pickup tube when vertical? I recently had to throw ut some 2K etch primer in a tin because of this issue