A thick typwrap (wire tie) clinched around the cord makes a nice restraining ring.

Can you post a schematic of your final design?

ak

My circuit is the one which was posted on page 2. The only difference is a 1000uf 200v cap, a bnc plug, a 68 and 15 ohm resistor in series for 82ohms, a pot adjusted to 390ohms and the other pot is for calibrating the meter. Its set to 1500ohms. Otherwise it's all the same as the schematic. I'll have to do the zip ties on the cord when I get back home.

 

A thick typwrap (wire tie) clinched around the cord makes a nice restraining ring.

Can you post a schematic of your final design?

ak

I wouldn't put my trust in a Ty-wrap for securing a mains lead.

Compression type cable glands are easy enough to get hold of - the hard work bit is enlarging the hole in the back of the case.

 

I wouldn't put my trust in a Ty-wrap for securing a mains lead.

Depends on how you do it. If OP drills a hole in the heatsink and secures the power cord there, it would be plenty secure.

Compression type cable glands are easy enough to get hold of - the hard work bit is enlarging the hole in the back of the case.

This is the better solution. I have a bag of them, but haven't had time to get one out to take a picture...

 

Depends on how you do it. If OP drills a hole in the heatsink and secures the power cord there, it would be plenty secure.

...

So does the cable then pass through a hole on the back panel with nothing to prevent chaffing through the insulation?

And how well is the heatsink bolted down if someone trips over the mains lead................................................

It used to be common practice to tie a knot in the mains lead and just pass the end through a hole in the back - that and a few other old practices are now illegal in most countries.

 

So does the cable then pass through a hole on the back panel with nothing to prevent chaffing through the insulation?

And how well is the heatsink bolted down if someone trips over the mains lead................................................

It used to be common practice to tie a knot in the mains lead and just pass the end through a hole in the back - that and a few other old practices are now illegal in most countries.

We were talking about strain relief. If OP considers chaffing an issue, my assumption is that it will be addressed. I just observed that the wires had no strain relief and the part of the enclosure where power enters was not shown; so I had no comment.

The pictures in the original post show that the heatsink is securely attached to the bottom of the enclosure.

OP considered a knot and said it wasn't feasible...

 

Heyco wire grommet. This one is for flat cord, but can be made to work with round...

 

Heyco wire grommet. This one is for flat cord, but can be made to work with round...
View attachment 96203

You're supposed to use the correct tool to insert or remove those - I find that a basic scissor action wire stripper has good enough reach to compress the insert bit.

 

You're supposed to use the correct tool to insert or remove those - I find that a basic scissor action wire stripper has good enough reach to compress the insert bit.

I didn't mention how to install them, but I use pliers if I can't compress enough with my fingers.

 

I didn't mention how to install them, but I use pliers if I can't compress enough with my fingers.

If you can compress enough with your fingers - its pretty much going to fall out.

 

If you can compress enough with your fingers - its pretty much going to fall out.

Kind of depends on your grip strength. Mine is in the 125th percentile for my age group for "strong" and it is higher than the 100th percentile for all age groups.

http://www.topendsports.com/testing/norms/handgrip.htm

 

From Tony van Roon: "You can add two silicon diodes (in series) to the output of the LM317 to drop the final 1.2V, giving the full 0-30V range

 

Both parts will dissipate the same power and require adequate heat sinking. Both parts have built-in thermal protection and will throttle without it.
Any surplus stores in your area?

Old Hi-Fi separates audio amplifiers are a good source of mains transformers.

 

Kind of depends on your grip strength. Mine is in the 125th percentile for my age group for "strong" and it is higher than the 100th percentile for all age groups.

http://www.topendsports.com/testing/norms/handgrip.htm

Another point about those cable clamps - they need a special punch for a hole with 2 flat sides.

The compression gland types fit a regular round hole, some are small enough if your drill had a big chuck - or there's always Q-max punches.

 

Another point about those cable clamps - they need a special punch for a hole with 2 flat sides.

I've found that an appropriate diameter round hole works fine.

 

My circuit is the one which was posted on page 2. The only difference is a 1000uf 200v cap, a bnc plug, a 68 and 15 ohm resistor in series for 82ohms, a pot adjusted to 390ohms and the other pot is for calibrating the meter. Its set to 1500ohms. Otherwise it's all the same as the schematic. I'll have to do the zip ties on the cord when I get back home.

This repair/upgrade is pretty much screaming out for an efficient buck regulator.

A bit more complex and possibly too noisy for audio or Ham radio work, but for general electronics experimenting - could output a lot more current without impersonating a room heater.

One of my favourites is the MC34063 SMPSU chip, it can be configured as either buck or boost and is well supported by appnotes and plenty of example circuits online.

 

I've found that an appropriate diameter round hole works fine.

That would allow the cable to rotate and eventually fatigue the wire terminations inside.

Not impossible with the compression gland type - but most people tighten them up properly.

AFAIK: those can be got with a locating spigot in the mounting hole so they can't rotate - but those also require a special punch and/or extra working on the hole.

 

This repair/upgrade is pretty much screaming out for an efficient buck regulator.

See post #49. This circuit would give most of the benefit of a switching regulator without having to worry so much about switching noise. OP was determined to use resistors and diodes to drop the voltage until it became apparent that the secondary voltage dropped to a tolerable level under light load.

One of my favourites is the MC34063

I like that chip and it's my go to for switching regulators when I'm not rolling my own. I always have dozens on hand.