Category: Project

Actually there was nothing wrong with it. It didn’t really need “fixing”. A variac is a kind of variable AC transformer. They are very useful for testing AC loads because they can give a variable output voltage usually from 0 up to some value. This particular one can output from 0 to 250V and supply about 12A of current.

It is rated at 3kVA which is quite a bit. A big horse of a transformer like this has a big inrush current when it is plugged in. The surge is so great, that it was tripping the circuit breaker on our distribution board. The breakers on TOG’s board have C-curve trip characteristic, so they’re really not suited to this kind of load.

So something had to be done to limit the inrush current. We thought about a power resistor and a shorting relay, but in the end opted to try an NTC type surge limiter. This is a type of resistor where the resistance falls with temperature. At room temperature the resistance measured was about 12 ohms. The resistance falls rapidly as the temperature rises. Even so, the thing gets hot at heavy load. We used the 2kw heatgun as a heavy test load. We mounted the limiter high up inside the enclosure, in free air. Plenty of insulation and some cable ties to secure it. Tested it and no tripping now. A bit more testing is required however. particularly at higher currents. Need to do some I²R calculations and temperature measurements. Pics here.

Take the TOG test by selecting the correct answer.

Q: Your washing machine dies and you get a new one. What do you do with the old one?

1. When your new one is delivered, let the delivery crew take the old one away.
2. Take the old one to your local WEEE recycling centre.
3. Take the old one apart to see how it works. Harvest all the useful parts and use the parts to make something else.

The correct answer of course is number 3, but you knew that anyway. That makes you the kind of person that would probably like TOG.

So the trusty washing machine from 1996 was getting a bit tired. The drum bearings needed replacing (a relatively straightforward job)…they were squealing louder and louder. The drain pump started to make a racket and wouldn’t empty after a wash…. maybe it was seized or something jammed in it. Looking inside, it was obvious that it was leaking a bit also, probably when it was spinning. Time for a new machine.

Taking apart the old one, there’s a lot of interesting and useful bits. There’s a nice AC motor and an electronic speed controller. There’s some pulleys and a drive belt. There are also assorted hoses, electrical bits and valves. There’s also the stainless steel drum. Removing the drum from its aluminium mounting, and adding a few steel legs….. we have instant patio heater. Who needs a chiminea! Being stainless steel, it wont rust either.

We gave the new heater a test run this week and it worked a treat. Come in and stand around it at the next open social. Lots of pics here

Having some fun with old hard disks…. by taking them apart of course 🙂 Pics here.

There’s some interesting parts inside. Some fantastically strong magnets and an air core coil are used to position the heads. Stepper motors are long gone from hard drives! Might try some wireless charging experiments with the coil.

The platters themselves are spun by a type of 3 phase motor. Connected this up to a spare speed controller (ESC) from a model aircraft. Was able to spin it right up to 15,000 rpm using the aircraft remote control. Checked the speed with the trusty laser tachometer. That’s 250 revs per second, or 1 rev every 4 milliseconds. Makes a great sound at full speed.

Now to figure out some use for such a tiny high speed motor. Gyroscopic effects are very evident at such high speeds too. Maybe make some self balancing widget!