gary – Page 15 – Tog Hackerspace

28/04/201610/05/2016

Electronic “Build-It” Workshop

line follower *** STOP PRESS …. Our workshop is full for this Saturday. We may run another soon. Get in touch with us on the “contact” link above if you are interested in taking part in our next one ***

We’re holding an electronic “Build-It” workshop in TOG on Saturday 14th May at 14:00. Many visitors to TOG tell us that they would like to get started with electronics, soldering or assembly, but they are unsure how to do so. This workshop will help. The workshop will run for approximately 3 hours. You will get to build (and keep) an electronic kit. The kit that we have chosen is a line-follower robot car. It will follow a black line or any line where there is reasonable contrast. You can see a video of the kit in action here.

The kit comes as a complete set of mechanical and electronic parts including a bare circuit board. You get to do all the electronic assembly and soldering as well as the mechanical assembly. If you’ve never built an electronics kit or soldered before, then this workshop is ideal for you. We’ll show you everything that you need to know. No previous experience at electronics, soldering or kit assembly is needed. We’ll explain the circuit and how it works too. All tools and equipment are provided. The workshop will take about 3 hours from 14:00 – 17:00.

26/04/201625/04/2016

E-Bike Battery Surgery

battery dead One of our long term visitors is an e-biker. One of his batteries was on the blink. There was no output on the normal output connectors, but there appeared to be an output via the charge port. We suspected that the balance circuit was shot, but when we opened the battery case, it looked like one of the cells was physically damaged. Lots of pics here.

We ordered a replacement cell. When we removed the bad cell, we noticed some others damaged. It looks like we need 4 replacement cells in all. We plan to cannibalise these from an old spare battery. We tested the remaining cells and they seem able to take a charge and deliver reasonable current. A 2 Ohm power resistor came in handy. Check back with us to see how the rest of the repair went.

23/04/201628/04/2016

Blackpitts Makeover

spruce up The front of our building is getting a bit of a makeover. Pics here. New cement render on the outside, painting, new bike racks, steps and ramp cleaned up. Inside we’re getting a spruced up entrance lobby, a new entrance door and other works. Drop in and have a look.

09/04/201611/05/2016

Fixing the Variac

variac

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.