PVC Cement and Hot Glue


Making an isolated hall effect current sensor with ring terminals

Making an isolated hall effect current sensor with ring terminals
simple isolated current sensor
Needed an isolated current sensor to sense the current in my cell level test fixture. Found a neat part made by alegro that has a compensated hall effect sensor with built in current shunt. Unlike a regular current shunt where the resistance of the shunt produces a voltage when current flows through it, this device has an integrated hall effect circuit built in. The device comes in many flavors, with unipolar or bipolar sensing up to +-150A. The best part is that the hall circuit is electrically isolated from the current path. The down side was that the device was designed to mount on a PC board, so attaching it to the big 1/4" studs that I required was dificult. I carefully straightened the heavy copper buss bar leads and sawed a slot in some heavy 1/4" ring terminals. The terminals were soldered to the straightened leads, and the fine hall effect wires were connected to three wires and strain relieved with some hot glue.
Works like a charm.

C-band dish solar furnace

C-band dish solar furnace
Canning Tomatoes with the sun
Back in the 60's I was given a nice rugged parabolic dish, and had covered it with mirrors. It works pretty well. I have reached aluminum melting temperatures, and run a steam engine.
Old radar dishes are not readily available but old C band dishes are.
Start with an old C-band satellite dish. Cut Bathroom mirror tile into 2" or 3" inch squares.
Glue tiles to dish with silicone rubber,then glue aluminum foil to the back with a thin coating of silicone to seal out moisture, and protect the mirrors back.The small gap between the mirrors will allow eventual total curing of the silicone, but it takes several months for a full cure. The layer of aluminum foil stops the degradation of the mirrors rear surfaces. My dish has been outdoors for over 30 years and the mirrors are still like new.
The horizontal and vertical drives are run by a sun tracking servo amp that keeps it pointed at the sun.
A schematic of the basic tracker is available on the downloads page:Simple Tracker schematic
This generic servo will operate on 12-24VDC, and will run dc motors over the same voltage range. The power transistors need to be mounted on a good heatsink with electrical isolation between the collectors and the heatsink. The servo gain pot will want to be tuned for best accuracy of tracking without oscillation.
The sensing photo detectors are mounted at + and - 45 degrees to form a half bridge.The + of one detector connecting to the - of the other. This "shorted" connection forms a current bridge where the two photo diode currents cancel when evenly illuminated, and change polarity and amplitude of output when unbalanced. The idea is to have the servo always drive the dish to the null point.
I Canned some tomatoes this morning. The 8 quarts of water and tomatoes reached boiling in 6 minutes, but then it was boiling too fast. I had to drape news papers over the mirrors to turn down the heat. I will need to make an adjustable shade for the thing, so I can adjust the boil to a slow steady one. Tracker worked well.I need a steam engine for the thing, and I could make some electricity or pump water.
More information on this project:
Plugging into the sun blog

Black tape and PVC cement

Black tape and PVC cement
Making it one piece
I have been using black electrical tape since I was a kid.
My Dad was a DIY of considerable skill, and I used to play in the basement and be his helper, he always had several rolls of tape so it became one of my toys.
Black tape has many uses, and has certain properties that make it a versatile tool.
Insulation:
The main use of black electrical tape is to cover bare electrical wires. If applied correctly, the tape will last for many years. If applied incorrectly, it will start to separate and get sticky in short order. Each wrap is good for 200-600V depending on the thickness, so a carefully taped wire can have better insulation than the wires on either side.
The tape is designed to be pliable and stretch so it can conform to irregular surfaces. The trick to making a tight long lasting covering with tape is in when and how much you stretch it.
Temperature extremes will make black tape stretch and contract, loosening the adhesion in the layers. To prevent this, when making the final wrap, always do it with nearly zero tension in the tape, to prevent the end from shrinking back when heated. A final and powerful way to make the taped joint stay together, is to use PVC pipe cement to coat the outer layer of tape and glue it together. The cement sets up in a few minutes, and will protect the tape for many years even outdoors in the weather, and the joint is waterproof.

The inner wraps need to be fairly tight so air is not trapped in side.
The quality of black tape is a measure of how much stretch can be put into the tape before it breaks. Never stretch to more than 70% of the breaking point, as breaking point and pliability drop when the tape joint gets cold, and the tape could crack through all layers.