Current limiter for a MOT welder

current-limiter-for-MOT-welder

[Mike Worth] wanted the option to run his Microwave Oven Transformer welding rig at less that full power. After being inspired by some of the other MOT hacks we’ve featured he figured there must be a lot of ways to do this. But his searches on the topic didn’t turn up anything. So he just designed and built his own adjustable current limiter for the welder.

At the beginning of his write-up he details what we would call a bootstrap procedure for the welder. Go back and check out his original build post to see that he had been holding the framework for the cores together using clamps. To make the setup more robust he needed to weld them, but this is the only welder he has access to. So he taped some wood shielding over the coils and fired it up.

The current limiter itself is built from a third MOT. Adjustment is made to the cores by changing out the E and I shaped pieces. This allows for current limiting without altering the windings. [Mike] holds it all in place with a couple of bicycle wheel quick connect skewers.

It just goes to show that you should never get rid of a microwave without pulling the transformer. Even if you don’t need a welder wouldn’t you love a high-voltage bug zapper?

Biodiesel equipment hacks

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[Oldman] took on a biodiesel project for some friends a few years ago. A fully operational processing rig was never achieved, but he did document some of the successful hacks he came up during the project.

The idea is to reclaim the waste oil from restaurants and burn it in your modified racing motorcycle or other mode of transportation. That makes it sound easy, but have you ever seen what happens to bacon fat after it cools? Granted, we’re talking oil from vegetable sources but the same type of coagulation presents itself. Pumping it through a processing rig becomes especially tough in the winter, and that’s why [Oldman] came up with the heated pump head on the right. It’s got three connections; two are part of a loop of copper tubing, allowing 150 degree water to be circulated to liquefy the grease. The third connection sucks up the melted oil. You also need to regulate the water content of the fuel. The inset images of a salad dressing jar are his test runs with applying vacuum to dehydrate the fuel. He learned that it needs to be heated slightly to reduce foaming. He had planned to scale up this concept to apply vacuum to fuel stored in propane tanks.

Dead drop concept inspired by [Ender Wiggin] family

encrypted-dead-drop-concept

[Tyler Spilker's] DDD project is a Digital Dead Drop system based on Python and a Raspberry Pi as a server. It’s pretty rough around the edges at this point — which he freely admits. But we like the concept and figure it might spark an interesting conversation in the comments section.

Now by far our favorite dead drop concept is this USB drive lewdly sticking out of a brick wall. But you actually need to be on-site where this drive is mortared into the wall in order to access it. [Tyler] instead developed a webpage that gives him a text box to enter his messages. These are encrypted using key pairs and pushed to his remote RPi server. This way he can write down his thoughts knowing they’re stored securely and never in danger of being accessed from a lost or stolen cellphone.

If free thought isn’t what you’re trying to transfer from one place to another you probably want something like a Pirate Box.

Protoboard line following robot

dspic-line-follower

We love a good line-following robot project and this really hits the spot. It’s got sharp edges, gobs of solder bridging, and look at all those jumper wires! Despite its appearance it puts in a performance that won’t disappoint.

It uses a dsPIC33 to read from half a dozen analog sensors on the bottom of the board. We’re not all that familiar with the chip’s features, but [Exapod] says it’s got an auto-scan feature he uses to read the sensors. This allows him to sample with 12-bit resolution from all six of them at about 30 kHz. No wonder the thing is so responsive in the demo video embedded below. The track he’s using is just some white printer paper with a fat circuit of black electrical tape placed in a somewhat squiggly pattern.

This is also a fun challenge with toys. Here’s one that hacks a hexapod to follow the lines.

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