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Hello, I moved here from mastodon.social in July 2021, so many of you may know me already, but here's an updated bio anyway.

I'm an electrical engineer working in power conversion, a , a and user, and a cat lover. I've got a list of projects including things related to renewable energy and home networking, which I make varying degrees of progress on. Expect posts relating to these now and then, along with animal pictures, music, and other things.

I sometimes post sporadically, but I usually keep an eye on my timeline. Feel free to poke me now and then.

For pronouns, he/him/they/them are good.

US Independence Day, Fireworks 

Staying in for tonight, since we went out for fireworks last night. There's plenty of booms and bangs and some flashes perfectly visible from home now.

Feels weird thinking about celebrating Independence Day with everything going on. Still, if going to see colorful explosions are your thing, enjoy, and if you take a more DIY approach please use caution and be mindful of your neighbors (human, canine, feline, etc).

For anyone with the hardware to listen, this site has a handy list of various radio frequencies used by different entities. It's mostly US-centric. Can be interesting.

radioreference.com/

Fireworks 

Went out for fireworks tonight instead of tomorrow. The big professional display was nice, but there were some smaller, err, amateur ones as well.

Vacation was good, although I ended up having to sleep on some pretty crappy mattresses that gave me a little bit of back pane. Still, after sleeping in my own bed again, I actually feel pretty good today. I needed to get away from some things for a little while (technically I'm still away from them for another couple days), and the mental break has been great.

Vacation, ocean, marine life 

More seals. This time about a dozen of them basking.

re: Vacation, marine life, sharks 

There have been shark sightings here, of course, so you have to be careful in the water. I haven't seen any personally, though.

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Vacation, marine life 

On the beach here on the Cape, on the Atlantic Ocean side, you sometimes see seals popping up. They don't come ashore at this particular beach, but they do swim into the shallower waters.

Today, walking around in the morning, we saw as many as six of them at one point, I think the most I've ever seen at once here. Here are some pictures of one of them, I was just using a camera phone without significant zoom.

Cat, eye contact 

Going on vacation with the family this week, so no wolf or fox pics tomorrow or the Sunday after. George is staying at my parents house with his cousins.

USPOL mention, eye contact, cat picture 

After today, I'm not really sure what to say. I think a lot of good points have already been made here, so I will leave you all with a cat picture.

Stay strong out there.

Here I am charging a battery in my car, with a couple extra resistors added in parallel. This is just with the car idling in my driveway (temporary, for testing), but the battery was pretty drained, around 11 volts when I started. (This is a lithium iron phosphate battery, that was probably too low.) Initially it drew around 4 amps, but now it's settling at around 2.45 (down a little from when I took the screenshot).

This type of battery is relatively flat voltage wise, so the current should be stead for a while. Remember, it's dependent on the difference between the cigarette light voltage and battery voltage, plus the diode drop, across the resistor. I added two parallel 0.9 ohm resistors, and I think this is about right.

The voltage and current is measured by another project I through together a while back, it's a board with an AVR microcontroller and a couple hall effect sensors connected to my laptop over RS485. I envisioned using this to measure energy over time, but sort of put it aside after just getting it to measure voltage and current. (The 'Raw' values in the screenshot are just ADC counts.) It's sitting between the diode circuit and the battery I'm charging, so the voltage it's seeing is after the diode and resistor drop.

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Here it is with longer wires attached, with Anderson Powerpoles connected. The longer, black cable is the input, I will probably connect that to a cigarette lighter plug. The middle pair is meant to connect to a small 12 volt battery (a lithium iron phosphate, in this case), and the last pair is for a load.

This is basically a UPS, since other than a little voltage swing on the output it can keep something running. The advantage to this is that it's dead simple - just some diodes, basically.

The downside is that it does have a voltage drop. That means that it gets hot, and is a little wasteful. It's also passive in terms of charging the battery. Ideally, you could replace D3 and R1 with a DC-DC converter that could properly charge the battery. This is tricky, because depending on the battery and the power source, the battery could be at a higher or lower voltage. A non-inverting buck-boost converter would be ideal, there are ICs that will control this.

It is also possible to have an 'ideal diode' circuit, using a MOSFET controlled to act like a diode. (A MOSFET is kind of a bad diode that you can short out.) This is more complex, but there are ICs that do this too.

As is, this is probably good for something like keeping a Raspberry Pi running. It's kind of a hack, but it (kind of) works.

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I had a heat sink, also garbage picked. One thing to note - a lot of parts like this (TO-240 or similar package) are not electrically isolated on their cases. This heat sink has an electrically insulating thermal pad. You can find these on Digikey, Mouser, etc.

Keep in mind that the power dissipation is the current times the diode forward drop. So if you pull 5 amps to the load side, and the forward drop is 0.4 V, D1 will dissipate 2 watts of heat. (Obviously a little more, since these have a higher drop.) So a heat sink is a good idea, unless this is very small.

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Here's the schematic. The load you're powering is connected through a diode OR to the input power source and the battery. The input power source also connects to the battery through another diode, and a resistor.

The forward drop of these diodes (garbage picked from $DAYJOB years ago) is around 0.4 volts according to a multimeter, but the drop is a bit lower when I've tried power something, closer to 0.6 V. (I haven't pulled the datasheets.)

This assumes that the power source is a volt or two higher than the battery. The resistor trickle charges the battery; you may need to play with the value. Right now I have two 2.2 ohm resistors in parallel, I think I may add a third.

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I put this together the other day. The intent of this is to trickle-charge a 12 V battery from my car cigarette lighter plug, while also powering something else. And then seamlessly switching to the battery when power from the car is removed.

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hackers.town

A bunch of technomancers in the fediverse. This arcology is for all who wash up upon it's digital shore.