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Comment by jtickle | Hacker News Reader

This is amazing to see. I have some audio recordings, digitized from tapes recorded in the 1960s, of my great-grandfather who was raised on a farm in Iowa. He talks about his experiences in amateur radio in the early 1900s-1920s. He mentioned bringing telephones out into the field that could be clipped to the fence wire to make calls back to the house, which was not hooked up to an electric grid but had batteries. Sadly, he did not say how the batteries were re-charged.

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The batteries were either charged using a "telephone magneto", or were taken to a local town to be charged off of mains electricity:

https://www.1900s.org.uk/1920s60s-windup-phones.htm

From what I understand, the crank was used to ring the exchange's bell, not to reload the phone battery.

Yes, in the old systems, you'd get about 90 volts AC down the line to ring the mechanical bell ringer. Once saw a guy nearly fall off a ladder, splicing phone lines with bare hands. He thought the relatively low voltage was safe enough, but then someone rang him in the middle of the job.

I know 30+ years ago as I kid I learned this in my parents basement as I was rigging something up.

It is more the surprise, as if one is ignorant to this fact it is not expected at all.

I had to refresh my memory about the hybrid use of AC and DC current in telephone networks.

The Alternating Current signals could be used over longer distances and were effective at making the bells ring, moving the clapper back and forth. This back-and-forth is exactly what makes AC so deadly in the body, should it cross through your cardiac muscles, for example, and set the muscles twitching at 50 or 60 times per second.

There’s nothing inherently deadly about AC nor anything inherently safe about DC. If there’s enough voltage available to drive current through your body, then electricity is deadly regardless of if it’s AC or DC.

In general AC tends to be a little safer than DC, because the voltage is constantly reversing, which means it’s constantly passing through 0V, creating moments where you don’t have current driving through your body and forcing all your muscles to contract. Those 0V crossings create moments where you can let go of whatever is electrocuting you. DC on the other hand has no such 0 crossings, if there’s enough voltage there to drive current through you, then all your muscles will be stuck contracting until either the power is turned off, or until they’re all so fried they’re not physically capable of contracting anymore.

My father in law grew up in the Denver area. His father made his living as a handyman, and one of his regular customers was Molly Brown (the Titanic survivor known as "The Unsinkable Molly Brown"). Every week he would go to her house to exchange her radio battery, then bring the old battery back to his workshop for charging.

There’s a great radio museum in Howth, Ireland, a waterfront town near Dublin. The founder was a lifelong radio enthusiast who grew up in a poor rural community and was mesmerized by the power of radio from an early age. I remember him telling me he had never heard a language other than English until radio came to town and he heard a broadcast in French. He also talked about using very basic acid batteries and having to go into town to change out the acid. I believe he said it was also a serious problem if you spilled any in the house because it would damage or dissolve anything it came in contact with.

The phone batteries weren't a high load kind of affair. They merely needed to change the varying resistance of the carbon microphone into an audio voltage - on the order of milliwatts of power - to send down the line. A more modern phone, still using a carbon microphone but powered by the line, needed about 20mA of loop current to do this. The telephone terms for the old system vs. the newer is "local" vs. "common" battery.

Heavy duty batteries - specifically the "A" batteries that powered the vacuum tube heaters in early radios - were made rechargeable to save cost.

This might be a bit of a tangent but I couldn't help but wonder if the appearance of 20ma here is related to the old fashioned, but I understand commonly used, 4-20ma current loop signalling in industrial applications.

It's almost never a coincidence. Before digital switching everything was done mechanically, and before mechanical switching everything was done by people with plugs. If you have a big enough industry like telephone switching equipment then you're bound to see a lot of suppliers expand their market by selling the same parts outside of their home industry. Current flow is a nice signalling mechanism because you can tell the difference between short, open, and functional circuit. So I'm guessing it got used in telephone switching equipment and then preserved because there was no reason to change.

And current through a wire stays the same on every point of the wire, more or less regardless of the length, as long as the supply can provide enough voltage to maintain it. This in turn dramatically simplifies the electronics needed to interact with it.

> Sadly, he did not say how the batteries were re-charged.

Dry-cell batteries had to be changed, they weren't recharged.

https://www.reddit.com/r/diyelectronics/comments/y7qmhq/15v_...

My grandmother from rural Saskatchewan said that back then they would exchange their radio batteries when they went to town.

Her husband, my grandfather, lived in Regina but worked on a traveling threshing crew and mentioned seeing a windmill driving an old generator from a car to charge batteries at one stop.

If the batteries were rechargeable at all (some radio 'A' batteries [0] were), they could have been recharged by a small wind turbine [1].

[0] - https://en.wikipedia.org/wiki/Vacuum_tube_battery

[1] - https://www.wincharger.com/

Maybe they used a Delco-Light Plant

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