lmccoig

modified 5 years ago

Hearing - Aid Battery Charger

181

01:05:02

Mercury cell hearing aid batteries can be charged with this "D" cell battery booster if hearing aid batteries are not completely dead.  We drain current from high capacity battery into smaller mercury cell.

With batteries positive to positive held by bent wire (like 3/32 inch brass or bronze brazing wire) to hold batteries together with ends of bent wire in hooks to clamp on bottom of larger D cell negative terminal and make contact with negative terminal of hearing aid battery.

Use hearing aid batteries for one day then charge 4 hours with this charger. Use other two hearing aid batteries next day so you rotate battery use to every other day.

If slight hum or whistle after charging set the cell aside for a few hours and then it should work okay.

After two months start with all new batteries.

The two 1 micro ohm resistors are to run in simulator.

published 5 years ago

Robert_Kidd

5 years ago

Is that an explosion I hear?

wyoelk

5 years ago

Darn no led in flames😭. Please read the comments at the bottom of that section in this circuit. Hope it helps somehow. _ http://everycircuit.com/circuit/5150506518052864

Robert_Kidd

5 years ago

DON’T DO THIS!! RISK OF BURNING AND EXPLOSION!!

Robert_Kidd

5 years ago

Note: if you don’t know how to follow @wyoek’s link - one way is to simply put 5150506518052864 into search bar at top of screen. Alternatively just click on the link (EC on Apple devices don’t allow this).

lmccoig

5 years ago

This was published in Popular Mechanics magazine. Touching 12 volts to button battery like striking a match moment to excite chemicals in button cell is when you worry about explosion. As D cell and mercury cell are equal in voltage soon the current would be slowing down with time.

Robert_Kidd

5 years ago

No, not really. You are thinking that if the cell is gassing out a spark might ignite the gas causing an explosion. I’m talking about a gas buildup in the cell suddenly getting released as pressure builds and is suddenly cell ruptures.

Robert_Kidd

5 years ago

Have Googled Practical Mechanics and found article. Still don't like it!

lmccoig

5 years ago

Batteries may not have been Alkaline in early 1960' s.

Robert_Kidd

5 years ago

Not sure of the relevance?

lmccoig

5 years ago

1963 batteries might not be battery power of today. Nice older ones get free hearing aid batteries in other countries.

Robert_Kidd

5 years ago

Had a quick look - nothing guaranteed here :-). Googled, supposedly mercury cell is 1.35V and it’s internal resistance is 0.035 Ohms. Dry cell is 1.5V and 0.30 Ohm. Don’t know how reliable the resistances are and they obviously increase as energy is depleted.

Robert_Kidd

5 years ago

Assume mercury cell is partly discharged so it’s dropped to 1.1V and it’s internal resistance has increased to 0.1 Ohm and that 1.5V is a new cell. Charge current going through mercury cell is (1.5-1.1)/(0.3-0.1)=2 Amp. This is a hell of a charge current for a cell you’d probably normally take a few milliamperes from! Obviously the mercury cell terminal voltage would rise thereby reducing the current flow. This is all guesswork but I’d not like to be nearby during the charging (or should I say explosion). Lol

Robert_Kidd

5 years ago

Oops, calculation error, current = (1.5-1.1)/(0.3+0.1)=1 Amp.

BillyT

5 years ago

Not many hearing aid batteries use mercury now days, a lot of them are 1.4V Zinc - Air,

Robert_Kidd

5 years ago

Quite right. EU has banned them.

lmccoig

5 years ago

As I remember back in 1963 - people tried things out to see what worked and did not do "scientific" thinking. With battery terminals same polarity I would expect some resistance to full current flow.

Robert_Kidd

5 years ago

I also remember 1963, JFK died. You’d stand little chance of coming across an I/C in those days (first integrated circuits were made in 1959).

Robert_Kidd

5 years ago

It’s simply Ohm’s law. If there’s a potential difference then current will flow in the circuit, limited by any resistance present.

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