Build an 8 Volt Adjustable Battery Charger

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Build an 8 Volt Adjustable Battery Charger

Postby JohnMihevic » Sat Aug 31, 2019 9:07 am

This circuit will help if you have an 8 Volt battery in your cub. I built this adjustable 8 Volt battery charger for my friend that had an 8 Volt battery in his model T Ford. The circuit is shown below. It uses a standard 12 V charger and then drops the voltage using diodes that are forward biased and drop about 0.5 volt across each diode. The rate of charge is controlled by which diode is connected to the battery.

The diodes are available from Newark electronics (part # 76k5515) and cost $0.93. Any standard terminal strip will work. The maximum current the diodes can handle is 6 amps.

John M.


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Re: Build an 8 Volt Adjustable Battery Charger

Postby John *.?-!.* cub owner » Mon Sep 02, 2019 9:52 pm

Looks like it should work with no problem, but the newer smart chargers may not like it. Will probably need old style manual charger.
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Re: Build an 8 Volt Adjustable Battery Charger

Postby halftonstude » Sat Jan 11, 2020 9:02 am

that's one of the problems with newer chargers they know what they're connected to and sometimes cross their arms and say Harumph!!!! and refuse to put out electricity. i have to keep old chargers because if i need a 12 volt source to power something on my bench and no battery a new charger won't do anything. John interesting selection for a diode, a fast switcher. The specs i read were slightly different than your drawing but that's the best way to lower voltage at varying currents as long as the minimum current of the battery is sufficient to keep the diode forward biased. I found max forward average current at .375" is .25 amps, but couldn't find minimum. nice little circuit!

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