555 based constant current lead-acid battery charger

Posted on Thursday, January 24th, 2013 in project logs by DP


Kennith needed a 1A constant current lead-acid battery charger for his HAM radios. He augmented the 555 contest winning battery charger circuit by replacing the relay with an LM317 in constant current mode.

Since the SLAs are relatively small, and I only need them charged between radio outings, I opted to build a 1A constant current charger, based on the 555 Battery Charger which won first place in the 555 Design Contest Utility category. Using a 555 is a rather clever way to get two comparators and a Set-Reset latch in a single 8DIP package, which is needed for the high and low trip points. The major difference between my design and Mike’s is that instead of using a relay like him, I use an LM317 as a constant current source to limit my batteries charge rate.

This entry was posted on Thursday, January 24th, 2013 at 9:00 pm and is filed under project logs. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.

One Response to “555 based constant current lead-acid battery charger”

  1. A.N. says:

    Hi Kenneth,
    while using ICM7555 from Intersil with 18V Vcc limit, why not use either internal discharge FET (Pin 7) or even the output in lieu of 2N3904, and feed the timer from the 12V battery voltage? Any suggestions?

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