Charging 24V lead gel battery - Page 1
Forum section: electronics / projects

author: m-joy
author_rank: Contributor
timestamp: January 22, 2014, 08:54:24 am
content: Hi there,i am trying to charge 2*12V lead gel batteries in series. The 24V Batteries should be a backup supply, i want to charge them with trickle charge.Trickle charge is specified as 2,3V-2,4V / Cell.That means ~27,6V full charge.I tried to find a cheap and working solution so i came up with a voltage regulation with current limitation.My base voltage is 30V from which i want to load.The idea is to limit the voltage with voltage divicer R6/R7 (minus UBCE and UD1) to get around 27,5V (better less) and use the constant current source with current limmting resistor R2.I build up the attached circuit for testing, the battery is charging and the current limit seems to work somehow, but now the battery is stuck at 26,5V/100mA..Any solutions?

author: LeWidget
author_rank: Regular Contributor
timestamp: March 22, 2014, 09:07:34 am
content: Hey guys,Sorry to piggy-back onto this thread, I have a quick question similar to the OP topic.I have one of those hand-held mini vaccuum cleaners that are re-chargable. i wasn't sure it was working (found in shed and it was dirty). I took it apart & decided to test the power adapter.When I connected the adapter to power, I was getting reading of about 21.2v DC , but the charger says its 16v DC .. is this right, am I missing something or is the power adapter possibly faulty ? Just a note, the 2nd picture shows glue/fabric that was attached to the battery, it's not acid or anything.

author: PChi
author_rank: Frequent Contributor
timestamp: March 22, 2014, 12:57:51 pm
content: Can you label the schematic with measured voltages? That might help diagnosis.Don't the expensive batteries deserve a more accurate charger?If the Rayform battery has 21.3 V across it it has probably been finished by being flat, deep discharge, for a while. It's probably time to take it to the recycling centre. The battery may be taking no current and the AC Adaptor may have poor load regulation. The label implies that it is an unregulated supply by stating SEC: 16V DC 200 mA. It may only be 16 V at 200 mA and 21.3 V at 0 A. That is unsuitable for charging a 12 V battery but it will sort of work but destroy the battery in months.

author: SeanB
author_rank: Super Contributor
timestamp: March 22, 2014, 01:23:41 pm
content: 21V across a SLA battery means it is dead. Shake it and it will rattle. Only solution is a new one and a better charger.As to the OP, the 100mA is normal as it will keep the battery float charged, and it would be better to use a 28V 1W zener diode in place of R7 as the power source is likely unregulated, and rises in voltage with low load. That would improve regulation on the whole. Easiest is to use 4 6V8 400mW zeners in series, with 2 forward biased 1N4148 diodes to compensate for the other diode drops across the transistor and isolation diode.

author: LeWidget
author_rank: Regular Contributor
timestamp: March 24, 2014, 08:16:23 am
content: Thanks guysYeh, looks like the battery is cactus :\ .. new one will set me back close to $50 whereas a new mini-vacuum is around the same price. Think I'll toss it & look at a replacement.Thanks again:)

author: peter.mitchell
author_rank: Super Contributor
timestamp: March 24, 2014, 09:15:28 am
content: Quote from: LeWidget on March 24, 2014, 08:16:23 amNo way will it cost you $50 mate, at $42 you can get a 4Ah battery of similar size and shape from supercheap auto, thats not even trying to find a cheap one;http://www.supercheapauto.com.au/online-store/products/Century-Rechargeable-Battery-PS1240-12V-4Ah.aspx?pid=128927&menuFrom=40604#Cross