At Christmas I was very ill with the flu and have been recovering for the last two weeks. This has given me time to get into my workshop for some play time.
A while ago, another member posted a question about the Dave Barker Lead Acid battery de-sulphator, and as my little club had been given a collection of used alarm back-up SLA batteries in various states of health ranging from "as new" to totally dead, it aroused my interest as to whether or not the process worked. I read many articles on the subject, and concluded that most had been written by "armchair experts" who probably were very knowledgeable on the theory of the chemistry, but had not actually done any practical testing. (Throughout my life, many time I've been told "that won't work" only to find in practice it does)
So, as the consensus of opinion seemed fairly evenly split between the advocates, and the dismissive, I decided to build one and see for myself.
First of all, I attempted to charge a small selection with my commercial maintenance chargers. Those that accepted a charge were then given a discharge/time test carefully noting the current and voltage over time. Trying this a couple of times showed pretty much the same results, they were all well below original new capacity, i.e a pair of 7A/h sla's only had about a quarter of that rating.
I built the Dave Barker design exactly as his schematic showed, and by using differential 'scope measurement across a 1 Ohm 10W resistor in series with
the battery, observed initially very short 15-20 microsecond 20Amp H.F ringing pulses increasing to over 30Amps into the battery at a repetition rate of around 2 KHz. After 24 hours, the discharge test was repeated, and to my surprise, now showed some recovery, up to about a third of full capacity. I reconnected the desulphator and left it for another 24 hours. Now the off load voltage (after allowing time for settling) had increased by 0.75 volts from the previous charge.
The discharge cycle was repeated and now was up to 2 thirds full capacity. The process seemed to be successful. At this point, I connected a completely dead 2.1Ah battery that had failed to accept a charge from the maintenance charger, and left it on for 24 hours.
( I should point out that I was powering the de-sulphator from a bench psu that had current limit set to a little over the maximum charge rate for the battery under test, but voltage was only 12 Volts. The final battery voltages were above this so it was not just "pass through" charging.)
Back to the "dead" battery", after 24 hours, it showed 11.5 volts, and a discharge capacity of about 0.25 Ah. I gave it a further 24 hours, let it rest for 24 hours while I charged the first one again, then gave it 36 hours. After that, I ran the discharge cycle and it was up to 1.8 Ah and the voltage was 13.7V!!!!! Wow, something good is going on.
I will continue charge/discharge test as time permits and see if the is any further improvement.
I have made a lash up of a somewhat more powerful version which is able to provide 90Amp pulses into a 17 Ah battery that is also recovering well.
My conclusion so far, is, They were previously useless batteries, and now they are working and useful, so from the above, feel free to comment and draw your own conclusions.
Once my camera battery is charged, I will post some pictures
A while ago, another member posted a question about the Dave Barker Lead Acid battery de-sulphator, and as my little club had been given a collection of used alarm back-up SLA batteries in various states of health ranging from "as new" to totally dead, it aroused my interest as to whether or not the process worked. I read many articles on the subject, and concluded that most had been written by "armchair experts" who probably were very knowledgeable on the theory of the chemistry, but had not actually done any practical testing. (Throughout my life, many time I've been told "that won't work" only to find in practice it does)
So, as the consensus of opinion seemed fairly evenly split between the advocates, and the dismissive, I decided to build one and see for myself.
First of all, I attempted to charge a small selection with my commercial maintenance chargers. Those that accepted a charge were then given a discharge/time test carefully noting the current and voltage over time. Trying this a couple of times showed pretty much the same results, they were all well below original new capacity, i.e a pair of 7A/h sla's only had about a quarter of that rating.
I built the Dave Barker design exactly as his schematic showed, and by using differential 'scope measurement across a 1 Ohm 10W resistor in series with
the battery, observed initially very short 15-20 microsecond 20Amp H.F ringing pulses increasing to over 30Amps into the battery at a repetition rate of around 2 KHz. After 24 hours, the discharge test was repeated, and to my surprise, now showed some recovery, up to about a third of full capacity. I reconnected the desulphator and left it for another 24 hours. Now the off load voltage (after allowing time for settling) had increased by 0.75 volts from the previous charge.
The discharge cycle was repeated and now was up to 2 thirds full capacity. The process seemed to be successful. At this point, I connected a completely dead 2.1Ah battery that had failed to accept a charge from the maintenance charger, and left it on for 24 hours.
( I should point out that I was powering the de-sulphator from a bench psu that had current limit set to a little over the maximum charge rate for the battery under test, but voltage was only 12 Volts. The final battery voltages were above this so it was not just "pass through" charging.)
Back to the "dead" battery", after 24 hours, it showed 11.5 volts, and a discharge capacity of about 0.25 Ah. I gave it a further 24 hours, let it rest for 24 hours while I charged the first one again, then gave it 36 hours. After that, I ran the discharge cycle and it was up to 1.8 Ah and the voltage was 13.7V!!!!! Wow, something good is going on.
I will continue charge/discharge test as time permits and see if the is any further improvement.
I have made a lash up of a somewhat more powerful version which is able to provide 90Amp pulses into a 17 Ah battery that is also recovering well.
My conclusion so far, is, They were previously useless batteries, and now they are working and useful, so from the above, feel free to comment and draw your own conclusions.
Once my camera battery is charged, I will post some pictures