If you own a motorcycle, a motor home, a caravan, a lawn mover, a day
cruiser or maybe a vintage car you must at some point had to write off a
lead acid battery. When a battery is improperly charged or allowed to
self-discharge as occurs during non-use, sulphate crystals build up on
the battery's plates. The sulphate preventing the battery from being
fully charged and therefore it is unable to deliver its full capacity.
When trying to charge a battery in this state it only gets hot and
looses water, the gravity of the electrolyte is not increasing to its
normal “full charge” state.
Pulse Charger for reviving tired Lead Acid batteries Circuit Diagram
The only thing you do is killing the battery
completely. If a battery has a resting voltage of at least 1.8
Volts/cell and no cells are shorted, desalination of its plates can be
done. This circuit is an add-on and part for a modification of a normal
charger and it takes care of the sulphate problem.
The project:
get hold of an old charger, big or small it’s your choice depending on
the size of batteries you normally handle (bigger is better). There are
some tricks to boost the performance if you need it. Start by ripping
out everything except the transformer and the rectifier. Some older
chargers are equipped with fin rectifiers, which have high voltage drop
and must be replaced. Replace with a rugged bridge rectifier that can
cope with the amperes. All wiring on secondary should be short and heavy
wire. The rectifier should be bolted to the chassis to keep cool. If
the charger have a high/low switch it’s a bonus, if not you can in some
cases add a few turns of wire on the secondary winding.
The circuit; a
14-stage ripple counter and oscillator IC 4060 produce a pulse, which is
the heartbeat of the circuit. The pulse is feed to the 555 timer that
deicide the length of the active output. With the switch you can select
long or short pulse output. The output of the 555 timer triggers the
zero-cross opt isolator triac driver MOC 3041 via a transistor. This
gives the charger transformer a soft start via the triac and the snubber
circuit. A small power supply is necessary for the circuit and consists
of T1 a transformer 15V 0.1A secondary, a bridge rectifier, a regulator
and two caps. Because this project include a charger that is (X) the
outcome can differ in performance from one case to another. However this
do not mean that your project doesn’t work, but the efficiency can
vary. Some notes the snubbercap is a high voltage AC type (X) and the
resistors on the mains side is at least 0.5W type. Use a triac that can
take 400V+ and 10A+, I use BTA 25.600 but this is overkill in most
cases. No PCB sorry!
How it works:
Well the short version. The object is to get the cell voltage high enough for the sulphate to dissolve without boiling or melting the battery. This is achieved by applying higher voltage for shorter periods and let the battery rest for a while. The pulses on short range is about 0.5s on / 3s off and the long pulse range is 1.4s on / 2s off. These times can vary depending on component tolerances. Start on long pulse and if you discover “boiling” (more than with normal charging) in the electrolyte switch to short puls. Don’t leave the process unattended, at least until you know how your specific version of this project turns out. I built ver.1 of this circuit some 10 years ago and have experimented with it but I’m sure someone can improve it further.
Well the short version. The object is to get the cell voltage high enough for the sulphate to dissolve without boiling or melting the battery. This is achieved by applying higher voltage for shorter periods and let the battery rest for a while. The pulses on short range is about 0.5s on / 3s off and the long pulse range is 1.4s on / 2s off. These times can vary depending on component tolerances. Start on long pulse and if you discover “boiling” (more than with normal charging) in the electrolyte switch to short puls. Don’t leave the process unattended, at least until you know how your specific version of this project turns out. I built ver.1 of this circuit some 10 years ago and have experimented with it but I’m sure someone can improve it further.
