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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING Charger for sealed lead (gel) batteries. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / Chargers, batteries, galvanic cells This story began when we decided to go to the forest on the night from Saturday to Sunday - my brother had a jam day, and we decided to celebrate him in the fresh air with barbecue and vodka. They began to gather. We took a couple of flashlights for lighting, and a small radio boombox to direct the musical background. Of course, we bought batteries for all this, which cost us a tidy sum. With the faces of happy idiots, we broke into the forest and briskly set about collecting firewood, soberly (for the time being) judging that it would be nice to break this very firewood before it got dark. And firewood was needed for two fires - for barbecue and for heating - lighting the place of celebration. Well, what I want to tell you ... the next day I could hardly unbend myself, because in order for there to be enough light from the fire, firewood must be constantly thrown there, which must be chopped in the forest, in which, after sunset, it became dark, like ourselves you know where the batteries in the lanterns had to be saved and the place of drunkenness had to be lit with a fire, for which it was necessary to chop wood. I'm repeating myself, right? Well, that night I had a lot of such repetitions. In this connection, the next day, two questions arose - "Did I rest?" Or "where and how to make sure that this does not happen again?". First of all, batteries - it is clear that batteries are needed, but after looking at the prices of modern nickel-cadmium batteries, my toad categorically refused to buy them. Then I remembered the UPS-s - you know, such banduras so that your computer does not cut out at the most inopportune moment, when you finish passing the 100x100 sapper, and the good neighbor has already plugged the self-made welding machine into the outlet and happily turned it on, de-energizing , thus half a house. So, these banduras use sealed lead batteries - they are also called gel batteries. In terms of cost, they are not comparable with Ni-Cd batteries - the former cost significantly less than the latter. I went to the store and bought myself quite an average battery with a voltage of 12 volts and a capacity of 7,2 ampere-hours.
As you can see, it is even quite small in size, weighs around 2,5 kilos, so even if you go to the forest not by car, but on your own two feet, it does not pull your hands much. Then everything was simple - we take a 10-watt car light bulb, hang it on a long wire on a tree and connect it to the subject - the light is ready. And to connect the radio, we sculpt a simple stabilizer on KREN8A or its bourgeois counterpart LM7809, fasten the wires to the terminals in the battery compartment - e voila - we have light and music. I must tell you that a similar scheme has already been tested - it lasts for the whole night of continuous operation and the battery does not completely discharge. But you understand that everything is not good until the end - there must be somewhere a drop of waste of human metabolism, which should poison the whole idyll. In this case, the ambush is that these batteries cannot be charged with conventional car battery chargers. Conventional lead-acid batteries are charged with a constant current, while the voltage at the terminals grows all the time and when it reaches a certain value, the electrolyte in the battery boils, which indicates the end of the charge. Let's imagine what will happen when a sealed battery boils. I believe that casualties and destruction are unlikely to be avoided. Therefore, these boxes are charged in a different way: the charge current is set to 0,1C, where C is the capacity of the battery, and the charging current is limited, since this comrade is "gastrically unsatisfied" and is ready to gobble up everything that is given to him, the voltage is stabilized and set to within 14-15 volts. During the charging process, the voltage remains almost unchanged, and the current will decrease from the set value to 20-30mA at the very end of the charge. That is, it was necessary to assemble a charger. I didn’t want to bother terribly, but then the bourgeoisie helped out - ST Microelectronics - they, it turns out, have an almost ready-made solution - the L200C chip. This crap is a voltage regulator with a programmable output current limiter. Ess, I said. Meow, said the Cat - he completely agreed with me. The documentation for this chip is at st.com/stonline/products/literature/ds/1318.pdf. The charger circuit in Figure 2 is practically a typical switching circuit.
In general, there is nothing to describe in particular, I will focus only on a couple of points. First of all - current-setting resistors R2-R6. Their power should not be less than that indicated on the diagram, and preferably more. Well, if you, of course, are not a fan of smoke special effects and do not trudge from the sight of blackened resistors.
The microcircuit, of course, must be installed on a radiator, and, also, do not be greedy - all this economy is designed for long-term operation, therefore, the easier the thermal regime of the elements is, the better for them, and therefore for you. Resistor R7 adjusts the output voltage within 14-15 volts. Diodes are better to take ours, domestic in metal cases, then they do not need to be installed on radiators. The voltage on the secondary winding of the transformer is 15-16 volts. Personally, I did not make any board, there are not so many details here - I assembled everything on a breadboard. What happened can be seen in the photo.
Everything works as predicted in the theory - the current, at first, is large, by the end of the charge it has dropped to negligible and has been living in this state for several days. By the way, the manufacturer recommends just such a small current for a long time to maintain battery capacity. Documentation for the battery itself can be found at csb-battery.com Well, good luck, look carefully with a soldering iron. Publication: radiokot.ru
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