Initiation au bricolage par Serge-Henri
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compteur météo
A fast charger for battery 12 v


Material :
  • 1 transformer 220/110 volts - 400 volts-amp.
  • 1 ammeter 0 to 6 amp. (45 x 45 mm)
  • 1 voltmeter 0 to 30 volts. (45 x 45 mm)
  • 1 bridge of diodes 25 amp.
  • 1 metal box 310 x 170 x 140 mm.
  • 4 adhesive legs or to screw.
  • 1 fuse holder : 6,3 x 31,5 mm.
  • 1 fuse 10 amp : 6,3 x 31,5 mm.
  • 1 selector 1 tracks with 4 selections.
  • 1 head for the selector (blocking by screw).
  • 3 contactors : 250 v - 12 amp.
  • 1 ligght switch : 220 v - 10 amp.
  • 2 crocodile clips.
  • 1 plug 2 Poles + T - 220 v/10-16 amp.
  • 3 meter cable : 3 x 1,5 mm².
  • wire : 1 mm² and 2,5 mm².

    Advice :
  • I warn you : this system is a little sophisticated, never the less it can be done by everybody as long as you've got all the materials and a bit of courage.
  • The basic principles are the same : 1 transformer 220/12 volts and 1 bridge of diodes will be an excellent battery charger.
  • To make it a fast charger, you need several outputs on the outputs of the transformer. That makes the transformer being a 5 legs sheep which you don't find in shops. So you might as well make it by yourself !
  • There are 2 types of transformer : one whose plates of the airgap are assembled in quincunx, the other whose plates are soldered in one part.
  • In those 2 types, you need the transformer whose output is wound outside the frame.
  • As far as I'm concerned, I salvaged a transformer 220/110 volts of 400 volts-amp I've unwound and rewound with some enamelled copper wire (20/10) : it will be able to output 10 amp. (that will be enough !)
  • You can also double the whorls if you've only got 10/10 wire, for example.
  • Make a machine to wind with a hand drill, on which you put the frame of the transformer. The transformer is centered by a drilled wooden cube.
  • Count how many whorls are unwound, because it'll be useful to know the tensions you need.
  • If for example, I unwound 110 whorls on my transformer 220/110 v, a simple rule tells me I need 12 whorls to get 12 volts.
  • There's of course, a formula to know how many whorls according to the airgap surface and the tension you need, but this is too difficult and I prefer my intuition.
  • The ideal thing would be to find a transformer 220/48 volts.
  • Here we are, all of that being said, we still have a small trap to avoid : the voltage drop which is caused by the bridge of diodes = square root of 2 or 1,414.
  • What comes down to saying the alternative 12 v output will only give 10,5 volts in D.C., a loss of about 1,5 volts. Take it into account for your differents couplings.
  • Very important : when you wind, locate well the inputs (E) and outputs (S) to be prevented from all the confusions in the coupling of the differents reels added.
  • If you think that the contactors you're using for the coupling are a bit sophisticated, replace them by connecting blocks and a base which can be salvaged on an old electric motor.
  • Don't forget, for the wiring, count 5 amp a mm². So the power (on the output) will be wired with a 2,5 mm² wire and the control (on the input) with a 1 mm² wire.

    Explanations :
  • The charger being under tension and the selector on position 1 (the most used), the contactor R1 starts and makes output S0 and E0 in the bridge of diodes.
  • The ammeter, connected in series on the positive one, will have to show about 2 amp, according to the state of the battery.
  • The volmeter, connected in parallel, will have to show 10,5 volts and the charging time mustn't exceed 3 hours.
  • The selector on position 2 will active only the contactor R2 and will couple the second reel with the first one : short-circuit E0 and S1 and output 13,5 volts S0 - E1.
  • The intensity will become 4 amp and the charging time will be 1 hour !
  • The position 3, that I never use, is to be used with precaution because of the limits of the ammeter. (short-circuit E0 and S1 + short-circuit E1 and S2 = output 15 volts in S0 - E2)