Vehicle Battery Jogger-keep your battery fresh and young （3）

Published:2011/8/7 22:56:00 Author:Phyllis From:SeekIC

By Karel Walraven

Safety

Most people don’t realise that despite the modest voltage, working with vehicle batteries can be quite hazardous. This is because such batteries can deliver especially high currents. That means you have to be especially careful with metal objects in the vicinity of a charged battery. A dangerous short circuit can be caused not only by a simple screwdriver or wrench, but also by dangling jewellery and wrist-watches, both of which are notorious causes of avoidable suffering.

If something goes wrong with the circuit, there’s thus an especially good chance that something will be destroyed. Normally, the victim will be the power resistor, the FET (see the inset) or a track on the circuit board. It’s certainly possible for this to be accompanied by the release of heat, or even a bang and a bit of smoke. Consequently, you should always fit the circuit in an enclosure and ensure that no flammable materials are in the vicinity. Disconnect the circuit before charging the battery in the usual manner. Use flexible mains cable with a reasonably large cross-section (2 x 0.75 mm2, for example) for the connections to the battery.

Everything OK?

For initial testing, we recommend leaving CI off the circuit board and temporarily soldering a 100-nF capacitor to the board in its place. The LED should then flash approximately once a second. With a 10-uF capacitor fitted in this position, the period is a lot longer (2 to 3 minutes), and that’s not so nice for testing. If the lamp blinks, you can confidently solder the 10-uF capacitor in place on the circuit board.

Voltages are marked at various places on the schematic diagram. If the circuit does not immediately work the way it should, you can compare your circuit with our tried & tested prototype by measuring these voltages. Here we should note that if you make measurements on pen 2,6 or 7ofICl, proper operation of IC1 will temporarily be disturbed, and you may have to wait a little while for the reading to stabilise. The stated values were measured using an electronic multimeter (10 Mil impedance).

Six volts too

Many old-timers (vintage cars and motorcycles) use 6-volt batteries. Strictly speaking, this voltage is usually bit on the low side for switching a FET fully on- As a result, in practice the current through Tl will be a bit smaller, but it will still be sufficient to ensure obtaining the proper effect (keeping the battery fresh). It’s thus not necessary to reduce the value of R8, since the circuit is designed to be used with 6-volt and 12-volt batteries without any modifications.

Reprinted Url Of This Article: http://www.seekic.com/blog/project_solutions/2011/08/07/Vehicle_Battery_Jogger_keep_your_battery_fresh_and_young__（3）.html

Print this Page | Comments | Reading(330)