1: Cut out the Vero-board and make the nine cuts with a 3mm drill bit.
2: Solder the components. Begin with the smallest one.
3: Mount a heatsink capable of absorbing atleast 15W on the BD139
4: Wire up the power input receptable, the current adjust potmeter (preferably a multiturn potmeter to make it easyer to adjust the current), the 2,7 Ohm resistor (connects to the two holes marked 'R', see layout) and the two fuses. Mount the 1 Amp fuse closest to the battery. Solder the wires from the battery on the copper side of the board. Use heavy gauge wire to minimise voltage loss.
NB!! DO NOT SKIP THE FUSES!! In event of a short in the tester, the wires quicky catch fire and the battery lets the smoke out. (Trust me!)
I recomend using a Digital multimeter to measure the current. Connect it in series with the battery with banana-plugs.
Read trough the prosedyre before you begin.
1: Start the Qbasic program in Winblow$.
2: Connect a charged TX battery and power up the hardware.
Check the current from the battery. It should be less than 1 mA. If so, go to step 3
If not, check the voltage at pin 1. (Pin 1 control the dischargecurrent: Low=on High=off)
If lower than 3.8v then the program uses the wrong paralellport address. Change the number in line 16 to the address of the parallellport the tester is connected to. (&278,&378 or &3BC)
If higher than 3.8v then there is a problem vith the hardware. Fix it! :)
3: Check the raw output from the MAX 187 A/D converter. (The upper right number)
If It is zero, 4095 or no number at all, the program uses the wrong paralellport address. Change the number in line 16 to the address of the parallellport the tester is connected to. (&278,&378 or &3BC)
4: Simuntanely measure the voltage over the battery and take note of the number in the upper right corner. This is the raw output from the MAX 187 A/D converter. It should be somewhere between 3000 and 3800.
If not, check the voltage to pin 2 of MAX 187, it is supposed to be ca. 1/3 of the battery voltage. If not, fix!
5: Insert the voltage reading and the sample count in line 7.
6: Check the voltage reading on the screen with different battery packs with different number of cells. It should be within +- 0.01V of the actual voltage applied. Also check that it reads 0V with no battery connected.
1: Start the measurement, Input the capasity of the battery and dischargecurrent (use 1000mA).
The tester should then begin drawing the graph.
2: Adjust the current to 1000mA with the current adjustment pot.
3: wait until the graph flattens. (ca 10 minutes)
Meanwhile, check that the BD139 is not becoming too hot. Wet your fingers and touch the heatsink. If you hear a nice frying sound, it is too hot!
4: Re-adjust the current to 1000mA. The current rises a bit as the BD 139 heats.
5: Simultanely note the voltage shown on the screen and measure the real battery voltage.
(Measure the real battery voltage where the wires from the battery enters the battery connector)
6: subtract these values and the result are the resistance in the wires connecting the battery to the tester and the resistance in the fuse, the amperč meter and the battery connector.
A 'normal' value is below 1 Ohm.
7: Enter the result into line 6 in the program.
Please follow this procedure when testing a battery.
1: Start the Qbasic program in Winblow$. I used Qbasic V1.1 when making this program.
2: Power up the battery tester hardware.
3: Connect the battery you want to test.
4: Press 1 and then enter the numbers of cells, and then the capasity printed on the battery in mAh.
Then enter the current you wish to dishcarge the battery with in mA
A typical TX draws 200 mA and a typical RX setup draws 100-200 mA.
The test starts immediately after entering the last number.
5: Use the current adjustment potmeter to adjust the current drawn from the battery to match the value you entered in step 4.
With the higher current settings, the current will rise a bit as the BD 139 heats. Since this rise is less than 5% you can ignore it. However, to reduce this effect you can install a better heatsink or just re-adjust the current adjustment potmeter.
The current is turned off when the test are finnished.
6: When the test are finnished, press 'Print Scrn', switch back to Winblow$ and start Paint.
Press 'Ctrl + V' to paste screenshot to paint.
If this doesn't work, use a screen capture program.
7: Disconnect the battery.
8: Remove the power to the battery tester hardware.
9: Quit the Qbasic program.
Turning off the computer or running other programs that uses the parallellport, while the battery tester hardware is powered up, might turn on the dishargecurrent. Also if the program stops running due to Winblow$ crashes during a test:
One of two tings happens:
- With a battery connected: The battery will be completely disharged to zero volt. Nicad batteries does not like that.
- Without a battery connected or with a completely disharged battery: The current in the 7805 rises, and since it does not have a heatsink, it will shut down due to the internal overheating protection. It will start up again when it cools down.
If you make any interresting test, please feel free to mail the image to me.
Feel free to modify the program and hardware to suit your needs. The MAX 187 together with the voltage reading part of the program makes a good startingpoint for your own experiments.
You can ofcource e-mail me your questions about this project.
Have fun, and don't do anything I would not do!
Rolf