Self-powered Fast Battery Tester Circuit

[tobarger]

I have been trying to get this circuit posted on your site to operate for three days now. I've followed the schematic and instructions to the letter. Checked and rechecked all connections, replaced components and rewired over and over again. I've even tried to simulate the circuit with PSpice to no avail. I can't get C8 to charge above .7v with a 1.5v battery, so LED D7 will never light. Also,am using CMOS 555 timers as specified. Do you know of any problems with this circuit? Can you give me any advice or information about this circuit? Has anyone else tried to build this circuit? Any assistance will be appreciated.
Thanks
Tom

[audioguru]

Hi Tom,
The circuit looks OK to me. C8 should charge to about 4 or 5 Volts when the circuit is powered by a 1.5V new battery cell. It probably won't work if the battery cell is rechargeable, used or a button cell.

1) What size of battery cell did you try?
2) What is marked on your Cmos 555's?
3) Did you use 220uF for C8?

[Guest Alun]

Could you please post a link to the circuit - I can't find it on this site.

[audioguru]

Self-powered Batteries Tester project:
http://www.electronics-lab.com/projects/power/012/index.html

[tobarger]

Thanks for responding audioguru,

1) What size of battery cell did you try?
1.5v AA and also tried 5vdc straight from a power supply.
With 5vdc C8 only charges to approx. 3.5v.
Used a logic probe to ring out the chips, IC1 pin 3 is definitely oscillating but I lose the signal on the other side of C2 at pin 6 of IC2. IC2 does not seem to be working (inverting). From my understanding, unless the outputs of both ICs are very close to 180 degrees out of phase the voltage multiplier will not operate effectively. Am I correct in this assumption? When I tried to simulate the circuit in PSpice IC1 is oscillating fine, the output of IC2 is not inverted but slightly shifted out of phase approx. 45 degrees. Then when I add all the diodes and capacitors to the output of IC2 I can't get any meaningful waveforms anywhere in the circuit.

2) What is marked on your Cmos 555's?
NE555N
S8123

3) Did you use 220uF for C8?
Yes, electrolytic

Thanks again for your time.

[audioguru]

Hi Tom,
There's your problem.  :o
The NE555 is the original one that is not Cmos. Its minimum supply voltage rating is 4.5V.
You need LMC555 Cmos ICs that are guaranteed to work with a supply voltage as low as only 1.5V.
The ICM7555 and TLC555 Cmos ICs are guaranteed to work with a supply voltage minimum of 2.0V.  ;D

[tobarger]

Thanks audioguru,
I appreciate your time and patience.
Its rare to find someone thats so knowlegable and quick to help as yourself, you made my day.
Thanks again.
Tom

[tobarger]

I swapped the IC chips with TLC555 Cmos and the voltage at C8 is better but still only about 1.8v. This is still not near enough to light the LED. With 5vdc applied to the circuit the voltage at C8 is also low.

[audioguru]

Hi Tom,
As I said earlier, The TLC555 probably won't work with a supply voltage of 1.5V, it needs at least 2.0V.

Maybe the values of your capacitors are incorrect. 10nF is 0.01uF and sometimes is marked "103". 100nF is 0.1uF and sometimes is marked "104".
C8 should have a whopping voltage across it if the pot is turned down so it isn't loaded. With a 5V supply, I calculate about 21.5V. See my marked schematic: