The Museum of HP Calculators

HP Forum Archive 09

 Re: I'll try this...Message #1 Posted by Stephan (Germany) on 6 Jan 2003, 4:22 p.m. Dear Luiz, last year I got a battery pack of a 19C back to live by this method. I used 40000 uF and just a few Volts (around 8 Volts from a DC power supply). It worked well. Important is to discharge only on the "dead" cell, not connect the capacitor to the complete pack. As the internal resistance of a shortened cell is almost not present, and also no residual voltage is left, I bet even lower voltages will do. Please do yourself the favor and try it with as small a voltage as possible - even if the thrill is less. By this way you also minimize the ugly burn marks, where the connection closes and the spark shows up. Best regards and success, Stephan

 Re: I'll try this...Message #2 Posted by Vieira, Luiz C. (Brazil) on 6 Jan 2003, 4:40 p.m.,in response to message #1 by Stephan (Germany) Hi, Stephan; thanks for the new guidelines. I was reading again the original article and I saw one thing I did not notice before: polarity. As a voltage source, any battery is supposed to have a low internal resistence WHEN fully charged and direct current is considered. I always plugged the battery poles as if the battery is a polarized charge for the capacitor circuit, say, serial connection: (-) pole from capacitor in (+) pole in the battery and (+) pole from capacitor in (-) pole in the battery. This way, the current surge flows the same way as if the battery is connected as the voltage source in a circuit. The scheme when power supply and battery are connected with the same polarity is uded only to charge the battery. Am I wrong? I agree with you when you mention a lower voltage, but I always thouhgt of a high voltage peak (and current) to "remove" the short-circuit cause, an internal, abnormal connection between both (+) and (-) poles. Will it have the same efficiency with lower voltages? As we are not working with "manufacturers recommended operating conditions", I was reasoning about it. I still have three 1.5 volt cells from an 82143A batt pack that did not have their internal short-circuit removed and I'll give them a try. Thank you all for the brainy, valualble guidelines. Best regards.

 Re: I'll try this...polarityMessage #3 Posted by Stephan (Germany) on 6 Jan 2003, 4:51 p.m.,in response to message #2 by Vieira, Luiz C. (Brazil) I connected capacitor to cell + to + and - to minus, as in a charger circuit. It worked well. BTW, your oil filled capacitor is a real bomb. Fully charged it can make traces similar to ark welding. Stephan

 Re: I'll try this...polarityMessage #4 Posted by Vieira, Luiz C. (Brazil) on 6 Jan 2003, 4:58 p.m.,in response to message #3 by Stephan (Germany) Hi; I'm sorry for the misspelled words. It is an "oil-can"-shape, 40.000uF/70Vwv electrolytic capacitor. And it will probably burn the wire tips out... Cheers.

 Re: I'll try this...polarityMessage #5 Posted by Stephan (Germany) on 6 Jan 2003, 5:15 p.m.,in response to message #4 by Vieira, Luiz C. (Brazil) Dear Luiz, Please be careful in any case (you are a too valuable contributor in this forum to be be lost). Not every capacitor is capable to withstand impulse loads which would occur in your application. I still can smell the acid spread around in my room when a 2200 uF 16 Volts popped. And I don't want to imagine the effects of your much larger "oil can" on house and health. Stephan

 Re: I'll try this...polarityMessage #6 Posted by Vieira, Luiz C. (Brazil) on 6 Jan 2003, 6:47 p.m.,in response to message #5 by Stephan (Germany) Hi; I'm flattered, thanks! And that's enough reason for me to take triple care about this high electrical parameters (everything, except for isolating impedance, is dangerous when more than 1K in Electricity...). I'll experience a bit before going any further. I'll try to deserve taking place with the valuable contributors (as all actual contributors) by firstly not messing things up! Thank you.

 Re: I'll try this...Message #7 Posted by Tony Duell (UK) on 6 Jan 2003, 7:44 p.m.,in response to message #1 by Stephan (Germany) My experience with 'zapping' NiCd cells is that although it will clear the shorts, and although the cells will charge after 'zapping', they don't have much capacity, and they are liable to short again. I've zapped cells in many battery packs to get a battery pack that works well enough to test the unit in question (and thus to confirm it's worth buying some new cells and rebuild the pack properly), but I wouldn't use a zapped pack in any machine I inteded to use regularly.

Go back to the main exhibit hall