Calculator battery pack. - Electronic Circuits Projects Diagrams Free

on1aag · 17th April 2007, 04:00 PM

I recently acquired a couple of hp 41CV's and one came with a
rechargeable battery pack. when I tried to recharge the battery pack
it didn't seem to be very cooperative and I decided to use a power
supply to give it a little push. And so the little push became a bit
bigger and bigger until my battery pack got short-circuited.
When I opened the damn thing I noticed that I got more than I expected.
And yes I fried the zener diode across the battery terminals, it was
well-done because it left it's mark on the pcb.

Could someone with a hp 41CV calculator measure the voltage across the
battery terminals with a fully charged pack and the charger connected.
The zener voltage could be 6V2 or 6V8, but it's also possible that they
used a custom zener. Most parts in the circuit had meaningless numbers
except for the voltage regulator, the two capacitors and the resistor.
I hope I'm not the only one who can't handle a "normal" calculator.

on1aag.

RODALCO · 17th April 2007, 07:59 PM

It looks that you have 4 cells in series which would indicate a 4.8 Volts nicad battery type.
These will get charged at max of 5.6 volts, so your zener may be something in the range of that value like 5.6, 6.2 or 6.8 Volts.
By ensuring the correct polarity and leaving the zener of while carefully charging / testing, see if you get a voltage across your battery.

RODALCO · 17th April 2007, 08:04 PM

Just have an other good look at your circuit.

The 365 ohms series resistor is there to limit the charging current from the 12 volts regulator, the zener will clamp the excess voltage to protect the battery from overcharging.

Somehow i think a spike may have killed the zener.

Have you checked the output voltage of your 12 volts regulator ?

on1aag · 18th April 2007, 12:07 AM

Hi Rodalco,

Thanks for your reply, but I destroyed the zener diode myself.
I was trying to revive the dead batteries with a power supply
directly connected to the rechargeables. I succeeded to revive
them but fried the zener in the process. I wasn't aware that
there were other parts present in the battery pack. I would
have expected the presence of a diode and/or a thermal fuse
but not a zener diode accross the terminals of the batteries.

on1aag.

Thread Tools
Show Printable Version Email this Page
Display Modes
Linear Mode Switch to Hybrid Mode Switch to Threaded Mode

Similar Threads
Thread	Thread Starter	Forum	Replies	Latest
Repair LI-ION battery pack (Gallopwire)	2PAC Mafia	General Electronics Chat	9	24th November 2005 06:31 AM
Portable Battery Pack?	DragonMaster0121	Electronic Projects Design/Ideas/Reviews	10	11th August 2005 01:32 AM
Battery charger for a special pack	Magnus Wedberg	General Electronics Chat	4	4th February 2005 05:38 AM
Charging circuit for my camera external battery pack	Wuey	General Electronics Chat	7	2nd May 2004 10:08 AM
digital camera external battery pack	dj_sly	Electronic Projects Design/Ideas/Reviews	0	18th November 2003 10:43 PM

17th April 2007, 07:59 PM	(permalink)
RODALCO	It looks that you have 4 cells in series which would indicate a 4.8 Volts nicad battery type. These will get charged at max of 5.6 volts, so your zener may be something in the range of that value like 5.6, 6.2 or 6.8 Volts. By ensuring the correct polarity and leaving the zener of while carefully charging / testing, see if you get a voltage across your battery. __________________ There are more ways to get to Rome. Electricity, Electric clocks, Meters and Trains are great.

17th April 2007, 08:04 PM	(permalink)
RODALCO	Just have an other good look at your circuit. The 365 ohms series resistor is there to limit the charging current from the 12 volts regulator, the zener will clamp the excess voltage to protect the battery from overcharging. Somehow i think a spike may have killed the zener. Have you checked the output voltage of your 12 volts regulator ? __________________ There are more ways to get to Rome. Electricity, Electric clocks, Meters and Trains are great.

18th April 2007, 12:07 AM	(permalink)
on1aag	Hi Rodalco, Thanks for your reply, but I destroyed the zener diode myself. I was trying to revive the dead batteries with a power supply directly connected to the rechargeables. I succeeded to revive them but fried the zener in the process. I wasn't aware that there were other parts present in the battery pack. I would have expected the presence of a diode and/or a thermal fuse but not a zener diode accross the terminals of the batteries. on1aag.