K7300: To Charge or not to charge!

I have followed the instructions exactly and although I do realize most problems are due to soldering, I do not believe this to be the trouble.
I have checked and rechecked component polarity, soldering joints and for short circuits.

At the point: Adjusting built-in clock.
Set shunt for CAL, 52 min. and 1.2V. Apply power 15 VDC. RV1 set to mid position.
Both LD1 and LD2 are OFF. Depress SW1, LD1 [Discharge] comes on. Release SW1, LD1 goes out and LD2 [Charge] comes on and stays on for 12 seconds.

This is not how I interpret the instructions. But the timer times out and it is adjustable by RV1.

Proceed to discharge/charge 8.4V 200mAh NiMH battery.
Remove CAL shunt and set 14 HRS. 8.4V and 15mA.
LD2 [Charge] comes on immediately I apply power. Depress SW1 and LD2 goes OFF. LD1 switches ON.

During charge the battery current does measure 15mA. and in the discharge mode the current reading was 240mA. Which appears to be correct for this type of battery.

During the course of fault finding I have noted the +V voltage which in standby measures 12.34V. [junction of R36 and ZD2] then with SW1 depressed this dropped to 9.25V. Although the 15VDC supply was maintained the total supply current measured 41mA with LD2 ON and 74mA with LD1 on.

I was suspicious of the LM324 quad Op-Amp and have exchanged this for a new one but with no success. I am not familiar with the CD4536 Timer, and do not have a replacement to exchange, but as the 12 second calibration test worked this component does appear to be OK.
Based upon the above information, does anyone have any ideas as to where my trouble may be?

Norman Allum

Sorry, but you got us confused here. What seems to be the problem (in brief) ?

With apologies for confusion.

Section 23. Adjusting the built-in clock.

Apply power. Neither the Green [LD2] or Red {LD1] LED are illuminated.

I now assume that when I press SW1, the Green LED will go on for 12 seconds.

But:

When I push the push button SW1, the Red LED lights up. Release SW1 the Red LED goes out and the Green LED comes on for the 12 second time period.

Is this correct?

Norman Allum

Hi,

I built this kit recently according to the instruction manual and the adjustment of the internal clock worked exactly as the manual said it would.
I think the problem in Norman’s case could be the result of a component failure. Try replacing the two IC’S as they would normally be the first components to fail. Remember that the CD4536 is C-MOS and needs special attention during assembly.
On my kit I experienced erratic timing results after the third use, caused by a failure of RV1. I replaced RV1 with a multi-turn Bourns type trimpot of the same value and this solved the problem.

Can Velleman perhaps elaborate on the correct sequence of operation of the kit. According to the manual, the discharge cycle should only start once SW1 is pressed. On my kit it starts immediately upon power up irrespective of the status of SW1. I would also like to know what happens after the 14 hour charge cycle has elapsed and the NiCd is still attached to the charger. Does the charger switch to trickle mode, or is the current to the battery shut off completely?

Regards

Carl.

It has been a while since my initial report. The original problem, as I attempted to explain, is basically a 9 volt (8.4V) NiMH battery will not go through the discharge cycle.
My initial use of 8.4V NiMH batteries were found to be of insufficient capacity for the application intended. I have since changed to 6 X 2000 mAH AA batteries.
In over 12 months I have had no problems using the K7300 battery charger using three sets of the AA NiMH cells. Set to 200mA and 7.2 volts the charger cycles through discharge and charges (14 Hours) without any problem.

I can find no retail, ready built, charger that will automatically discharge a 9 volt (8.4V) NiMH battery. Even though some universal chargers may include provision for charging a 9 volt battery, specifications to automatic discharge are only applicable to the higher capacity A, C or D cells.