UK Vintage Radio Repair and Restoration Discussion Forum - View Single Post - Electrolytic capacitor reformer meter circuits

Philips210 · 20th Sep 2018, 11:14 pm

Hi.

Many years ago I built the Radio Constructor electrolytic capacitor reformer which was originally published in the May 1969 issue. This unit has proved to be invaluable and whilst some question the point of reforming old electrolytics I can vouch for its effectiveness.
I decided to add meters for both capacitor voltage and leakage current. I had a couple of Monocor moving coil meters to hand which were pressed into service.
For voltage measurement, I used a 50uA FSD meter which has a coil resistance of 3k Ohm. I decided on having four ranges 0 to 10V, 0 to 50V, 0 to 100V and 0 to 500V which should cover all possible requirements. Calculations were made for the necessary multiplier resistors and testing revealed quite accurate results.
Similarly, for current measurement, I used a 100uA FSD meter. This has a coil resistance of 1k Ohm. Three ranges were thought to be adequate viz 0 to 100uA, 0 to 1mA and 0 to 10mA. The shunt resistors for the 1mA and 10mA ranges were then calculated. Again, this proved to be quite accurate when compared with my Fluke 23 multi-meter.

Something worth considering, is the switch for the current range ought to be a make before break MBB type to protect the meter. The voltage range switch should conversely be a break before make (BBM) type again to protect the meter.

By having meters for voltage and current, the reformer is also particularly useful for checking non electrolytic capacitors for leakage by subjecting them to their maximum working voltage whilst monitoring the current.

Attached pics showing the original RC circuit diagram, my meter circuit add-on, and some pics of the completed unit.

I hope these notes will be useful.

Regards
Symon

20th Sep 2018, 11:14 pm	#1
Philips210 Nonode Join Date: May 2007 Location: Redruth, Cornwall, UK. Posts: 2,579	Electrolytic capacitor reformer meter circuits Hi. Many years ago I built the Radio Constructor electrolytic capacitor reformer which was originally published in the May 1969 issue. This unit has proved to be invaluable and whilst some question the point of reforming old electrolytics I can vouch for its effectiveness. I decided to add meters for both capacitor voltage and leakage current. I had a couple of Monocor moving coil meters to hand which were pressed into service. For voltage measurement, I used a 50uA FSD meter which has a coil resistance of 3k Ohm. I decided on having four ranges 0 to 10V, 0 to 50V, 0 to 100V and 0 to 500V which should cover all possible requirements. Calculations were made for the necessary multiplier resistors and testing revealed quite accurate results. Similarly, for current measurement, I used a 100uA FSD meter. This has a coil resistance of 1k Ohm. Three ranges were thought to be adequate viz 0 to 100uA, 0 to 1mA and 0 to 10mA. The shunt resistors for the 1mA and 10mA ranges were then calculated. Again, this proved to be quite accurate when compared with my Fluke 23 multi-meter. Something worth considering, is the switch for the current range ought to be a make before break MBB type to protect the meter. The voltage range switch should conversely be a break before make (BBM) type again to protect the meter. By having meters for voltage and current, the reformer is also particularly useful for checking non electrolytic capacitors for leakage by subjecting them to their maximum working voltage whilst monitoring the current. Attached pics showing the original RC circuit diagram, my meter circuit add-on, and some pics of the completed unit. I hope these notes will be useful. Regards Symon Attached Thumbnails