I have an equipment that just cant run or work if the old Nicads are present. Can old Nicads somehow cause a short or something?
Also is it not when the charging is on while circuit is being used. The circuit is using the voltage from the charger? So how can old bad Nicads make the circuit not work as if the circuit is depending on the batteries even when charging? Is this possible?
Anyone has similar experiences?
Yes.
Here's a writeup of one piece of equipment showing how the designers protected against the consequences.
https://www.eevblog.com/forum/testgear/fluke-8125a-military-dmm-teardown/msg2540730/#msg2540730There's a worse example of NiCds being a pain... Tek 1502 TDRs have a (fortunately) unique PSU where the NiCd charging is controlled by a PUJT and SCR. The equipment is protected against failure by preventing the internal SMPS operating if the NiCd battery voltage is too low (i.e. discharged) or too high (i.e. missing). That means it won't work on the mains without an operational battery.
To compound that, even when switched off, the batteries are discharged at 1mA. That leads to the requirement that the battery pack must either be removed or charged once a month, but not for more than 16 hours since the charger's crest factor damages the battery.
Consequently, if you obtain a Tek 1502 with a battery pack, the cells have usually disintegrated to produce a hazmat toxic waste site.
Shame, because the 1502 is still a
delightful instrument to use. Oh, make sure the sealing is still intact before you operate it in driving rain or store it under 30cm of water
