HP-71B 4Kb (CMT32k FrontPort) Memory Module "Battery" - FRAM

[KimH]

This is VERY helpful, thanks! Learned something new - again, I was sure I would..

I have bought some 10uF & 22uF of the X5R 25V version (off course the versions I have are 6,3V )

As Dave from the EEVBlog would say - "For those playing along at home" - the way to read the MLCC is:
X = Min temp -55°C
5 = Max Temp 85°C
R = Tolerance +/- 15% (Temperature Driven) - another reason why X5V sucks (+20% to -85%)

Once I have the 25V versions, I'll try both 6,3 and 25V and report here

(01-22-2021 08:24 PM)Garth Wilson Wrote:  Note that the piezoelectric effect on MLCCs is huge, and the capacitance drops off rapidly above approximately 20% of the WVDC. The dielectric type has an effect too, Y5V being considerably worse than X7R. A Y5V will lose over 85% of its capacitance at its WVDC, whereas the X7R only loses 70%. There's an article on this in EDN magazine, Apr 12, 2007, starting on page 77. (Would it be a no-no to post it here?) So for a power backup capacitor for the module, you'll want to get the largest capacitor that will fit mechanically, a 25V (5 times 5V) X7R capacitor with the highest capacitance that will fit.