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Supercaps - what did the early 8753's use?

Question asked by drkirkby on Jan 2, 2016
Latest reply on Feb 4, 2016 by drkirkby
I wonder if Joel knows what sort of super capacitor (supercap) was used in the 8753. I don't have one of the early 8753's which is fitted with a super capacitor,  but I just got an HP 4291B 1.8GHz Impedance/Material Analyser, which looks and feels remarkably like an 8753, despite the 4291B was developed in Japan. 

The 4291B manual says the "battery" takes 10 minutes to charge and lasts 3 days. That sounds similar to the early 8753's, which used supercaps. I'm concerned that the capacitor fitted may be of the wrong type. 

The capacitor is marked:

* Tokin *FS*
* 5.5 V
* 1 F
* L6 (L6 is the date code, but I don't know what date L6 is) 

Looking at the data sheet for the Tokin/NEC super capacitors, which I attached, the *FS series* of supercaps is designed for low impedance loads, +"Back-up for 1 hour or less"+ - hardly the 3 days that the 4291B manual says the +battery+ is designed to have. 

I'm tempted to replace this capacitor, which is almost certainly an FS0H105ZF, with an FYH0H105ZF, which is the same capacitance (1 F),  voltage (5.5 V), lead spacing (10.16 mm), but is from the *FY series*, which are designed for higher impedance loads, with longer term backup.  At a sufficiently low current, the FY series can have a backup time of about 3 x 10 ^8^ seconds, which is 10 years! In contrast, the FS series is designed for backup times several orders of magnitude shorter than that. 

I'm wondering if 

* Someone has replaced the capacitor in the past and fitted the wrong type. 
* HP had good reason for using an FS series capacitor - perhaps the FY series did not exist. 
* I'm overlooking something

Dave

Edited by: drkirkby on Jan 2, 2016 12:04 PM

Edited by: drkirkby on Jan 2, 2016 12:17 PM  

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