[Diy_efi] supercap

[Bill Washington]

Bevan, Steven,
    Any thoughts on using a rechargable battery - (2 or3 cell)NiMH 
probably, for the RTC, and higher temp range 100uF electros for the 
reservoir caps on the remainder of the circuit? - the NiMH could be 
trickle charged by Diode during normal operation and diode switched to 
the RTC at power down - the RTC would then operate at full rail voltage 
minus one diode drop during normal operation, and NiMH minus one diode 
drop at power down. Configuration, etc would depend on the Min operating 
voltage of the RTC...
Thoughts?

Regards
Bill
>
>   
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> ------------------------------------------------------------------------
>
> Subject:
> Re: [Diy_efi] PCB layout/circuit design
> From:
> Bevan Weiss <kaizen__ at hotmail.com>
> Date:
> Tue, 27 Feb 2007 08:01:17 +1300
> To:
> diy_efi at diy-efi.org
>
> To:
> diy_efi at diy-efi.org
>
>
>
>
>> Bevan Weiss wrote:
>>
>>> I haven't looked into temperature ratings for super caps lately, but 
>>> last I looked they weren't great.  Something like -5degC to 45degC..
>>
>> Eep. is that failure at -5 degrees, or simply that they lose their 
>> charge? (the latter isnt much of a problem in our case unless they 
>> REALLY lose it)
> That's rated temperature.. so outside of that anything can happen.  
> Generally you'll get a deviation from the rated capacitance.  In most 
> cases it will fall significantly.  With lower temperature generally 
> the ESR will also increase (much like a battery), and the leakage 
> current will also decrease.
> It's not a big issue so much, apart from the slightly increased 
> possibility of container rupture (which would be a bad thing).  Super 
> caps tend to work best in situations where they aren't hot or cold.. 
> otherwise batteries tend to do a better job.
>>
>>> I applaud you for taking on this design in such a public manner.  
>>> Sorry if it seems like we're telling you how to suck eggs, just want 
>>> to make things easier for you :)
>>
>> I'm no expert on analogue electronics either, so Im here for all the 
>> learning I can get too :-)
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>