> I have to power a load that draws 2A @ 7,5V during one second each
> 15 seconds. So I think a 40,000uF capacitor charged to 20V powering a
> switcher would do the job.
> The charger circuit (air turbine generator) would need to charge the
> capacitor to 20V in 14 seconds. The air pressure available is ~10BAR.
> I could use a battery instead of capacitors.

If you use a battery you can monitor the long term voltage. As long as you 
get more energy in than neded on average you can use an extremely simple 
regulator - either clamping the voltage at a desired point well below max 
capacity or shutting off the input. Clamping sounds better if you use an air 
turbine :-).

Battery wants to be large enough that 2A load does not constitute a nasty 
load. 2AH would be sensible minimum for many chemistries. More better. The 
battery is essentially floated. Two series connected LiIon cells sound about 
right for this. 2 x 18650 at typically 2000+ mAh would be 'about right'. 
Double would be better but you get a little into series-parallel 
arrangements. Float arrangement should lead to longish life. SLA may be OK 
but voltage is annoying. 7 x NimH about right. Load down to about 7.5 - 8.5 
range depending on various factors and charge at up to 10+ volts. Even NiCd 
may have a plave here. Got an old drill battery pack ? :-).(Watch quality).

  Russell McMahon




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