capacitor power source?

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ogivemeahome
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capacitor power source?

Postby ogivemeahome » Sun Oct 23, 2011 11:28 pm

Hey all, why capacitors?
pros -
fast charge (seconds/minutes as opposed to hours)
simple charge circuit (from car cigarette lighter socket)
many charge cycles with no loss of capacity (long life)
current technology now means greater total charge (eg - (from Jaycar catalogue) two 5.5v 1F in series for up to 10V 0.5F giving 5 Coulombs of charge) - 1 Amp = 1 Coulomb/sec => 5 Amps for 0.1 sec should be possible(?) Is this enough to fire a e-match (or similar).

What I have in mind is to run a 'Stratologger' on some smallish lithium batteries and have the 'Drogue' output turn on a smartFET(?) (constant current source?) so that the capacitors can provide the energy to fire a deployment charge. At the end of the flight, the capacitors would be unplugged, charged and re-fitted for the next flight. I have some schematics (see pics) but seriously doubt that it can be that simple. I'm guessing this may have been done before by someone with lots more experience in electronics. Could a 'Clustermatic' be modified for this purpose?

Any help appreciated (before I have to start experimenting)
Attachments
CapSupply.jpg
J1 connects to the 'Drogue' output. J2 to the e-match(?).
CapSupply.jpg (23.68 KiB) Viewed 1663 times
CapChrgr_0002.jpg
J1 connects to the car cigarette lighter socket. J2 to the capacitor. Components are selected to provide less than the maximum voltage for the type of capacitor/s used. R3/R4 are for current limiting.
CapChrgr_0002.jpg (24.56 KiB) Viewed 1664 times
A smooth sea never made a skilled mariner. (English Proverb)

strud
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Re: capacitor power source?

Postby strud » Mon Oct 24, 2011 5:44 am

What is important in this instance is the current capacity of these caps. Some of the high capacity caps are for low current memory backup applications hence would not be suitable for the purpose you had in mind.
However, there are plenty about that are suitable.
My opinion though is that a small Lipo will be much more suitable and likely deliver more or similar current and store more energy for a given volume AND be cheaper :D

CS

ogivemeahome
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Re: capacitor power source?

Postby ogivemeahome » Wed Oct 26, 2011 3:17 pm

I've had an unreasonable aversion to Lipo's because of their; potential toxicity, potential fire hazard if damaged/incorrectly handled, special charging requirements. However...

strud wrote:My opinion though is that a small Lipo will be much more suitable and likely deliver more or similar current and store more energy for a given volume AND be cheaper :D CS


Your opinion appears to be well informed! After some (brief) research, I found an online calculator for capacitors at cooperindustries. The best combination there was the minimum in terms of reliable power (only just) and twice as big (plus) as the available space that I have. No point checking the price - if it doesn't fit, it won't work.
Lipo's on the other hand - these will fit in the available space:

Turnigy 138mAh 1s 10C 3.7g 35x12x6 x2of in series (these would be minimum in terms of power delivery), or
Turnigy 160mAh 1s 30C 4.3g 37x12x6 x2of in series.

ex HobbyKing (US) ~ under $2(US?) each (not including charger or freight)
ex hobbyunicorn ~ $5 and $10(?) each respectively (not incl. chrgr or freight)
Turnigy LiPo balancer and charger (ex hobbyunicorn) $10 (plus freight).

Clearly, they are the best option for what I'm doing (on this occasion).
A smooth sea never made a skilled mariner. (English Proverb)


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