Replacing batteries with capacitors in battery based Dashcams

Looks interesting! But, what about when the cap is discharging, won't the transistor then return to off as current now wants to go from the collector side to emitter?
The transistor in this configuration won't much care what the load (supercap) is doing. It will simply make the calculated amount of current available. The load can take it or not take it.
It might be better to think of "load" being the supercapacitor and camera connected in parallel. (Or at least the parts of the camera that are relevant.)

NB the transistor might get hot, depending on the current and voltage difference between E and C (emitter and collector.)
 
FYI, while a capacitor initially looks like a short circuit and climbs to look like an open circuit, a choke (coil) initially looks like an open circuit and drops to look like a short circuit. So all you would need is a choke balanced to the capacitor, on the input. You would probably want the choke to go to short, before the capacitor goes to open, in order to make sure the capacitor charges as fast as possible. This all goes back to current flow, through the capacitor and the choke, and involves another whole bunch of computations that I have neither the time nor the memory to go into. It's not that my brain cells are dead. In fact, they're quite active. It's just that all those years of feeding them scotch have turned them into dead-beats, that don't want to work. You would think those brain cells would be more appreciative. After all, it was really good scotch.
 
I always had a dislike of inductors (chokes/coils) for some reason, and never used one in any of my electronics projects. Probably an unfair prejudice, because LC circuits don't waste energy like RC circuits.

However, the problem remains : Do they make super inductors to match super capacitors?

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However, the problem remains : Do they make super inductors to match super capacitors?

You wouldn't need any kind of super inductor. All you need is a choke that will slow that immediate short circuit surge, when the capacitor begins to charge. It would only be needed for the first few seconds of charge, till the capacitor began to show resistance. After that, the choke would look like it wasn't there, till the input power shut off. Then it would try to supply a last little bit of energy to the capacitor. The choke would also be only on the charge side of the circuit. The capacitor would bypass the choke on output.
 
I always had a dislike of inductors (chokes/coils) for some reason, and never used one in any of my electronics projects. Probably an unfair prejudice, because LC circuits don't waste energy like RC circuits.

However, the problem remains : Do they make super inductors to match super capacitors?

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Yes, you can even get mega inductors capable of storing 20 MWh of power, however they are rather expensive since they need to be made out of super conducting wire which requires cooling with liquid nitrogen to operate.

For an overview: http://energystoragesense.com/superconducting-magnetic-energy-storage-smes/
 
I do have a large inductor - one Henry - but it sucks .
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I was interested in doing this conversion myself. Thank you to the main op for the numbers. For the balancing circuit I was planning to use several silicon diodes in series across each capacitor. The resistors solves the balancing problem, but it fights the charging by consuming some of the charge current. The bigger issue is the resistors bleed the capacitors down when not on charge. The diodes won't conduct until the capacitor voltage exceeds the forward voltage of the diode series. I guess zener diodes could work for this too, maybe a better choice too. I would just make sure the the current rating to the diodes is higher than the charging current. I'm also a little skeptical that the cameras charge circuit will care about the capacitors being completely discharged. After all this, I'm considering just buying a 1A buck stepdown voltage converter off ebay for $1, wiring it to constant battery power, setting it to 4.2V and calling that my battery. Then of course you have to worry about the converter not being an isolated supply so if the ground of the camera battery is not the same potential as the car battery's you'll have problems. I guess you could use an isolated converter, but the cheapest I ever found was $15 for 1A. Maybe I should just replace the cams battery every year? No free lunch I guess....
 
I was interested in doing this conversion myself. Thank you to the main op for the numbers. For the balancing circuit I was planning to use several silicon diodes in series across each capacitor. The resistors solves the balancing problem, but it fights the charging by consuming some of the charge current. The bigger issue is the resistors bleed the capacitors down when not on charge. The diodes won't conduct until the capacitor voltage exceeds the forward voltage of the diode series. I guess zener diodes could work for this too, maybe a better choice too. I would just make sure the the current rating to the diodes is higher than the charging current. I'm also a little skeptical that the cameras charge circuit will care about the capacitors being completely discharged. After all this, I'm considering just buying a 1A buck stepdown voltage converter off ebay for $1, wiring it to constant battery power, setting it to 4.2V and calling that my battery. Then of course you have to worry about the converter not being an isolated supply so if the ground of the camera battery is not the same potential as the car battery's you'll have problems. I guess you could use an isolated converter, but the cheapest I ever found was $15 for 1A. Maybe I should just replace the cams battery every year? No free lunch I guess....
Given that the capacitors spend most of their time either full or empty, your diodes will need to "consume" just as much power, and if you don't limit that power by also using a resistor then they will use a lot more until they overheat and die!

For 4.2 volts you only need two 2.7 volt capacitors in series, there is no need to balance the capacitors, just choose two of very similar capacitance so that they share the voltage equally and stay well within voltage specification. If you are worried, or want to store 5 volts, then add a 3rd capacitor so that they are nowhere near their voltage limit. That way you don't need resistors and don't waste any power.
 
Given that the capacitors spend most of their time either full or empty, your diodes will need to "consume" just as much power, and if you don't limit that power by also using a resistor then they will use a lot more until they overheat and die!

For 4.2 volts you only need two 2.7 volt capacitors in series, there is no need to balance the capacitors, just choose two of very similar capacitance so that they share the voltage equally and stay well within voltage specification. If you are worried, or want to store 5 volts, then add a 3rd capacitor so that they are nowhere near their voltage limit. That way you don't need resistors and don't waste any power.
I think you may have misunderstood what I was saying. The only purpose of the diodes across the caps will be to keep the individual caps from exceeding the 2.7v rating for them. As mentioned earlier in the thread, caps have leakage and will get out of balance when used in series. The diodes will shunt the excess voltage the same as the resistors. However, they will only conduct when there is excess voltage and only as much current as the charging circuit of the camera. My 1N4006 diodes show a forward voltage of 0.6 before conducting. Put 4 in series and they begin to conduct at 2.4v. Or you could use a 2.5v zener diode to do the sake thing. It doesn't matter if the capacitors are perfectly balanced, just that they don't exceed 2.7v and don't get polarity reversed. So 2.7v zeners could work. One cap would eventually end up at 2.7 and the other at 1.5v (4.2v charging voltage).
 
I think you may have misunderstood what I was saying. The only purpose of the diodes across the caps will be to keep the individual caps from exceeding the 2.7v rating for them. As mentioned earlier in the thread, caps have leakage and will get out of balance when used in series. The diodes will shunt the excess voltage the same as the resistors. However, they will only conduct when there is excess voltage and only as much current as the charging circuit of the camera. My 1N4006 diodes show a forward voltage of 0.6 before conducting. Put 4 in series and they begin to conduct at 2.4v. Or you could use a 2.5v zener diode to do the sake thing. It doesn't matter if the capacitors are perfectly balanced, just that they don't exceed 2.7v and don't get polarity reversed. So 2.7v zeners could work. One cap would eventually end up at 2.7 and the other at 1.5v (4.2v charging voltage).
The leakage in the capacitors is the same as having a small resistor - it will help balance the capacitors, and since leakage in super capacitors increases with voltage, I think it is better than a resistor...
 
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