Switching power sources without restarting the system

[Shank]

Imagine: You are playing Metroid Prime 2 on your sweet ass portable you just finished. After many attempts, you have finally defeated the stupidly difficuilt boost guardian. BUT WHATS THIS?!?!?!?! Your red LED turns on: you are low on battery. You only have a few minutes left, and there isn't a save room close enough: you wont make it in time. You have your wall power adapter and charger nearby, but switching over means losing your progress and fighting the boss again.

No. Those days are over.

I call it the charge and play uninterupted (CAPU)

Pop a cap in that old charge and play circuit, because this one solves that problem. Literally. Take a capacitor, connect one end to power, and the other to ground, and it keeps the console on for the split it takes to switch power. Easy as that.

I recommend using a voltage rating higher than any power adapter you plan to use, but not extremely higher or its just a waste of space. I went with 50v. For capacity, 2000uf works well from my testing. Less will work too, but the more you have the less likely it is to reset when you flip the switch slower.

Thats all

 

[bentomo]

Nice, have you looked into an super caps for space efficiency?

 

[Shank]

Super capacitors? I wonder what those are...

(does google search)

...oh my...

Edit:
A bit more research and I have found that super capacitors don't have voltage ratings high enough for this application. I don't know a way around that.

 

[Cllinw]

A bit more research and I have found that super capacitors don't have voltage ratings high enough for this application. I don't know a way around that.

So is this not possible then?

 

[Shank]

No, the circuit described above does work. I have tested it and it works perfectly.

Bentomo was discussing replacing the normal electrolytic capacitor another type of capacitor (super capacitor) that would allow for a much smaller form factor. However, those type of capacitors are only made in lower voltage ratings. Circuitry to get around that would probably be big and complicated enough to not be worth it.

 

[bentomo]

Oh well, I'll be releasing some details soon on a certain project that will make the whole charge and play a thing of the past.

 

[CrashBash]

I made something.

If anyone wants me to change the voltage/regs or whatever feel free to ask.

 

[Fluxedo]

Zenloc's guide says you need two caps on the 1.7 reg. Also where can I find a small 2000uf 12 cap? I'm having a hard time finding one that will fit in my case.

 

[Shank]

Im not familiar with regulators but as for the cap...

If doesn't need to be 12v, just more volts than you plan to use as a power source. If you are using 7.4v batteries you could probably get away with a 10v cap. It can have more or less capacity, that's just what I settled on for my Wii.

It requires a minimum of 10.1 (I think. 10 point something) volts to run. I was using a 12v power supply and a 14.8v battery. I needed enough capacity where the voltage wouldent drop from 12 to 10 in the split second of flipping a switch.

I worked with the capacitors I had and had a consistant success rate with 2000, but wound up using 3400 just to give me some leway in case I flip the switch a little too slow.

You could figure out exactly how much capacity you need, as to minimize the size. Figure out the power draw of your console, source voltage, the minimum operating voltage, and then you just kind of... you know... math. But I just used trial and error to figure out what worked and went with that.

I got my capacitors from an old tv circuit board. Where you find one and how you fit it in your case is up to you. Its a reletively large capacity capacitor, so it won't be tiny

 

[dark_samus]

Very neat... Ok so doing a little research, a capacitor's size is generally not related to its rating in uF but in voltage, so a 10v 2000 uF cap is fairly small but a 50v 2000 uF cap will be much bigger

 

[Rodney McKay]

Would it be possible to just use a switchable power Jack and wire it that if nothing is plugged in, the System gets it's Power from the Batteries and if the Power Supply gets plugged in, the battery gets disconnected and you can flip the switch to Wall Power? I'm just curious if this would work like i think.

 

[Hermaphroditus]

This thread's just over a year old, so a bit of a necropost.

At any rate, you would run into the same issue that this is trying to fix, for a very brief period of time there would be no power delivered as it's switching sources. The cap would definitely be needed in that sort of application.

Alternatively there're some interesting circuits out there that switch between battery to power sources, but that's neither here nor there and would require more components than just a capacitor.

 

[Prog]

Who are you replying to? Rodney? Because that would be pointless considering that someone with a BS in Electrical Engineering did so with more detail in November.

On topic: could an inline inductor work? Would potential hardware bugs from undervolting during its charging period render that impractical? Or maybe emf could be an issue? Would it offer any pros or cons over a parallel resistor?