Super Capacitor Battery for Mouse

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Introduction: Super Capacitor Battery for Mouse

Let's make unlimited times and quickly chargeable Supercapacitor battery for mouse.

What we need:

Step 1: Schematic. Difference Between Capacitor and Battery

As You can see in diagram ordinary battery don't have so big voltage drop during discharging as capacitor have. Because of that 5.5v ultracapacitor will work until it drops from 5.5v to about 1.5v so voltage limiter will supply to mouse about 1.1 volt.

Step 2: Build & Charge & Go...

Step 3: After Word

At the end it turn out that it of course is not keeping charge as long as ordinary battery. Also Capacitor have quite quick self discharge.

May be in near future I will add some resistor for limiting current going to mouse. Probably adding diodes between charger<->capacitor and capacitor<->voltage regulator would be nice idea as well.

P.S. Mouse warranty is voided.

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27 Discussions

Actually it is not the capacitors fault that it won't last as long as the battery.

I'm assuming the mouse draws on avarage less than 1mA active, and down to several uA when not used. Open the datasheet of the 1117 and read the electrical specification. You should notice the entries "Minium load current" and "Quiescent current", that is the current permanetly drawn. No wondere the mouse doesen't last long, it increses the consumption by more than 5 times!

The obvious solution is replacing the 1117 by a better LDO with lower quiescent current. In that regard on of the best on the market is microchips MCP1710, it features a quiescent current of 20nA (!), thats 0.0004% (!). The dropout voltage is about 450mV, not bad at all. Also, when selecting filter capacitors make sure you pick ceramic ones (preferably X7R/ X5R type), other types can have a significan leaakage current of several uA. A smart choice would be to pick a 1.2V regulator to be able to use ub as much of the capacitors charge as possible.

To estimate the final runtime this calculator is super helpful. With the new regulator I get about 1 hour of runtime, which is enough considering the very short charge time.

3 replies

Wow, never thought something like a mouse can last for 1 hour with the capacitor. But how long it take to charge the capacitor?

I'm glad you ask.

The charge time heavily depends on the capacitor type used, especially it's internal eqivilant series resistance. I've looked up a few examples and as an avarage value you have to expect around 30 ohms with the shown type. This leads to an "RC-constant" (yes, this is a real thing) of R*C = 30ohm * 1F = 30s. As a rule of thumb after about 5RC (2,5min) the capacitor will be fully charged. You should also take in consideration that the capacitor won't be drained completely and this are only rough calculations. I'm assuming you could get at least 30min runtime out of a 1min charge time, more than enough for a power point presentation.

what would be sweet is a magnetic mouse pad and some inductors in the mouse so the motion of the mouse would generate electricity and store in a supercapacitor. it would probably produce more than it needs. or worse case an induction mouse pad plugged into a usb port to keep it charged.

So that means tda is good since my mouse takes up 3.3 volts (2 aaa battery)

The TDA3663 is indeed a very neat LDO, it features a very low 15uA while offering an inpput voltage up to 45V and 25V reverse protection. I haven't heard of it till now but it'll go straigt into my datasheet collection as it's very unique in the wide voltage range.

However the chip is as far as I'm aware of only available in a 3.3V output version, which makes it unuseful for this application. you want to choose a regulator with an output voltage close to the expected 1.5V (alkaline) or 1.2V (NiMH/ NiCd) battery voltage. Also make sure the device runs at low input voltages.

I hope this helps.

Cool!

Smart idea to use a 5v super cap sot it functions until it's down to 1.5.

This is cool.

What is the comparable capacity to an AAA at 1.5V?

an AAA rechargable has a capacity of about 900mah

besides the mouse battery, you are using a supercapacitor for electronic device what else?

I totally forgot about the charging circuit. If you want to use just the pin headers (like you do) a reverse polarity protection is vital imho. You should also consider to limit the current to less than the 500mA limit of USB ports. A nice all-in-one sollution is the LP2951, it has a schematic to implement a curent limiting solution right in the datasheet. It also provides reverse and overvoltage protection (set the output voltage to 5.5V) from -20 to 30V! This chip a a quite high quiescent current as well, but it doesn't really matter for an USB port.

1 reply

Well, I just noticed the internal resistance of the capacitor is relativly high (30 ohms), which serves as a simple but effective current limitation. If you don't need overvoltage protection you can use a simple Schottkey diode, they have a lower forward voltage (= less loss = faster charging) than standard silicium diodes.

I fly radio control model airplanes. I understand caps have a quick self-discharge rate, but could you give me the weight to usable capacity ratio compared to NiMH or LiPo batteries?

1 reply

They cannot replace a battery pack so far. Supercaps are great for some applications but for rc purposes they re pretty much useless because of their low energy density.

You might want to look at http://en.wikipedia.org/wiki/Supercapacitor#Parametric_comparison_of_technologies