Batteries versus supercapacitors ...



#9

In my last incursions on Internet, I found some interesting new (at least to me) electronic devices.

First, the big ones: Farad capacitors for car's audio systems. I've never had one in my hands, but I believe they are very big.

After some months, I saw in Ebay the little cousins: Panasonic 1Farad very small capacitors.

Very interesting, but, because its high internal resistance, the delivery current is small, just enough to keep memory circuits. Of course, there is a line that could delivery Amps, but their size does not allow their use in the 41C battery pack or battery holder.

Continuing my researches, I found the Aerogel Capacitor. They are small in size and don't lack the high internal resistance, allowing Amps to flow instantaneously.

Well, I was wondering in using 4x 3.3F , 2.5 V or the 1.0F, or 2x 5.0V in my 41.

The problem: they accept only 50US$ min. orders from internatinal buyers... anybody in USA could try and let us to get some these small wonderfulls?

Here are the links:

Manufacturer

Seller

The models I was wondering are B1020-2R5335 or PB-5R0V105

Best regards,
Artur


#10

Hi Arthur,

In Germany you can buy these Capacitors (sometimes called "goldcaps") from any electronic distributor. If you can't find these in your country, I offer you my help!


#11

Hi, Klaus

Here in my city they are not avaiable yet.
But the GoldCaps aren't the ones from Panasonic? These have internal resistance too high and I believe they will not be usefull in calculators.
If you have any time and could verify the other brand (Aerogel from CooperEt), I would appreciate very much your help.
Thank you very much,
Artur


#12

Hi Arthur,

I don't knwo much about Gold Caps (regarding their resistance). I found a capacitor called "UltraCap", it is dischargable with a current of 400A and its capacity ranges from 4F to 110F at 2.3V

Dimensions in mm:

5x23.9x15.6 for 4F : 8€
5x23.9x30.6 for 10F : 9€

110F is cylindric: Length = 67.5, diameter = 25.5 :35€

Are you planning to put in a voltage regulator as well?


#13

Whats wrong with rechargeable nicad batteries?

I think you will find the capacitors you are talking about are unsuitable for the 41.

All I would say is: Make sure you don't wreck your calculator
by mucking around with it. I don't think what you are doing is
a very good idea.

Any high current high capacity capacitor is going to self-discharge
and you know yourself the low current parts won't work.
Why muck around if you don't know what you are doing?
It's not worth it... It really isn't.

The high current high capacitance parts you are taling abut are massive. I have some out of a MAINFRAME COMPUTER power supply;
they are 58000 uF (0.058F), 25 volt, very high current.
The parts are FIVE INCHES round and stand about EIGHT inches high.
No I am not kidding.

When it is running a program the HP41CV draw 4.5 millamps.

Kind regards,

Don W


#14

To get as much use between charges as you'd get with one set of alkaline N cells, you'd need somewhere around 1kF-- yes, a thousand farads. That't assuming you used the energy before the capacitor's own leakage discharged it. The supercaps do hold a charge for a long time, but I don't know about years like alkaline batteries manage.

Farads=Amps x seconds / voltage_change

The alkaline N cell gives about a 500mA-hour (not amp-seconds). That's about 1800 amp-seconds, to get from 1.55V down to about 1.2V where the HP-41 low-battery indicator comes on. That's per battery, so multiply by four, assuming the capacitor can handle 6V so you don't have to put them in series. So in the equation above, the "voltage_change" term becomes 4(1.55-1.2), or about 4*.35, or 1.4. The result is almost 1,300 farads-- not microfarads, or even millifarads, but farads. Hardly practical.

To make it worse, suppose the capacitor can't handle the whole six volts. If it can handle three, you'll need two in series, each one of double the capacitance. If you need four in series, each one needs four times the capacitance, or about 5kF. If you say you're only going to charge the set up to 5V instead of 6V, now the "voltage_change" term above becomes smaller, and the required capacitance value further increases-- dramatically!

Edited: 28 Aug 2005, 8:26 p.m.


#15

Not meaning to offend anyone, but...

RIGHT On, Garth!

happy experimenting, you guys...

Don W

#16

Hi,

Thank you for the electronic class! It is really impossible to use the caps to run the HP. I believe not because it can deliver Amps instantaneously and this could damage the calculator, as the discharge current also depends on the internal resistance of the circuit that are being powered. If HP uses mA only, it will keep using the mA only, it doesn't matter if I use N cells or a truck battery with a voltage regulator, am I right?
Just an examination (using 48's solve function) on the formula, with the DeltaV of 0.2V (1.5 to 1.3) and the time of 3600s, the F is very high!
Any way, thank you for the class and saving my money!

Artur


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