Using Ultra Capacitors to Replace Batteries

[krw]

Another important difference between batteries and capacitors
is the flatness of discharge voltage; a battery is nearly flat
over most of its range. I don't think a capacitor, no matter
how large, will be remotely as flat.

Yeah, kinda. Since C = Q/V, the voltage across the capacitor is
proportional to the charge on the capacitor, I.e. the discharge curve
is linear.

 

[SP]

Yeah, kinda. Since C = Q/V, the voltage across the capacitor is
proportional to the charge on the capacitor, I.e. the discharge curve
is linear.

Depends on the load- if it's drawing constant power like a regulated
SMPS with constant load (or a switching motor controller with constant
output power) it curves downward as the voltage drops and the current
therefore increases.

 

[krw]

Depends on the load- if it's drawing constant power like a regulated
SMPS with constant load (or a switching motor controller with constant
output power) it curves downward as the voltage drops and the current
therefore increases.

Of course! You added a squared term in there. Battery discharge
curves (at least all I've encountered) show charge vs. voltage.
Since that was the comparison...

 

[LVMarc]

Ultra capacitor example:
http://www.elna.co.jp/en/ct/pdf/DZNe.pdf
10F
2.5V
18mm x 35mm
About $30.00 at digikey.

Question is.... Are these ultracaps replacing batteries in some
designs?

Maybe implemented in a cordless optical mouse or Mp3 player?

Can ultracaps outperform batteries?
D from BC

Ultra-caps can replace a car battery and start a gas burning auto
engine, no problem!

Marc

 

[Spehro Pefhany]

Of course! You added a squared term in there. Battery discharge
curves (at least all I've encountered) show charge vs. voltage.
Since that was the comparison...

The cheap primary batteries such as carbon-zinc and alkaline (for some
reason) usually are specified with constant resistance load, so the
current drops as they discharge (and the voltage drops a lot as they
are used up).

More expensive ones like NiMH are typically spec'd with constant
current load as you suggest (but they are fairly constant voltage
throughout most of the useful part of the discharge). I have not seen
one spec'd with constant power load, although that's probably more
typical of today's loads (maybe with some pulsed aspect to the
loading).


Best regards,
Spehro Pefhany

 

[D from BC]

Ultra-caps can replace a car battery and start a gas burning auto
engine, no problem!

Marc

mmmm....
12V/2.5V ~ 5 Ultracaps in series.
5 Ultracaps * $30.00 = $150.00.... about the cost of a car battery.

10Farads/5 = 2Farads..

Isn't it something like 100Amps applied for about 1 second to start a
car...??


D from BC

 

[krw]

The cheap primary batteries such as carbon-zinc and alkaline (for some
reason) usually are specified with constant resistance load, so the
current drops as they discharge (and the voltage drops a lot as they
are used up).

Actually, that makes some sense for primary cells (think
flashlights).

More expensive ones like NiMH are typically spec'd with constant
current load as you suggest (but they are fairly constant voltage
throughout most of the useful part of the discharge). I have not seen
one spec'd with constant power load, although that's probably more
typical of today's loads (maybe with some pulsed aspect to the
loading).

Are DC motors constant power? I know induction motors are, more or
less.

 

[Eeyore]

Isn't it something like 100Amps applied for about 1 second to start a
car...??

One second ????

Graham

 

[Vladimir Vassilevsky]

D from BC wrote:

mmmm....
12V/2.5V ~ 5 Ultracaps in series.
5 Ultracaps * $30.00 = $150.00.... about the cost of a car battery.
10Farads/5 = 2Farads..

Why not. It would take somewhat 60000 capacitors like that to replace
the standard 45A/h battery. This bunch will fit in a box size of a
refrigerator and the cost will be the mere 1.8M$

Isn't it something like 100Amps applied for about 1 second to start a
car...??

Actually, it is a known fact that a big capacitor (>100,000uF) helps
cranking if the battery is weak. The initial surge current required to
shift the crankshaft from the dead stop is in the kiloamp range. So the
capacitor supplies for it. However why messing with capacitors if you
just need a good new battery.


Vladimir Vassilevsky

DSP and Mixed Signal Design Consultant

http://www.abvolt.com

 

[D from BC]

One second ????

Graham

From the time I turn the ignition key to engine start ..I think it's
about 1 to 3 seconds..
D from BC

 

[pklammer]

I don't know if this counts for "outperform" but a super/ultra cap is
certainly capable of "replacing" the battery:

From www.designmsp430.com, one of the winning entries:

"Tiny Temperature Recorder without Battery
Abstract: The tiny temperature recorder is directly built on the
eZ430-F2013 USB kit with only a capacitor, a diode, and a resistor
added. The device can measure temperature with a resolution better
than 0.02C. A tiny capacitor replaces the bulky battery to power the
system. A single instantaneous charge allows the device to record
temperature for up to 60 hours. The data is stored in flash memory and
is read back to a PC through the USB port built on the kit. It is
simple and low-cost but effective."

Ultra capacitor example:http://www.elna.co.jp/en/ct/pdf/DZNe.pdf
10F
2.5V
18mm x 35mm
About $30.00 at digikey.

Question is.... Are these ultracaps replacing batteries in some
designs?

Maybe implemented in a cordless optical mouse or Mp3 player?

Can ultracaps outperform batteries?
D from BC

Pete Klammer, P.E. / ACM(1970), IEEE, ICCP(CCP), NSPE(PE), NACSE(NSNE)
3200 Routt Street / Wheat Ridge, Colorado 80033-5452
(303)233-9485 / Fax303)274-6182 / Mailto[email protected]
"Idealism doesn't win every contest; but that's not what I choose it
for."

 

[Spehro Pefhany]

Actually, that makes some sense for primary cells (think
flashlights).

Yes, that's probably the origin of it, predating radios and such like
(or maybe just the A battery on early portable radios).

Are DC motors constant power? I know induction motors are, more or
less.

Hmm.. if you just hook them across the battery (as in a non-electronic
toy) they're more like constant current with a constant load-- they'll
slow down (less back EMF) to deliver similar torque. So if junior is
running his toy truck up an incline, the constant current test should
be fairly close to the real operating conditions.

I don't think you get the negative resistance characteristic showing
up that strongly except with electronic switching regulators.


Best regards,
Spehro Pefhany

 

[Spehro Pefhany]

Actually, it is a known fact that a big capacitor (>100,000uF) helps
cranking if the battery is weak. The initial surge current required to
shift the crankshaft from the dead stop is in the kiloamp range. So the
capacitor supplies for it. However why messing with capacitors if you
just need a good new battery.

Because maybe you're in the Arctic (where the cranking capacity of
your regular battery is drastically reduced), and your armored
personnel carrier needs to start *now* because you're under fire from
an enemy. The few thousand dollars for a booster cap will seem like a
real bargain.



Best regards,
Spehro Pefhany

 

[Spurious Response]

One second ????

Graham

Since everything is fuel injected or throttle body injected these days,
and we don't have the ills of the carburetor age any longer, it shouldn't
take very long to start a modern engine.

One second does seem a bit quick though. Maybe two... one at 100 Amps,
and one at about 80 or so.

 

[Spurious Response]

The initial surge current required to
shift the crankshaft from the dead stop is in the kiloamp range.

Maybe in Alaska.

 

[Eeyore]

From the time I turn the ignition key to engine start ..I think it's
about 1 to 3 seconds..

I reckon one second is a bit optimistic.

Graham

 

[Eeyore]

I don't know if this counts for "outperform" but a super/ultra cap is
certainly capable of "replacing" the battery:

"Tiny Temperature Recorder without Battery
Abstract: The tiny temperature recorder is directly built on the
eZ430-F2013 USB kit with only a capacitor, a diode, and a resistor
added. The device can measure temperature with a resolution better
than 0.02C. A tiny capacitor replaces the bulky battery to power the
system.

Umm..... Tiny ? If it uses that little current you could use a watch cell.

Graham

 

[Eeyore]

Since everything is fuel injected or throttle body injected these days,
and we don't have the ills of the carburetor age any longer, it shouldn't
take very long to start a modern engine.

One second does seem a bit quick though. Maybe two... one at 100 Amps,
and one at about 80 or so.

Two seconds sounds more like it to me.

Graham

 

[Eeyore]

Maybe in Alaska.

A figure of around 300 Amps comes to mind from somewhere in the depth of my
memory.

Graham

 

[D from BC]

Umm..... Tiny ? If it uses that little current you could use a watch cell.

Graham

I have digital calipers that use a watch cell.
If it used an ultracap, I would never need to buy batteries.
I could charge the calipers in seconds and it'll could run long enough
for me to make my measurements.

Another idea..
I brush my teeth for about 2 minutes. Maybe a charged ultracap could
last that long.

D from BC