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Author Topic: Ultra Capacitor For E Power  (Read 3295 times)

W6EM

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Ultra Capacitor For E Power
« on: January 05, 2019, 01:37:36 PM »


I saw several ‘six-packs’ of UC’s on EBay for somewhat reasonable prices and wondered how long could one depend upon using one of those in place of or instead of a battery?

First, a couple of assumptions.  Charging voltage 14V, lowest acceptable voltage 12V.  Constant load resistance of 2.8 ohms, that yields discharge current of 5A at 14V, and drops to 4.29A at 12V.

Here’s the formula:  V = V0*e-t/RC
Where R= 2.8 ohms, Six pack C assumed to be 100F, and V0 of 14V and V of 12V.  Solve for the number of seconds, t.
This works out to be t = R*C*(ln V0-ln V)
Substituting, t = 280*( 2.64-2.49) or about 42 seconds. 

Feel free to change R and C to any convenient values and see what can be done with these capacitors.  Or, V and V0 for that matter. One thing for certain: Charging can be much, much quicker than with a conventional battery.  Maybe too fast for your fuses.....unless you limit inrush current.
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NC5P

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RE: Ultra Capacitor For E Power
« Reply #1 on: January 06, 2019, 09:36:59 PM »

Be careful selecting these capacitors because a lot of them cannot handle higher current.  Always check their internal resistance and current limit specification!  The ones that can handle high current are usually quite expensive.  Also those will have very high inrush current so you need a circuit to limit the current when charging them up.  You can harvest more than twice the energy you calculated by using a boost converter on the output to allow the capacitors to discharge to around six volts.  I calculated around two minutes given the load you have.  These are great to keep electronics up while starting a generator after commercial power goes down.  Much less trouble than batteries that must be replaced every few years.  Maxwell is a reputable manufacturer of them. 
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W9IQ

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RE: Ultra Capacitor For E Power
« Reply #2 on: January 07, 2019, 03:52:39 AM »

Lee,

A variation of the formula you used, but based on power instead of load resistance is:

     t=1/2C(Vs2-Vf2)/P

An advantage of this form is you can easily include boost converter inefficiency in the calculation. For example, using 85% converter efficiency with a 60 watt load and drawing the cap down to 6 volts:

     t=50(196-36)/(60/.85)=113 seconds

As mentioned by Doug, you also should factor in the ESR and mind the charge/discharge limits so as to avoid overheating the caps.

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

K6BRN

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RE: Ultra Capacitor For E Power
« Reply #3 on: January 07, 2019, 06:38:42 AM »

Lee:

Per the arithmetic above and plenty of on-line use data, despite their high potential charge/discharge rates, the total energy storage of an "ultracapacitor" is still VERY small compared to a battery - so they will not be replacing batteries anytime soon as mass energy storage devices.

Their voltage limits and overvoltage tolerance is also very low compared to conventional capacitors and uncontrolled voltage spikes (which can easily happen during rapid charge/discharge if not accounted for) can lead to microshorts within the capacitor, which can lead to "...venting and deformation.." per many manufacturers warnings.  In other words, they can "pop" pretty badly and if you are in close proximity without eye protection, you can easily be injured.  So... be careful if experimenting and use eye protection.

Due to these issues, I'm not sure how ultracapacitors would be useful for emmcomm - when rock-solid reliability and as much small, lightweight energy storage as possible is needed.

They are fun to expriment with, though.

Brian - K6BRN
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W9IQ

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RE: Ultra Capacitor For E Power
« Reply #4 on: January 07, 2019, 07:01:19 AM »

In general, batteries will have higher energy densities (e.g. Wh/kg) while ultracapacitors will have higher power densities (e.g. W/kg). Thus ultracapacitors are often used for peak shaving and short term ride-through applications.

Keep an eye on the ultracapacitors used for automobile start-stop applications. These are widely used in Europe and are beginning to show up in US made vehicles. The car engine shuts off when you come to a stop and it immediately starts again when you release the brake in order to increase fuel efficiency. The underlying technology in many of these designs are ultracaps that are across the starter circuit or integrated with a battery.

These caps will tolerate a wide temperature range and handle the voltage spike requirements of the automotive industry (although some designs are lower voltage capacitors that act as a voltage boost for the primary electrical system). As with most automotive industry parts, their volume consumption will spell much lower prices for the hobbyist.


- Glenn W9IQ
« Last Edit: January 07, 2019, 07:14:02 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

NC5P

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RE: Ultra Capacitor For E Power
« Reply #5 on: January 07, 2019, 01:49:52 PM »

These capacitors are sold with those obnoxious car stereo systems to provide the high current peaks needed to shake the ground while sitting at traffic lights.  Crutchfield has them though the price isn't real cheap there. 
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W6EM

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RE: Ultra Capacitor For E Power
« Reply #6 on: January 07, 2019, 05:26:20 PM »

Thanks to all for the constructive comments.  Certainly a good idea to use a boost inverter, and of course caution about low ESRs and need to control inrush.

Charging, since usually were 6 individual capacitors in series, could present an overvoltage problem for individual capacitors.  Most of the packs seemed to have over voltage protection circuitry of some sort to avoid damage to individual capacitors.  Capacitor voltages all were under 3V.

Glenn, your point is, as always, spot on with respect to energy density being greater in battery cells, generally.  UCs offer a unique and desired property to be able to smooth-out effects of high transient charge or discharge rates.  The EV recharge problem may be resolved through use of them so as to allow very large power/energy transfer in a short time while in motion.  But, look out for harmonics of 85kHz, the standard frequency for air gap charge in motion power transfer systems.....
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K6BRN

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RE: Ultra Capacitor For E Power
« Reply #7 on: January 07, 2019, 10:02:03 PM »

Quote
Keep an eye on the ultracapacitors used for automobile start-stop applications

In every application I've seen, ultra/super caps are used for a quick burst of power, most often for load smoothing, which includes start/stop vehicle starting and , yes, supersound systems.  Seconds,  Not minutes or hours.  So not very useful for emmcomm.

But when I was looking at short-term accumulators for the solar plant that runs my CA station (when I'm having fun and only when the sun shines, which is a lot, over here), the most practical device to smooth out the power flow over 5-15 minutes was a simple 100 A/Hr SLA battery.  Not a capacitor bank, or a LiFePo battery (wrong charging curve, high cost), but one of the oldest and least expensive techs around.

But for EmmComm... generators are always in demand by the professionals.  And they last  long time.

A good choice would be the Honda EU2200is "suitcase generator". It can run an HF station with a 600W amp, or lights and a refrigerator or A/C or an electric heater.  The rolling oil fields we are surrounded with provide a ready source of fuel, even in an emergency - and it is very efficient.  It is a little pricey.  But if you also have occasional blackouts, it can do double duty and is way easier to justify.  Just ask anyone from Florida or the East Coast who need power after a hurricane or nor'easter.
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W9IQ

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RE: Ultra Capacitor For E Power
« Reply #8 on: January 08, 2019, 02:05:21 AM »

Brian,

I thought it was pretty clear from the numbers and formulas that we were talking about minutes (ride through).

- Glenn W9IQ
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

W9IQ

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RE: Ultra Capacitor For E Power
« Reply #9 on: January 08, 2019, 02:36:39 AM »

Lee,

You are right about charge and discharge management circuits for the capacitors. Some of the ones that are used to boost voltage sag (i.e. in series with the primary voltage source) can be quite sophisticated.

I designed a charge/discharge management circuit for peak shaving (parallel to the primary) to allow a 100 watt SSB transceiver to use a cigarette lighter connection. It works quite well. Some day I may write an article on the design.

The available ultracaps are really amazing: > 500 farads with > 30 amps continuous (> 300 A peak) discharge. Just makes you want to go design something else!

- Glenn W9IQ
« Last Edit: January 08, 2019, 02:52:54 AM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

WB4SPT

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RE: Ultra Capacitor For E Power
« Reply #10 on: January 08, 2019, 06:59:52 AM »



I designed a charge/discharge management circuit for peak shaving (parallel to the primary) to allow a 100 watt SSB transceiver to use a cigarette lighter connection. It works quite well. Some day I may write an article on the design.

...

- Glenn W9IQ

I know some TDMA cell phone designs had large cap across the Li primary cell for peak current management.  This was a couple of decades ago.    It led to increased battery life, sine the IsqR losses are lower for the C than for the battery. 
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NC5P

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RE: Ultra Capacitor For E Power
« Reply #11 on: January 08, 2019, 12:55:59 PM »

About ten years ago a couple of us at work developed a clever capacitor hold up circuit that charged up the capacitors using a dc-dc switcher, then used that same switcher turned around to hold the output voltage steady as the capacitor discharged.  We were short on physical space and weight so the capacitors had to have as much energy squeezed out of them possible.  It was all done with FETs hard wired.  Of course you could probably do it easier with a micro-controller instead.  Our customer had issues with anything that ran code so we did it all in hardware to keep them happy.  The load was around 600W at 28 volts.  A later project we had so little room in the box we joked about putting capacitors into the rack bailing handles. 
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K6BRN

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RE: Ultra Capacitor For E Power
« Reply #12 on: January 08, 2019, 08:08:22 PM »

Hi Glenn:

Quote
Brian,

I thought it was pretty clear from the numbers and formulas that we were talking about minutes (ride through).

- Glenn W9IQ

No criticism intended, but ride through what?   Looking at the conversation, what seemed to be missing was a productive use.

Since we are on an emmcomm forum, my first thought along this line was solar backup power (a popular emmcomm topic) ride-through, which is really minutes, not seconds, leading to my observation that a simple lead-acid battery made a better accumulator for that purpose. 

Then you commented on a use you found to support short term HF rig high power demands on a low-current supply (cigarette lighter plug) and thought that was interesting.  Maybe useful.

So really, as you free-associated on the arithmetic of capacitor charge/dischrge cycles I was doing the same concerning applications.  And I'd be interested in hearing the group's thoughts on this, emmcomm related or not.

Super/ultracaps have become much better, much less expensive and much more available.  It would be very productive if we could find a use for them in the ham world.  Worth some thought, at least.

Brian - K6BRN
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W9IQ

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RE: Ultra Capacitor For E Power
« Reply #13 on: January 15, 2019, 01:54:33 PM »

About ten years ago a couple of us at work developed a clever capacitor hold up circuit that charged up the capacitors using a dc-dc switcher, then used that same switcher turned around to hold the output voltage steady as the capacitor discharged.  We were short on physical space and weight so the capacitors had to have as much energy squeezed out of them possible.  It was all done with FETs hard wired.  Of course you could probably do it easier with a micro-controller instead.  Our customer had issues with anything that ran code so we did it all in hardware to keep them happy.  The load was around 600W at 28 volts.  A later project we had so little room in the box we joked about putting capacitors into the rack bailing handles.  

Doug,

It is very interesting that you had this experience. LTC now make chips that do exactly that! They also manage the charge balance for series stacks of capacitors so they don't over voltage. Their top of the line chip includes an I2C bus that allows a supervisory uP to monitor and control all critical parameters - such as monitoring a capacitor's ESR to sense degradation.

The real nice feature is that you can set a current limit on the source supply and the chip will charge the capacitors using the remaining available current. It automatically detects that the output voltage to the load is dropping below the set point and switches to a boost mode from the cap bank to level off the supply at the regulated minimum. 

The chip costs ~ $8.00 quantity 1. Add a handful of parts and the supercaps and you have an off the shelf 10 A peak shaving supply with an adjustable output voltage. With a little massaging, a 25 Amp version is possible.

- Glenn W9IQ
« Last Edit: January 15, 2019, 02:02:00 PM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

KB8VUL

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RE: Ultra Capacitor For E Power
« Reply #14 on: June 20, 2019, 07:22:24 PM »

It's a bunch of energy in a small package, but they have their limits.
First is cost.  If you are wanting capacity over time, it's going to be expensive.

Second is they are fragile.  They don't like being overcharged at all.  And they fail explosively. Not a good time.

They do have their applications if you are wanting to drop them in a backpack and operate on a mountain side that requires you to hike in. 
For anything else where you have any sort of vehicle access, use an SLA or AGM battery.

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