Anyone have experience with ultra capacitors?

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iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Hello all -
Has anyone done any work involving ultra capacitors? The application I'm looking at involves using batteries between a DC gen and an inverter. I'm looking at replacing the batteries with an ultra capacitor - maybe something in the 24V, 100F range.

The reason for the batteries is the system has large, short term, cyclic loading. A battery bank allows the gen to be sized a lot smaller and keeps the gen rpm/output voltage stabile.

The idea is a bit outside of the box, but if it works, I think it will significantly simplify the system.

Iceworm
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
Just a guess, but I doubt a capacitor can store enough energy to do what you are asking. If it could, I'd think the UPS manufacturers would have caught on by now.

Someone else may want to check my math, but the energy stored in a capacitor is given as 0.5 * C * V squared. So for a 100 F capacitor, with 24 volts, you can store 28800 Joules. (I'm not sure ultracapacitors are rated for voltages that high??).

Lets say you have a 10KW load. I believe watts are equal to Joules per second, so if we divide 28,800 by 10KW, we only get 2.88 seconds of backup power.

That's if you completely discharge the capacitor, but in reality, you will have some minimum voltage you need to keep on the Cap to drive the output, so you will actually get even less backup time.

That also ignores losses in the capacitor. There will be a I sqared R loss in the capacitor that will rob some of your energy. My guess is that ultra capacitors are made to discharge very slowly, so trying to make one give a rapid discharge might not work at all.

But again, take this with a grain of salt - I may be completely off base.

Steve
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Wow. 100 Farads is a lot of storage. You could spot-weld with it.

If someone told me they wanted 100F, I'd suggest wet-cell batteries.
 

winnie

Senior Member
Location
Springfield, MA, USA
Occupation
Electric motor research
I don't have direct experience with ultracapacitors, but I've been following their development as part of my work with inverters and motors for drive systems.

Ultracapacitors have much lower energy density than even lead acid batteries. If you need to store lots of watt seconds, go with batteries.

Ultracapacitors have higher power density than batteries. If you need to supply high power for only a few seconds, an ultracapacitor can give you a system that is much lighter than a battery.

Charge control is easier with a capacitor; simply control voltage. Charging current will naturally fall off to zero when the capacitor voltage equals the supply voltage. With batteries you have to deal with the non-linear voltage versus charge relationship.

Ultracapacitors can tolerate much greater numbers of charge/discharge cycles.

Ultracapacitors are vastly more expensive that batteries of either the same power rating or the same energy rating; if you can tolerate the space and can deal with the control issues, then batteries will be lots cheaper.

When you say 'short term cyclic loading', how many seconds at how many KW, with what sort of repetition rate? I don't think that ultracapacitors are a good choice unless you are talking about 5-10 seconds at most, or numerous charge/discharge cycles.

-Jon
 
I designed an ultracapacitor bank for a fuel cell system a while ago. The goal was to provide bridging power to the 3kW load until the fuel cell completely started up (about 1 min).

There were 20 ultracaps of 1800F placed in series, for a total of 90 Farad. Each cap was 2.5V for a total of 50V. This gave a total energy storage of 110kJ. The caps were placed in series to keep the voltage as high as practical for long enough for the load. (More on that in a bit).

As you know, capacitors discharge exponentially. Thus, for a constant load, the current will be increasing exponentially. The currents can get unruly pretty quickly. You need to be able to disconnect the load when the voltage gets to a certain threshhold. You also need to provide overcurrent protection (460.8 (B)), a way to discharge the stored energy when needed(460.6). Having an exponentially decreasing voltage with an exponentially increasing current wasn't practical for my application, so the output of the capacitor bank was fed into a wide input range power supply, which keep the system output voltage relatively stable for most of the discharge cycle. The power supply could be set to cutoff when the input voltage reached a point at which the currents were too high.

Hope this helps, good luck.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Hey guys and girls -
Sorry I didn't get back sooner. But I couldn't find the thread.

This is what I'm looking at.
http://www.cantecsystems.com/can-crank.html

probably two 24PP30 in series.

Just a guess, but I doubt a capacitor can store enough energy to do what you are asking.
Enough to start big equipment diesel engines

If someone told me they wanted 100F, I'd suggest wet-cell batteries.
The whole idea is to get rid of the wetcells. In specific the charger and the plc needed to control shifting the bats over to the gen /inverter

Ultracapacitors have much lower energy density than even lead acid batteries.
That's my understanding

Ultracapacitors have higher power density than batteries.
Yes again

Charge control is easier with a capacitor; simply control voltage. Charging current will naturally fall off to zero when the capacitor voltage equals the supply voltage. .
That"s the part I like

With batteries you have to deal with the non-linear voltage versus charge relationship
That's the part I want to get rid of

Ultracapacitors are vastly more expensive that batteries of either the same power rating or the same energy rating;
That's one of the parts I don't know about yet. I have to give the vendor a call. Maybe there is a US distributor.

When you say 'short term cyclic loading', how many seconds at how many KW, with what sort of repetition rate?
2 sec on 8 sec off. The test load was 48VDC, 3kw. The gen is 48VDC, 4kw. The application calls for the load switching to be one hour duradion.

A test run was made using a resistive load bank, With two 8D bats in series as a buffer, no charger. The bats were connected in parallel with the gen. The battery discharge during the on-time was 70A, the charge during the off-time was 20A. I don't know what the gen current was running

EEStore is still "vaporware" as far as anyone knows though.
Any knowledge about Cantec?

It sounds like the perfect opportunity for Flywheel Energy Storage.
Very elegant solution. However, the goal is less complexity


Need some numbers for this to start making sense. what voltage and current is needed, for how long, and how frequenctly?
Well, the voltage, current, and how long are above. The frequency is ................... ah ..... zero - It's DC:roll:

I designed an ultracapacitor bank for a fuel cell system a while ago. The goal was to provide bridging power to the 3kW load until the fuel cell completely started up (about 1 min).

There were 20 ultracaps of 1800F placed in series, for a total of 90 Farad. Each cap was 2.5V for a total of 50V. This gave a total energy storage of 110kJ. The caps were placed in series to keep the voltage as high as practical for long enough for the load. (More on that in a bit).

As you know, capacitors discharge exponentially. Thus, for a constant load, the current will be increasing exponentially. The currents can get unruly pretty quickly. You need to be able to disconnect the load when the voltage gets to a certain threshhold. You also need to provide overcurrent protection (460.8 (B)), a way to discharge the stored energy when needed(460.6). Having an exponentially decreasing voltage with an exponentially increasing current wasn't practical for my application, so the output of the capacitor bank was fed into a wide input range power supply, which keep the system output voltage relatively stable for most of the discharge cycle. The power supply could be set to cutoff when the input voltage reached a point at which the currents were too high.

Hope this helps, good luck.
Yes that did help. Thankyou. Particularly:

You also need to provide overcurrent protection (460.8 (B)), a way to discharge the stored energy when needed(460.6).
I hadn't got that far yet. If this proves out, those will have to be incorporated.

Additional question: Were there any problems with keeping the voltage equalized across the caps - so that none were overvoltaged?


thanks all for your comments.

W
 
Last edited:

LEO2854

Esteemed Member
Location
Ma
:-?
Hello all -
Has anyone done any work involving ultra capacitors? The application I'm looking at involves using batteries between a DC gen and an inverter. I'm looking at replacing the batteries with an ultra capacitor - maybe something in the 24V, 100F range.

The reason for the batteries is the system has large, short term, cyclic loading. A battery bank allows the gen to be sized a lot smaller and keeps the gen rpm/output voltage stabile.

The idea is a bit outside of the box, but if it works, I think it will significantly simplify the system.

Iceworm

Hey guys and girls -
Sorry I didn't get back sooner. But I couldn't find the thread.

This is what I'm looking at.
http://www.cantecsystems.com/can-crank.html

probably two 24PP30 in series.


Enough to start big equipment diesel engines


The whole idea is to get rid of the wetcells. In specific the charger and the plc needed to control shifting the bats over to the gen /inverter




Any knowledge about Cantec?


Very elegant solution. However, the goal is less complexity


Well, the voltage, current, and how long are above. The frequency is ................... ah ..... zero - It's DC:roll:


Yes that did help. Thankyou. Particularly:


I hadn't got that far yet. If this proves out, those will have to be incorporated.

Additional question: Were there any problems with keeping the voltage equalized across the caps - so that none were overvoltaged?


thanks all for your comments.

W

WOW!!!!Welcome to the forum how did you post all the quotes into one post?
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Thank you for the welcome. I don't have much time available to post. However, I have been listening in for a few years.

There have been several posts on describing the technique for multiple posts. Use the quote marks at the bottom of each post, use the quote radio button for the last one.

W
 

LEO2854

Esteemed Member
Location
Ma
Thank you for the welcome. I don't have much time available to post. However, I have been listening in for a few years.

There have been several posts on describing the technique for multiple posts. Use the quote marks at the bottom of each post, use the quote radio button for the last one.

W

THANKS ICEWORM if you don't have time to post thats good that meens you have lots of work going on thats great for you and god speed.

Things are as slow as ever I have been in the trade since the 1970s and this past 3 years have been the worst ever since the depression.
 

hurk27

Senior Member
:-?



WOW!!!!Welcome to the forum how did you post all the quotes into one post?

look for the
multiquote_off.gif
button down at the bottom right corner of each post you want to include in your post, then select the
quote.gif
button for the last one and presto you will have e'm all in one post.;)
 

LEO2854

Esteemed Member
Location
Ma
look for the
multiquote_off.gif
button down at the bottom right corner of each post you want to include in your post, then select the
quote.gif
button for the last one and presto you will have e'm all in one post.;)

Hey thanks HURK FOR THE INFO GOOD MAN!:grin:
 
Last edited:

LEO2854

Esteemed Member
Location
Ma
Hello all -
Has anyone done any work involving ultra capacitors? The application I'm looking at involves using batteries between a DC gen and an inverter. I'm looking at replacing the batteries with an ultra capacitor - maybe something in the 24V, 100F range.

The reason for the batteries is the system has large, short term, cyclic loading. A battery bank allows the gen to be sized a lot smaller and keeps the gen rpm/output voltage stabile.

The idea is a bit outside of the box, but if it works, I think it will significantly simplify the system.

Iceworm

Just a guess, but I doubt a capacitor can store enough energy to do what you are asking. If it could, I'd think the UPS manufacturers would have caught on by now.

Someone else may want to check my math, but the energy stored in a capacitor is given as 0.5 * C * V squared. So for a 100 F capacitor, with 24 volts, you can store 28800 Joules. (I'm not sure ultracapacitors are rated for voltages that high??).

Lets say you have a 10KW load. I believe watts are equal to Joules per second, so if we divide 28,800 by 10KW, we only get 2.88 seconds of backup power.

That's if you completely discharge the capacitor, but in reality, you will have some minimum voltage you need to keep on the Cap to drive the output, so you will actually get even less backup time.

That also ignores losses in the capacitor. There will be a I sqared R loss in the capacitor that will rob some of your energy. My guess is that ultra capacitors are made to discharge very slowly, so trying to make one give a rapid discharge might not work at all.

But again, take this with a grain of salt - I may be completely off base.

Steve

Wow. 100 Farads is a lot of storage. You could spot-weld with it.

If someone told me they wanted 100F, I'd suggest wet-cell batteries.

I don't have direct experience with ultracapacitors, but I've been following their development as part of my work with inverters and motors for drive systems.

Ultracapacitors have much lower energy density than even lead acid batteries. If you need to store lots of watt seconds, go with batteries.

Ultracapacitors have higher power density than batteries. If you need to supply high power for only a few seconds, an ultracapacitor can give you a system that is much lighter than a battery.

Charge control is easier with a capacitor; simply control voltage. Charging current will naturally fall off to zero when the capacitor voltage equals the supply voltage. With batteries you have to deal with the non-linear voltage versus charge relationship.

Ultracapacitors can tolerate much greater numbers of charge/discharge cycles.

Ultracapacitors are vastly more expensive that batteries of either the same power rating or the same energy rating; if you can tolerate the space and can deal with the control issues, then batteries will be lots cheaper.

When you say 'short term cyclic loading', how many seconds at how many KW, with what sort of repetition rate? I don't think that ultracapacitors are a good choice unless you are talking about 5-10 seconds at most, or numerous charge/discharge cycles.

-Jon

http://en.wikipedia.org/wiki/EEStor

EEStore is still "vaporware" as far as anyone knows though.

It sounds like the perfect opportunity for Flywheel Energy Storage.

Need some numbers for this to start making sense. what voltage and current is needed, for how long, and how frequenctly?

I designed an ultracapacitor bank for a fuel cell system a while ago. The goal was to provide bridging power to the 3kW load until the fuel cell completely started up (about 1 min).

There were 20 ultracaps of 1800F placed in series, for a total of 90 Farad. Each cap was 2.5V for a total of 50V. This gave a total energy storage of 110kJ. The caps were placed in series to keep the voltage as high as practical for long enough for the load. (More on that in a bit).

As you know, capacitors discharge exponentially. Thus, for a constant load, the current will be increasing exponentially. The currents can get unruly pretty quickly. You need to be able to disconnect the load when the voltage gets to a certain threshhold. You also need to provide overcurrent protection (460.8 (B)), a way to discharge the stored energy when needed(460.6). Having an exponentially decreasing voltage with an exponentially increasing current wasn't practical for my application, so the output of the capacitor bank was fed into a wide input range power supply, which keep the system output voltage relatively stable for most of the discharge cycle. The power supply could be set to cutoff when the input voltage reached a point at which the currents were too high.

Hope this helps, good luck.

Hey guys and girls -
Sorry I didn't get back sooner. But I couldn't find the thread.

This is what I'm looking at.
http://www.cantecsystems.com/can-crank.html

probably two 24PP30 in series.


Enough to start big equipment diesel engines


The whole idea is to get rid of the wetcells. In specific the charger and the plc needed to control shifting the bats over to the gen /inverter




Any knowledge about Cantec?


Very elegant solution. However, the goal is less complexity


Well, the voltage, current, and how long are above. The frequency is ................... ah ..... zero - It's DC:roll:


Yes that did help. Thankyou. Particularly:


I hadn't got that far yet. If this proves out, those will have to be incorporated.

Additional question: Were there any problems with keeping the voltage equalized across the caps - so that none were overvoltaged?


thanks all for your comments.

W

:-?



WOW!!!!Welcome to the forum how did you post all the quotes into one post?

Thank you for the welcome. I don't have much time available to post. However, I have been listening in for a few years.

There have been several posts on describing the technique for multiple posts. Use the quote marks at the bottom of each post, use the quote radio button for the last one.

W

look for the
multiquote_off.gif
button down at the bottom right corner of each post you want to include in your post, then select the
quote.gif
button for the last one and presto you will have e'm all in one post.;)

No problem.:D

I might add that you need press them in the order you want them to appear in your post, with the last one being the one you use the
quote.gif
button.

Thank for the help hurk.
 

iceworm

Curmudgeon still using printed IEEE Color Books
Location
North of the 65 parallel
Occupation
EE (Field - as little design as possible)
Leo -
I sure hope you plan on recycling all those bits:roll:

I'll be back is a few days - I'm working this weekend then off to go hunting for a couple of weeks

later

W
 

Speedskater

Senior Member
Location
Cleveland, Ohio
Occupation
retired broadcast, audio and industrial R&D engineering
Last edited:

dbuckley

Senior Member
Need some numbers for this to start making sense. what voltage and current is needed, for how long, and how frequenctly?
Well, the voltage, current, and how long are above. The frequency is ................... ah ..... zero - It's DC
Such a pity a typo got in there - I meant to ask how frequently, not frequency.

This is to do with time to recharge the source between uses.
 
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