Questions/curiosities bout Super Capacitors....

[jjchvl]

I did a quick search in here for the Super Capacitor topic and didnt find a whole lot so here I am. Several years ago, I made a 16.2v, 83f super capacitor bank(six 2,7v, 500f capacitors connected in series via charge controller chips). At the time, I had just been experimenting out of curiosity and had no practical use for the capacitor bank. Fast forward to a couple of days ago, I read an article on the benefits of connecting a super capacitor bank in parallel to a solar battery storage bank. In such a configuration, the supercapacitor bank is supposed to supply the brief, high startup current demands of certain appliances (like fridges and vacuum's). After meeting the start up demands of said appliances, the capacitor bank recharges from the battery bank at a slower rate than the appliances would have required for startup. This is supposed to reduce stress on the battery bank that the Capacitor bank is connected to. I'm not stating this as fact. I'm stating it as I understand it from what I read.

So I connected the supercapacitor bank that I made years back to my 900ah AGM battery storage bank. In theory, every time that my fridge compressor starts now, it yanks that first few seconds of high amps that it needs to start up directly from the capacitor bank. I think I understand well enough how that works. My question is related to another phenomenon that I noticed since connecting the Super Capacitor bank to my battery bank. It seems to have "smoothed out" voltage fluctuations in the battery bank. For example, during times of continuous, moderate to highish loads, the voltage of my battery bank use to drop some. In rare instances, it would drop low enough to trigger my inverters low voltage protection causing the inverter to shut off for a moment.

With the Super Capacitor connected, the voltage doesnt drop much and doesnt fluctuate as much when a load is being drawn from the battery bank. Is this a normal "side effect" of using a capacitor bank in such a way? I would also be appreciative of more information or any advice from anyone with experience using supercapacitors in conjunction with their solar power set up. I like what Ive experienced so far but are there downsides that I dont know about? Thanks.

 

[farmhand]

?Following?

Any pics JJCHVL?

 

[DIYrich]

Capacitor is like another battery that can quickly charge and discharge. It will smooth out voltage at any time, up to the power stored. As a side benefit, it suppliments power as the battery voltage drops, including during heavy drain.

 

[Will Prowse]

Running a large motor with an undersized lead acid battery bank? A super capacitor bank can work wonders. But for solar with a properly sized lithium ion batteries? Absolutely not.

No benefit to large stationary storage lithium ion batteries. Voltage sag is not an issue. The discharge C rate is plenty and most do not exceed .2C when sized properly (2+ days of autonomy). So inductive loads are never an issue.

Super capacitors are expensive and heavy. Long cycle life if kept at a good temperature. Not worth it for most. Better off buying more batteries.

 

[Ampster]

??

 

[TorC]

Interesting, in that the bank being connected to is, in fact, a lead acid bank. Guess the @jjchvl may actually be in the group who might find this of use. But, agreed, for lithium, if it provides a noticeable benefit you probably have another problem to more profitably spend the money on.

 

[toms]

Interesting, in that the bank being connected to is, in fact, a lead acid bank. Guess the @jjchvl may actually be in the group who might find this of use. But, agreed, for lithium, if it provides a noticeable benefit you probably have another problem to more profitably spend the money on.

I disagree, if you wish to have a long LiFePO4 cell life it is better to not exceed 0.5C discharge.

If you have large startup loads, you can get away with using a smaller battery if you combine it in parallel with a supercap.

I have access to used Maxwell supercaps and use these in my setups.

The price difference is thousands in favour of using a supercap.

As with most off-grid things, every system has very different requirements.

The main advantage of using a secondary bank for large inductive loads that are non-critical is you can run the battery to minimum SOC daily as you have a primary bank to run the critical loads overnight.

I’m happy to compare with an existing system to discuss further any advantages/disadvantages.

 

[jjchvl]

Running a large motor with an undersized lead acid battery bank? A super capacitor bank can work wonders. But for solar with a properly sized lithium ion batteries? Absolutely not.

No benefit to large stationary storage lithium ion batteries. Voltage sag is not an issue. The discharge C rate is plenty and most do not exceed .2C when sized properly (2+ days of autonomy). So inductive loads are never an issue.

Super capacitors are expensive and heavy. Long cycle life if kept at a good temperature. Not worth it for most. Better off buying more batteries.

?Following?

Any pics JJCHVL?

Hey Farmhand. Ill post some pics if you promise not to laugh too loudly or criticize too harshly lol! Financial constraints force me to be one of those type who make do with readily handy and/or "found" supplies. You will see this in my pics ?

 

[jjchvl]

Capacitor is like another battery that can quickly charge and discharge. It will smooth out voltage at any time, up to the power stored. As a side benefit, it suppliments power as the battery voltage drops, including during heavy drain.

Thanks for the reply and info. I know the primary function of capacitors in many systems is to provide a current "boost" for start up needs. Thats probably a poor way to put it but please know that i do understand how capacitors work in that way. What I didnt realize was that a capacitor bank would smooth out voltage fluctuations during load draw but what you said about "up to the power stored" makes sense.

 

[jjchvl]

Running a large motor with an undersized lead acid battery bank? A super capacitor bank can work wonders. But for solar with a properly sized lithium ion batteries? Absolutely not.

No benefit to large stationary storage lithium ion batteries. Voltage sag is not an issue. The discharge C rate is plenty and most do not exceed .2C when sized properly (2+ days of autonomy). So inductive loads are never an issue.

Super capacitors are expensive and heavy. Long cycle life if kept at a good temperature. Not worth it for most. Better off buying more batteries.

Hey Will. Thanks for the reply. I imagine people write to you a lot asking for advice so im grateful that you had a moment to address my question!

Im using my capacitor "bank" in conjunction with an AGM battery bank, not a lithium battery bank. My system does use 1000ah of LifePo batteries as primary storage but Ive set up my "old" 900ah's of AGMs as "backup" storage.

I had already guessed that connecting capacitors to a bank of lithium batteries might be, in a way "redundant" since lithiums already allow for relarively fast, high amp discharge. Maybe not as high or fast as capacitors but surely enough for most household needs.

As an uninteresting side note, all of my AGMs are a year old or less and never DC'd below 80%. I couldnt just set them aside to rott after converting to lithium.

PS: I purchased multiple 200ah Weize LifePo's after watching a video of you cracking open a Weize 100ah battery. Im happy to report that, so far, the Weizes are serving me well. Temps hit -30f here a couple weekends back and the Weizes cold temp charging protection kicked in when temps in my battery compartment dropped into the mid 30s. They were still putting out but the outout voltage got squirrelly at around 38f.

 

[jjchvl]

Interesting, in that the bank being connected to is, in fact, a lead acid bank. Guess the @jjchvl may actually be in the group who might find this of use. But, agreed, for lithium, if it provides a noticeable benefit you probably have another problem to more profitably spend the money on.

Agreed. It didnt occur to me to connect my homemade capacitor bank to my lithium bank(i use a lithium bank as primary storage and the "old" AGM bank I upgraded from as "backup" storage). Its not that I worried the capacitor would harm the lithium bank. Only that lithiums can already provide the start up needs for most household appliances with little to no stress.

 

[RCinFLA]

Supercap across input of MPPT PV controller can screw up its ability to find MPPT point. Most MPPT controllers allow PV voltage to rise to Voc then starts MPP search at 0.6-0.7 x Voc and creep upward until MPP is found.

The time MPPT controller allows for this assumes a normal PV panel time response which is very quick. An added supercap will greatly slow this down. Voc sample will likely be low because when MPPT releases load the supercap slows the rise to Voc significantly. It may also screw up current limiting in SCC because when SCC sets up for 0.6 x Voc loading it sees a massive current surge caused by supercap.

Just like Li-ion cells, supercaps need balancers to keep a series stack of supercaps balanced in voltage and from exceeding their voltage limit which is about 2.7-3.2 vdc.

Supercaps also have series resistance. Resistance of good quality supercap is about the same as moderate AH LFP cell. It can help mitigate cable length voltage drop if caps are placed close to inverter. Probably cheaper to use larger gauge cable to reduce startup surge current voltage drop on cables.

100AH LFP cell are about 0.25 milliohm. 3000F Maxwell supercap are about 0.20 milliohms, but more series stack of supercaps are necessary for their voltage limit. 4x LFP cells = 1 milliohms initial Rs, 6x 3000F super caps = 1.2 milliohms.

100F Maxwell supercaps have Rs about 10 milliohms each.

A six cell lead-acid AGM have an initial series resistance of about 2-3 milliohms. A four cell 100 AH LFP battery will have about 1 milliohm plus 0.5 milliohm for BMS initial resistance. AGM lead-acid has a much greater overpotential voltage slump that increases over several minutes of load compared to LFP. Supercaps will not help much for overpotential voltage slump. Overpotential is the result of chemical/kinetic process within battery to sustain demanded battery current.

Be careful of cheap Chinese imitation copies. They even counterfeit the Maxwell labelling. Their series resistance is greater than Maxwell supercaps.

 

[jjchvl]

I disagree, if you wish to have a long LiFePO4 cell life it is better to not exceed 0.5C discharge.

If you have large startup loads, you can get away with using a smaller battery if you combine it in parallel with a supercap.

I have access to used Maxwell supercaps and use these in my setups.

The price difference is thousands in favour of using a supercap.

As with most off-grid things, every system has very different requirements.

The main advantage of using a secondary bank for large inductive loads that are non-critical is you can run the battery to minimum SOC daily as you have a primary bank to run the critical loads overnight.

I’m happy to compare with an existing system to discuss further any advantages/disadvantages.

Thank you SO much for a perspective in support of capacitors and for explaining in decent detail why you support their use. Although I hadnt considered connecting a capacitor bank to my lithiums, after reading your reply, I cant think of any reason-other than cost-that doing so could cause any harm. And if there is a chance that connecting a capacitor to my lithiums might offer a benefit, and I dont mind spending the few extra dollars, why not? Again, thanks for jumping in.

 

[jjchvl]

Supercap across input of MPPT PV controller can screw up its ability to find MPPT point. Most MPPT controller allow PV voltage to rise to Voc then starts MPP search at 0.6-0.7 x Voc and creep upward until MPP is found.

The time MPPT controller allows for this assumes a normal PV panel time response which is very quick. An added supercap will greatly slow this down. Voc sample will likely be low because when MPPT releases load the supercap slows the rise to Voc significantly. It may also screw up current limiting in SCC because when SCC sets up for 0.6 x Voc loading it sees a massive current surge caused by supercap.

Just like Li-ion cells, supercaps need balancers to keep a series stack of supercaps balanced in voltage and from exceeding their voltage limit which is about 2.7-3.2 vdc.

Supercaps also have a series resistance. Resistance of good quality supercap is about the same as moderate AH LFP cell. It can help mitigate cable length voltage drop if caps are placed close to inverter. Probably cheaper to use larger gauge cable to reduce surge current drop on cables.

100AH LFP cell are about 0.25 milliohm. 3000F Maxwell supercap are about 0.20 milliohms, but more series stack of supercaps are necessary for their voltage limit. 4x LFP cells = 1 milliohms initial Rs, 6x 3000F super caps = 1.2 milliohms.

100F Maxwell supercaps have Rs about 10 milliohms each.

A six cell lead-acid AGM have an initial series resistance of about 2-3 milliohms. A four cell 100 AH LFP battery will have about 1 milliohm plus 0.5 milliohm for BMS initial resistance. AGM lead-acid has a much greater overpotential voltage slump that increases over several minutes of load compared to LFP. Supercaps will not help much for overpotential voltage slump. Overpotential is the result of chemical/kinetic process within battery to sustain demanded battery current.

Be careful of cheap Chinese imitation copies. They even counterfeit the Maxwell labelling. Their series resistance is greater than Maxwell supercaps.

Ok so no supercaps in my system lol! Seriously thougg, Im very happy for your input as well. I confess that I didntunderstand a bunch of what you wrote but did comprehend the part about supercaps possibly interfering with the function of an MPPT controller. Im not sure how applicable this problem is to my set up but you are absolutely right. It deserves much more research on my part. I do use three 60amp MPPT controllers in my charging system but only one of those is connected to my AGM/capacitor battery bank and then only when I flip over to the AGM bank. Unless I flip to the AGM bank, all three of my panel arrays and their controllers are connected to my lithium bank. Anyway, Ill need to read and digest your reply better and then do some more research. This stuff is all fun until it kills you!!

 

[McKravitts]

There definitely are applications where a super cap makes sense. One common application is for large audio amplifiers separated from the battery bank by long wires.

Say you wanted to use a powerful PA system off a vehicle battery. As mentioned in a previous post, you could use additional batteries, but in the limited space of a vehicle it isn’t always practical. A super cap connected directly to the input of the audio amp can help limit audio distortion that can occur due to occasional high current demands. There are many different models on the market and some with built in circuitry to limit charge current.

I think it’s well worth experimenting with them in solar applications.

A capacitor can deliver very high current without risking damage to it. That's not true of batteries.

In a recharge cycle, after a motor start for example, the partially discharged capacitor is like a near short circuit on the batteries, if connected directly to the output terminals of the battery bank.

To protect the battery bank, it is always recommended to use a unidirectional current limiting device between the capacitor and the battery bank.

The price of super caps is dropping rapidly and I wouldn’t be surprised to see them become a standard addition to a solar system using a low frequency inverter in the near future.

 

[jjchvl]

There definitely are applications where a super cap makes sense. One common application is for large audio amplifiers separated from the battery bank by long wires.

Say you wanted to use a powerful PA system off a vehicle battery. As mentioned in a previous post, you could use additional batteries, but in the limited space of a vehicle it isn’t always practical. A super cap connected directly to the input of the audio amp can help limit audio distortion that can occur due to occasional high current demands. There are many different models on the market and some with built in circuitry to limit charge current.

I think it’s well worth experimenting with them in solar applications.

A capacitor can deliver very high current without risking damage to it. That's not true of batteries.

In a recharge cycle, after a motor start for example, the partially discharged capacitor is like a near short circuit on the batteries, if connected directly to the output terminals of the battery bank.

To protect the battery bank, it is always recommended to use a unidirectional current limiting device between the capacitor and the battery bank.

The price of super caps is dropping rapidly and I wouldn’t be surprised to see them become a standard addition to a solar system using a low frequency inverter in the near future.

A "unidirectional current limitting device"? That actually sounds logical/interesting, although in the research Ive done so far, i havent read nention of such a device being used in solar builds where folk have used capacitors. My question would be how the refill "speed" of a super capacitor would harm a battery bank more than the faster start up demands certain appliances would place on the same batteries without a S capacitor involved?

 

[jjchvl]

There definitely are applications where a super cap makes sense. One common application is for large audio amplifiers separated from the battery bank by long wires.

Say you wanted to use a powerful PA system off a vehicle battery. As mentioned in a previous post, you could use additional batteries, but in the limited space of a vehicle it isn’t always practical. A super cap connected directly to the input of the audio amp can help limit audio distortion that can occur due to occasional high current demands. There are many different models on the market and some with built in circuitry to limit charge current.

I think it’s well worth experimenting with them in solar applications.

A capacitor can deliver very high current without risking damage to it. That's not true of batteries.

In a recharge cycle, after a motor start for example, the partially discharged capacitor is like a near short circuit on the batteries, if connected directly to the output terminals of the battery bank.

To protect the battery bank, it is always recommended to use a unidirectional current limiting device between the capacitor and the battery bank.

The price of super caps is dropping rapidly and I wouldn’t be surprised to see them become a standard addition to a solar system using a low frequency inverter in the near future.

As you said, it does merit some experimentation! Right now my concern is what RCinFLA brought up; Will capacitor use interfere with proper function of my MPPT controllers? Ive got to study his post and figure out what he's explained.

 

[RCinFLA]

There definitely are applications where a super cap makes sense. One common application is for large audio amplifiers separated from the battery bank by long wires.

Say you wanted to use a powerful PA system off a vehicle battery. As mentioned in a previous post, you could use additional batteries, but in the limited space of a vehicle it isn’t always practical. A super cap connected directly to the input of the audio amp can help limit audio distortion that can occur due to occasional high current demands. There are many different models on the market and some with built in circuitry to limit charge current.

You really think a few milliohms difference in battery supply line resistance makes a difference when you have maybe #8 wires to 4 ohm impedance speakers? Reducing speaker driver impedance improves dampening factor on speakers that inhibits speaker cone ringing due to impulse response to bass frequencies, but speaker wires are normally the limiting factor on speaker dampening.

Like gold plated connectors, Monster cables' advertising makes all the difference to auto boomers spending money on their rigs.

 

[jjchvl]

Supercap across input of MPPT PV controller can screw up its ability to find MPPT point. Most MPPT controllers allow PV voltage to rise to Voc then starts MPP search at 0.6-0.7 x Voc and creep upward until MPP is found.

The time MPPT controller allows for this assumes a normal PV panel time response which is very quick. An added supercap will greatly slow this down. Voc sample will likely be low because when MPPT releases load the supercap slows the rise to Voc significantly. It may also screw up current limiting in SCC because when SCC sets up for 0.6 x Voc loading it sees a massive current surge caused by supercap.

Just like Li-ion cells, supercaps need balancers to keep a series stack of supercaps balanced in voltage and from exceeding their voltage limit which is about 2.7-3.2 vdc.

Supercaps also have series resistance. Resistance of good quality supercap is about the same as moderate AH LFP cell. It can help mitigate cable length voltage drop if caps are placed close to inverter. Probably cheaper to use larger gauge cable to reduce startup surge current voltage drop on cables.

100AH LFP cell are about 0.25 milliohm. 3000F Maxwell supercap are about 0.20 milliohms, but more series stack of supercaps are necessary for their voltage limit. 4x LFP cells = 1 milliohms initial Rs, 6x 3000F super caps = 1.2 milliohms.

100F Maxwell supercaps have Rs about 10 milliohms each.

A six cell lead-acid AGM have an initial series resistance of about 2-3 milliohms. A four cell 100 AH LFP battery will have about 1 milliohm plus 0.5 milliohm for BMS initial resistance. AGM lead-acid has a much greater overpotential voltage slump that increases over several minutes of load compared to LFP. Supercaps will not help much for overpotential voltage slump. Overpotential is the result of chemical/kinetic process within battery to sustain demanded battery current.

Be careful of cheap Chinese imitation copies. They even counterfeit the Maxwell labelling. Their series resistance is greater than Maxwell supercaps.

Just read your reply again(and will need to read it again, again!). It almost sounds to me as if you think Ive istalled a supercap between my panels and charge controllers. If so, that isnt the case. Ive connected Supercaps directly in parallel with an AGM battery bank. After thinking about it, Im having trouble imagining how a supercap connected in parallel to my AGM battery bank would interfere with my charge controllers. My reasoning for this is that the voltage of a supercap cant be higher than the voltage of its charge source. So wont be higher than the battery bank its connected to. And the voltage of the battery bank is what a charge controller goes by to charge that battery bank. Does this sound right or am i missing sonething essential here?

 

[jjchvl]

By the way. I did solder one of those balancer discs to each of my 2.7v 500f capacitors before connecting them in series. The balancers limit the overal voltage of the bank to 15v.