Using 16v 83F Super Capacitors 2ith Lead Acid Battery Bank

If it is already working well, then the proposed improvement may be difficult to justify.

There seems to be a mismatch between the inverter and the required power out anyway: <...220 watt AC out....> seems to be a bit on the small side for <...power for Tv, Video player, Desktop Pc, printer, lighting, microwave, induction cooker, fridge and small chest freezer...>. Maybe not all of these loads are on at the same time.

My guess is he meant 220 volt output.

Maybe, though that is not what is stated in the original post.

All I can see in the original post is the 220 watt (or volt) that we're querying. The loads are clearly domestic and while I don't know offhand what supply voltage is in the Philippines 220 volt would be reasonable.

OP can you clarify?

This will not work as you hope: the supecap will indeed supply some current, but remember that the voltage at the supercap terminals will always be the same as the battery voltage. It will probably help, but not as much as you would like (and may not be worth the cost).

I don't see any need either....I would add a couple more batteries...maybe more solar panels....I would set up a monitor to determine my charging capabilities vs battery capacity and power usage, to determine balance in components....then determine if I should add more batteries or solar panels, to fine tune the setup...I would also check amp draw at max demand for each appliance to see what my battery pack was capable of supplying....Your batteries should have peak load amps written on them, just add them up and you will know what starting load they can handle...amps * volts = watts

Oops! yes -the inverter is mislabelled in the diagram.

the Inverter is a pure sine wave with a 220 volt 3,500 watt (7,000watt surge) output! Usually the load is around 200 to 300 watts, except when using the microwave or the induction cooker. when the load approaches 2000 watts

This is not a 24/7 system. The gross electrical consumption of my home on a normal day is between 4 - 5 KW. On a good day this system produces around 3 KW. My options include assisting the solar array with a mains powered 40 amp battery charger (not shown in diagram) or running the house on main supply for around 6hrs a day.

Getting back to my original question. The general consensus here appears to be that this device will not protect the battery bank from brief heavy demands.

Now I do get cross when a question is posted on the forum & the poster then disagrees with the replies that others, with more knowledge, have taken the time to compose & post.

However, to help me understand why this device will not do what I thought it might do, can anyone tell me how many amps can be stored in an 83 Farad capacitor? . If, on start up, the fridge demands less amps than those stored in the capacitor,will not these amps be drawn from the capacitor?

"How many amps can be stored in an 83 Farad capacitor?" is a bit of a meaningless question. The current depends on the load connected. If you connected a short-circuit, the current would be limited only by the ESR (Equivalent Series Resistance) of the cap, which is typically very small, so the current could be huge.

A capacitor stores charge (the total stored being the product of the capacitance and the voltage). The current is the flow of charge out of the cap. Read more here: https://en.wikipedia.org/wiki/Capacitor.

But back to your case of a cap in parallel with a battery. As soon as you start to draw current, the capacitor charge (and thus voltage) would start to drop, so to try to "keep the voltage up" (remember they're connected so the cap terminals are always at the same voltage as the battery terminals), current would come from the battery.

For your idea to work, you'd have to have a fairly complicated set-up with something to sense the inverter input current, and disconnect the battery when it was over a certain limit, and re-connect the battery when the cap voltage was too low to maintain the inverter output voltage.

A bit waffley, I'm afraid, but I hope it makes a bit of sense and gives you an idea of why it won't work as expected.

Are there really capacitors of 83 farad available these days? I remember when 10 microfarad was big!

The original poster claimed to have found one on a well-known internet auction site, so the answer is affirmative.

Yes, most of these supercapacitors are for audio purposes, as in car stereo.

I think OP should avoid messing with the supercapacitor, as it can produce lethal current, but perhaps, so could the battery bank.

Caveat BB gun enthusiast: Don't do it, you will put your eye out!!!

Same here!

Wikipedia mentions "Practically, these storage principles yield a capacitor with a capacitance value in the order of 1 to 100 farad " ( but also says ^{[citation needed]}).

This capacitor bank http://www.ebay.co.uk/itm/like/262082531166?lpid=122&chn=ps&adgroupid=13585920426&rlsatarget=aud-133395220866%3Apla-142405552626&adtype=pla&poi=&googleloc=9045746&device=c&campaignid=207297426&crdt=0 is rated at 16V 36F (and costs US $65 +P&P). I guess there are bigger ones around (for bigger bucks!) but I can't be bothered looking.

Capacitor technology has come a long way. 3000F 2.5V 15.5kA peak current cells are now available and not too expensive (Ioxus for example), although the cell balancing kits needed to create series battery strings seem prohibitively expensive to me.

The technology still has a long way to go to replace battery banks thou (if ever except for specialty applications).

I remember at school around 1958 asking my Physics teacher how big would a 1 Farad cap would be (then!). He answered that it would be physically around the size of a football pitch!!!

Never forgot it!!

When I bought my first super cap (1 Farad) years ago, I spent just minutes staring it with a blissful face....Totally blown away......

I have got used to them nowadays!!! Just about!!

Yes, available.

Codemaster:

The inverter is 220vac 60hz 3.5KW output, which is the same voltage/hz as the Philippine grid, hope that makes it clear.

Thanks, that's what I thought.

I don't know much about what you're asking, but go along with other posters that it's likely to be more trouble than it's worth. Lead-acid batteries can handle short-term high currents OK, a typical car battery of say 60 Ah capacity gives a couple of 100 amps to start the engine. Your battery is much bigger.

Even more like 300-600 amps depending upon engine size and type......

Look for this pdf:-

Engine_Starting_SNC_AppliBrochure_EN_0715_Protected (1).pdf

<...batteries do not like...> Batteries are inanimate objects and are not capable of expressing opinions, either singly or collectively.

I dunno, sometimes batteries are pretty animated. There also seem to be things certain batteries clearly do not like.

<Tips hat towards an opinion-free video, and unsubscribes>

"It is my understanding that batteries do not like sudden heavy drains, such as those imposed by fridge & freezer start ups."

Not the least bit true provided you are using them below their rated cranking amp rating or C rating which with 100 AH deep cycle batteries thy more than likely have at least a 500 cranking amp or 5C rating giving your battery bank a minimum of 2000 amps or roughly 24 KW's peak short-term output capacity without going outside the batteries designed capabilities.

Many thanks to all who have helped me understand that what I was contemplating was pretty silly!

The only "silly question" is the one that no-one asks.

My lead acid batteries get a "sudden heavy drain" every time I start my car.

The battery can be modeled as a pure voltage source in series with a small resistance. The typical internal resistance of a lead acid battery of your size is probably about .003 ohms.

http://www.power-sonic.com/images/powersonic/sla_batteries/pg_series/PG-12V200_11_Jan_12.pdf

So, for example, if you draw 100 A, the voltage would drop 100 x .003 = 0.3 volts.

The supercapacitor can be modeled as a pure capacitance in series with a small resistance. Typical internal resistance is .03 ohms.

https://en.wikipedia.org/wiki/Supercapacitor#Internal_resistance

Using the above example:

If you connect a load which drops the battery voltage 0.3 volts, 100 amps comes from the battery. The 0.3 volts across the internal resistance of the supercapacitor would mean that the capacitor would initially supply 10 amps which would slowly decay with an RC time constant of .03 x 83 or 2.49 seconds. (The RC time constant is the time the current reduces to 1/e = 36.7 % ).

So the answer is that based on the internal resistances, the supercapacitor would only help about 10 percent.

BruceFlorida, Altho my batteries are deep cycle & not auto (which are designed & built for sudden heavy discharge) your comment does bring home to me that my original concerns were pretty groundless!

Combine this with Rixters detailed explanation of what a small difference that this unit would make reinforces that this woud be a useless expensive experiment!

Thanks again to all for contributing to this thread

The manufacturer's info would help!!

I think what all of you are forgetting here is the time domain. We are talking transient response.....not steady state output here.

These large super caps are used commonly in car stereo setups. They are called "peaking capacitors" for a very good reason. When used in high power audio setups in a car environment, large transient audio signals from the power amp get clipped because the MOSFET power supplies can't react fast enough, with full power, to a 25 hz, 5000 watt single sign wave impulse when powered only by the car's battery/alternator. The peaking caps supply that brief power for considerably less than a second.

At this point, forget about your comments as to "why" someone would want that much audio power in a small car.

I have designed many such systems over the past 30 years. I have proven many times by comparison oscilloscope traces that the super "peaking" caps work. The peaking caps also tend to keep the car's electrical system from drooping in voltage for those brief peak voltage/current demands on the car's electrical system.

This person asked whether or not the peaking cap across the battery bank's terminals would help improve transient response from his power supply during initial startup of high torque loads, such as from the fridge compressor. Rixter, redo your math for a 0.75 second draw from the battery bank (simulating the very brief current surge in the fridge compressor at start up) with....and without the peaking cap.

Darnit Wolfie62!,

Are you saying that there is some substance to my ignorant guess that this device could protect my batteries?

I have to say that I have now been convinced by other contributors that my battery bank can suffer this brief sudden load without harm. I now think that the cost of the device (128USD) would be better spent on an extra 100amp deep cycle battery........

This system proposed by will NOT work. I have seen the discussions and someone has already told- but not clearly WHY!!!!!

You cannot have a COMMON charge controller for battery and super capacitors. Both need independent charge controllers. Then discharge rates are different. Hence separate DCDC converters are connected to battery and Super cap- both boosting the voltage a common DC cap to say 400 V. The inverter is connected across this common 400V cap. An additional micro-controller firm ware will be needed co-ordinate charging and discharging for Super Cap or Battery.

I am working on such a system solution with a PhD student. Objective is to charge cap fast and let Battery get charged slowly thereafter. While discharging let cap discharge first and let battery prolong the discharge. Now that cap is discharged, but battery may still be full, PV can be diverted to charge cap alone with MPPT algorithm. System solution is far complex than simplistic approach you have taken.

"I think what all of you are forgetting here is the time domain. We are talking transient response.....not steady state output here."

XYZ, again, you don't get it. You keep talking steady state here, not short impulse.

You talk about separating the charge controllers and even the discharge; discharging the super cap then sequentially the battery.

"Hence separate DCDC converters are connected to battery and Super cap- both boosting the voltage a common DC cap to say 400 V." This statement alone tells me you have no real idea what the poster is even talking about.

"An additional micro-controller firm ware will be needed co-ordinate charging and discharging for Super Cap or Battery." Even more proof you have no idea what the author of this thread is talking about.

You have let your project interfere with the intent of this author's goal and problem.

When I was in college, a common saying was, "RTFQ". I think this applies to your response.

I do not want to go into details of why etc. BUT I AM JUSTIFIED in taking that stand- which I have clearly stated and stand by it. Super capacitors do not discharge in a transient- like other capacitors and I am fully aware of it. I am practical and working on it and not making theoretical statements.

Isn't that convenient?!

First, you say this: "I have seen the discussions and someone has already told- but not clearly WHY!!!!!"

Then, you say this: "I do not want to go into details of why etc."

OK. Guess we'll have to keep guessing what you are talking about.....

So, I guess super, or ultra-caps are slow to discharge? In the first second of discharge, how slow are they?

And, I am not saying it (super cap) will "protect" your batteries. It will augment the short term power of the batteries. And in my applications, the super cap lasted years after the battery was sent in for recycling.

Also, I think the 83 F rating of the cap is over the top for what you want. (Where did you get this number?) A couple of Farads should do the trick nicely. Cheaper than an additional battery, and will outlast any single battery in your bank.

You are after short term voltage/current boost during the high current inrush, or demand, of the high torque load (the refrigerater compressor). Now, an inverter is much like the MOSFET power supply for the large audio power supplies I have dealt with. To handle that inrush current of the high torque load, you need instantaneous current and voltage. The super cap can help with that short term load. After that, it's all up to the batteries. Then, you get into all the help and advice offered here about care and feeding of batteries. (But even that is not universally accepted, if you listen to all the mfrs of battery charge controllers!)

I do not see an advantage in adding caps, as someone else also mentions, that money would be better spent on adding battery capacity.

Furthermore, lead acid batteries were (at least the ones I know about, the ones in general usage anyway) designed to handle sudden large loads and surges.....they actually like the "exercise"! It improves them, like an athlete training for a race!!

Where you might be better to look as, is to not charge them to 100% - ever - as this makes them really very inefficient, causes gassing, water loss and shortens their lifespan.

Depending upon the battery manufacturer, its usually best to charge to around 70% of a full charge and have a far great capacity (more batteries).....This will dramatically increase the life span of the batteries as well as reducing water usage (therefore gassing!) to almost nothing!!!

Having a proper charger, with "high end voltage" cutoff, will help, especially if each battery is charged independently, or at worst, identical batteries are paired in series to a single double voltage charger.

Also, batteries should not be "over" discharged as well, see manufactiúrer's data for that as well.....

Remember, a hattery has cells. In a single battery (any chemistry!) there is a weak and a strong cell. The weak cell gets stressed when its full first, and stressed when its empty first, therefore it fails first.

Once a cell is damaged, the battery is basically useless......

Each battery having a charger that a) charges to a set and safemax voltage and b) that removes the batter from the load once it goes below a certain low value, will basically give each battery a far longer life. This is basically true of any chemistry by the way.....

Technically, if each cell had its own charger (totally impractical of course), they would get increased life span. The trick is not to over or under charge any cell in any battery as far as possible.....and keep the battery in its most efficient band of voltage.

So don't buy the caps!!

Do check carefully the manufacturers data to find the charge most efficient "sweet spot".

Leisure batteries can accept a deeper discharge better, but often cost more.

An ME probably shouldn't comment on electrical stuff, but my take is that it depends in the impedance of the battery v/s the super-capacitors. If the current is somewhat shared, you may be on to something. I would measure the discharge current for each of the components to determine whether the super-caps are doing what you expect them to.

My (untested) opinion is that a large cap, to do its job well, must be able to charge and discharge at high rates.

Also, the size of the conductors to it should take this into consideration, or they will act as low value resistors and slow the rate down.

I do not know if these huge value capacitors can handle rapid charge/discharges over long periods though, maybe they may run too hot. Just guessing though!!

But as I previously posted, my personal take is that larger battery capacity is the correct way to go, using leisure type/deep discharge types and seeking the sweet spot for the most efficient max charge level, avoiding full charges like the plague with LA batteries of ANY type..