54 Ultracapacitors in series with 12 12 volt batteries

[michaeljaycla]

I have 54 Maxwell 2.7 volt 3000 farad ultracapacitors and would like to know if they can be placed in series with 12 12 volt lead acid deepcycle 200 ah batteries. all in series.

would it work? why yes or why not?

this is a circuit to operate a electric vehicle.

 

[Fish4Fun]

Michaeljaycla,

Welcome to PF!

I assume you understand what a capacitor is and does? But then again, why would I assume that? The total series capacitance of 54 * 3000F capacitors would be:

3000F/54 = 55.5F

The rated voltage of your series would be:

2.7V * 54 = 145.8V

Since most 12V lead-acid batteries actually have a nominal voltage of 14.4V when fully charged, you would exceed the voltage rating of the capacitor string by:

14.4V * 12 = 172.8V ==> 172.8V - 145.8 = 27V

Next, DC current flow through series capacitors is limited by:

I = E/R * e^(-t/RC)

Perhaps you meant to use the capacitor string in parallel with the batteries? I am not sure what you are attempting to achieve with the capacitors. Anyway, you might consider do some reading:

http://www.allaboutcircuits.com/vol_1/chpt_13/4.html
http://hyperphysics.phy-astr.gsu.edu/hbase/electric/capchg.html#c1

After you have done a bit of reading, you might consider re-phrasing your question. If you indeed have 54 of these $100ea capacitors, certainly you have some purpose in mind for them?

A more typical EV would use Lithium Ion batteries, typically a LOT of them. The 18650 form factor seems to be a popular choice. Nominal voltage is 3.7V each with storage capacities ranging from 1.6Ah to 3Ah. For a motor voltage ~150V, you might use 40 in series. If you wanted a range of ~200 miles, you would need ~50kWh, this amount of storage would require:

50,000Wh/148V = 337Ah

337Ah/2.8Ah = 121 parallel connected strings of 40 series batteries, for a total of: 121 * 40 = 4840 batteries. You can likely source this quantity of batteries for ~$5ea, for a total battery pack cost of ~$25,000.

Using 2.7V 3000F capacitors, to store 50kWh of energy would be considerably more expensive!Fish

 

[michaeljaycla]

the experiment here to see how the capacitors will take away the job of sending 600 amps in one second away from the batteries which do an awful job of doing that.

ultracapacitors are getting used in these situations by battery manufacturers. hybrid battery-capacitors are being built to handle situation where constant high current discharge is needed.

the caps were purchased much less than 100 each. I want to experiment with these I have, I can always resell them if the testing fails to prove anything.

I have learned that all series will create a bottleneck unless a switching circuit adds them into the circuit, they are discharged, then removes them right before they reach zero, recharge them and reinsert them into the circuit charged.

Ill put them in parallel.

the batteries will be charged to 144 volts by a battery charger. I can see the alarm about how they will be more than the 145 volts when immediately removed from the charger. I may just take one battery out of the string to allow for that.

 

[Averagesupernova]

If you plan on wiring all those in series do you have a way to guarantee that all capacitors see the same voltage instead of some being overvoltaged?

 

[michaeljaycla]

If you plan on wiring all those in series do you have a way to guarantee that all capacitors see the same voltage instead of some being overvoltaged?

maxwell suggests I use a 54 ohm resister as a bleeder in the vent of overcharge.

the raises a question of what kind of 54 ohm resistor ? 54 ohms and ?. plus where should it be wired in? parallel to a bus bar? or directloy inbetween the + and - of two caps.

 

[Averagesupernova]

You need a resistor across each capacitor if they are all wired in series.

 

[TurtleMeister]

Ultracaps have a much lower internal resistance than chemical batteries. They can increase the efficiency of a battery powered system. A common application is to have the ultracaps as electrically close to the load (control electronics) as possible. The battery then becomes just an energy source, and not an energy source and a power source. The ultracaps can provide short bursts of very high current that would otherwise not be possible because of the internal battery resistance and wiring.

michaeljaycla, your circuit shows the series ultracaps connected in series with the battery bank. That will not work. The series ultracaps should be in parrallel with the battery bank.

Edit:
This is a dangerous experiment. It can kill you. Please be sure you have the necessary knowledge and/or experience before proceeding.

 

[uart]

I really have to wonder if someone that doesn't understand the difference between series and parallel should even be in the same room as a high voltage high current source!

 

[Fish4Fun]

Michaeljaycla,

I do not mean to sound unkind, but I would advise you to sell your capacitors while they still have value. It is readily apparent you do not have the knowledge to complete any useful project involving them, and it is quite likely you could sustain serious injury meddling with them.

If you feel compelled to play with them, I would suggest you begin with a 1.5V DC motor and a SINGLE 2.7V, 3000F capacitor. You can learn a TON about electronics, capacitors, energy storage and power from simple experiments, w/o putting yourself in harm's way.

The physics of energy storage in the quantities needed to power a passenger vehicle are complicated. Think of it like this: if you had enough energy storage to move a passenger vehicle some number of miles, that energy would be the equivalent to the energy stored in some volume of gasoline. To move that same vehicle with electricity the same number of miles you will need roughly the same amount of energy stored in capacitors or batteries.

The fact that you can readily purchase a gallon of gasoline does not imply that you can design a system to efficiently and safely convert that potential energy into useful work. The most likely outcome of laymen experiments with gasoline involve unintended fire and potentially death and/or destruction. Do not assume because you can legally purchase high capacity capacitors that they are inherently safe, nothing could be further from the truth.

Fish

 

[michaeljaycla]

thanks for the concern. I am discussing this with many different people and getting all the ideas and opinions to find the answer.

I am not doing this alone, there are many EV people looking at this as well.

I understand parallel and series no problem there.

there seems to be different opinions on how ultracaps can be used in electric vehicles.

 

[Fish4Fun]

michaeljaycla,

Let's approach this from a different point-of-view. Do you understand that charging a capacitor is NOT a lossless event? That is to say, do you understand that charging a capacitor, by ANY MEANS, incurs energy loss? The best example involves a losseless switch and two ideal capacitors, one charged, the other completely discharged; here is the very simple math:

Q1 = C1 * V1
U1 = 1/2 * C1 * V1^2

Q2 = C2 * V2
U2 = 1/2 * C2 * V2^2

After the switch is closed for some period of time:

Vf = (Q1 + Q2)/(C1 + C2)
Uf = 1/2 (C1 + C2) * Vf^2

Now, for:
C1 = 100uF
V1 = 100V
Q1 = 0.0001 * 100 = 0.01 Coulombs
U1 = 1/2 * 0.0001 * 100^2 = 0.5J

C2 = 1000uF
V2 = 0V
Q2 = 0.001 * 0 = 0 Coulombs
U2 = 1/2 * .001 * 0^2 = 0J

Now, Close the switch and:

Vf = (0.01 + 0) / (0.0001 + 0.001) = 9.09V
Uf = 1/2 * 0.0011 * 9.09^2 = 0.0454J

Please Note Efficiency = (1 - 0.0454/0.5) = 91% Energy Loss!

I honestly cannot explain where the energy "goes", some references state that it is lost in I^2R losses while others simply show that it is "gone". Perhaps someone can explain where this energy "goes" in ideal components, (I suspect the answer lies in the current and voltage being out of phase), but I don't have a definite answer to it. In the case of charging a real capacitor from a real source, the answer is in I^2R losses during "charge", and decreasing energy as V drops during discharge.

Anyway, the primary role capacitor banks play in EV's is in providing short-term, large current demands, and regenerative braking. In the former case, the losses associate with the charging of the capacitors is off-set by savings in battery design, and pretty much the same in the latter case, but in both cases the capacitor banks play a supporting role to the batteries.

In the cases where capacitor banks are used as primary energy storage, the price of available energy must be cheap, and readily available. For instance, a train that stops every Xkm could use capacitor banks to store enough energy to accelerate a motor to some predetermined speed and then use regenerative braking to recapture some portion of that energy as it stops. While stopped, the capacitor banks could be "topped off" from the grid; however, this does NOT imply a random journey could efficiently use capacitors as a viable, primary storage mechanism.

Anyway, I will re-iterate my concerns for your safety should you attempt to power a high-voltage motor from your "super capacitors". Any experiments you attempt beyond 1.5V motors and a single capacitor are quite likely to end in electrocution, explosion, injury or component failure. Please insure you fully research any experiments. Please Post ANY CIRCUIT you are contemplating prior to implementation. No One here wants to see you fail, nor do we want to see anyone injured as the result of experimentation. 55F @ 140V will fry you like an egg, BE CAREFUL.

For another example of how much energy you are "playing" with, assuming you had 1 ohm of series resistance and a 120Vac "outlet" rectified as your "charger", your capacitor series (54 * 3000F = 55F) would initially draw 170A (this assumes your mains rectified = 170Vdc), and after 1 minute would still be drawing 67A. The largest UL approved 120V breaker is 30A. The 1 ohm resistor would initially be dissipating 29.8kW (170^2)! PLEASE treat these components with the proper respect.

Fish

 

[michaeljaycla]

I agree that these experiments must be taken with SERIOUS respect for the power I am using.. An electrical engineer at a local college told me putting 60 ucaps in series makes him nervous even thinking about it. I purchasing the active balancing boards for the ucaps. The kits came with 6 boards for 6 ucaps in series so I bought more ucaps to give me a total of 60.

I have a 15000 watt generator I want to use as onboard charging and range extender. I purchased a 33000 watt bridge rectifier and ran experiments. The generator is AC so on the 240 volt 50 amp outlet I was able to get 240 vdc at almost 100 amps. I put the video on youtube of the experiment.

All ideas are posted on forums before they are tried.

As far as putting the capacitors in series with capacitors, Maxwell replied that it can be done with extensive controlling to make sure the caps do not end up sending current in reverse back into the battery bank behind them. That sends me to other options.

that would be to place the capacitors in parallel with the battery pack. have a way that on initial takeof the vehicle draw from the ucaps. when the crusing speed is reached, the batteries are put in and the ucaps taken out. the ucaps are then filled up by the batteries through a controller that would only allow 200 amps to go from the batteries to the ucaps.

the way I understand motor controllers they do exactly what I am looking to do. send the 160 vdc to the caps from the batteries at 250 amps. the purpose of limiting the current is so the batteries in this entire application do not see anything above 250 amps. I decided on 250 amps because a 5000 pound vehicle requires about 250 amps at least to maintain 55 mph on a flat road. This was determined by a 4300 pound electric S-10 I have. It was at a little under 200 amps at 55 mph so i deduced that for 700 more pounds ill need roughly 250 amps.

for testing purposes Id like to know if I could use 4 PWM controllers rated at 40 vdc 100 amps each to be able to transfer power from the batteries to the ucaps and be able to control the current. The reason for this is to keep the price down and to answer a question if multiple controllers can be used on 1 motor.

 

[Fish4Fun]

that would be to place the capacitors in parallel with the battery pack. have a way that on initial takeof the vehicle draw from the ucaps. when the crusing speed is reached, the batteries are put in and the ucaps taken out. the ucaps are then filled up by the batteries through a controller that would only allow 200 amps to go from the batteries to the ucaps.

You would likely be better off to simply keep the capacitors in parallel with the batteries all the time. This would essentially give you two parallel current sources, one with much lower impedance than the other.

Let's look for a minute at the actual storage capacity of your capacitors:

3000F/60 = 50F Total Series Capacitance
60 * 2.7V = 162V Maximum

Assuming you still want to use 12V lead-acid batteries,

162V/14.4V = 11.25 ==> 11 * 14.4V = 158V Nominal System Voltage.

The capacitors will be able to store:

1/2 * 50F * 158V^2 = 624,100 Joules of energy when charged to nominal system voltage. There are 3,600,000 Joules in 1kWh.

Your 210Ah lead acid batteries should not be discharged past 50%, so you will have a nominal 105Ah of usable current @ ~14.4V, or optimistically, 1.5kWh of power. If we assume each of your batteries are capable of ~640A, then this implies an internal resistance of ~ 0.25 ohms ( 158V/640A = 0.247865). 11 of these batteries in series gives you a total internal impedance of 11 * 0.25 = ~2.7 ohms. So, your series connected batteries should have a maximum current of 158V/2.7ohms = ~58A.

A 250A load @ 158V implies a load resistance of 0.632 ohms. Assuming you were "running" on the 50F capacitor bank alone, initially charged to 158V, you would initially provide 250A to the load. 1 second later, you would be supplying only 182A, and the capacitor voltage would be 115Vdc. @ 2 seconds you would be supplying 133A @ 84V.

Designing a viable electric vehicle requires engineering the entire vehicle from the ground up. "Adding" a 15kW generator (typically a 25hp to 30hp ICE) pretty much defeats the purpose. In any case, I can't see how these capacitors are going to do you much good as a primary storage media, they may be of some use for a second or so, but not a lot else.

As far as using multiple PWM controllers, the simple answer is "no". You could use multiple units if you were willing to separate the capacitors into "charging groups", and then "switch them back" to a single series, but this has its own problems that I won't go into because I think the entire way you are attempting to use the capacitors is flawed.

Good Luck!

Fish

 

[michaeljaycla]

these are wild ideas and i ask because I am sure these ideas have been in the minds of others.

I am changing the 12 12 volt batteries to 26 6 volt batteries. the battery pack will be 156 volts and the caps 160 volts.

they will be placed in a simple parallel circuit. the idea of trying to isolate them for take off is a later idea.

I do get the comments that I am wasting time and it will never work, yet, the AFS trinity seems to work nicely.

there are more EVers that use capacitors. they use simple parallel configurations.

Ive even seen pictures of a box truck that weighed 15000 pounds propelled to 45 mph by 126 2500 farad ultracapacitors.

in 2003 an EV1 was resurrected and a BYU team was able to power it with 280 2500 farad ultracapacitors and set the record for capacitor only 1/4 mile at 15 seconds. if anyone wants the caps they still have 200 of them selling for $10 each.

I always expect to be told it won't work but yet, I see them working in real world applications. that's why I ask different ways and different forums to get ideas from different people.

the reason the people that use ucaps usually don't speak up in forums is because of the exact response I just got.

so let's put the negative opinions aside and just talk about the subject and how to get it to work.

the mythbusters always take a myth that seems to be "busted" then try to see if they can get it to work even with ridiculous means. I especially liked the cement truck dynamite episode. the myth that dynamite would get the dried cement out of the drum was busted, yet they decided to use a ridiculous amount of explosives to get the cement out, of course the truck was blasted to tiny pieces but yet they got the cement out! LOL

so let's follow that guideline if we could.

 

[sophiecentaur]

@michaeljcla
You say that you know about series and parallel but what is the possible point of such a series connection? How long do you want your motor to run for? Once the capacitors have charged up it will stop and it doesn't take very long for 55F to charge up with the sort of current a motor will be taking.
Are you Sure you're Sure about any of this?
"Crazy ideas" are very seldom of any use in a hard nosed subject like Electrical Engineering. If a seemingly crazy scheme worked it's because someone actually knew what they were doing and it wasn't that crazy. Don't believe everything you see on TV, either.

 

[michaeljaycla]

I thought about how much power is really there in the capacitors.

Tecate has a capacitor sizing tool where you can size up how many ucaps you would need to supply a contast current or constant power.

My motor controller will draw 600 amps under full power, that would be wide open acceleration.

That won't be drawing that much current very often at all.

so with that said, the tool indicated that 60 capacitors would be able to deliver 600 amps for 11 seconds and the ucaps will still have 30 volts left.

600 amps will only be the launch of the vehicle when i want that much power.

that and seeing other cars with non super caps indicates there is something here.

I have seen pictures of a 15000 pound boxvan launched to 45 mph by 136 2600 farad ultracapacitors.

 

[sophiecentaur]

Capacitors don't have "power" in them. They store Energy using Charge separation.
Perhaps you could talk us through how your circuit is supposed to work. You ignored my last comment on the way the circuit would work so I assume you don't know. Are you planning for some switching to be employed?

 

[michaeljaycla]

This circuit is going to be in an electric vehicle. The motor controller will be a soliton junior that can deliver 600 DC amps on a constant basis.

the ultracapacitors will be in parallel with the batteries at this point. That seems to be the least expensive way to do these tests at this point.

 

[sophiecentaur]

Do you know of the exact situation when you connect a capacitor in parallel with a capacitor? It is very different, practically, when compared with a couple of AA cells in parallel with a few F.
Is this a well known strategy for temporarily eliminating the effect of the battery internal resistance or is it just something you wanted to try? The battery will still get a pretty good caning under a heavy load as it will be expected to recharge the capacitor with some pretty high currents (feeding into an effectively very low series resistance.

Are any people with real experience reading all this?

 

[michaeljaycla]

the capacitors will not be whiched in and out of this circuit. they will remain in parallel the entire time.

the only time there will be a draw of more than 250 amps from the cap and batt banks is under acceleration. the caps will deliver the current under demand and the batts should start filling the caps as the caps send their current to the motor controller.

I have inquired what the amperage draw would be on the batts as this happens but because of the amount of varibles involved, it cannot be calculated.

A 600 amp shunt will be placed on the positive cable going to the motor controller from the batt bank. the same for the cap bank. these measurements will decide the argument once and for all.

the test vehicle is a 1994 chevy s-10 that weights 4500 pounds. the batteries are brand new, 24 235 amp hour deka pro master series 6 volt batteries. the next test vehicle is a 1996 gmc jimmy.

 

[sophiecentaur]

At least you've changed from series connection to parallel (title and OP). ;-). That makes some sense.

 

[michaeljaycla]

Maxwell says in an email that series can be done but with some extensive control circuits to be sure the caps never try to send current back to the batteries and flow backwards.

we'll try parallel for now.

 

[sophiecentaur]

Unless you are trying to use your capacitors at excessive voltages there is absolutely no point in using series connection. It just means that the resulting net capacity is significantly less.

A lot of potential problems are hidden within that magic word "control". What could work at 'signal levels' is a lot more difficult to implement with 100s of A.

 

[Fish4Fun]

sophiecentaur,

Thank you.

michaeljaycla,

As I have stated, my greatest worry is for your safety. You do not have a clue what you are doing, and you are playing with some very dangerous components. You have continually rejected good advice, and insinuated that the good advice was in some way attempting to hinder your "valid" experimentation. NO ONE here is trying to stop you from experimenting, we (I) am simply trying to prevent you from catastrophic failure. You are bent on catastrophic failure, so, please do it without putting others in harm's way. Obviously at this point that is the best we (I) can hope for.

I have shown in simple math that you have not demonstrated a valid use for the capacitors. You keep waving your hands and talking about concepts you do not even partially understand. Go for it, but please make sure there are no innocent bystanders near-by. You are headed down a bad road.

I do not know how to make it any more plain.

Fish

 

[leokunz]

you have probably found a lot since u last posted on this thread. I have a question and i think u can help me.

I have a 22V Lipo with 150A max discharge, 2.7V, 130A maxwell ultra cap 3000F. a 42V, 23A Solid oxide fuel cell, 800 to 1000W dc brushless motor 45A. i want to design a parallel hybrid system. any advice?

 

[muskoka1030]

Fish4Fun wrote about two capacitors, one charged, the other not, connected with a switch, calculating the stored energy before and after:

>Now, Close the switch and:
>
>Vf = (0.01 + 0) / (0.0001 + 0.001) = 9.09V
>Uf = 1/2 * 0.0011 * 9.09^2 = 0.0454J
>
>Please Note Efficiency = (1 - 0.0454/0.5) = 91% Energy Loss!
>
>I honestly cannot explain where the energy "goes", some references state that it is
>lost in I^2R losses while others simply show that it is "gone".

The current must flow in a loop when it flows between two capacitors equalizing their voltages. Close the switch and there is a very high current in this loop for a short period of time. For "ideal" capacitors that are able to output infinite currents at full voltage (no internal resistance) and zero resistance wires, all of the energy goes into an electromagnetic pulse or radio energy. Adding real internal resistances to the capacitors and wires, most of the lost energy is lost as I^2R energy, heat in the components, but still some is lost as radio energy.

A spreadsheet calculating (for a series of small timesteps) the currents, power losses, and total energy losses to I^2R resistances will provide an idea of how much is going to radio energy.


In general, I agree with the other posters, Michaeljaycla is in danger of making a very high energy event by accident and hurting himself or others. If it is a sudden discharge, or equalization, then radio enthusiasts all over the world may hear it as a single crackle in the background static.

I do not believe ultracapacitors are at all necessary for an electric vehicle. Buck-Boost switching power supplies, using massive inductors, and modest capacitors can be switched at high frequency. Something like this can provide the smooth acceleration in response to various accelerator positions. The batteries supply a more constant current to keep the input side capacitors charged, output side capacitors can smooth the voltage to the motor. Again, the key is high frequency to keep the voltage change on the more modest capacitance capacitors small.

Q = CV
Delta Q = C (Vi-Vo)
Average Current during discharge = C(Vi - Vo) / Td

Td = time for discharge
Tc = time for charge

Average current drawn from batteries over a full cycle = C(Vi - Vo) / Td * (Td / (Td+Tc))

Switching frequency = F = 1/ (Td + Tc)

So the average current drawn from the batteries = C(Vi - Vo) * F

C * F is now a tradeoff for a particular average current. Lower Capacitance requires a higher Frequency. Throwing some numbers at that,

If C = 10,000 microF, F = 10 kHz, Vi-Vo = 5 volts, average current = 500 A ?

For a 170 V battery bank (capacitor goes from 170V to 165V back to 170 V during cycle), that is 65kW or close to 90 hp. That is a lot of power for an electric car motor.

 

[Baluncore]

Switching DC from submarine batteries can be surprising.

Submariners in WWII gave the most frequent and consistent accounts of small ball lightning in the confined submarine atmosphere. There are repeated accounts of inadvertent production of floating explosive balls when the battery banks were switched in or out, especially if mis-switched or when the highly inductive electrical motors were mis-connected or disconnected. An attempt later to duplicate those balls with a surplus submarine battery resulted in several failures and an explosion.

 

[muskoka1030]

In a buck / boost circuit, there is a diode or power fet providing a path forward for the motor current when it is disconnected from the batteries. The inductance of the motor is being used to pump power from the ground rail when the power shuts off. This uses up the energy stored in the inductance and, if the power were to remain shut off, the current through the diode would go to zero over a safe period of time.

 

[TRLWNC]

I have been thinking about an idea I came up with a while ago, and decided to do some research, and ended up here. After reading this thread, I realized I am WAY out of my league. But, let me present this and see what is said. (Please be nice, it's a hypothesis, not a reality.)

I want to send power to a capacitor (bank, obviously) that will power a battery and motor in parallel. The battery will charge, and the motor will run from the power supply until the battery is charged (enough) to run the motor for a while, thus allowing the engine to be shut off, saving fuel.

I have put this idea into a video on You Tube:


Please bear with the quality of the video. I am not wealthy enough to have a good monitor OR camera. Thanks.

I shared this with some others I know, and got a wake-up call about the capacitors, so don't flame me about the run time of a capacitor. Read the note I added below the video, and let me know if I am totally off my rocker or if this idea has any merit.

Thanks before hand,
TR

 

[mistareno]

Like the original poster, I have been thinking about using a bank of Capacitors in an EV.

Maxwell make a 125v Transportation Module with balancing and cooling integrated into it.
http://www.maxwell.com/products/ultracapacitors/images/ultra_125v_transportation_module_cameo.png

They are used in electric forklifts to reduce peak loads on the traction batteries which greatly extends both the charge life and the service life of the battery.

I have however struggled to find out if the unit runs in parallel, but can only assume it does as it mentions that the cap bank must be disabled to prevent accidental vehicle movement when the battery is out.

It may be possible (in my feeble mind) to run the bank in series too.

If the nominal voltage of the EV is (for arguments sake 72V) but the controller and motor are rated to handle a peak of up to 200V and 1000 amps then all that would be needed to integrate the two in series would be a control unit that detected a predetermined Amp draw value (say 250A) was being pulled from the traction battery by the controller.

When this occurs, the control unit switches a secondary contactor and feeds in the Capacitor bank energy in series with the battery, instantly providing the controller with a surge of energy to get the motor started or to accelerate (where current draw is at it's highest). The contactor would remain open until the current draw falls below the target value (this may result in complete discharge of the Caps) and then close.

The driver would be unaware of any transition as the capacitors taper off in discharge over two or three seconds at which time it falls back to the battery output.

The charge circuit for the cap bank could feed from the batteries via diodes (to stop the caps trying to charge the batteries under high load) and also from the vehicles regenerative braking system, where they can accept much higher charge levels than the battery.

This is what I want tor use - http://www.maxwell.com/products/ultracapacitors/products/125v-tran-modules