# ultracapacitors and batteries

Discussion in 'The Projects Forum' started by michaeljayclark, Mar 13, 2011.

1. ### michaeljayclark Thread Starter New Member

Mar 13, 2011
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have an idea for a circuit:

60 ultracapacitors and 26 6 volt deep cycle batteries in an electric vehicle

can these be placed all in series?

C = Ultracapacitor
B = Battery

Motor - Controller -(60 C 2.7 vdc each 160 vdc) - ( 26 B 6 vdc each 156 vdc))

This type of circuit is already in an electric vehicle but the capacitors are in parallel with the batteries.

2. ### beenthere Retired Moderator

Apr 20, 2004
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What would be the purpose of the ultracapacitors in series?

3. ### michaeljayclark Thread Starter New Member

Mar 13, 2011
16
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the ultracapacitors would take the initial power drain (600 amps DC) when the vehicle starts from zero mph. the batteries should be able to fill the caps as they drain, the capacitance of the capacitors is 50 farads. they are 3000 farad maxwell ultracapacitors. the ESR of the capacitors is a total of 17.4 milliohms.

from these numbers I believe as the capacitors drain at 600 amps the batteries will be filling the ucaps back up. at 17.4 milliohms the batteries would be able to fill the caps and not see over 200 amps.

the purpose of this circuit is to eliminate the peukart effect on the batteries and to eliminate the voltage sag. this should make the batteries be able to deliver the maximum amount of rated amp hours, in this case they are 235 amp hour batteries, and have a longer lifespan.

the batteries in this case are lead acid. the goal is to give the EV more range and make the batteries have a longer lifespan.

4. ### beenthere Retired Moderator

Apr 20, 2004
15,815
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You have a series circuit, so current in any part must be the same in every component.

Placing capacitors of any sort in series with batteries feeding a motor will effectively block the DC current (that's part of the definition of a capacitor). Your action
is very close to perpetual motion. If the motor needs 600 amps, then something has to provide that level of current.

This can be a very simple experiment to conduct with some loose batteries and some capacitors. See what happens with the capacitors in series with the batteries. Then in parallel. If you have a meter, you can watch current and the voltage sag. Arranging a load on the motor will exaggerate any effects.

Aug 27, 2009
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6. ### Papabravo Expert

Feb 24, 2006
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Doesn't look like a series circuit to me.

7. ### michaeljayclark Thread Starter New Member

Mar 13, 2011
16
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not going for perpetual motion, just range extending. no generator or process in the world can produce more energy then you are using to propel a vehicle, of course i wish there was. all we can do is try to make the energy system more efficient and try to counteract the things that try to make it inefficient.

the battery's amp hour rating is 235 amp hours however that drops depending on the discharge rate. good ol peukert.

In an electric vehicle, the further you go in range the higher the amount of voltage sag occurs.

eliminate or greatly minimize those two factors and the EV can get the full, or close to the full, 235 amp hours from the battery.

lowering the amount of discharge the battery sees also drops its temperature. heat is one of the biggest killers of batteries. The nickel metal hydride battery is very susceptible to heat and I know at least one owner of a 2002 toyota RAV4 EV whose batteries were damaged by heat from a high current charger.

my main question would be with the capacitors between the batteries and the motor controller would they be able to replace the energy that is used by the motor controller that is sent to the motor.

with a total esr in the entire string of capc at 17 milliohms, I believe the batteries can keep up and not discharge at a high rate.

Ill experiment with an existing EV I have at my house, a 1994 chevy s-10. Ill put a shunt between the capacitors and the controller and a shunt between the batteries and capacitors to see what the amp ratings are during the time that the truck accelerates from zero to what ever speed it can maintain.

with a tool from maxwell's distributor, tecate, has a sizing tool that can calculate the energy in the capacitor string and tell you how long the capacitors can deliver a determined amount of energy.

http://www.tecategroup.com/ultracapacitors/designtool.php

I gave the constant current tool 11 seconds at 600 amps and the capacitors can deliver the 600 amps for 11 seconds and still have 20 volts left, meaning they will not be completely drained.

so how many seconds does the batteries take to replace say 100 volts in the capacitors?

since Im not very good with formulas, the only constant I can provide is I do want the batteries to see a discharge rate above 200 amps. with the low esr of the capacitors I dont think thats a problem however can a formula be calculated to see if I am correct?

8. ### michaeljayclark Thread Starter New Member

Mar 13, 2011
16
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the mit study is for a lightweight cart with low current. the components they used could not handle the current I am looking to use.

9. ### Kermit2 AAC Fanatic!

Feb 5, 2010
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You say the battery will fill the caps back up. Think about that and then describe to me where the energy will come from to provide 'extended' range.

The batteries are a source. The caps are simply storage. They can provide nothing more than what they are given from a SOURCE.

If you do not provide MORE source capacity the battery will not extend range even one inch.

Improving 'efficiency' of the torque producer(the motor). Creating an environment in which energy from the source is utilized more completely. Resulting in increased range FROM THE SAME AMOUNT OF ENERGY. Your previous post seems to be saying that you think the caps will increase the batteries amp hours. Nothing but more/different batteries will change the amp hours of the battery.

10. ### nsaspook AAC Fanatic!

Aug 27, 2009
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It's not parallel, look closer. The 150F 16V cap is in series until discharged then it's turned off and bypassed by the right set of SSRs for battery power. The first set of SSRs on the left select the battery power or place the Ultracap in parallel with the motor for regen brake recharging.

11. ### michaeljayclark Thread Starter New Member

Mar 13, 2011
16
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this is the way I wanted to build the circuit. the capacitors are in the circuit till drained then removed before they reach zero. they are filled back up with regen then reinserted into the circuit after recharged. for the currents I am using the controllers to do require more budget then I have. Ill be looking into it after the vehicle is finished.

For now I must choose between placing the capacitors in series versus placing them in parallel.

the batteries only have a certain amount of energy yes, but the peukert effect and voltage sag reduces that energy before it gets to the motor. a battery rated for 235 amp hours under heavy discharge will not deliver 235 amp hours. if we remove the peukert effect and the voltage sag from the equation we get more efficiency and thus more range. the same amount of energy is there, i am just trying to get more energy to the motor and reduce the losses from the energy storage to the actual use of the energy.

this can be compared to gasoline engines. there is a set amount of energy in the gasoline. if you can make the engine more efficient it will be able to use more energy from the gas to go longer distance. increase miles per gallon get more distance. for electric vehicles, reduce the amount of watts per mile used and increase the range.

12. ### mjhilger Member

Feb 28, 2011
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It looks to me like it is contrable depending on settings for the MOSFETS, it can be in 3 configurations
1) Caps supply energy for motor
2) Batteries supply energy for motor
3) Caps & Batteries are in series to supply motor

Looks like versitle routing setup, but not sure the series setup would do much as the current would be same through all components. Maybe if the batteries were low and you pull the regen from braking into the caps, the extra voltage capability would provide boost for low battery, but would drain very quickly. Will be interesting to see how the MIT team uses it.

13. ### michaeljayclark Thread Starter New Member

Mar 13, 2011
16
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I emailed maxwell regarding if the circuit is feasible or benefical or if just placing the caps in parallel with the batteries is just as well.

14. ### shortbus AAC Fanatic!

Sep 30, 2009
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Just like Kermit2 said the capacitors being charged from the BATTERIES is not going to help. They are still being charged by the batteries, still giving the same 'peukert effect.' You must charge the capacitors from a different source (regen braking) to make any difference in the end amount of energy expended.

Your not going to get a different answer here than you did over on the Electro Tech Online site. The same laws of Physics apply here. Like they told you, go to an 'over-unity' forum to hear anything different.

15. ### michaeljayclark Thread Starter New Member

Mar 13, 2011
16
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I know the batteries will still be charging the capacitors but not at 600 amps. the question I am trying to get is what will the batteries see as far as amperage charging the capacitors actually equalizing with the capacitors once the capacitors are drained and have yet to get an answer.

maybe because the answer cannot be calculated? that would make sense.

other reason is there are EVs that have capacitors and they are seeing the peukert effect eliminated. They only have the capacitors in parallel with the batteries. I am working with an EV owner that would like to see how this works with the capacitors in series that has capacitors in parallel, so before I wire things up Id like to see if the outcome can be calculated.

Ive seen a 15000 boxvan accelerated with ultracapacitors to 45 mph.

An EV1 was loaded with capacitors in 2003 without the batteries and it did the 1/4 mile in about 15 seconds.

16. ### beenthere Retired Moderator

Apr 20, 2004
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You may be having that problem with an answer as it is close to impossible to parse that sentence.

Can you draw up a diagram of your battery and capacitor arrangement?

17. ### nsaspook AAC Fanatic!

Aug 27, 2009
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2,163
With the capacitors in parallel with the battery you can never fully use most of the energy in the cap because as soon as the voltage drops to the the battery loaded voltage the battery will supply almost all the current then. Only in a 'Pulse' demand system of usage will the capacitor provide any cost-effective advantages over just a battery only.

This is a link provides a model for a battery/capacitor energy source.

http://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=1262142

An account might be necessary to see the entire document.

18. ### Wendy Moderator

Mar 24, 2008
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2,535
Putting 2 capacitors in series halves their capacitance (and doubles the breakdown voltage), and it only gets worse when you add more capacitors.

The point of the battery taking over when a capacitor is discharged below the battery value is also a good one. Both batteries and capacitors are storage devices, but the battery is a constant voltage (relatively), while a capacitor is not (look up RC curves).

There is an effort to use capacitors as batteries in cars. There are technical issues, it is far from perfect, but it could be solved eventually. The cap is charged to over 10 thousand volts, and the charge is slowly metered out via electronics. I can hardly wait for the technical questions on that mess on this site. Google eestor.

Last edited: Mar 14, 2011
19. ### shortbus AAC Fanatic!

Sep 30, 2009
4,003
1,521

To get 600 Amps out of the capacitors, you have to put more than 600 Amps into them. The battery doesn't know whether it is charging the capacitor or turning the motor, it's still it's using power to do it.

The boxvan and the EV1 both were charged from a outside source, Not the on-board battery.

You can't get something from nothing.

20. ### steveb Senior Member

Jul 3, 2008
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Stop accusing the OP of trying to get something for nothing. He has made it clear that this is not his goal. He is trying to improve efficiency by combining caps and batts which is possible in some applications. If you believe this application is not one of them, then stick to that fact. If you believe his approach is not effective, then stick to that issue. If you have another point, then make it without a false accusation. This type of accusation is quite insulting to most members here.