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electric vehicle and ultracapacitors

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michaeljayclark

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I have 52 maxwell 3000 farad 2.7 volt ultracapacitors.

my project is to wire them in series to get 140 vdc.

the electric vehicle is a 1994 chevy s-10 that has already been converted to electric. It is a DC system similar to a golf cart.

the motor is a 9 inch 72 volt DC motor. The controller is rated to work with 144 volt system and is rated at 500 amps. the transmission is the existing manual transmission.

the truck weights 4300 pounds. It has 24 6 volt batteries wired in series to give 144 vdc.

My project is to unhook the batteries, and hook up the capacitor pack. I want to see how far the truck travels just on the capacitors. Since I am not an electrical engineer, i want to know if the capacitors can be drawn down to the point the truck stops.

will this damage the capacitors?

this is just one step in my project but a very im portant one, I do not want to blow up 2000 in capacitors right out the gate
 
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Drawing them down will not hurt them but I suspect your controller will have some sort of minimum voltage shutdown point.

Relating to far as how far will it go well you can hold your breath on this one literally being they will run out of power before you are done holding your breath that is. :(

Your $2000 investment will likely have been far more useful someplace else.
 
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previous uses

well my real question was would they be damaged.

as far as distance I am not expecting any distance, just a way to start the vehicle and get up to speed before then switching to batteries.

a case was made that a capacitor bank of 2600 farad supercaps was able to start a 150000lb box van from 0 to 45.

trying to extend range and save the batteries from the outrush of current at 500 amps dc

there have been studies made by the doe, mit, and other electric vehicle builders with capacitors and all show promise.

The cost is high i know.

my next question would be once the vehicle is moving and the controller says there is no power to use I would need a current controller so the batteries can recharge the capacitors. ill be able to see where the controller starts to quit and then contactor in the batteries. if i just click them together the batteries would see a short and the outrush of current I am trying to save them from would happen anyway.

ive seen lightbulbs used as current limiters to precharge capacitors, but i suspect the amount of current I am trying to move from the batteries into the capacitors would be more than an average lightbulb can take, of course it would not be just ONE lightbulb... but if i must i guess i can use 52 lightbulbs, one for each capacitor.

so.. what can I use other than a lightbulb?
 
I am not sure of all the logistics of what you are doing other than those capacitors have to stay under their 2.7 volt working limit and having 52 of them stacked in series is likely going to be a big balancing problem without some level of automatic voltage control or limiter for each one in the stack.

I don't see what the purpose of trying to save your batteries from a 500 amp load is for. For a good quality deep cycle thats no different than when starting any normal big engine. I had a Ford Electrica some years ago that used 16 6 volt 220 AH golf cart batteries and they had no problem handling 500 amp peaks after I rewired the controller to take them that far. The cabling and connections are more of a concern than the batteries at that amp load.

In regards to current limiting the capacitor bank I don't see why you would want to be dissipating useful energy in the form of heat with a current limiting device. At 144 volts any common 120 volt rated light bulb will do just fine as a current limiter. If it was me I would be looking at using the capacitors in part of a regenerative breaking system and not charging them off the battery's.

Taking energy out of the battery's and putting it into the capacitors has energy losses associated with it and then taking that energy out of the capacitors and using it to move the vehicle has more energy losses again. I see two energy loosing steps being used to do the work of one in a system that has a finite amount of usable energy to work with as is.

Thats just my thoughts anyway.
 
ev and ultracaps

that is true... we wouldnt want to waste the energy but we need to control the current flow from the batteries to the caps if that is the reason.

the regen would fill the capacitors first then the batteries if any energy is left after the caps are refilled. this would mean a connection from the caps and batteries so that almost dead short may exist in the scheme of things.. the caps would suck amps all day but the batteries would die very quickly.

so i thought this system would be better served that the caps would be for take off from zero and to be refilled by regen. and be seperate from the batteries all together.

but there will be cases when the regen energy might be more than the caps and therefore needs to be placed into the batteries or be wasted.

also when the caps empty when the vehicle launches the motor controller cannot be disconnected from the caps and then connected to the batteries. the controller shuts down when the energy is taken away. so before the contactor or other device disengages the caps, the battery pack will be in parallel to the caps for a brief second, but still the flow needs to be controlled.

so this leads me to a question about the lightbulb. if the lightbulb can handle the voltage, what about the amperage? if the batteries are set to replenish the caps we would want to do it at a high enough amperage, 100 amps or so.
 
Not to be rude but it sounds like you need to learn a lot more about electrical and electronics physics and practical application of that knowledge.

What you are asking and saying does not add up on this end.
 
not rude at all... I know Im not an electrical engineer by any means and I am just learning this stuff.

Im just trying to put together what Ive learned, and to slapped in the head and told, this is it, not that then so be it. Ive been told I have a hard head.

I have seen this system in action, afstrinity.com, and Ive been told that it wont work, but yet it does. MIT is still doing projects about it with ultracaps. A EV group in texas uses ultracaps in their systems.

I posed a question of how many capacitors would it take to "dump charge" a battery pack in a vehicle that has a 33 kilowatt hour pack. I got the same reactions, the same "why would you even think of that?" yet, the tennessee transit authority, which is the most forward thinking transit in just about all the US has buses that do just that, a quick recharge from caps into the batteries of the buses.

Id like to know how this can be done, without cost being a factor. I know the ROI of this syetm is way out or not even there.
 
The way I learned energy charges is with Farads. Farad - Wikipedia, the free encyclopedia

Using the F = (A * S)/V formula a battery can sort of be modeled as a super massive capacitor in theoretical terms.

So say you have a 220 AH 6 volt battery and you can theoretically use its full rated charge of 220 * 6 = 1200 watt hours.
In Farad terms thats 220 amps times 3600 seconds divided by 6. (220 * 3600) / 6 = 132000 farads. Now you take that times your 24 batteries and you get a theoretical capacitor equivalent of 3,168,000 farads.

As you can see it gets to be absolutely massive in terms of a capacitor equivalent meaning your 52 3000 F capacitors still only add up to an energy storage of 156,000 Farads or roughly 156,000 / 3,168,000 which is about 5% of your battery capacity in theoretical terms.

However being capacitors exhibit a fairly linear voltage drop as their charge is used up you only get 10% of that available energy going from a 144 volt peak down to 130 volts where as the battery's give you about 90% of their energy capacity before dropping that 10% of their working voltage.

When thats factored in your capacitors are down to roughly .5% of the battery's usable discharge energy for the same voltage drop. :eek:
 
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batts and caps

I think we are uncovering something here. in theory i agree when you compare a battery to a capacitor the numbers are huge. I think the purpose of the two is where the numbers seem to change a bit.

batteries are meant to be able to store energy and release it slowly. There is a push to make batteries deliver energy faster however the batteries are still stuck at 3C discharge rates for prismatic cell lithium ion phosphate (Lipo) and 4C with cylindrical cells. each of these rates creates high heat and the cells will fail quicker. Even Nissan says about the lithium ion cells in its Leaf will fail prematurely if the pack is charged with level III charging, 440 volt 100 amp charging.

capacitors are designed to store energy but release that energy almost instantaneously. and over time designers are trying to make capacitors act like batteries. I checked with maxwell about how fast maxwell ultracaps can be drawn from and received this reply:

Please note that the rated current for the 3000F part is 130Arms @ 15C rise and 210Arms @ 40C rise. The caps have to be appropriately cooled to keep the temperature rise within specifications, while drawing large currents.

It is safe to discharge the caps fully.

I read that the 3000 farad 2.7 vdc cap is almost equal to a 1Ah battery!


the BIGGEST difference between the two is the internal resistance. I think if we can add in the internal resistance to the equation I think we uncover what is happening here and why I am meeting more people that say ultracapacitors can be paired with batteries that the ultracaps will do what they are designed for, to deliver the large currents and charge up quickly and help the batteries do their job of releasing energy slowly and charging up slowly, well not slowly but slower than capacitors.

the ultracaps I have have an internal resistance of .23 m ohms.
a lipo cell made under the headway label has 11 m ohms ( I found higher numbers but we'll go with that)

afstrinity.com is a saturn vue that uses this system I am describing here and they say testing shows the LIPO pack of batteries to last 10 years and 150,000 miles when helped by ultracapacitors.

Id like to have the same protection for my batteries. Ive talked to a north texas ev association and they are using a regular cap pack and see a increase in range.
 
I know exactly what you're getting at and what you want to do.

When the vehicle is braking, you want to recover energy by using the electric motor as a brake, and store this energy. Under heavy braking, this could be a significant amount of energy - more than what the batteries could accept at their recommended charge rate.

So you take this regenerated electrical energy and dump it into a bank of capacitors, which can take more current in a short period of time than the batteries can. Once the capacitors are charged up, if you're still braking then excess energy goes to the battery pack, at a reduced rate the batteries can handle.

When you accelerate from a stop, you want to first use the energy in the capacitors (since this is basically free energy you recovered from braking), and once the capacitors have been discharged you switch to batteries.

The advantages of this system is that you can recover more energy from braking as you are not limited by the charge rate of your battery pack. The disadvantage is a far more complex and expensive controller. And this is going to be your biggest problem. Using a bank of capacitors with an electric vehicle is not as simple as "connecting them up alongside the batteries". I consider myself to have a very good understanding of vehicle electrical systems (it's what I do for a living), and building a controller to do what you're describing is light years beyond anything I'd ever want to attempt (which means you're going to have to buy one from someone and that's going to be very expensive).

Even afstrinity.com states one of the biggest challenges was creating the electronic controller to integrate capacitors, batteries and the motor control. If a company of electrical engineers found it "challenging" to make such a controller, what foes that say about how complex such a system is?
 
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Well,

Your 2.7V ultracaps need to be protected from overvoltage. This means you need a 52 channel balancing and protection circuit. This is not complicated to do (for an EE) and not very expensive, until you multiply everything by 52, at which point it is likely to be big, very expensive, very long to build, and not necessarily very reliable, unless even more complex and expensive protection circuits are added.

Note that running a 2.7V rated capacitor at 144/52 = 2.692 V leaves absolutely NO margin for error. Some derating would be needed, perhaps 2.5V, meaning 56 caps, or 130V.

Ultracaps are not batteries. A battery has a rather constant voltage, a capacitor does not. In your case, once the capacitor bank goes from 130V (full charge) to 72V (controller shutdown) you only extracted about 70% of the energy, and 30% remains in the capacitors. But 70% is good enough.

Same thing for regen braking : if you want to store energy in the caps the voltage across them needs to rise. So you can't parallel them with the battery, you need a dedicated controller.

I've made a simple 2.5V 10F supercap controller using a bidirectional buck-boost converter for my dynamo bike light. It's quite simple and cheap. At 130V and 500 amps, it's a different game entirely. Besides, in the end, I dropped the supercap and used LiIon instead, energy/weight ratio was just too bad.

Draining your 52 caps from 130V to 72V gives you 600 kJ of energy which, assuming 80% efficiency, is enough to accelerate your 2 ton tank to about 80 km/h, which is good. So regen braking and then reusing the energy to reaccelerate would work, but you'd need a monster controller.
 
the protection boards are already made by maxwell for the super caps. its 1000 dollar investment but if it saves the caps then i could get the funding for it.

It is the firm believe in the EV world that a DC motor cannot regenerate or it will destroy itself. I have a single phase AC generator that will do the regen. It will be in front of or beside the traction dc motor and have a clutch that will engage it when I hit the brakes and do the regen. I already have a bridge rectifier that changes the AC into DC. the energy then can be directed to where it needs to go.

with an active balancing system within the capacitor bank a circuit could be established that when the caps are full a contactor or some kind of circuit then directs the remaining energy into the batteries? when I let off the brake the circuit then goes back to the capacitors. the capacitors are full at this point and ready for the next take off.

incase I do not break enough to fill the cap bank, the "bleeder" can feed power into the caps from the batteries.

The buck-boost converter is something that MIT did with a gocart. the size difference here is huge but they gave diagrams and everything to what I am trying to do. Its an interesting read, not to detailed but gives good information.

https://www.electro-tech-online.com/custompdfs/2011/02/everpres.pdf
 
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So for the most obvious question what type of battery's are you using?

I assumed that at 6 volts they where most likely the common 6 volt golf cart type which means comparing C rates for a type of battery you are not using is pointless here.

Also regarding the 2.7 volt limit per capacitor issue and your 144 volt system. My math says 52 * 2.7 = 140.4 so you are already over the rated working voltage for each one at that point.

My view of this whole issue comes down to the practicality of they system and its gains Vs the outright up front costs. Putting $10,000 worth of high end capacitors, safety devices, and charge control systems in a vehicle to get a theoretical gain of only a few percent extended range out of it in stop and go driving seems like a poor use of money and materials.
For me I would have dumped that extra cash into a different type of battery system and made up some driving efficiency by just having far greater overall battery capacity by means of using a form of battery that is superior to the assumed lead acid ones you are using now in its energy to mass ratio and or service life. That is use a lithium based battery system s that is both lighter and of more capacity than a lead acid system.

Just my thoughts as a former electric car owner.
 
the life of the battery pack is where the gain would be seen. afstrinity tested and simulated the batteries would last 150,000 miles and go 3000 plus cycles. they were lithium ion. I would be using lead acid at this point. If I could get a 1500 pack of batteries last 8 years instead of 5 that would be a nice gain.

the EV world is a bit skeptical of the life of lithium ion phosphate batteries. they havent been around long enough to see what the real lifespan has been. The mistrust comes from the fact they are made in china. A123 is three times as much as the china batteries and testing by MIT is showing they are very susceptible to heat and degrade quickly under such heat. the cap system would save them from that problem.

they production evs, volt and leaf are giving 8 year 100,000 mile warranty on those lipo batteries but those batteries will not get to consumers for quite some time and when they do the price will be huge. Id imagine some people have their eyes on the junkyards and told them any volts or leafs that get there they have dibs on them already to see about getting the batteries, or even insurance yards and volts or leafs that end up there will be grabbed immediately.

Now if I could get my hands on a 100 amp hour pack of nickle metal hydride bateries the same used in the rav 4 ev from early 2000, the life on these batteries are 8 years in some cases! they HATE heat so this cap system would save them from heat and possibly extend them to 10 years!

so us lowly home ev builders are stuck with china lithium batteries or lead acid ;(
 
While I find discussing electric vehicles and technology interesting, I find the idea of building one myself rather silly. I've visited the various forums and sites for people making these vehicles and I can't help but be reminded of articles on Brown's Gas.

Sorry, but I just don't see the point of trying to make something so expensive and complex when you'd be better off to just buy an existing hybrid or electric car.
 
While I find discussing electric vehicles and technology interesting, I find the idea of building one myself rather silly. I've visited the various forums and sites for people making these vehicles and I can't help but be reminded of articles on Brown's Gas.

Sorry, but I just don't see the point of trying to make something so expensive and complex when you'd be better off to just buy an existing hybrid or electric car.


In a way that has been my main reason for not participating in those sites either. Ignoring their obvious over design and related costs and accepting the looses seems to be the last thing they want to hear or discus.

I had an electric car. It was a Jet industries conversion of a 1983 Ford Escort hatch back. Even though it was based on 1980's tech used 16 6 volt 220 Ah batteries and weighed over 4000 pounds it could easily do 65+ MPH on the highway for about 20 miles and if driven conservatively it has a good 35 - 55 mile driving range on one charge. It had no fancy regenerative braking or ultra capacitors but just a basic 500 amp PWM speed controller and drive motor similar to that of a common electric forklift.

Unfortunately I don't drive conservatively and where I do need to go is further than its average range at highway speeds would allow so I sold it to my mom and her husband in Iowa where it is still being actively used today.
 
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I have an electra that is in pieces, the motor and controller and such had been left out in the elements and are wasting away. the car is junk a big piece of rust at this point. got it free so id figure we can try to save it but i dont think so.

$10,000 to build an ev compared to buying a $41,000 volt or $32,000 leaf is pretty good. even spending $20,000 is good. still puts you ahead. a 2009 or earlier prius can have batteries added to it that cost $10,000 and make the first 50 miles all electric. the prius selsl for $25,000 or more so that still puts them in the $35,000 area. a hybrid can at best get 50 miles per gallon. an electric car goes 100 miles on $3.00 of electric so now that compares to 100 miles per gallon. when gas goes up and it will that miles per gallon will raise.

to drive a gasoline hybrid costs $1000.00 a year if you go 15000 miles per year. thats 6.5 cents per mile just for gas. add in the oil changes, the filter changes, the cost of repair of the gasoline engine over time and that cost can double. also dont forget gas is going up. so those numbers go up.

to drive an electric car costs $450 a year for electric for 15000 miles. thats 3 cents per mile. there are no oil changes, no filter changes, and no repairs to a gas engine. the battery carries a 8 year 100000 mile warranty. the cost of the battery for the leaf RIGHT NOW is in debate but it seems the average is $10,000. thats todays price and doesnt really account because the next eight years is all under warranty. if the battery was to fail due to failure within the 8 years say at 6 years, you now have a new battery pack and now have another 8 years before you have out of pocket expense. as production rolls on the price will drop for batteries. consumer china batteries for us ev builders is $333 per kilowatt hour or $1.25 per amp hour. I will admit however if the car companies jump ship on the electric cars the owners are going to trade in their electric before the warranty expires I am sure.

me lead acid pack will cost $1100 and last 5 years, maybe more with the capacitors. that means I am spending $2200 per 10 years for my batteries.

now I can really make electric cars cheaper by the miles if you charge from solar panels at home. This is actually the way it should be and makes the most sense.

driving electric has advantages in that you are not tied to the pump and a price that rises. it has fallen over the years but the cost of extraction of oil isnt going down and opec has admittedly said they like 100 a barrel and will keep production to make it that price. we are also seeing evidence of peak oil. it was predicted in america and we reached our peak about 1970.

and as far as oil goes, there is many more factors that make the price higher. The price which cannot be even calculated is human life. 100's of thousands of people have died for oil over the last 100 years, maybe even a million.

I would just like to drive electric, charge off solar panels and not even think about oil for my car. I am not a supporter of man made global warming at all. so that isnt even a thought.

if you prefer gasoline hybrids, I say everyone has choices to what they drive and noone is wrong.

so with that out of the way, how about getting back to the project, even if it is theoretical. I am sure many have had this discussion about ultracapacitors and Id like one to end with a solution rather than forget it, it costs too much. :)
 
I can relate tot he cost per mile equivalent thing very well. I have set up all of my pickups to have dual fuel propane systems. I even did my last one as a full propane only engine as well. https://www.electro-tech-online.com/threads/mazda-b2600-full-propane-conversion.110835/

My Mom and her husband charge the Electrica from their off peak power system so it only costs about 3 cents a KWh which works out to around 1 cent a mile the way they drove it.

I like the idea of electric vehicles for specific applications but at this point too many of them just don't justify the cost Vs what you get for the price. Most are not any better for realistic driving ability's and range than what was available 30 years ago despite having far more price and likely unnecessary complexity in them now.

Considering electric propulsion system tech has greatly advanced and lithium based battery tech pushes a near 10 to 1 power to size ratio over the old lead acid storage battery's thats where I have issues with the new tech being electric cars didn't gain any substantial driving range or capacity in 30 years despite the ten fold gain in the parts and tech that powers them.
 
the tech hasnt changed that much. just the batteries and thats only because every cell phone has lithium ion. not the same for electric cars of course. laptop batteries as well but not the same chemistry.

a new dc motor controller was just designed last year to replace a dc motor controller that was designed 10 years ago and is far superior. the ac systems have been improved but are not within reach of the ev builder unless you want to spend $50,000

part of my goal here is to also show that DC systems still have their use. Higher voltage dc systems are coming into play. The dc motors are crosing the 200 volt threshold and ge has a motor that can handle 300 volts dc.

lithium ion is here but they cannot handle over a continuous 3C discharge and charge without being damaged in some way.
 
now I can really make electric cars cheaper by the miles if you charge from solar panels at home. This is actually the way it should be and makes the most sense.

How many solar panels would you need to charge your batteries over an 8 hour period (or however many hours of sunlight you get in your area in one day)? Taking into account the amount of energy that gets stored in the battery vs the amount you put into it (since batteries don't charge at 100% efficiency).
 
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