Capacitor Pack Recommendation

"buffer any over charge"? If you think that will happen, or that capacitors will prevent it, then you shouldn't be doing this conversion at all.

 

As someone who is part way through her own DIY conversion of a Prius to PHEV I'd second that. Spend your money on a properly designed charger. When charging the batteries you need to make sure you don't cook them, but any professionaly built appropriate EV charger should do that. I'm currently looking at the Brusa charger range as I'm using OEM NiMH batteries.

I think what you are referring to are super capacitors, but to my knowledge there's not yet been any DIY conversions using them. You can use them for short power bursts and to store charge faster than a battery can - but integrating this in a Prius PHEV isn't going to be easy and to be honest, I can't see a need for it. The Stock OEM pack and PHEV packs can capture pretty high power levels as it is. I'd advise against complicating things with super-capcitors unless you're an EE or have a really good support team!

The Prius' OEM BCU and ECU should prevent overcharging from things such as long downhill regen etc., by using engine braking when the battery becomes too hot or too high a voltage.

If you are in ANY doubt about the conversion get someone else to do it or join the Eaa-PHEV project discussion list. It is not a project that you should get involved with if you are in any doubt about how the HV system works or what is needed. Get it wrong and you may end up with a fried car or worse.

Good Luck!

Nikki.

 

Capacitor Pack is only good for fast acceleration so you don't let the battery pack provide that fast energy

 

My point exactly... and if the stock pack provides 30-35 KW quite happily then what's the point of a Super Capcitor pack? I'd only expect them to be of any use if the batteries you were using had a high internal resistance and couldn't provide a high current...

 

I am an EE, and I can attest that super capacitors have a lot of attractive points. Price isn't one of them. We are still at least a few years away from any practical power packs composed of capacitors - super, ultra, or garden variety. What's more, they have to be handled properly to avoid damage, fires, or explosions.

Leave the capacitors to the experts for the moment.

Tom

 

maybe cheap lead acid batterys in a plug in conversion?

 

There have been some announcements of demo systems but I don't believe there are off-the-shelf units. It is not a trivial problem because batteries are current storage and capacitors are voltage storage.

A battery voltage is driven by the electro-motive force of a chemical reaction and is fairly fixed. What happens is 10% charged battery with no load will have pretty much the same voltage at 90% charge. All that has changed is the ratio of charged vs. discharged molecules and that happens from the electrons, the amps, that convert molecules from one form to another.

A capacitor stores energy by the electric field between the plates. To add energy, the voltage increases by the square root, and to take it out, it decreases by the square root of the voltage. Now the problem is these voltage swings are pretty large, much larger than the battery that tends to hold a relatively steady voltage. So to make a capacitor storage system, you need two switching power supplies: (1) one to charge up the capacitor to store energy, and (2) one to discharge the capacitor and deliver energy.

So what happens if you put a capacitor across a battery? Nothing remarkable. Now if you have a lot of noise on the battery bus, the capacitor will serve as a short-circuit for that noise. Instead of being converted into charged molecules, the noise becomes ohmic heating of the capacitor leads and internal paths. The capacitor would get warm and that energy is lost forever.

Now if you still want to run the experiment, look for motor starter capacitors. You should have no problem finding them in the voltage range of your pack. Your car; your money; have fun.

Bob Wilson

 

The Prius battery pack is rated at 25kW (100 amps) and less when the battery is at temperature limits. But I would be careful in reworking my Prius and I am an Electrical Engineering professor.

JeffD

 

Capacitors and super-conducting coils have their place but energy levels of our battery pack makes them somewhat impractical, today, as a battery replacement or assistant.

BTW, you have some pretty hefty caps already in your inverter. They are used as part of the voltage doubling to bring the 200VDC battery bus up to the 400-500 VDC used to power MG1 and MG2. But in these cases, the time intervals are so short, measured in milliseconds, that the excellent storage characteristics of the capacitors can be used quite handily.

Just remember, I'm a member of the "right tool for the right job" club which means each has its time and place. But using a hammer where a screw driver is needed ... well the results are often disappointing. <GRINS>

For our EE friends, yes the capacitor energy storage varies as the square of the voltage. However, if we are talking about storing fixed quantities of energy, kw-hr or such, the voltage changes are going to be by the square root of the voltage:
0 joules
10 joules
20 joules
30 joules
...
n joules

The voltage between each increment increases by the square root. ... Work it out or better still, put it on a test for undergraduates. <GRINS>

Bob Wilson

 

heck with that. wait until eestor's ultra cap is marketed, ditch the battery pack completely.

 

messing with the battery is very dangerous, i created a charger that used very low charging rate, but enough voltage, this led me to charge the battery until the floating voltage reached half of what the pack was, which was 140 volts on the 2001 prius, then i did the other half the exact amount of time as the other side, let it sit a day and hooked up the service plug to join the two halves together.

you cant just go in there with a screwdriver and touch stuff, the power of the battery will cause arcing without proper tools.

the inverter contains capacitors, as i remember the 2001 prius had three of em, i have to take a look at my pictures.

right now im looking at modifying the gasoline engine to provide better gas mileage, i notice by improving the power output of the gasoline engine you would also increase miles per gallon, my 2001 prius with a coolant bypass, resonator removed, and some problems with my battery gets about 60-70 mpg consistently.

 

Just make sure you use the Oxygen free Monster 4 guage cable to hook it all up!!! Would'nt want to waste a microjoule of that raw reserve power!!!

I believe there is another thread talking about a super brillo pad you stuff up your tail pipe to improve FE!

We should bundle these 2 ideas together and do a group buy!!!

Seems P.T Barnum had a saying .....





Pat KK6PD

 

Hi Pat!

There's a difference between energy and power.

A battery pack has a fair amount of energy stored in it, but can't put out quite as much power as we might like. IIRC, the Prius 2nd gen battery pack is rated at 21 kW.

A supercapacitor might not store as much energy as a battery pack, but it could have a VERY high (100s of kW) power capability. In this case, it would make sense to have a battery with a capacitor that can store enough energy to get the car moving up to 70 MPH or so. That way, the battery stores the energy you need to go any distance, and the caps can provide a high peak power level to permit you to accelerate much faster than you would if you were limited by battery power alone.

That said, the caps will have to have frigging large (10s or 100s of Farads) amounts of capicatance in order to do this.

 

I do indeed like your posts!!!

But isn't there a warning in the owners manual about towing things with a Prius, well like super massive caps with larger than life capacitance/Farad ratings...

The trick would be to get a unit about the size of a car battery that actually does some good!!!

Keep up the Gooooood Posts!!
73 de Pat KK6PD

 

I did a calculation:

Assume the car is going 60 MPH (=26.82 meter per sec)
Assume it has a mass of 1500 kg (roughly 3000 lbs)
Then, the energy is about 540 kJ
(E = 1/2 m v^2)

Assume that the battery is 200 Volts
Then,

E = 1/2 C V^2

Solving for C, you get about 27 Farad

So, all you need is a 27 Farad, 200 Volt capacitor

You could get this by putting about 20 capacitors in series, each one good to 10 volts or so. Each series stage would need to be 540 Farad.

You could build a 540 Farad 12 V cap by putting 270 two Farad caps (like you can buy at Fry's or other automotive sound system stores) in parallel.

270 x 20 = 5400 of those caps that you can buy at Fry's.

Each cap is about the size of a tall-boy beer can, which is about 1/2 liter. So, this would be about 2700 liters, or about 2.7 cubic meters.

The ultracaps that they're proposing had better be quite a bit better than what's on the market today!

And, I bet a short in that capacitor bank would be spectacular!

Feel free to correct the math!

 

well, definitely not disputing the claims that the ultracaps if they perform as advertised, will completely change the face of automotive technology or for that matter, any current battery operated device...

would be nice to charge your laptop overnight and not be able to exhaust the charge during the day... charge your cellphone once a week.... ya it would be nice.

 

I agree with what Khonen above says. My education is not so grand as his or the Prof above, but as a hands on type. BS EET type. I have seen some nasty big caps blow. Not something you want to be around while it's happening.

I think we are close to ultra caps that are safe and efficient but they will be expensive for a while. I would bet that when they are profitable for Toyota and a good deal they will be in the car.