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You can Post any comments, questions, or suggestions regarding this article here on this discussion page. Please note that this page is not the EAA-PHEV_Maillist:.


These should be fleshed out and may eventually warrant their own page, for now they live here.

Energy Efficiency

Need links for items addressing well to wheel, pump to pavement, or cradle to grave energy efficiency.

Plugging in

It takes but a few seconds to plug in once you reach your destination. Though at the gas pump you need to wait arround and watch the thing, make sure it doesn't overflow, noone takes the prescious juice on your dime. The more you plug into an electrical outlet the less time you have to spend plugging into oil and gas.

Prius Controller Questions

Here are some questions from Richard Himley, Anyone want to take a stab at a reply? I'm not familiar enough with the Prius to do this justice.

I just looked at the EAA-PHEV document from Seattle. From that document I would like to have more information about the battery management computer and the hybrid controller. Here is my current list of questions:

  • How do your determine SOC? Is it by amp-hr used or is there some other sensor? Do you have the same capability with the battery pack?
  • One statement is to keep the BOC’s indicated SOC at 80% until we can have significant braking? What is the actual SOC for regenerative braking to be significant and what does significant mean?
  • Why do you keep the indicated SOC between 70% and 80% until the real SOC is near its lower limit? What is that lower limit and how do you know what that value is?
  • What value of SOC for the battery pack is that value which causes a complete cycle of charging? Is that a hard limit or is the number of charges dependent on how far you discharge the batteries?
  • I really don’t have a quantitative measure of the statement "bad for the battery." I know this refers to cycles of charging but it hasn’t been quantified. Not wasting gasoline is a good idea. But might it not be better to waste some in a trade for getting more cycles out of the battery?
  • Also, the controller is stated to "work to discharge the battery" when SOC is above 60%. Does this mean that the Prius is in EV only mode or is there a quantified ratio of gasoline to electric?
  • Statement is made (I think) that EV-only mode is set when all the following is true:
    • Speed < 34 mph
    • Power request (accelerator position) <120
    • SOC > 49%
    • And a few others
  • What is the ratio of gasoline to electric when any one of these is not met? It sounds like it is controlled by only the SOC, but I’m not sure.

PHEV Suplemental Battery Pack


Here is my reply to Richard Himley to a number of questions he had about batteries after looking at Ron Gremban's battery spreadsheet. I answered the ones I knew off the bat, but there are others that I don't know the answers to. Anybody out there have additional information to share on this subject?


Jerry Pohorsky

Hi Richard,

Don't have time to fully research the answers today, but I can answer a few of your questions right off the bat.

1. 2C means a discharge rate twice the amp-hour rate of the battery. For a 10 A-H battery, the 2C rate is 20 Amps.

2. SOC is state of charge. 100 is fully charged, 50 is half discharged. For lead acid batteries it is best to recharge when you get down to 50 % SOC. It shortens battery life to go below 20% and going to 0% really shortens battery life. NiMH batteries can tolerate discharges to 0% much better although all batteries have longer life with shallower discharges. On the stock Prius, the NiMH battery SOC is maintained between 60 & 80 % by the onboard computer controls.

10. Cobasys batteries are not for sale anywhere.

11. Cycle life has not been well tested for most of these batteries because they haven't been around very long. For example, the Valence U charge lithium battery is supposed to be good for 2000 cycles to 20 % SOC but they have only been available for a few months so nobody has put that many cycles on them yet. Some folks think this claim of 2000 cycles is not real.

4, 5, 8. If you have a Prius, you can check the storage area above the spare tire yourself to see how much room there is for the batteries. If not, there are some photos that Ron took that I can post to the PHEV SIG website later that show this area filled with the lead acid electric bicycle batteries (I think he is using 18 of them in two rows of 9 each). This gives a nominal voltage of 216 for the pack. By the way, that is what determines the number of cells. Multiply the voltage per cell by the number of cells to arrive at a voltage of around 216 V. The idea is to fool the Toyota computer into thinking it is looking at the original Prius battery pack. Too low of a voltage and the gasoline motor will turn on to charge the battery pack. Too high a voltage and the pack will not be used at all because Toyota designed it to stay no higher than 80% SOC and they think it will be overcharged.

If the NiZn battery is the same as the "Zebra" battery, it is not a good choice. This battery needs to be kept at a high temperature (400 degrees, I think) and is still in the experimental stage.

I would have to look it up, but I think the 211V module is made of NiMH "D" cells. If I recall correctly, it would take 4 strings of these in parallel to give the needed AH rating. This creates a problem with cell to cell imbalances for charging as well as discharging.

I'll look at this in more detail at a later date.



P.S. - Ron has just replaced the pack on his Prius with another lead acid pack since the first one was already showing signs of wearing out. He showed my some photos taken during the swap out last week that are still in his camera. He also recently sent out an email saying they expect a NiMH pack from an east coast company specifically designed for the Prius Plus in the next few months. Hopefully that is the pack that we will be able to use for the rest of those who want to do this conversion. The Valence Lithium batteries will also work (that is what E-Drive plans to use) but the cost is much higher than the NiMH. Let me know if you didn't see that email and I can forward it to you.

Original Message -----


Thanks for the battery spread sheets that Ron did. I have several questions/comments:

1. What is a 2C discharge rate? 2. What does SOC stand for? 3. Which pieces of information are from the manufacturers? Looks like at least: V, rated Ah, Weight, Volume, and # cells. What else? 4. One note says that the depth of the Prius trunk storage space is 7 in. Does this mean that we are only considering batteries of 7 in high or less? 5. What is the area of the space available for the batteries? Some of the batteries take upwards of 1000 in2. 6. Is 5 mi/kwhr a documented value or is it just an educated guess? 7. How is usable Ah determined? 8. What limits the number of cells and what is the value of that limitation? 9. Same question for weight. I would think that weight would be a tradeoff, not a limitation. 10. There are quite a few batteries that don’t have an accurate quote for costs: they say a form of "guess." For some of these, the guesses result in too high a $E-mile so I wouldn’t worry about those. However at least the following two should be considered and would require more reliable values:

2/3 Cobasys 550

211V module

11. Cycle life figures are stated to be "often fuzzy or non-existent." We really need to know these values.

12. Biggest question is how much we should discharge the batteries while driving. And that would be strictly a function of the chemistry. As part of that we need to know the cycle life as a function of the % of discharge for each candidate selected battery. Only then would we be able to develop the minimum life cycle cost for each battery pack.

From Ron’s data, at this point, the candidates are:

Chemistry Model

NiZn MB40-12-8

PbAcid EVP20-12

Li-ion U-charge VU1

Cr-F-Li none

NIMH 2/4 Cobasys 550

NIMH 211V module

However this is just a preliminary list. If indeed a different % discharge is selected, that will possibly change the candidate list.

I calculated $/E-mile for all the batteries from Ron’s data, except I just did four of the large list of NIMH batteries. For some of these, I got the exact same values as Ron, but others were off. Since mine were calculated by the computer, I think I have the right values. Doesn’t appear that any were for those batteries that we would consider, so it probably isn’t significant.

I would appreciate any information you can find on the above.


PHEV Ratings

A PHEV is a Plug-in Hybrid Electric Vehicle, usuaily also augmented with a -## that denotes it's BEV range, a PHEV-20 would have a 20 mile range on electricity before gassoline would be required.

There has been a lot of discussion on rescent "250 mpg" claims from the Prius+ folks and/or the press and media from people who point out the lack of consideration for the electric fuel that skews those mileage figures. I Posted this and it's the latest summary of the whole situation.

Prepair for a Tangent !
--- In, "Robert Strattan" wrote:
> This then gves a more accurate indication of the fuel
> economy related back to raw energy used from fossil fuel sources.

Wouldn't it be interesting to use raw solar energy as the original
source and then re-run the analysis. Here's what I came up with:

I can see both sides of the argument, some prefer to consider the electric energy usage seperately since it's properties, like Cost, CO2, and Effeciency vary far more than gassoline. Some people may even generate their own electricity, in which case their electric energy is essentially free once the initial investment in the collection technologies is paid off.

Here's [1] what I've come up with.

My PHEV empg ( unofficial )

This Is a far better explanation. I use $0.06/kWh. The Prius achieves 3 miles per kWh and 50 mpg. I'm using 33.6kWh/gal to calculate kWh Equivilant mpg or empg. Calculation formula is:
Total Distance - PHEV-Range = Distance using Gassoline.
Distance using Gassoline / gas mpg = Gassoline Consumption.
Gassoline Consumption + kWh gas equivilant / Total Distance = empg.

  • PHEV-20 (6.6 kWh, $0.40) = 0.2 gas gal equivilant
    • Total Distance, Gassoline used = Empg / mpg (electricity considered seperately)
    • 20 miles uses 0.00 gas gal = 100 empg / Inf mpg
    • 40 miles uses 0.40 gas gal = 67 empg / 100 mpg
    • 60 miles uses 0.80 gas gal = 60 empg / 75 mpg
    • 80 miles uses 1.20 gas gal = 57 empg / 80 mpg
    • 100 miles uses 1.60 gas gal = 55 empg / 62 mpg
  • PHEV-40 (13.3kWh, $0.80) = 0.4 gas gal equivilant
    • 20 miles uses 0.00 gas gal = 100 empg / Inf mpg
    • 40 miles uses 0.00 gas gal = 100 empg / Inf mpg
    • 60 miles uses 0.40 gas gal = 75 empg / 150 mpg
    • 80 miles uses 0.80 gas gal = 66 empg / 100 mpg
    • 100 miles uses 1.20 gas gal = 62 empg / 83 mpg
  • PHEV-80 (26.6kWh, $1.60) = 0.8 gas gal equivilant
    • 80 miles uses 0.00 gas gal = 100 empg / Inf mpg

Note also that various vehicles with achieve different miles/kWh and mpg. The ACP T-Zero achieves 6miles/kWh and ~30mpg. ...T-Zero table...