[major]

Hi All!

I have been following these forums for about a year now and I am considering taking the plunge and converting a vehicle.

I am aiming to convert a London TX4 taxi into an electric vehicle and I am hoping you can all help me out Specs here.

The main aims of my project is to have a vehicle that can:

- Range around the 100 miles.
- Have a 5C recharge time.
- Not extortionately expensive.
- Has a battery life similar or the same as LiFePo4.

I initially want to be able to use this vehicle as a personal vehicle but if it is successful I want to start a small business converting taxis in the UK!

Cells.

One of my main aims is to have the vehicle fast recharge within 10 minutes, I am looking at a charge rate of 200Kw. I am looking to have a large battery unit at my house to power at these kind of rates.

Ideally I am looking at LiFePo4 chemistry battery's that can charge at 5C rates but I have seen other chemistries (such as Enerdel) which might be affordable (and available). I am looking for 80% DOD on the cells to extend battery life.

- Do any of you have suggestions of different manufacturers that are available at the moment?
- I know that CALB CA cells do 3C charging but could they do 5C comfortably with an 80% charge?

Pack Size.

There is an issue with the vehicle running in the region of 2,500kg (5,500lbs) when the vehicle is completed. I am trying to get the vehicle weight down as much as possible but I reckon I will only be able to shed around 500kg maximum. Does this mean I will be running a pack at around 50Kw?

Motor.

I plan to buy the DMOC inverter and Siemens AC motor from EVTV, I plan to have high Re-gen on the vehicle as I will be using it in the city and I will be start-stopping all the time.


Charger.

I want to keep the charger externally to the vehicle (200kw) would be a crazy waste of space in the taxi (!)

Does anyone have a preferred charger that I can run several in parallel?

I know the SAE level 3 DC charging is proposed to have 400a and 400v charging ability so i would like to match that.

From there I was going to use a standard DC-DC converter the Borg Warner single speed transmission.

The main issue I will need help with is the weight and battery choices I need to work with.

If you guys have any suggestions I would be grateful.


Thanks!

Leigh

Hi Leigh,

That's an ambitious project. I'll comment on one aspect. I'm unsure as why you need a 10 minute charge, but at 200 kW assuming 100% efficiency, you will store 33.3 kWh. I doubt that will be sufficient energy for a reliable 100 mile range on the heavy vehicle in traffic with the required creature comforts. I suspect the charging system to be similar in complexity and cost as would be the vehicle conversion.

Cheers,

major

 

[lnpurnell]

Hi Leigh,

That's an ambitious project. I'll comment on one aspect. I'm unsure as why you need a 10 minute charge, but at 200 kW assuming 100% efficiency, you will store 33.3 kWh. I doubt that will be sufficient energy for a reliable 100 mile range on the heavy vehicle in traffic with the required creature comforts. I suspect the charging system to be similar in complexity and cost as would be the vehicle conversion.

Cheers,

major

Major,

My main aim for the 10 minute fast charge project is to prove that an electric vehicle can compete with normal taxis and remove the idea of range anxiety from the vehicle for any people who are not used to electric cars.

I could always opt for a 30Kw pack and run at a reduced range, I still have the original issue of substantial weight as the design of the taxi, as it is of a twin chassis design (God only knows why for a vehicle that runs on the flat roads of London :-S )

The only cells that I have seen that can do 5C are the Enerdel cells but I am seeing if there are other options before pressing ahead.

Thanks,

Leigh

 

[CrazyAl]

I read that those London Taxis (TX4) have a curb mass of 2,520 kg (5,556 lb).
Having never been in one of those taxis in real life, it makes me wonder what makes up most of the mass?
To me, it does not look like a 4WD or SUV so if there is a way to loose some of the mass, then, it could make way for a lot of batteries.
Just a thought.

 

[major]

I could always opt for a 30Kw pack and run at a reduced range,...

I think you mean to say 30 kWh. Please make the effort to use the correct units for energy (kWh) and power (kW).

And there are other battery choices for 5C. But I do like EnerDel. You will pay a premium for cells with this capability and also suffer cost and mass with the on-board system to support 5C continuous.

 

[lnpurnell]

I read that those London Taxis (TX4) have a curb mass of 2,520 kg (5,556 lb).
Having never been in one of those taxis in real life, it makes me wonder what makes up most of the mass?
To me, it does not look like a 4WD or SUV so if there is a way to loose some of the mass, then, it could make way for a lot of batteries.
Just a thought.

Hi CrazyAl,

To be honest there is no reason to why it is so heavy, just that it may be easier to build the vehicles this way, just as they have been doing them for the past 40 years.

There is a separate chassis on these vehicles which is way over engineered for what it is required for. To the extreme I would like to separate the chassis all together and build my own one (but this may be too extreme)

The bodywork is still pretty heavy and maybe bonnet (hood) of the car is around 30kg (66lbs) so changing that with just a plastics reinforced one would work well.

Leigh

 

[rwaudio]

I don't think I'd get so hung up on the 5C rating. 12.5 min vs 20 min.

Why not spend the extra to buy more CALB cells instead of the expensive ones and build the pack so that you can put in the same amount of energy in during that 10-12 mins. IE if you have a 50kwh pack of CALB it might cost the same as a smaller enerdel pack but you could probably put the same amount of energy (30kwh or something) staying at the 3C rating.

So you would start the morning with a full pack and have a larger buffer between charges, you would also be keeping the pack closer to the middle increasing cycle life.

 

[lnpurnell]

I think you mean to say 30 kWh. Please make the effort to use the correct units for energy (kWh) and power (kW).

And there are other battery choices for 5C. But I do like EnerDel. You will pay a premium for cells with this capability and also suffer cost and mass with the on-board system to support 5C continuous.

Sorry, I did mean 30KWh :-S

When you talk about the on-board system do you mean charger? I am aiming to have external chargers for the vehicle.

Thanks,

Leigh

 

[major]

I don't think I'd get so hung up on the 5C rating. 12.5 min vs 20 min.

Why not spend the extra to buy more CALB cells instead of the expensive ones and build the pack so that you can put in the same amount of energy in during that 10-12 mins. IE if you have a 50kwh pack of CALB it might cost the same as a smaller enerdel pack but you could probably put the same amount of energy (30kwh or something) staying at the 3C rating.

So you would start the morning with a full pack and have a larger buffer between charges, you would also be keeping the pack closer to the middle increasing cycle life.

Regardless of the C rating, you're talking about a 200 kW charger. And that is for a one car fleet. I was told that a L3 fast charger for the Leaf was on the order of $35,000. He's talking about a higher power level and a energy buffer (stationary storage). Like I said, the charger will as hard or harder than the EV conversion.

 

[major]

When you talk about the on-board system do you mean charger? I am aiming to have external chargers for the vehicle.

No, not the charger but the cell interconnects and charge port/cables need to handle 200 kW or more on a continuous (10 minute) basis which is greater than the propulsion system duty cycle. And it is likely the battery will require active cooling of some sort for 10 minutes at 200+ kW. And this may get into special BMS features.

 

[lnpurnell]

Regardless of the C rating, you're talking about a 200 kW charger. And that is for a one car fleet. I was told that a L3 fast charger for the Leaf was on the order of $35,000. He's talking about a higher power level and a energy buffer (stationary storage). Like I said, the charger will as hard or harder than the EV conversion.

I am willing to spend more on the external charger than the electrification of the vehicle itself. The reason I would like a charge of approx 10 minutes is the ability to use the taxi as a work vehicle. If I am doing over 200 miles in a day for work in my area then a fast (10 minute) recharge is essential.

This is why I am enlisting the help of this community!

 

[Siwastaja]

Do you have knowledge on power electronic design or know someone who has who could do the job? You know, you cannot just buy such a charger for any reasonable price. Be prepared to spend about a million in R&D unless you find someone who is interested to do the job "just for fun". In that case, the parts cost may be around $5000-$10000. There's nothing fundamentally difficult there, but designing electronics always takes time, and time is money.

It's also possible that you start experimenting and learning the required electronics by yourself, but it would take a lot of time before you have a working product.

You could also look at the EMW charger kits discussed on the forums. Get those new higher power versions and put 10 in parallel.

 

[Semper Vivus]

Hello,

just a crazy thought, but what about:
- 2x Netgain ImPulse 9" Motors
- 2x SynkroMotive 900A / 192V DC Controllers
- 2x 55S1P Packs of Winston WB-LYP90AHA
- stationary Pack for DC charging with help of the dual SynkroMotive setup (see http://onegreenev.blogspot.de/2012/07/dc-charging_17.html)

Then use only about 50% of the 30kWh that is installed in the car and you can recharge that 15kWh with 90kW DC charging from the SynkroMotive Controllers in 10 minutes. I would guess that gives you at least 60km of range. And you have some spare energy to argument that the car is able to do over 100km ;-).
But I don't know if that really works. I've never used a SynkroMotive or even a dual controller setup.

In general, achieving all your goals just won't be possible...besides you have a lot(!) of money. And also range AND fast charging together just makes no sense in my opinion.

Regards
Tom

 

[major]

This is why I am enlisting the help of this community!

Good for you

I am willing to spend more on the external charger than the electrification of the vehicle itself. The reason I would like a charge of approx 10 minutes is the ability to use the taxi as a work vehicle. If I am doing over 200 miles in a day for work in my area then a fast (10 minute) recharge is essential.

Not all would realize the extent (cost) of fast charging. I was making sure you do. And like Siwas says, there is nothing on the market. You might check with AeroVironment. They have made some monster chargers.

Of course, there is the option of battery swaps. Electric forklifts have used this method to run multiple shifts for years. They have a hoist and swap a 2 ton battery in a few minutes with just a single man. You then have hours to recharge the battery to get ready for the next swap. Your fast charge system would have required a second battery (or energy buffer of some sort) anyway. Just make both batteries fit the cab and charge at C/4 straight from the grid with a commercially available charger when the battery is off-board.

 

[lnpurnell]

Do you have knowledge on power electronic design or know someone who has who could do the job? You know, you cannot just buy such a charger for any reasonable price. Be prepared to spend about a million in R&D unless you find someone who is interested to do the job "just for fun". In that case, the parts cost may be around $5000-$10000. There's nothing fundamentally difficult there, but designing electronics always takes time, and time is money.

It's also possible that you start experimenting and learning the required electronics by yourself, but it would take a lot of time before you have a working product.

You could also look at the EMW charger kits discussed on the forums. Get those new higher power versions and put 10 in parallel.

Hi Siwastaja,

I am relatively competent in power electronics and I have some friends who are extremely good in this subject.

I think my best option at this point for speed and reduction in R&D is to base the external charger on a paralleling of existing charger designs, so the EMW kit may be a good option to start with.

Thanks,

Leigh

 

[Duncan]

Hi Inpurnell

For a really fast charge you won't be able to charge from mains AC as the power requirements will be too high
You would be better slowly (relatively) charging a buffer battery

The fast charge problem then becomes one of transferring the power from your buffer battery to your taxi

The internal resistance of both batteries is going to be inescapable - so you may be able to use this to limit the current flow

It may be necessary to use a number of different buffer batteries and switch them on one by one

The buffers will end up at different charge states - but the mains chargers can take care of that while you are out driving the taxi

 

[lnpurnell]

Hi Inpurnell

For a really fast charge you won't be able to charge from mains AC as the power requirements will be too high
You would be better slowly (relatively) charging a buffer battery

The fast charge problem then becomes one of transferring the power from your buffer battery to your taxi

The internal resistance of both batteries is going to be inescapable - so you may be able to use this to limit the current flow

It may be necessary to use a number of different buffer batteries and switch them on one by one

The buffers will end up at different charge states - but the mains chargers can take care of that while you are out driving the taxi

Hi Duncan,

My initial idea is to have the charging unit at my house and run it as a 'proof of concept'. If it is successful and have ironed the kinks out I would like to run it as a small business, outfitting other taxis and providing them with the same service.

This is where the 10 minute charge comes into play.

If it is 20 minutes+ then people still have the 'range anxiety' that they cannot get anywhere fast. now I know that once you drive an electric car that this isn't the case but I fell that the convenience of a 10 minute charge will increase adoption for the commercial vehicle sector.

This type of charging can be done (yes I know the charging units will be more expensive than normal), the only restriction in the past was the battery chemistry. Now it is the power source for charging the vehicles. It just means less weight for battery's in the vehicle and a similar 'refuelling' experience as a normal car.

I also have plan to have a factory on an industrial estate to increase the power supply capabilities for the charger. This is to enable the uptake and continued use of people using the charger

Duncan, I like the idea of using a slow charger to fill a battery bank as a buffer. The only consideration I will need to take is the increase in charges from the station would require an increase in charging output to the buffer pack.

------

The reason for setting up this thread was to ask for assistance for the two main hurdles -

A- Picking the appropriate battery.

B- Brainstorming some ideas on the best way to create an external charger.

One of the better options I thought and have already heard in this thread is to parallel existing charger designs and work from there. The main hardware challenge would be a controller to communicate with the car and to control the current output.

I like the idea of using the Calb CA cells and to use more of them to reduce the C rating. I just think the weight gained by doing this by adding a 20Kwh buffer would be huge overkill. I just don't think the 3C rating on the CA cells is going to be good enough. I would rather spend more on the Enerdel 5C charge cells and go from there.

Any ideas?

 

[Siwastaja]

Hi Siwastaja,

I am relatively competent in power electronics and I have some friends who are extremely good in this subject.

I think my best option at this point for speed and reduction in R&D is to base the external charger on a paralleling of existing charger designs, so the EMW kit may be a good option to start with.

Thanks,

Leigh

Then you have no problem! Just design a charger module with relatively high power such as 50 kW which is still easy to design, and parallel a few of those. You need a boost PFC stage and then the charger stage. Nothing special in principle, just countless design hours.

Maybe design three 240V chargers, 66 kW each, to be run off 3-phase system? You would need 275 amps which is not very common, unlike 3x125A which is found practically "everywhere".

200 kW is not that much that it would inevitably need a separate buffer, but it depends on where you install it.

So, you'd need to start from querying power companies whether you can get 3x300A supply where you charge the car. If not, or if it's more expensive than getting the buffer battery pack, then go with the buffer. Then I'd place the buffer after the PFC stage, at the highest voltage possible. Then you'd have a relatively low-rated PFC stage (maybe 3x32A, or even a single-phase?) and the 200 kW rated final stage.

 

[Duncan]

Duncan, I like the idea of using a slow charger to fill a battery bank as a buffer. The only consideration I will need to take is the increase in charges from the station would require an increase in charging output to the buffer pack.

Hi Inpurnell
I don't understand what you mean?

Example
Buffer pack 120Kwhrs
Car - 30Kwhrs

Car charge rate - 10C
Buffer Discharge rate - 2.5C

Car drives away
Recharge Buffer using 10Kw charger - 3 hours to recharge ready for next power transfer
Or wait until nigh-time for cheaper power

If you split the buffer into sections you can use smaller chargers
3 sections - 3.3Kw per charger

Easier than getting into 300Kw chargers
and you are using off the shelf technology

Also - you could use the buffer to run your house so you only use night rate electricity

 

[jk1981]

I am willing to spend more on the external charger than the electrification of the vehicle itself. The reason I would like a charge of approx 10 minutes is the ability to use the taxi as a work vehicle. If I am doing over 200 miles in a day for work in my area then a fast (10 minute) recharge is essential.

200,000W of charging is some really serious high voltage, high power grid connected electronics. I presume your plan is to have a large 'dump pack' of continuously trickle charging batteries to power this monster charger rather than drawing all of that from the grid during the day?

If so, why not simply make the pack in the taxi interchangeable then keep one or two reserve packs trickle charging at base. You prolong the service life of the packs by using/charging each one less, charging it less abusively and you have much lower losses during charging making the whole thing greener and more cost effective.

Design it right and a 'recharge' takes seconds, not ten minutes, the whole build will be a fraction of the cost of your current proposal and you can probably even run it off your single phase domestic supply without getting into costly upgrades. It also opens up the possibility of elective charging at lower cost overnight and/or when there's a generated surplus (>50Hz) doing your bit for a more robust grid. You're also back into the realm of relatively low cost off the shelf technology.

jk