# Fast charging (30kw+) thundersky LiFePo4s



## frk2 (Jan 2, 2009)

Even 380V AC 3 phase is a non-issue, so I have learnt


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## CroDriver (Jan 8, 2009)

The charger will be a problem.

50 Amp chargers cost 3.300$

http://www.evcomponents.com/ProductDetails.asp?ProductCode=PFC-50

A 30 kW charger would probably be to big for a in-car use.

As far as I know Tesla's quick charger is not in mounted in the car.


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## frk2 (Jan 2, 2009)

I'm not going to mount it in the car - these would be charge stations mounted at petrol / CNG stations. CNG stations already have that kind of power supply from the grid.


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## CroDriver (Jan 8, 2009)

frk2 said:


> I'm not going to mount it in the car - these would be charge stations mounted at petrol / CNG stations. CNG stations already have that kind of power supply from the grid.


Oh, that would be great in this case.

This charge stations are being installed now in Germany and afterward in all EU countries I hope:
























































As far as I remember the maximum current they can deliver is 36 Amp.

Disappointing...


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## frk2 (Jan 2, 2009)

disappointing indeed. im hoping to get like a 2C or 3C charge - on 90Ah batteries should be 270A


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## frk2 (Jan 2, 2009)

well for bikes with 20Ah or 40Ah batteries that aint too bad.


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## CroDriver (Jan 8, 2009)

I agree but what about cars?

I stick to my opinion that we still are not ready for pure EVs. They must have a range extender except if you use the EV just for going to work and back.


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## frk2 (Jan 2, 2009)

I wonder what these guys are upto:

http://www.greenmotorsport.com/green_motorsport/products_and_services/3,1,388,17,26941.html


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## TheAtomicAss (Feb 19, 2009)

CroDriver said:


> I agree but what about cars?
> 
> I stick to my opinion that we still are not ready for pure EVs. They must have a range extender except if you use the EV just for going to work and back.


Nothing wrong with having to get a range extender once in a great while. In America, we have an entire industry for rental cars. Some people rent cars when going out of town just to keep the mileage down on their daily driver. 

I ride 2 very efficient motorcycles, (65-80mpg), and I would STILL save money by going electric, enough to rent a range extender for my longer trips and have money to spare.

I'm ready for a pure EV. The people in my family have commutes that could easily be serviced by an EV, even if they aren't mentally prepared to make the leap.


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## frk2 (Jan 2, 2009)

EVs are fine. Believe it or not my range with bad batteries right now is around 20km - I still use the EV since my work is 8km. It saves me a TON of money (my ev goes around 90Whr/km) With my deep cycles for the current EV - it would become a daily driver for sure.


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## Tesseract (Sep 27, 2008)

How many volts do you need to supply 270A at? Even at a relatively puny 96V you are already talking about a 26kW charger. Your charger might very well cost most than your EV.


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## frk2 (Jan 2, 2009)

tesseract - around 270A at 120V. First I need to know if this will fry my 90Ah batteries, secondly roughly the cost. Anywhere from $6000-10000 would be reasonable since the idea is that these be installed at commercial charging stations. Hell of a lot cheaper (capex wise) than maintaining a full battery swapping station stocked full of LiFePo4 battery packs


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## Tesseract (Sep 27, 2008)

frk2 said:


> tesseract - around 270A at 120V. First I need to know if this will fry my 90Ah batteries, secondly roughly the cost. Anywhere from $6000-10000 would be reasonable ...


First, I don't think there is ANY good data on high rate charging for the TS and SE cells. I know that there is data for the A123 cells, but even those aren't charged much beyond 4C (and they are capable of up to 50C rate discharges). My guess is that charging efficiency will be a little less than discharging efficiency so 3C may not be realistic in large format cells (with less surface area to volume ratio).

That said, either charging at 2C or only doing a partial charge at 3C is unlikely to hurt the large format LFP cells. The real problem here is how do you BALANCE the cells in your pack when charging at such a high current? Most cell balancing circuits I've seen can MAYBE bypass 1A out of 10A. Following the 1/10th rule, you would still need to bypass some 27A. Not that it can't be done, just that it will cost you quite a bit more per balancer than the usual $15-$25.

Second, your price range for the charger itself, though, sounds fairly realistic.


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## dimitri (May 16, 2008)

Fast chargers don't have to balance the pack, that's the job for slow overnight chargers. Fast chargers should stop at safe level, say 3.6V per cell, to ensure that no one cell in the pack gets over 3.8V.

Fast charging has so many safety concerns that I doubt you can come up with a simple solution to serve various EV models, especially if they all have different pack sizes, both voltage and AH size.

It'll probably take years to standardize fast charging industry to the point of having common high power DC standards, including safety standards.


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## neanderthal (Jul 24, 2008)

I worry that the ts cells would have a shorter life with this kind of charge rate. After all, they are rated at 3000 cycles at 80% and 5000 at 70% DOD at c/2 charge rate. I imagine they will be ok with 1c charge rates, but 3c?. I think from the pdf on the Sky Energy cell they are supposed to take that charge without problem for seconds, not minutes. It doesn't specify on the TS cells. But I don't imagine there would be a huge difference between them.


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## dimitri (May 16, 2008)

Imagine a situation: 

- I pull up to the fast charging station and ask attendant "please give me 20 kWh at "pump" 3 , I have 128V pack and can take 160 amps"

- the guy at the next "pump" needs 144V at 200 amps

- attendant fat fingers on the panel and mixes up our orders 

If you think about it, public fast charging via DC current will need a standard BMS protocol ( CAN bus type ) which will allow the battery to tell the charger what it needs, so charger can dish out exact amount of volts and amps. This BMS signal would have to be incorporated into a massive standard DC connector, capable of 100s of amps at 100s of volts. Then there is noise issues, etc etc. Whole thing is a nightmare....


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## frk2 (Jan 2, 2009)

Agreeing on charging protocols would be an interesting problem to have - and I dont think we are quite there yet  

Where does it say 0.5C ?? I see on the datasheet that 3C is the max charge current. If you are speaking on the 'standard' charge/discharge I dont know what that means - since the constant current is listed as 3c and max at 10C. So i dont know to take the 0.5C charge current limit.

And Yes, I am talking about partial charging - so in a practical scneario we would be going from say 30-35% SOC to 65-70% SOC. Hence I didnt think the BMS would be a big issue. I guess I need to get my hands on a 200A charger from somewhere to test out on 

Thundersky's website has 600A chargers they apparently use to quick charge - wonder what they are upto


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## MN Driver (Sep 29, 2009)

If you are talking about rapid charging at a commercial power station, the 2009 SAE J1772 proposed standard supports up to 240 volts at 70 amps, or about 16,800 watts.

This standard is supposedly supported by Tesla, Nissan, Honda, Toyota, Ford, Chrysler, and GM. So basically it is a power plug that has two 120 volt contacts and two 240 volt contacts from what I can tell, along with a ground for a total of 5 contacts.

So basically the charger would pull it's own power and do its own BMS work while the infrastructure is just essentially a new electical plug designed to be universal.

Now if Tesla is supporting it and also advertising their super quick charge times, I see a little issue in the details. I do stop and think about how the house that I live in that was built in the 80's has a 100 amp service and how I'm pretty sure it is against the NEC to put in a 70 amp 240 volt outlet in the garage to hook this to. In the end, overnight works for me. I'd probably go with a more conservative 0.3C(the standard current rating on the 200Ah cells which with a 35 cell pack that I've got the plans to possibly use in time at 220 volts is a little over 30.5 amps of peak draw over the first 3 or slightly more hours with a total charge finishing in 4 hours or so) seems reasonable for me. Obviously your mileage likely varies based on your motivation to create the topic, so I figure that if you were doing this for the once every few months type trip where you go twice your range in a trip where this could be convienent, I'm sure they could handle a quick charge, but I'd personally probably stop for lunch and hang out for awhile and take the 30 minutes of time for a 2C charge. Granted if you take a look at the charge charts, it won't be 100% SOC, you will be able to pump the pack but the voltage tops out and you drop amps down to maintain the peak charge voltage, so basically you *might* get 3C for awhile and after 20 minutes you might get a decent charge to go on, but I wouldn't be expecting a 90% charge by any means.


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## dimitri (May 16, 2008)

This is different story, you are referring to charging stations which provide standard AC service, which assumes that all EVs have onboard chargers to convert AC to DC etc. This is fine, although even this simple thing took years to agree on plug standards, and still ended up with different US and European plugs.

However, IMHO, this is not "fast charging" if its limited to 16kW. In my opinion fast charging would be DC current straight from the station to the battery, at least 100 amps , up to 300 amps. But I guess we are very very far from this kind of public service.


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## neanderthal (Jul 24, 2008)

The TS pdf says it in the portion where life expectancy of the cell is shown. It says 3000 cycles at 80% dod at c/2. Usually cycles go down with charge and discharge rate. For example A123 rates their cells at 4000 cycles at 100% dod at 1c, and 1000 cycles at 10c.

So the life of the lifepo4 cells decrease as discharge rate increases, which I imagine means it also decreases with charge rate as well.


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## Tesseract (Sep 27, 2008)

neanderthal said:


> ...
> So the life of the lifepo4 cells decrease as discharge rate increases, which I imagine means it also decreases with charge rate as well.


That is a very safe guess!

Still, I imagine plenty of people would at least occasionally make the tradeoff between a lower cycle life for a faster recharge. If you got overnight to charge then by all means go with a 5-10 hour rate, but if you need a quick blast to get you to the next "oasis" then perhaps knocking a few (thousand???) cycles from the overall life won't sound so bad?!


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## peggus (Feb 18, 2008)

Aerovironment has already developed fast charging stations capable of 30, 60 , 125 and 250kW. 

If you're serious contact them through this page. 
http://avinc.com/ev_charging/fleet


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## frk2 (Jan 2, 2009)

I actually did contact Aeroenvironment - havent heard from them since. Have you guys tested your fleet chargers on TS LiFePo4s by any chance? I wish to know what real life experience with your fast chargers are? Another question: How are you fast-charging those forklift Pb batteries? I thought the maximum any Pb battery could take was 1.5C ?


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## frk2 (Jan 2, 2009)

Just to update - emailed thundersky about the 3C charge and this is their response:

Hi Faraz, 
Have a good day! sure we are test our batteries on 2C and 3C charging. If you charge with a 3C constant charge current, the cycle life of the battery will reduce 10%. So we suggest you do not charge the batteries with such a big current. 
Thanks & Regards, 
Cindy


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## Roy Von Rogers (Mar 21, 2009)

It seems to me this problem can only be solved by charging multiple batteries connected in series, by charging such batteries one at the time.

First of all the charger will need to be part of the vehicle and designed for that particular pack, so that charging stations only have to supply whatever mains voltage is available, this way the charging stations are universal in nature.

So just to simplify the idea lets say you have a TS battery pack, the charger is set to the max amperage each cell can handle safely, until it reaches the max bulk voltage. At that point one could stop or if vehicle was not needed, the charger could then charge to the voltage the battery pack was designed for.

There are two advantages for such type of charging. A charger that had to deliver lets say 3.6 volt bulk would have no problem delivering a large amperage, if such pack can handle it. It would also be charging as a BMS, for it would deliver the same to all. Also the charger could look at all cells after a pause time and determine if all cells are holding the proper amount, and if not so, go back to any cells to top off if needed.

Its a lot easier to give large amperages at a lower voltage, then trying to charge a whole series pack to whatever high voltages it was, for there is a limited amount of current a mains can deliver.

Now I simplified it all, but with present electronics such a system could be build with lots of other refinements.

Roy


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## neanderthal (Jul 24, 2008)

Not quite. Ufortunately if you connect a charger like this, electrically it all becomes a giant short. Kablam. Explosions and fried electronic stuff. You cant charge cell in series with one charger at 3.6v. Electrically its a short. Either you would need a bunch of separate chargers, or a big contactor between each and every cell that would disconnect the series arrangement. 

A good idea nonetheless, if modified, to have a bunch of high current low voltage chargers at each station. and a special connector in your ev.


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## Roy Von Rogers (Mar 21, 2009)

neanderthal said:


> Not quite. Ufortunately if you connect a charger like this, electrically it all becomes a giant short. Kablam. Explosions and fried electronic stuff. You cant charge cell in series with one charger at 3.6v. Electrically its a short. Either you would need a bunch of separate chargers, or a big contactor between each and every cell that would disconnect the series arrangement.
> 
> A good idea nonetheless, if modified, to have a bunch of high current low voltage chargers at each station. and a special connector in your ev.


 
I'm talking about charging one cell at a time in a series of cells. Lets say you have 10 batteries in series, go put a chrger on the first battery, then go to the next etc etc. You are now charging each individual cell, at a lower voltage but high amperage. The neat byproduct of such a procedure would be automaticly balancing each cell with the same amperage and voltage. The idea is to let the charger be in control, instead of a BMS.

Roy




You will be charging one battery at a time, by moving the positive and the negative to each cell.


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## Amberwolf (May 29, 2009)

That seems like it would take a while to charge that way. Perhaps no longer than it would charging all of them in series, I'm not sure.

I presume you're talking about an automatically-incremented charger, with contactors or similar that switch it from battery to battery?

That's a lot of extra cabling to the pack, with one or two cables to each battery.

In theory, if you design the switching system right you'll only need one extra cable per battery, except for the most positive and most negative. The switching system would "increment" positive and negative from pair to pair as it goes up or down the chain. Just have to build in some assurance that even if the switching system fails somehow that it cannot either short cell or charge it backwards!

A simpler switching system would require double the number of cables, though; one for positive and one for negative from each battery. Definitely better weightwise to make the switching system more complex, but cost may go up a lot. 

What were you planning on using for the switching system? Solid state relays? Contactors? Something else? Servo-motor controlled rotary switcher?


Hmmm. Now you have me pondering.... 

**Are you pondering what I'm pondering?
Well, I think so, Brain, but it's a miracle that this one grew back.**
________
Problems From Nexium


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## neanderthal (Jul 24, 2008)

Well to get the balancing effect you would have to wait for every battery to finish charging. We are talking about 3c charge rate here. If you have a moderate voltage pack with say 40 cells, all at 70% dod, you will need 15 min or so per cell. Thats a long while. If you for some reason need to leave unexpectedly (since we are talking about charging stations, not charging at home), you will end up with some batteries still at half full or less. Since a battery pack is only as full as its lowest cell, you could have spent 2 hours at a charging station and still only have the same capacity for range as you did when you arrived.

Like Dimitri stated Lifepo4 cells dont unbalance too bad during charging. just a bit, enough to become unbalanced over the course of many cycles. Charging them in series lets you charge fast at a station, and leave whenever, you can do a balance/finishing charge at home. 

I think you'll find in the end, the couple watts of shunt heat you've saved wont be worth it.


It is an interesting idea for a fast charge, but with this you would ABSOLUTELY HAVE TO wait for the charge cycle to be done on every cell. That sort of defeats the purpose of a fast charger. A quick boost to get you going a little further. I guess you could just deliver the same time on the charge to each cell. Or maybe you could charge each for 2 min and move on, round robin style, to make it possible to leave in a hurry.

But this would be much more complicated than just having a series charger and a simple bms with shunt balancing.


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## neanderthal (Jul 24, 2008)

I didn't mean to sound rude, I am just trying to state the many cons of this method. It is a great idea, don't get me wrong. I just think it would be tough to implement it and the extra work would not be much better financially or functionally than a series charger with a decent bms.


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## Roy Von Rogers (Mar 21, 2009)

neanderthal said:


> Well to get the balancing effect you would have to wait for every battery to finish charging. We are talking about 3c charge rate here. If you have a moderate voltage pack with say 40 cells, all at 70% dod, you will need 15 min or so per cell. Thats a long while. If you for some reason need to leave unexpectedly (since we are talking about charging stations, not charging at home), you will end up with some batteries still at half full or less. Since a battery pack is only as full as its lowest cell, you could have spent 2 hours at a charging station and still only have the same capacity for range as you did when you arrived.
> 
> Like Dimitri stated Lifepo4 cells dont unbalance too bad during charging. just a bit, enough to become unbalanced over the course of many cycles. Charging them in series lets you charge fast at a station, and leave whenever, you can do a balance/finishing charge at home.
> 
> ...


You would not have to wait for each battery to be charged before moving to next one, think about it, your using an intelligent charger that can be programmed to do whatever you program it to do. How much of a voltage rise is there between cut off and full charge. On a TS cell if you want to be conservative it would be 2.7 to 3.7, or whatever amount you decided on, thats a 1 volt rise for at least the basic bulk charge before having to taper it off. 

It would not be difficult the have a contoller that lets each battery recieve a .1v increase and then move to the next. The dwell time on each battery would be a function of the total pack and the amperage of the charge to each battery. Yes the charging copper would have to be heavy if you wanted to pump a lot of amps in to each pack, but if held close to the pack wouldnt be too bad.

One could also put sub packs together like 4 TS cells to make 13-14 volts each which would bring the volts up a bit, and the amps down to each charging wire.

Anyway, its been something thats been running around in my head for some time, and we have people here that are a lot smarter then me when it comes to this emerging technology, I just wanted to bring this idea to the table to see what can be done with it.



Roy


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