[Baldbruce]

Changing a dead lead EV to Lithium and wanted some opinions on my plan. 500 A maximum controller. 144V (12 each 12V 90Ah) existing system. Three LAs were mounted in the front engine compartment and 9 were mounted in seperate battery box in the rear.

Considering using a seperate pack of high power Headway LiFePo4 cells in the front. 48S?P as a standalone pack in front. 48 CALB 100Ah in a second standalone pack. Packs wired in parralel for easy charging.

By my simple Pspice electrical simulation, the lower resistance pack that is closest to the controller should handle a much larger portion of the high current draw. When the current requirement then goes lower, the higher resistance pack in the rear will recharge the lower resistance pack in front. Whole point is to get good performance without damaging the big pack in the rear.

What do you guys think? Good plan? Do I need to current limit the rear pack? (I have a 1000A IGBT module I could use if needed.)
Did I drink to much coffee in coming up with this plan???

Thanks in advance for your inputs.

 

[PThompson509]

You will need to be very careful about how you limit current from the two packs. CALB is limited to 4C (short duration), and I'm not sure what the max current is from the Headway.

If you monitor the current from the two packs, you will be able to gain insight into whether you are overdriving the batteries or not.

I sure wouldn't do this, but then again, I'm a lot more cautious about these sorts of investments. (says the guy with the chinese BLDC motor and controller).

My $0.02 worth - talk to some serious battery people and see what they say.

Cheers, Peter

 

[Ziggythewiz]

I think it sounds great. You shouldn't need to current limit anything on the CALB pack, they could take that full load themselves. With a 500 A controller I doubt you hit over 400 A for more than a couple seconds. As long as you parallel enough headways to handle its load you should be fine.

I'm doing an experiment mixing lithium with lead; on vacation at the moment but will get it all hooked up to test some load sharing once I get back next week.

Also, I'd be interested to check out your simulation if you can share.

 

[winzeracer]

I had also thought about this before, for an application with more amps. It would be cool to have an EV that had really nice acceleration provided by some high C rate cells and then some CALB's to give it more cost effective range. It will be interesting to see the results.

 

[skooler]

Hi,

Your 100AH CALBS will happily put out 500Amps for a few seconds without shortening the cycle life too much.

If I were you, I'd spend the money that you would spend on headways, on a slightly larger cell, mayber the CALB 180AH? that way your even more within the spec of the cells

The added complications are just not worth it if your only using a 500A controller, maybe it would be worth it for 1000A plus?

I'll also recommend looking at Sinopoly cells if you fancy dealing with customs for a slight saving. I have been extremely impressed with the 60AH (B) cells.

Hope this helps.

Cheers,

Mike

 

[PStechPaul]

I think you would be better off adding an ultracapacitor pack for short-term high -current draw and possibly dynamic braking with regeneration. In another post I figured that the ultracapacitors required for a full 30 mile range at 300 W-Hr/mile would cost $46,000 (about $5/W-hr). But if you only use them for burst power (or charging), you could probably use a much smaller pack. If you need 50 kW for 10 seconds, that is 140 kW-hr. That's about $700 using the cost based on the other post which are direct from China. For short-term power surges it seems the Ultracaps are a very good option. Look into the costs from local sources and see if it makes sense. But I think a few hundred dollars worth of ultracaps will give you a much improved "feel" since you will be able to command the maximum performance of your motor and controller for at least several seconds in order to negotiate steep grades or for high-speed passing.

Here is a discussion about Ultracapacitors vs batteries:
http://cleantechnica.com/2011/05/11/cheaper-ultracapacitors-for-electric-vehicles/
It gives a figure of $2400 to $6000/kW-hr, as of about a year ago. The price I used is $5000/kW-hr so maybe it's less expensive if you buy larger capacitors than the 2000 uF for which the cost was given.

 

[Baldbruce]

Thanks for the thoughtful comments! Your opinions are appreciated. I do anticipate upgrading the controller in the future and so that is a small factor in this discussion. I also am a big believer in not overstressing Lithium batterries in general and prismatics in particular. So these two opinions of mine do play into the equation. I realize others have different opinions on how much current you can pull from them but I am conservative. 4C max and 1C preferred for SE type CALB. 25C max and 10C prefered for Headway HP cells.

Is there updated information on the newer CA type CALB cells? Are they available yet in the USA? Price comparable to SE type?

I have looked at ultracapacitors in the past and found the cost to benefit pretty bad. A friend of mine put a fair amount of capacitance in parralell with his LiFePO4 pack on his motorcycle and it was only a small improvement. I think what most people forget in their calculations is that the cap is only useful for a small voltage range in this application. i.e. the 1/2CV^2 energy storage discharge is only on the delta V of the battery sag. Not that it can't help, it's just an awful lot of capacitance to do any good and they are large and very expensive. Maybe the prices and performance have dropped recently? Keep me apprised if that is the case....

Keep the input coming!

Thanks,

 

[PStechPaul]

It is probably not enough to just put the ultracaps in parallel with the batteries. For a large current surge the capacitors will provide full power but as they drop to maybe 90% of their voltage (81% of energy capacity) the batteries will start taking over and they can't be discharged much below, say, 80% nominal voltage. So you really need a special controller which limits the current of the battery pack and boosts the voltage of the capacitor bank so it can discharge to about 50% voltage where you will have used 75% of their energy capacity, rather than just 19% otherwise.

 

[skooler]

What is the advantage of the ultracapacitor pack if the cells are well within spec?

In my opinion the added cost is just not worth it.

Calb 180AH will happily put out 1000Amps for a few seconds.

I see no real benefit and a whole lot of cost!

EDIT: you might save say 500 cycles over the life of the cells but this is marginal compared to the price of the caps!

 

[Baldbruce]

CALB SE100 is 7 pounds. CALB SE180 is 12.8 pounds. 48 X (12.8 - 7) = an extra 278 lbs. I can add lets say 70 lbs of Headways to make up the current requirement and still save 200 pounds. Obviously not the same range, but fits better in my small space and this is not a huge range application. (40 Miles max) Still crazy?

 

[dougingraham]

I think you are trying to improve performance where you dont need to. If you have room for a 48 cell pack of 100AH calbs and a 48SXP pack where X is some number large enough to give you a stiff pack then you probably have room for a 48 cell pack of 130AH Calb cells. Maybe even 180AH size Calbs. The 100AH cells can do 800 amps for 10 or so seconds easily and your 500 amps for much longer than you probably need. If you have room for 48 of the 180ah cells use those. They can do your 500 amps continuous. I suggest you keep it simple and just use the prismatic cells. I think the additional cost of the headways would be more than going to the 180AH cells and the performance increase will be minimal. If you were going to do a really high power system then I would suggest a different answer.

 

[skooler]

I think you are trying to improve performance where you dont need to. If you have room for a 48 cell pack of 100AH calbs and a 48SXP pack where X is some number large enough to give you a stiff pack then you probably have room for a 48 cell pack of 130AH Calb cells. Maybe even 180AH size Calbs. The 100AH cells can do 800 amps for 10 or so seconds easily and your 500 amps for much longer than you probably need. If you have room for 48 of the 180ah cells use those. They can do your 500 amps continuous. I suggest you keep it simple and just use the prismatic cells. I think the additional cost of the headways would be more than going to the 180AH cells and the performance increase will be minimal. If you were going to do a really high power system then I would suggest a different answer.

+1 on that.

Keep it simple, the added cost and effort is better invested elsewhere.

 

[MalcolmB]

If you really want to know if it will work why not just try it on a small scale first? You could parallel a few Headway cells with a single prismatic, using roughly the same cable lengths you plan to use in the car. Then just connect them to a dummy load that matches your expected current draw and see how the cells share.