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#21
04-21-2012, 03:32 PM
 lazzer408 Senior Member Join Date: May 2008 Posts: 506
Re: The "FestEVa" project.

Quote:
 Originally Posted by mk4gti The bad news is my used batteries are toast.
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#22
04-22-2012, 10:56 AM
 mk4gti Senior Member Join Date: May 2011 Posts: 153
Re: The "FestEVa" project.

Thanks lazzer, will try that.

Quote:
 Originally Posted by mk4gti So although everything seems to work "as planned", I'm kinda disappointed with lead and thinking of jumping to lifepo4 cells. Can I get some help choosing the right pack ? My target range is 35 miles (no highway). I have: Impulse 9 motor Curtis 1221b 400A controller Albright SW200 contactor Would 38x 100ah cells be enough considering it's cold here (need heat)
On another note, I replaced a failing battery with one I had as a spare (thanks paktrakr!) and got 12 miles on a charge (stop & go).
#23
04-22-2012, 07:52 PM
 drgrieve Senior Member Join Date: Apr 2011 Location: Sydney, Australia Posts: 266
Re: The "FestEVa" project.

Can you measure your current wh/mile? This would make the calculation fairly simple.
#24
04-22-2012, 09:43 PM
 mk4gti Senior Member Join Date: May 2011 Posts: 153
Re: The "FestEVa" project.

240 Wh / mile (per average)

So if I understand the math correctly:

240Wh *35 miles / .8 (safety) = 10.5kw hour pack required.

Sooo considering Lipo is 3.2v and I'd like 120v pack (38 cells):

10.5kwh / 120v = 87.5 ah ??

How can I factor in the loss for running the car in the cold plus using the heater ?

Last edited by mk4gti; 04-22-2012 at 10:14 PM.
#25
04-22-2012, 10:25 PM
 Tatsushige Senior Member Join Date: Mar 2011 Location: Kanazawa, Kanagawa, Japan Posts: 225
Re: The "FestEVa" project.

WOW ... Fantastic Project ... In Australia the car was a Mazda 121. Great car for the city ...
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#26
04-23-2012, 05:57 AM
 drgrieve Senior Member Join Date: Apr 2011 Location: Sydney, Australia Posts: 266
Re: The "FestEVa" project.

Quote:
 Originally Posted by mk4gti 240 Wh / mile (per average) So if I understand the math correctly: 240Wh *35 miles / .8 (safety) = 10.5kw hour pack required. Sooo considering Lipo is 3.2v and I'd like 120v pack (38 cells): 10.5kwh / 120v = 87.5 ah ?? How can I factor in the loss for running the car in the cold plus using the heater ?
Are you driving 35 miles every day? For a every day figure size the pack so that you are @60% DOD. The 80% is meant to be maximum range. (Although if you bottom balance you can go to 100% in emergencies).

So 240 * 35 / .6 = 14 kWh.

Why the 120 volts?

But yes 14000 / 120 = 120ah. Calb cells come in 100 or 130. Using the 100ah would bump the voltage up to 140.

Running in cold can be mitigated by insulating the battery box and running a low wattage heater while charging. There are a few threads on this on the site.

Sizing for heater is fairly easy. Choose the heater size (not sure maybe 1kw to 2kw - have a look at other threads) then multiply this by your expected run time in hours (how long to drive the 35 miles) then divide by 0.6.

At a guess add 2 or 3 kwh to your pack. So instead of 14 go to 16.

16000 / 120 = 133. A calb 130ah can be got for around \$160. So that would be around 6k.
#27
04-23-2012, 08:44 AM
 dladd Senior Member Join Date: Jun 2011 Location: Novato, California Posts: 609
Re: The "FestEVa" project.

Quote:
 Originally Posted by mk4gti 240 Wh / mile (per average) So if I understand the math correctly: 240Wh *35 miles / .8 (safety) = 10.5kw hour pack required. Sooo considering Lipo is 3.2v and I'd like 120v pack (38 cells): 10.5kwh / 120v = 87.5 ah ?? How can I factor in the loss for running the car in the cold plus using the heater ?
I've observed up to a 30% loss in available energy in the winter, due to voltage sag and heater usage (which on my car is 18a at 150v whenever the heater is running). Looks like a 120v / 100Ah pack might be perfect for you. I'd think your stats should be very comparable to dtbaker's, his car is similar sized (and I think even uses the same controller?), and that's the pack he's running.
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#28
04-23-2012, 09:16 AM
 mk4gti Senior Member Join Date: May 2011 Posts: 153
Re: The "FestEVa" project.

Quote:
 Originally Posted by dladd I've observed up to a 30% loss in available energy in the winter, due to voltage sag and heater usage (which on my car is 18a at 150v whenever the heater is running). Looks like a 120v / 100Ah pack might be perfect for you. I'd think your stats should be very comparable to dtbaker's, his car is similar sized (and I think even uses the same controller?), and that's the pack he's running.
Thanks for your post. I agree 100Ah would be sweet (\$5K ish) considering they would fit in my battery box without major hacking.

Funny you mention dtbaker's conversion; I learned much from his blog. Major respect !

He doesn't get near the bitter cold of Canadian winters so 100Ah might be a tad small for my needs.
#29
04-23-2012, 01:16 PM
 mk4gti Senior Member Join Date: May 2011 Posts: 153
Re: The "FestEVa" project.

Back from another 10 mile run (groceries). Car handled like a champ in the snow we are getting today. My heater is not hooked up yet so it was cold-ish inside the cabin.

I'm hoping the range will increase more as the weather warms up.

Can someone help me out with some lithium lingo ? What does bottom balancing mean ? Is it having an alarm when the lowest cell reaches X voltage ?
What about top balancing? Is it a signal sent to the charger to stop charging when the first cell reaches X voltage? What is the meaning of "C"

I know, newbie LOL
#30
04-23-2012, 01:54 PM
 Ziggythewiz Senior Member Join Date: May 2010 Location: Houston Posts: 3,707
Re: The "FestEVa" project.

If you watch any EVTV you will learn all about bottom balancing. Jack Rickard has put together an 85 part series on the finer arts of bottom balancing, you should be able to watch it all in a week or two.../jk

Balancing is matching the voltage of all the cells so they run out or fill at the same time. Because lithium runs at 3.2 for most of a cycle, you can only do it when nearly empty, or nearly full, hence bottom or top balancing.

Basically bottom balancing makes it safer to go to a lower discharge level, while top makes it safer to charge to a higher level, any more details than that and we risk bloodshed...I've likely gone too far already.
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