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A DIY Electric Car Member, david85, has been testing a 200 Amp-Hour LiFePo4 Battery for a few weeks now and has been keeping a public journal of the results. If you're not familiar with LifePo4, it's a fairly new battery technology that promises greater safety than Lithium Ion or Lithium Polymer while still holding a good energy density and a decent discharge rate. Many new LiFePo4 manufacturers are popping up in China and Japan and prices continue to get lower which is very encouraging for use in EVs. So far the test results are encouraging and while the battery hasn't been tested for a full 1000 amp load, it is apparently up to par with storage capacity. David says that as a general rule, the going rate seems to be about $0.50/ watt hour of capacity which is for the cells only, as in no charger, or BMS (battery management system).

Here are the results from David's LiFePo4 Test Thread:

Test 1:

Voltage measured with no load at full charge: 13.43V

Voltage under load after

15 min: 13.16V
30 min: 13.14V
45 min: 13.13V
60 min 13.12V

Voltage after test:

5 min: 13.26V
10 min: 13.26V
15 min: 13.28V

Ambient temperature: 10 celsius

Test 2:

15 min: 13.12V
30 min: 13.09V
45 min: 13.08V
60 min: 13.08V

Voltage after test:

5 min: 13.25V
10 min: 13.26V
15 min: 13.26V

Ambient temperature: 7-10 celsius (test started and 7 and ended at 10)

Test 3:

15 min: 13.16V
30 min: 13.14V
45 min: 13.13V
60 min: 13.13V

Voltage after test:

5 min: 13.27V
10 min: 13.28V
15 min: 13.29V

Ambient temperature: 15 celsius (in direct sunlight, so battery was closter to 19)

I also turned the motor on and measured the voltage sag at each of the 5 settings:

no load: 13.43V
Setting 1 (10A): 13.38V
Setting 2 (15A): 13.36V
Setting 3 (25A): 13.3V
Setting 4 (30A): 13.27V
Setting 5 (62A): 13.07V (this setting is fun)

Test 4:

Amp draw reads 28 Amps on setting 4, but could be 30, I need to verify the specs of the motor and see what others are seeing with this motor.

Closed circuit voltage:

1:00 = 13.33 volts <<< I measured a voltage after 1 min to show initial voltage drop
15.00 = 13.04 V
30:00 = 13.03 V
45:00 = 13.02 V
60:00 = 13.02 V <<< I took measurements every 15 minutes only for the first hour to act as a control for previous tests, then every 30 minutes for the remaining 4 hours because I've got other things to do!:D
1:30:00 = 13.01 V
2:00:00 = 12.99 V
2:30:00 = 12.97 V
3:00:00 = 12.93 V
3:45:00 = 12.92 V <<< sorry, I was late checking the voltage.....(other things....)
4:00:00 = 12.91 V <<< ambient temperature 12.2
4:30:00 = 12.90 V
5:00:00 = 12.88 V

SHUTDOWN.......

Open circuit voltage after load:
5:05:00 = 13.08 V
5:10:00 = 13.10 V
5:15:00 = 13.10 V <<< ambient temperature 11.3

Test 5:

outside temperature: 9 Celsius
Battery open circuit voltage: 13.33 volts

Test begins....

1:00 = 13.11 V
15:00 = 13.05 V
30:00 = 13.04 V
45:00 = 13.03 V
60:00 = 13.03 V
1:30:00 = 13.02 V
2:00:00 = 13.00 V
2:30:00 = 12.96 V
3:00:00 = 12.94 V
3:30:00 = 12.92 V
4:00:00 = 12.91 V <<< outside temperature 11.5
4:30:00 = 12.89 V
5:00:00 = 12.88 V

Shut down....

5:05:00 = 13.10 V
5:10:00 = 13.11 V
5:15:00 = 13.12 V <<< outside temperature 13

Test 6:

Voltage before test: 13.60V
outside temperature: 9.5 celsius
Powersetting: 5 (62+amps)

Test starts:

1:00 - 12.79V
5:00 - 12.69V
10:00 - 12.69V
15:00 - 12.69V
30:00 - 12.68V <<< amp reading now shows 61 amps

Problem found......

There was a loose connection between two of the cells, instead of scrubbing the test I tightened the terminal bolt and carried on. You can see the voltage increace after I tightened the bolt.

36:00 - 12.76V
45:00 - 12.72V
60:00 - 12.70V
1:15:00 - 12.68V
1:30:00 - 12.68V
2:00:00 - 12.63V
2:30:00 - 12.55V
3:00:00 - 12.38V <<< outside temperature 10.5 celsuis
3:15:00 - 12.20V
3:20:00 - 12.07V <<< amp gauge now shows 60 amps
3:25:00 - 11.92V
3:30:00 - 11.72V
3:35:00 - 11.44V <<< I've been told by my contact that the lowest safe voltage is 9.2V

Shut down:

1:00 - 12.20V
5:00 - 12.48V
10:00 - 12.59V
15:00 - 12.63V

Test 7:

Voltage before test: 13.37V
Outside temperature: 9.5
Setting : 60 amps

1:00 - 12.82 V <<<62 Amps
5:00 - 12.78 V <<<61 Amps
10:00 - 12.77 V
15:00 - 12.75 V
30:00 - 12.73 V
45:00 - 12.68 V
60:00 - 12.66 V
1:30:00 - 12.62 V
2:00:00 - 12.50 V
2:30:00 - 11.95 V <<<60 Amps
2:45:00 - 11.08 V <<< 59 Amps
2:50:00 - 10.59 V <<<58 Amps
2:53:00 - 10.30 V <<< 50 Amps....test terminated (outside temp 10.5)

Here is the main testing thread which includes comments, photos and discussion.

Thanks to david85 for keeping a detailed journal of his tests.
 

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Discussion Starter #2
I heard my name....and I did what!!??:eek:

Oh wait, that was me....:D Hi Robert.

Officially the tech is about 5 years old and thats why the projected shelf or calender life cannot be verified for sure (unless you have a time machine or something). Cycle life has supposedly been verified on thundersky batteries by independents, I think the claims for cycle life can generally be trusted. Thundersky is a competitor of the company I am working with and they both sell LiFePO4 batteries intended for EVs.

Pricing still seems to be in flux, but I can say that the general trend is for falling prices. If you are quoted more than $0.50/ watt hour, than they are probably charging too much, you can afford to demand better because competition within china to sell LiFePO4 batteries is heating up at the moment.

My testing has primarily served to verify the discharge curve profile, as well as the total energy stored in the cells. My discharge curves look exactly like that of the documentation of the battery from the supplier. Informal testing of Higher C loads seems to indicate results that agree with the factory claims. Sadly I have no way to personally verify the cycle life. I've done all that I can.
 

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Any idea when we'll be approaching .10/wh? I've got a 33kw pack so at .50 that's a chunk of money! At 5c/wh we're talking long range driving!

Great work David, I've followed your thread as well.
Thanks for the kind words.

When will we see $0.10/watt hour? If I had the answer to that, I would have it made! LOL. What I've learned so far, is that even at the retail level, $0.50/watt hour is the upper limit of what you should pay. Larger purchases could probably drop the price to half that, but I have not yet seen prices in the $0.25/watt hour range. But prices are going in that direction, and a big enough order could probably yield such results already. Don't ask me how big an order it would take though, I don't know and I don't think I would want to know.
 

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Thanks for the kind words.

When will we see $0.10/watt hour? If I had the answer to that, I would have it made! LOL. What I've learned so far, is that even at the retail level, $0.50/watt hour is the upper limit of what you should pay. Larger purchases could probably drop the price to half that, but I have not yet seen prices in the $0.25/watt hour range. But prices are going in that direction, and a big enough order could probably yield such results already. Don't ask me how big an order it would take though, I don't know and I don't think I would want to know.

my guess is 10,000 units OR 100,000 units (depending on the factories size) is when you'd see the lowest prices.

This could be any size however... so possibly 3.2v x 100ah packs at that size could yield a 20 cent/wh price, if you were manufacturing 1000 cars of course :p
 

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Hi Technologic, Long time no see.

You are probably right about the volume. I only wish I could even dream about building 1000 EVs....:(

I'll feel better when I start driving my EV this spring (if all goes well).
 

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Hi, following on from david85's comment above - with regards to smaller LiFePO4 packs, I have had two orders from Optimum Batteries (http://www.optimum-china.com/) of 36V 15Ah and 36V 10Ah packs which i can't fault - manufacturing was very tidy (pulled one apart to have a closer look), i have had no problems with any of the packs (16 in total) and found Optimum to be very professional and obliging. I use the packs for electric skateboards - doubles the range compared to the original SLA packs and delivers great performance. The built in BMS on the packs deliver up to a constant 45Amps with no discernible drop off in performance until flat....Hope that helps, Cheers Nigel
 
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