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View Full Version : Upgrade-itis vrs Lifepo4 cycle time



DRZ400
01 April 2012, 0944
With the recent availability of cheap A123 20ah cells I'm seriously considering upgrading my 24 Calab 40AH either completely or a 20AH sub pack. The CALB's are rated at 3C where as the A123's are reported to be 15C continous. Although I've been very happy with the Calabs, they were a huge improvement over the AGM's....15C cells are hard to ignore! Makes me think, I have about 75 cycles on my Calabs that were supposed to last me some 2000 cycles. Does cycle time really matter in a technology that is improving so much every year?

ardhout
01 April 2012, 1100
What do you mean with a sub pack? An extra pack just parallel to the original Calbs? Or a pack that will be used only when requiring many amps when accelerating fast?
75 cycles is not much, maybe you can use them for something else?

Skeezmour
01 April 2012, 1120
I also like the CALB cells very much but for bikes I need just a bit more power from them. I think a small pack of those 20ah A123 cells would be so much fun.

DRZ400
01 April 2012, 1208
What do you mean with a sub pack? An extra pack just parallel to the original Calbs? Or a pack that will be used only when requiring many amps when accelerating fast?
75 cycles is not much, maybe you can use them for something else?

Yes in parallel. Oh, I'll find something to do with them!

DRZ400
01 April 2012, 1210
I also like the CALB cells very much but for bikes I need just a bit more power from them. I think a small pack of those 20ah A123 cells would be so much fun.

Yeah, I'd like to see the ~10 volt sag during accelleration go away!

ardhout
01 April 2012, 1217
I read a while ago that Mark had an extra Lipo-pack or something on top of his LifePo4 pack which kicked in when a lot of power was needed, keeping the discharge from the LiFePo4 pack below 3C.

DRZ400
01 April 2012, 1230
Yeah, he made sure his sub pack was at a lower voltage and used a diode between them. Doing it that way you have to charge the packs independently.

Doctorbass
01 April 2012, 2023
Here is my review of my A123 20Ah pouch i got from victpower last week:

http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=37955&start=15
http://www.endless-sphere.com/forums/viewtopic.php?f=14&t=37955&start=30

Doc

liveforphysics
02 April 2012, 1129
Yeah, I'd like to see the ~10 volt sag during accelleration go away!

I so hear you on this. Saggy packs are so unsatisfying to use.

Skeezmour
02 April 2012, 1131
I so hear you on this. Saggy packs are so unsatisfying to use.

Is lipo the new "little blue pill" :)

DRZ400
02 April 2012, 1146
I so hear you on this. Saggy packs are so unsatisfying to use.

Yeah, not so bad in the summer....but below 60F the bike feels soft even right off the charger, plus I loose about ~3 mph. Funny, when I switched to Lifepo4 from lead last spring I was so happy....now the thought of going from a 4c to 15c cell. Well, at least I can still use my mini-bms! Plus I think I'll add a cell just for a little more punch. Upgrade-itis.... may help explain the 6 flat panels in my house!

DRZ400
02 April 2012, 1153
Is lipo the new "little blue pill" :) I won't put Lipo in my bike (in my garage attached to my house)...I've been flying RC choppers and planes for 15 years....lots of puffed packs, dead cells and a couple fires while charging. In my club there have been at least a dozen stories of lipos catching fire while charging, use and even storage (little harmless looking 3S 2200 packs). I won't argue about performance...they are outstanding. Lipo and brushless motors made the electric RC market catch fire! err made it x100!

markcycle
02 April 2012, 1408
I fully understand ones caution with Lipo and coming out of the RC world and I can see why one wouldn't use the stuff.
But my personnel experience has been less eventful and I think it's because the the RC world treats batteries differently than one would (or should) in an EV. Most fly there planes until the battery is fully discharged pull almost the max C rate, let them sit out in the sun and cook and charge them as fast as they can. I'm sure there are stories of the batteries just bursting into flames for no know reason.

Now look at applications where the batteries are used conservatively like cell phones - every cell phone some fires yes but far less than is seen in the RC world.

Lipo can be dangerous no doubt about it, but how they are used, monitored and treated is as important as the chemistry being used.

My 8P 28S pack 115 volt fully charged 2 volt drop at 250 amps

DRZ400
02 April 2012, 1448
Yeah, unfortunately my experiance with them in RC makes me shy away from putting 60lbs of them directly under my yam bag. Prior to Lipo I used Nicad and Nimi...never had one flame on me. Course, I'll never go back....Lipo's are power houses! You have a good point though, my 3d planes pull 50 amps from a 30C 2200mah cell.

ardhout
03 April 2012, 0020
My 8P 28S pack 115 volt fully charged 2 volt drop at 250 amps

Mark, can you supply me again with a link to the wiring diagram for the Lipo sub-pack ?
Maybe that's something I want to implement later. (always need to have some new projects :-)
Now I have a 153V/32Ah battery-pack for my MHM-602 motor but maybe I will be stressing the batteries (16Ah 40160S headway cells) too much, not sure yet.
Hope to test-run this spring.

markcycle
03 April 2012, 0617
Here you go
http://dl.dropbox.com/u/3803661/voltage Booster.jpg (http://dl.dropbox.com/u/3803661/voltage%20Booster.jpg)

Zachary Rubin
03 April 2012, 1918
What does paralleling those diodes do for you?

DRZ400
04 April 2012, 1524
What does paralleling those diodes do for you?

Likely nothing unless the diodes themselves are PERFECTLY matched...otherwise which ever has the lowest forward voltage will take 100% of load. If the wire runs have enough series R could help. I like the idea of a booster pack though...may do myself.