# Upgradig from Flooded - to AGM or LiFePO4?



## VoltC (Jan 5, 2009)

Hi,

I've been running my Porsche 911 with 9" NetGain DC motor, 500A controller and 12x12v (144V) 20kWh flooded lead batteries for several months. It all works fine, except the performance is rather anemic. The range in real driving is 30-40 miles and I can't use the full 20kWh anyway - once the battery drops almost dead and the car barely moves, it refuels with about 13kWh.

I want to improve the performance, including being able to keep high current (at least 500A) for longer time at minimal voltage drop (now it drops to about 300A in several seconds and voltage drops substantially too). Plus improve the range a bit. I will be upgrading to a 1000A controller in the future, but not yet (so the batteries should work with 1000A as well).

What is the battery improvement recommendation? 

Will going to AGM offer much improvement? I see drag races are using them.

Or should I go straight to lithium? I'm thinking something like 45 of Thunder Sky TS-160Ah or similar, which would give me 23kWh. 

Has anyone been driving both lead and lithium for comparison? Is lithium really holding voltage and high current for longer time and is worth the extra $$$$$? How much of that 23kWh is really usable - how much energy do you charge in (refuel) after discharging it (compare to my 13kWh refueling of lead)?

Any pointers appreciated

thanks

George


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## AndyH (Jun 15, 2008)

Just a quick side by side. 36V 12Ah SLA VS. 36V 10Ah LiFePO4, both at 10A/~1C.

Range and acceleration will go up significantly if you dump lead. Weight will drop significantly as well for similar performance.

You might want to use larger cells if you want to use Thunder Sky or Sky Energy and pull 1000A from them...and still want less voltage sag. 3C will take the cells down to around 2.9-3V in the summer. 1.5C continuous is probably a better target.

How much time do you spend with the pedal all the way down?


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## EVfun (Mar 14, 2010)

I'm moving from AGM to Lithium right now. I don't have a ThunderSky powered vehicle yet so no direct comparison, but AGMs are an expensive way to go. A double string of group 34 AGMs (like Optimas) won't get you a real world 13 kWh. They only have around 30-33 amp hours available at EV discharge rates. 

Here is my case for Lithium. 13 Optimas would cost about $2200. 40 ThunderSky 60 amp hour Lithium cells cost me $3000. Both require a regulator/management system. If the TS cells can deliver 36 amp hours in the EV service the range is the same. The EV is lighter and easier to build with the TS cells. So I scrapped my Optima battery racks (front and rear racks) and built a front battery box. I won't have to make any suspension changes now as the weight and weight distribution will be nearly stock. 

I suspect that high performance is still cheaper with AGMs. After all, about $260 each will get you 12 volt AGMs that will dish out over 1000 amps (I have the group 34 Hawker battery in mind.)


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## Sunking (Aug 10, 2009)

AGM is not going to gain you anything, just cost you 2 to 3 times what FLA does. AGM is still lead acid. Its only advantage is the jar will not crack in sub arctic temps, and can be mounted in unusual orientations.


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## EVfun (Mar 14, 2010)

Sunking said:


> AGM is not going to gain you anything, just cost you 2 to 3 times what FLA does. AGM is still lead acid. Its only advantage is the jar will not crack in sub arctic temps, and can be mounted in unusual orientations.


...and performance! Golf cart lead will only give a vehicle about the performance of an old 40 horsepower VW Beetle. 12v flooded lead can do better but still not great. AGMs can get you sports car performance if you don't need a lot of range (check out the White Zombie, for example.)

A golf cart battery is about 60 lb. and can dish out about 500 amps at 5.25 volts for about 17 pounds per horsepower, just for the battery (and not including motor losses.) An Optima can dish out about 800 amps at 10.5 volts for about 3.6 pounds per horsepower.


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## DavidDymaxion (Dec 1, 2008)

I would love to see pics of your conversion -- do you have a web page? I have a 911 conversion in progress, my page is http://ExplodingDinosaurs.com .

Since I want performance and not range, I went AGM. To get AGM performance out of Thundersky batteries I calculated about the same weight of batteries.

A123 batteries are the power monsters that are setting records, but that would be something like $40k+ for batteries.


VoltC said:


> Hi,
> 
> I've been running my Porsche 911 with 9" NetGain DC motor, 500A controller and 12x12v (144V) 20kWh flooded lead batteries for several months. It all works fine, except the performance is rather anemic. The range in real driving is 30-40 miles and I can't use the full 20kWh anyway - once the battery drops almost dead and the car barely moves, it refuels with about 13kWh.
> 
> ...


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## EVfun (Mar 14, 2010)

I keep a few picture up on a simple page at EVfun. The best pictures to see what is changing under the hood are #23, #26, and #28. That last picture is just the batteries sitting on some 3/8 inch thick aluminum on the battery frame. The pack when installed will be 5 rows of 8 batteries each.


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## jackbauer (Jan 12, 2008)

I'm running 8 Odyssey PC2150 batteries. Yes they are heavy. Damn heavy. But sag is almost non existant. The pack easily sustains 250amps without dropping below 96v.


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## DIYguy (Sep 18, 2008)

Sunking said:


> AGM is not going to gain you anything, just cost you 2 to 3 times what FLA does. AGM is still lead acid. Its only advantage is the jar will not crack in sub arctic temps, and can be mounted in unusual orientations.


I would say that this is not acurrate. AGMs have a lower peukerts due to lower resistance which also translates into more ah out and higher discharge rates than flooded....signifcantly higher in fact. They also perform much better in cold weather. The lead-tin chemistry is a common high current version. 
I can spin both wheels on dry pavement (posi-trac) in a small pick up truck in first gear (with 1600 lbs of lead... pull over 1100 battery amps and have had the truck over 100 mph before letting off (still climbing...and not slowly either). 
(Yes, I would still like Lithium )


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## VoltC (Jan 5, 2009)

I rarely keep the "pedal to the metal" but when I do it's usually for 5-10 sec, that's the time during which the current gets halved. Peukert's law works against me :-(

I have not got a chance to post the pictures etc on a web site yet, but should do it soon. I'm using size 31 batteries (US Battery 31 TMX, $1.3k for the pack) so it would be an easy conversion to AGM which come in the same sizes, but based on the feedback it sounds like LiFePO4 would probably be better overall - just going through one instead of 2 upgrades 

A quick price check is not encouraging though - about 8 times more for lithium with battery controllers etc vs flooded lead. The best I see is around $1.05 per Ah which still comes to over $10k for a complete solution, vs $3k for AGM. Needs more research, but looks promising. Thanks to all who chimed in. 

David - looks like you have a cool conversion coming up - you mention the Salt Flats on your web site - are you somewhere near by? I will be driving past the Flats next Friday (Apr 16th).


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