# Lithium Mixing Old and New - How New is Old?



## T1 Terry (Jan 29, 2011)

Are you thinking of running the new pack directly in series with the old pack, as in, 
one old cell and one new cell linked to make the added capacity?
or
another 32 cell pack run in parallel?

If you can organise your battery boxes so the one old and one new cell in parallel and as long as you don't drag the old cells down below 2v under load I think you could get away with around 200 cycles and not have a problem.

If you can only do the second pack as a parallel connection then there will alway be a problem between old and new cells and the new will be punished excessively till they are weakened to the level of the older pack.

T1 Terry


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## green caveman (Oct 2, 2009)

T1 Terry said:


> Are you thinking of running the new pack directly in series with the old pack, as in,
> one old cell and one new cell linked to make the added capacity?
> or
> another 32 cell pack run in parallel?
> ...


I hadn't really considered the configuration. One old/one new in parallel would be fairly easy if the capacity is the same (so the sizes are the same). With different sized cells it would be a bigger rebuild.

Do you really think that they degrade that rapidly? 200 cycles is only a little more than 5% of the life of the cells.


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## T1 Terry (Jan 29, 2011)

green caveman said:


> I hadn't really considered the configuration. One old/one new in parallel would be fairly easy if the capacity is the same (so the sizes are the same). With different sized cells it would be a bigger rebuild.
> 
> Do you really think that they degrade that rapidly? 200 cycles is only a little more than 5% of the life of the cells.


Fixed my goof, but at least you understood what I meant.
It's the 3C that ages the cells rapidly, the 3,000 and 5,000 cycles quoted are at a 0.5C discharge and charge rate so comparing those quoted figures with figures for a discharge rate 6 times higher isn't a realistic comparison. By 1,000 cycles the degradation will be noticeable but that is 3 yrs use on a virtually daily basis. That now make 200 cycles 20% of the service life, makes more sense now doesn't it?
The cells aren't dead after 1,000 cycles, just the 3C causes a far greater sag, by doubling the capacity the discharge rate per cell drops to 1.5C and the life is longer, as long as the discharge is even across the cells, the jury is still out on how exactly to achieve that.
Dropping the cell voltage below 2v while discharging heats the electrolyte, above 60 deg C the electrolyte starts to separate and some of the material coats the carbon anode trapping lithium ions and sealing off potential spots for intercalation, no ion transfer, no electrical current created and the problem compounds, not only is the potential C rating reduced but so is the capacity because the lithium ions are lost. This reaction is not reversible, it's there for ever.

T1 Terry


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## EVfun (Mar 14, 2010)

The buggy in my avatar runs a 32 cell pack of 60 amp hour cells. The range is about 30 miles city or 20 miles freeway. I am close to 3C (180 amps) at 60 mph. The car only weighs 1100 lb. so I wouldn't expect a such a pack to go 30 miles in a more normal car. Still, it should be enough for a 20 mile range. I'm rather hard on the throttle. Most cars converted with such a pack have a shot at being lighter than they where before.

You should be able to parallel cells from the same manufacturer and capacity if the new ones are purchased later. For the first year or two of service they should remain close enough to add more cells. The catch is, no one knows when the a given manufacturer will make a change significant enough to make paralleling an issue.


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## green caveman (Oct 2, 2009)

Terry,



T1 Terry said:


> It's the 3C that ages the cells rapidly, the 3,000 and 5,000 cycles quoted are at a 0.5C discharge and charge rate so comparing those quoted figures with figures for a discharge rate 6 times higher isn't a realistic comparison.


Good point, and what sucks about that is that you're obviously more likely to pull 3C from the smaller pack. It's not paranoia if the world really is out to get you.


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## green caveman (Oct 2, 2009)

EVfun said:


> The buggy in my avatar runs a 32 cell pack of 60 amp hour cells. The range is about 30 miles city or 20 miles freeway. I am close to 3C (180 amps) at 60 mph. The car only weighs 1100 lb. so I wouldn't expect a such a pack to go 30 miles in a more normal car. Still, it should be enough for a 20 mile range. I'm rather hard on the throttle. Most cars converted with such a pack have a shot at being lighter than they where before.
> 
> You should be able to parallel cells from the same manufacturer and capacity if the new ones are purchased later. For the first year or two of service they should remain close enough to add more cells. The catch is, no one knows when the a given manufacturer will make a change significant enough to make paralleling an issue.


What would gets us to 3C is the hills. The conversion that will get the Lithiums is a Suzuki Sidekick. 2D softtop so it'll probably be about 2200lbs with lithiums. We have an old Jet Industries Electravan that with LA is about that same weight or just a little more and it will pull somewhere between 150 and 200A at 25mph on the hills.

I'm thinking the sweet-spot might be 80Ah (some 60's some 20's a couple of 40's who knows). There's really not much value here in having much more than 20 miles range. That'll get anywhere around town and to get anywhere else you need 60+ miles.


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## Duncan (Dec 8, 2008)

_There's really not much value here in having much more than 20 miles range. That'll get anywhere around town and to get anywhere else you need 60+ miles.

_That is what I found- so I went and bought a pack of Headways_, 
_I am going with 44S2P 16Ah Headway cells - 10C continuous, 15C for 10 secondsThey are a bit more expensive than the CALB's but should cope with me playing at silly buggers much better


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## EVfun (Mar 14, 2010)

I have my controller turned up to 420 amps right now. That means my peaks are 7C. Thunder Sky and CALB both spec their cells for peak currents greater than 3C. Realistically, it is hard to use up the full range in 1 hour with normal traffic and time at your destination(s) so the average discharge is not more than 1C. I've never felt any warmth coming out of the terminals or sides of the cells and I check often. You pays your money and you takes your choice.

If you are going to run a 102 volt pack make sure you have a motor that will makes plenty of rpm per volt (less torque per amp.) I'm running a Prestolite MTC-4001 and my peak horsepower (420 volts at about 87 volts) is at about 3000-3100 rpm. If you use a ADC 9 inch FB-1 or Netgain WarP 9 the you will pull the rpm at peak power down to about 2400-2500 rpm (with more torque.) That is not the range your transaxle is geared for, you will find yourself in the higher gears and struggling for higher speeds. For a Geo Metro/ Chevy Sprint I would recommend an ADC 6.7 inch motor (one of the larger ones with a 1-1/8 inch shaft), ADC 8 inch motor, or a Netgain Impulse 9 (that is shorter than a WarP 9 and favors more rpm at less torque.)

How about a pack of 40, 70 amp hour CALB cells? That would help the motor rev better and since it is about 45% more capacity your peaks could be lower. For instance, you could have the same 40 horsepower I get from my pack at 336 amps, which is only a 4.8C peak discharge rate. I'd love to tell you that the cells like this kind of demanding service just fine, but you would have to wait a few more years for me to find out. It's what I'm figuring out now.


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## madmike8 (Jun 16, 2011)

Evfun, I'm building a t-bucket that from my estimates will come in under 1000 lbs. I'll be using a 7.2" Prestolite motor mju-4006 it's 15" long and around 100 lbs. I only need a range of 20 miles since my Daily trips are under 15 miles. 45mph is the top speed in the area I drive. I was originally going to just copy your buggy and use 32 60ah cells... But what do you think about 45 40ah CALB cells limited to 400A max?


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## green caveman (Oct 2, 2009)

EVfun said:


> Realistically, it is hard to use up the full range in 1 hour with normal traffic and time at your destination(s) so the average discharge is not more than 1C. I've never felt any warmth coming out of the terminals or sides of the cells and I check often. You pays your money and you takes your choice.


I'm not really worried about over heating, although with a 3C draw and then a 0.5(??)C regen maybe I should be.



EVfun said:


> If you are going to run a 102 volt pack.[...]
> How about a pack of 40, 70 amp hour CALB cells?


The 104V was fixed because we had 13x8V floodies that a local guy sold to us slightly used. So bought the controller, DC/DC, etc. based on 104V. This build has been going on for a while, and in the meantime we bought the Electravan (Subaru 600 microvan, very cool, maintenance nightmare). Floodies went into that (was 102V 17x6) but the Sidekick is still stuck with 104V even though I won't be buying more lead.

Motor is also fixed - it's been around for a while. 10.5" GE sepex forklift. 

I could just go out and buy a pack but I'd rather get creative and build a pack incrementally or from surplus cells - so long as it's creativity and not stupidity. It sounds as though incrementally, unless the increment is very short, may not work that well. And if the increment is short you end up dismantling the car as soon as you've finished it, so probably not worthwhile.

In the worst case and small pack could go into the Electravan whenever the floodies die (which, after tonight's drive is looking as though it might be sooner than I'd like).



madmike8 said:


> Evfun, I'm building a t-bucket that from my estimates will come in under 1000 lbs. I'll be using a 7.2" Prestolite motor mju-4006 it's 15" long and around 100 lbs. I only need a range of 20 miles since my Daily trips are under 15 miles. 45mph is the top speed in the area I drive. I was originally going to just copy your buggy and use 32 60ah cells... But what do you think about 45 40ah CALB cells limited to 400A max?


Same situation, fastest road within range is 45mph (there's a short stretch of 50mph, but that's leading out of town - a place we don't want to go).

If you go with 48 40Ah, then the packs have the same storage and I think the only thing you'd get is a better top speed. 45 is a slightly smaller pack you're going to be pulling (slightly) more XC Amps. 


EDIT: Just found the words to describe why I don't want to go out and just buy a pack (courtesy of Neal Stephenson's book _Cryptonomicon)_ it "offends my native frugality"_.
_


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## EVfun (Mar 14, 2010)

madmike8 said:


> Evfun, I'm building a t-bucket that from my estimates will come in under 1000 lbs. I'll be using a 7.2" Prestolite motor mju-4006 it's 15" long and around 100 lbs. I only need a range of 20 miles since my Daily trips are under 15 miles. 45mph is the top speed in the area I drive. I was originally going to just copy your buggy and use 32 60ah cells... But what do you think about 45 40ah CALB cells limited to 400A max?


If your motor is a 36 volt or 48 volt motor designed to run at a decent rpm it might work even better than my MTC-4001 with a 32 cell pack (the very low gearing of a 40 HP Bug transaxle doesn't help me either.) That said, I would be inclined to go with 48, 40 amp hour cells (same pack capacity.) 

If you use a controller that can handle the voltage and has separate settings for motor amps and battery amps (Zilla, Soliton) you can extend your power band with the larger number of lower amp hour cells. To make my explanation math easy I'll just call each cell 3 volts under load. My Zilla is set for 840 motor amps and 420 battery amps (7C.) My motor can see 840 amps up to 48 volts and then it slides to 420 amps at 96 volts. From that point upward in rpm the voltage won't rise but the amps continue to fall, so that is the upper end of peak power (about 3000 rpm.) If I had 48, 40 amp hour cells I could set my Zilla for 280 battery amps (7C) and 840 motor amps. I could apply 840 amps to the motor up to 48 volts. From there the motor amps will drop as the motor voltage rises. One point on the line is 96 motor volts at 420 motor amps, just like with the lower voltage pack. The thing is, the higher voltage pack can continue to push the motor voltage higher so the power won't start dropping at that point. I could keep the motor at full power up to 144 volts at 280 amps, somewhere around 4500 rpm (provided your motor can take 144 volts, or more realistically 130 volts.)


48 volts at 840 amps = 96 volts at 420 amps = 144 volts at 280 amps = 40320 watts


If the smaller cell will happily handle a higher C discharge rate you get more power too. I don't think the 40 AH cell will really be happy at 10C, but perhaps 8C. I will most likely add another 3 cells to my Buggy over the winter. I have a total of 42, 60 amp hour Thunder Sky LiFeYPO4 cells from the same batch (Feb, 2010.) 35 cells will be at the upper limit of my current DC>DC converter. Perhaps I'll use the other 7 as a 24 volt (almost) battery for a rechargeable lawn mower with some serious run time.


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## EVfun (Mar 14, 2010)

green caveman said:


> I'm not really worried about over heating, although with a 3C draw and then a 0.5(??)C regen maybe I should be.
> 
> The 104V was fixed because we had 13x8V floodies that a local guy sold to us slightly used. So bought the controller, DC/DC, etc. based on 104V.


My experience says you will have no heating problems to worry about. I'm not seeing heat and its a buggy -- I drive it like I stole it. 

Then 104 volts (+/- a few volts) it is! If you have had the car running on a 104 volt pack you already know how it drives. Making it Lithium will make it a bit quicker because it will loose weight and perhaps even a little faster since the voltage sag at full load will likely be less. I wouldn't go changing all that stuff in a working EV either. 

You will most likely need a new charger as Lithium does have to be charged correctly. For 32 cells I would recommend a charging voltage limit of 111 volts (3.47 vpc) to 116 volts (3.63 vpc.)


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## major (Apr 4, 2008)

EVfun said:


> If your motor is a 36 volt or 48 volt motor designed to run at a decent rpm it might work even better than my MTC-


Hi EVfun,

His MJU motor is similar to your MTC but has a 5 inch core stack where MTC is 7 inch. Both have the same 33 slot lamination and 33 bar commutator and same size brushes. So both motors would have about the same current rating but I suspect MTC would tolerate higher voltage. The shorter stack for MJU means proportionally less torque for a given current and higher RPM.

MJU was a 36/48V pump motor made mostly in unidirectional models for CW and CCW. It had the standard 4.5 degree advance for its rotation as did the MTC.

major


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## dtbaker (Jan 5, 2008)

madmike8 said:


> ... what do you think about 45 40ah CALB cells limited to 400A max?



10C is really pushing CALBs from the specs anyway, who knows how quick it will kill them.... if you want output, and don't need range, go with headways or pouch?

going with small cells, and planning to add more in parallel later just sounds like WAY too much time and possible points of failure.... just save up a little, and build with the 'final' configuration!


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## madmike8 (Jun 16, 2011)

400a is CALBs 10 second max based on their specs. In a 1000lb car I don't expect to pull that much very long. I'm just bouncing ideas around now, because talk is cheap  I will probably go with the 32 60ah-70ah cells.

Right now I'm still getting the chassis together. Hopefully I'll have it rolling by the end of the year.


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## GizmoEV (Nov 28, 2009)

I would caution against building the pack barely larger than needed for your regular run. When the cells get colder they will sag more under a given load and you won't get as much out of them and may end up short. Also, you will be discharging them lower which will shorten their cycle life. As the batteries age the useable range will decrease and the effective discharge will go higher with each use accelerating the aging process. If you need 12 miles range I'd size the pack for 24 miles.

You may also find you use the EV more when its range is higher than you usually need. When I had lead acid in my Gizmo I had about a 20 mile range at most. I usually limited drives to 15 miles. When I installed my LiFePO4 pack my range suddenly was 70 miles no matter how I drive it. Over the past 22 months I've had my Li pack installed I have put over 10,000 miles on it, over double what I put on in the previous 4+ years with a lead acid pack.


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## madmike8 (Jun 16, 2011)

I agree about having the range about double what is needed. I do have the ability to charge at work too if I need to. I've been driving my ICE car back and forth for about 15 years now. I go between 12-15 miles a day, and range is not a problem for it.


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## green caveman (Oct 2, 2009)

GizmoEV said:


> I would caution against building the pack barely larger than needed for your regular run. When the cells get colder they will sag more under a given load and you won't get as much out of them and may end up short. Also, you will be discharging them lower which will shorten their cycle life. As the batteries age the useable range will decrease and the effective discharge will go higher with each use accelerating the aging process. If you need 12 miles range I'd size the pack for 24 miles.
> 
> You may also find you use the EV more when its range is higher than you usually need. When I had lead acid in my Gizmo I had about a 20 mile range at most. I usually limited drives to 15 miles. When I installed my LiFePO4 pack my range suddenly was 70 miles no matter how I drive it. Over the past 22 months I've had my Li pack installed I have put over 10,000 miles on it, over double what I put on in the previous 4+ years with a lead acid pack.


All valid points. The counter-argument would be that the cost of batteries is still decreasing, at the moment that seems to be slowly, but there's some reasonable chance that they may fall rapidly. The technology of batteries is improving - the current and lifecycle performance has increased significantly even in the last few years.

So you could argue that if you buy a smaller pack now and trash the pack in, say two or three years, you may be able to buy more, better, batteries at that point. (Also take into account that people frequently trash their first pack). That is, for any given budget $X it may be that you can buy a medium pack now, or a small pack now and a large pack later. BUT this is pure speculation, it maybe that you can buy a small pack now and have to buy another small pack later (and then another for $X+$X/2).

Are you driving more or substituting more electric miles for gas miles?

EDIT: The Gizmo is cool! I assume that it must be comfortable if you've managed 10K+ miles in it.


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## GizmoEV (Nov 28, 2009)

green caveman said:


> Are you driving more or substituting more electric miles for gas miles?


A little bit of both but mostly substituting more e-miles for g-miles. When it is so inexpensive to refuel it is easier to be more careless with planning trips but that is a small percentage of the extra driving. I have some rental properties about 45 miles away and when I don't have to haul much equipment to go work on them I drive the Gizmo and recharge while I'm there. Mostly it has been that now I can still go do around town errands after getting home from work without having to attempt to recharge before going or risk running out of range.



green caveman said:


> EDIT: The Gizmo is cool! I assume that it must be comfortable if you've managed 10K+ miles in it.


It is more "cool" than comfortable. The suspension is a bit stiff so every pebble is felt. Putting LiFePO4 in it really made a big difference. When I have gone on longer runs my throttle finger gets a bit tired so I have to switch fingers when it is safe to do so. I really need a cruise control for those trips some times. If I had a full bodied heated EV I wouldn't drive the Gizmo on those longer trips as often but then my wife might drive the full size EV and leave me with the Gizmo so who knows.


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