# Mixing Lead and Lion



## meanderingthemaze (Jan 25, 2010)

Has anyone attempted to employ two packs in parallel with different chemistries. I was wondering if by having a larger lead acid pack and smaller Lion pack, if you would be able to get the benefits of Lion without braking the bank?

If there are no cases of people doing it, anyone care to speculate?


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## Ziggythewiz (May 16, 2010)

I know there was someone who did this, and reported good results. His implementation was using hybrid battery buddy packs. I have to dig for the link or messages sent.

The primary issue here is the difference in chemistry voltages. I don't remember what he was using, but flooded lead acid requires a higher voltage during charging than lithium could handle, but with an AGM it may work without independant charging.

I think the main drawback is that cheap batteries (flooded) aren't directly compatible, and AGMs are expensive enough anyway that you might as well just do lithium.


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## meanderingthemaze (Jan 25, 2010)

Ah, yes, good point about the voltage differences. It seems like it would almost require two completely different systems motor/controller/charger or some sophisticated way of regulating or adjusting voltage. 

If you find that example though, would be good to check out. Thanks!


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## Ziggythewiz (May 16, 2010)

Links:

Experiment: http://www.flickr.com/photos/mbarkley/sets/72157603514650280/

EVDL discussion: http://electric-vehicle-discussion-...ng-Lead-Batteries-with-Lithium-td3317351.html

Discussion here: http://www.diyelectriccar.com/forums/showthread.php?t=21315


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## meanderingthemaze (Jan 25, 2010)

Awesome, thanks for the links. My guess is that it's either too complicated or expensive to be practical, or no one is pursuing it because lead acid is so unappealing to everyone. 

But I'm going to read through all of that and see if I can contact that guy who built the hybrid pack.


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## Ziggythewiz (May 16, 2010)

Yeah, it's a cool thought but pretty complex/risky. Who knows how the cycles will add up. Is one light to the next a discharge/charge cycle?

I suppose the safest way would be to have a parallel string on a separate contactor, with volt/ammeters on each string so if the lithium got too low you could cut it out. It would require an extra charger, but I plan to make one anyway to upgrade to lithium someday so no extra cost there. Maybe even a mini test like that guy did with part of the pack would be good to test lifecycles over a year or two. With headways at $15-25 a small test wouldn't be too bad.

So much easier with the budy packs, but my 120V system hits 160 while charging.


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## DIYguy (Sep 18, 2008)

meanderingthemaze said:


> Awesome, thanks for the links. My guess is that it's either too complicated or expensive to be practical, or no one is pursuing it because lead acid is so unappealing to everyone.
> 
> But I'm going to read through all of that and see if I can contact that guy who built the hybrid pack.


Lithium iron phosphate and lead can co-exist in parallel strings. They actually help each other out. . lithium helping the lead likely more than vise versa. You don't need separate control systems. Depending on the lead type (floods vs AGM,GELs) and the number of lifepo cells, you may need separate chargers.


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## meanderingthemaze (Jan 25, 2010)

Right, so if you want to be safe, isolate everything. Otherwise you are venturing into risky territory, that could result in fire or explosion!

I sent an email to the guy who did those tests. But my guess is that it didn't totally pan out. Otherwise we probably would have heard of it on here.


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## scott (Feb 15, 2009)

Hi, Brian at BELKTRONIX(belktronix.com) did this and has a pic(http://www.belktronix.com/Scirocco1.html. hope this helps


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## TruEnergy (Apr 6, 2009)

OK, isolation is a good thing. Plus, separate charging.

So what about a dual pack setup - LiPo for surge, Lead for range.

Isolate packs with high power diodes for the LiPo and a DC/DC converter for the Lead.

Power process is as follows:
1. Tromp on throttle.
2. Power surge sags Lead pack so LiPo becomes main source.
3. Ease off throttle and Lead begins to contribute.
4. Cruising speed sees equal contribution from both packs.
5. LiPo voltage drops due to excessive spirited driving.
6. Lead pack voltage is slightly higher and contributes more energy.
7. Process continues till both packs need recharge.
8. In the event of excessive LiPo drain, the lead pack would become main source.
9. It would be wise to gauge system based on 50% DOD of lead. LiPo would not be fully utilized - unless the DC/DC cuts out at 50%. This would leave just LiPo to limp home.

Other links showed LiPo directly paralleled. Have not yet heard if this helped or if problems were encountered with inconsistent chemistry.

The DC/DC could be eliminated and more diodes used, but you would lose some control over the system.

Would this work? Or would the controllers have an issue with inconsistent current supply? Would the supply be overly inconsistent? I think most of this could be controlled through the DC/DC converter.... Thoughts????


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## DIYguy (Sep 18, 2008)

You don't need any isolation other than for charging. Just match the voltage and connect in parallel. Contactors to separate for charging, that's all.


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## TruEnergy (Apr 6, 2009)

My thoughts on the isolation were to prevent the LiPos from charging the Lead. Or vice-versa. I think separating them would give the max benefit from each type.

In a reduced current environment, the Lead should last longer and provide a better ROI on the pack as a whole.

If something like this were to actually work, that is....


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## rmay635703 (Oct 23, 2008)

TruEnergy said:


> My thoughts on the isolation were to prevent the LiPos from charging the Lead. Or vice-versa. I think separating them would give the max benefit from each type.
> 
> In a reduced current environment, the Lead should last longer and provide a better ROI on the pack as a whole.
> 
> If something like this were to actually work, that is....


Get a pair of motor run diodes out of an old $50 set of curtis 1204s and voila instant isolation.

Thing is I would think you would want the lead acid pegged at a specific discharge rate using the lithium as a cap.

If you knew what your average current draw was averaged over your typical trip you could figure the number of amps the FLA would have to donate the entire time using lithium to level out the peaks reducing the effects of Peukert.

Cheers
Ryan


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## DIYguy (Sep 18, 2008)

You want the two packs to share. This is the point. The lower resistance pack dishes out more of the current when demanded and the bigger capacity may replenish. 
It does work and has been done. Somewhere on this site is a thread where one chap talks about his experiences with it. There r others also. 

Match the voltage. Connect parallel and separate for charging.


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## TruEnergy (Apr 6, 2009)

Yep, easiest way is parallel to run and separate to charge. Agreed.

However, independently controlling the Lead would allow you to limit the max discharge rate and maximize the Lead life. So instead of replacing the Lead after 2 or 3 years.... what if you stretched that out to 5 or 6?

Until something like this is tested and proven, I'd still say the easiest and most economical in the long run is still pure LiPo; as many experienced EVers here have stated.

I'm still compiling parts and funds for my own build, but this is something I might try just to get started. A bench test on a smaller scale should give a good indication without a major investment or risk.


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## TexasCotton (Sep 18, 2008)

DIYguy said:


> You don't need any isolation other than for charging. Just match the voltage and connect in parallel. Contactors to separate for charging, that's all.


 The guys at cal cars and phev eaa started out with mix battery packs.
The 04 Prius oem HV pack was 273V Nimh oem and they used high amp contactors with a AGM lead pack increase capacity.To see images and history go to PHV EAA,Most plug in kits now have now gone with LifePo4cells because of energy density and other factors.Some have also gone with additional oem nimh hv packs.


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## Ziggythewiz (May 16, 2010)

TruEnergy said:


> However, independently controlling the Lead would allow you to limit the max discharge rate and maximize the Lead life. So instead of replacing the Lead after 2 or 3 years.... what if you stretched that out to 5 or 6?
> 
> Until something like this is tested and proven, I'd still say the easiest and most economical in the long run is still pure LiPo; as many experienced EVers here have stated.


Except that you don't want to just maximize the lead life. You want to maximize both, but if you had to choose one, you maximize the lithium. Obviously a straight lithium pack is best, mixing the two is just a way to bridge the gap from lead to lithium.

Say you have a decent lead pack, and what you want is a 100ah lithium pack. You can get a 10-40 ah lithium pack for $500-$2000 and ~30-120 lbs. Hopefully the lead will have a long enough extra life to justify the expense, but you certainly want the lithium to live long enough to be part of an all lithium pack as well. If you go 40ah you just need to add 60 down the road to reach your goal, or if you do a headway or A123 booster pack it can still act as a booster when you switch to full lithium.

I don't know that a bench test would help much as the main unknown is cycle life. That would take quite some time to test and if you had the required gear to do a decent test you could probably just go full lithium instead. I suppose a test could identify the sharing ratio, so you can appropriately size the lithium.


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## ga2500ev (Apr 20, 2008)

TruEnergy said:


> Yep, easiest way is parallel to run and separate to charge. Agreed.
> 
> However, independently controlling the Lead would allow you to limit the max discharge rate and maximize the Lead life. So instead of replacing the Lead after 2 or 3 years.... what if you stretched that out to 5 or 6?


The discharge rate isn't the issue. The discharge capacity is. Lead is killed when it is deeply discharged. You said earlier that you wanted to separate the packs and control the current so that one would not charge the other. This is exactly the opposite of what you want. If you can get the lithium to charge the lead you will extend the life of the lead no matter how hard you drive it current wise. It's the lithium that you want to protect from heavy current discharge. Most encased cells (Calb, Winston, Sinopoly) can only be driven at a continuous 2-3C current draw. Any more sustained will reduce the cycle life.

Generally the point of two packs is that the lithium is cost prohibitive. So that means that you have smaller lithium cells, which limits their current draw. So you use the lead to protect the lithium from the heavy current draw, and the lithium to protect the lead from deep discharge by recharging the lead when its voltage drops below the lithium operating voltage floor.

This requires a bit of fine tuning in terms of the voltages. But it's doable because lead's voltage drops steadily during discharge while lithium has a nearly flat discharge curve. So you set up the packs to that the lead takes the brunt of the work by having a higher operating voltage but the lithium has a higher resting voltage. So during discharge a nearly full lead pack will be drawn upon heavily, but during rest periods the lithium can recharge the lead so that it doesn't have deep discharge while operating.



> Until something like this is tested and proven, I'd still say the easiest and most economical in the long run is still pure LiPo; as many experienced EVers here have stated.
> 
> I'm still compiling parts and funds for my own build, but this is something I might try just to get started. A bench test on a smaller scale should give a good indication without a major investment or risk.


The solution I'm looking at is the gray market A123 lithium prismatic pouches in the 20 Ah capacity. They are cost competitive with both AGM lead and small cell lithium. The difference is that they are quite content to be discharged at 20C with no problem. So smaller packs can be put together that can handle the high current discharges that EVs require. 120 cells can be used to build an effective 6KWh pack under $3K USD.

ga2500ev


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## MN Driver (Sep 29, 2009)

I think the longest life would be pure LiFePO4, not LiPo. LiPo adds extra concerns such as not being able to charge it at low temperatures, which LiFePO4 seems to be much better at doing. LiPo puffed after the second time I did it and then I couldn't discharge it over about .25C and it was while I was holding it in my hand with me standing outside for about 45 minutes(was indoors with me right beforehand).

With that being said either make sure that LiPo never gets too cold or use 40Ah prismatics as your booster or a pack of 20Ah A123's since they are powerful and currently cheap and available(I don't expec them to be available for long, happened before when the Volt dropped them from consideration). Headway, I suppose but its pricey now that other options are cheaper and better. Either that or decomission your LiPo pack when it gets cold, but that's a harsh reality because lead is horrible to use when its freezing so that's the worst time for it to be on its own.

If I were using lithium of any sort to boost life of lead, the lithium pack would be small and cheap and would outlast the lead but I'd also have it working at its limit. Figuring lead acid pack conversions are usually cheap and use a low output controller with a 500 amp limit or so, a 40Ah LiFePO4 small pack appropriately voltage matched for the discharge profile of lead could take the gap and would have the rest time to cool off for a car that doesn't take forever to get going figuring it has a reasonable voltage(144v or so) and not too terrible of demands put on it. A 144v pack of 40Ah LiFePO4 would add a good 5760wh. Which isn't really that small, it's a 18 mile range boost if we figure a 250wh/mile more efficient and using 80% of the pack so it lasts awhile. The reduced voltage drop over the lead should help them last longer.

Due to the heavy nature of lead, it seems to me that you'd still be sitting with a low range pack but it should give a decent range boost, extra performance in any condition, especially the cold when lead is a bear.


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## MN Driver (Sep 29, 2009)

ga2500ev said:


> The discharge rate isn't the issue. The discharge capacity is. Lead is killed when it is deeply discharged. You said earlier that you wanted to separate the packs and control the current so that one would not charge the other. This is exactly the opposite of what you want. If you can get the lithium to charge the lead you will extend the life of the lead no matter how hard you drive it current wise. It's the lithium that you want to protect from heavy current discharge. Most encased cells (Calb, Winston, Sinopoly) can only be driven at a continuous 2-3C current draw. Any more sustained will reduce the cycle life.


Not quite. With a setup combining lead and lithium which the right nominal voltages chosen for the lithium, you won't be drawing continuously. Lead sags, a bunch. When it sags, the lithium takes the a large chunk of the load because it is a lower resistance and while cruising the lead doesn't sag as much and it will take a majority of the load at the point. It's the dymanics of the two chemistries. CALB rates their 40 to 70Ah packs at 10C for 10 seconds. A 40Ah pack can have 400 amps pulled from it for a short period. The lead will still have some load on it and I'm certain it will be getting over 100 amps drawn from it, it doesn't all do to the lead. A 20Ah A123 cell can handle an even higher discharge rate. I don't think you need to do much to protect the lithium. A car that has lead in it at all isn't likely going to have a 1000 amp controller with good design.


> Generally the point of two packs is that the lithium is cost prohibitive. So that means that you have smaller lithium cells, which limits their current draw. So you use the lead to protect the lithium from the heavy current draw, and the lithium to protect the lead from deep discharge by recharging the lead when its voltage drops below the lithium operating voltage floor.


I think the idea is more to get cheap range and protect the lead cells. Lead doesn't last long when you draw heavily from it. I've seen a Corvette conversion using a top of the line AGM pack lose two packs, one lasted less than a year. The lead will sag and the lithium takes the load. If everything is sized properly and the correct voltage for the lithium pack is chosen, you'd be fine.


> This requires a bit of fine tuning in terms of the voltages. But it's doable because lead's voltage drops steadily during discharge while lithium has a nearly flat discharge curve. So you set up the packs to that the lead takes the brunt of the work by having a higher operating voltage but the lithium has a higher resting voltage. So during discharge a nearly full lead pack will be drawn upon heavily, but during rest periods the lithium can recharge the lead so that it doesn't have deep discharge while operating.


Try putting lead and lithium together fine tuned so the lithium provides extra power for the lead under heavy discharge, the lithium isn't going to do much charging of the lead. It's the dynamics of the voltage drop. They both go back to their respective resting voltages which shouldn't be too far off when they are sitting. Also when you take a lead back and push voltage slightly above nominal it really doesn't take much current when charging, you need to hike the voltage a bit before lead will pull current and charge. They aren't going to balance their state of charge, but you don't need them to or really want them to. Ideally you'd want them both to discharge and not charge eachother at all, not to say it won't happen a little bit.


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## Ziggythewiz (May 16, 2010)

The lead has to charge the lithium, otherwise you need more lithium and there's no point.

I'm currently running a frankenpack anyway, so I'm now planning to add 40 AH cells as a booster to the weakest 36V chunk of my pack. With lots of luck this will extend the life of that chunk to match the rest of the pack, and when I fully switch to lithium the booster should have plenty of life to participate in the new design.

40 AH cells are rated for 10c max, and can do 2-3C continuous, so they should work fine in this application. My max draw is 400 anyway, and I can easily limit that to as low as 125 with decent performance. I'll setup an extra shunt and a few meters on the lithium portion to monitor it's behavior and see what happens. Under a 150A load I would expect the lithium to take around 100 of it.


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## DIYguy (Sep 18, 2008)

http://www.battcon.com/PapersFinal2005/NgPaper2005.pdf

There are other examples. 
GA2500 is right.... u want them to help each other. No isolation.

Do some small scale testing. It's not hard and u don't need too much equipment for a basic test to see the discharge rate/sharing.
Use LiFePo4 no Li-poly as suggested for life cycle. A123 if possible. 
Each variation of lead chemistry will perform slightly different . . but overall idea is the same based on the falling curve of pb vs more flat curve of Li.


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## TruEnergy (Apr 6, 2009)

Thanks for that paper DIYGuy. Interesting stuff there.

Battery chemistry will definitely come into play here. And it appears the internal resistance will govern the current contribution (somewhat obvious, I guess). Not sure what type of lithium they are using - so their particular internal resistance might be higher than A123's.

Fig 5a shows the Lead contributing the majority of the current upon startup, not the lithium. I believe we want the lithium to handle EV acceleration currents. So this will be dependent on the specific Lead and lithium packs used.

Ziggythewiz, I'll be interested to see the results. Especially under cruising vs accelerating conditions. Not sure if you have the internal resistance numbers for your packs, but it would provide a good comparison.


> I'll setup an extra shunt and a few meters on the lithium portion to monitor it's behavior and see what happens. Under a 150A load I would expect the lithium to take around 100 of it.


It seems to me the setup might depend on the ultimate goal. I think we want to reduce Peukert by reducing current draw on the Lead. Under cruising conditions, the power draw will be more constant and the Lead should be happier. Under acceleration, the lithium will handle the current surge. And if A123 packs are used, we can expect 10C. This would predominantly be drawn under acceleration. By reducing Peukert, we would effectively increase available capacity of the Lead pack.

MN Driver, exactly what I'm thinking.


> I think the idea is more to get cheap range and protect the lead cells. Lead doesn't last long when you draw heavily from it. I've seen a Corvette conversion using a top of the line AGM pack lose two packs, one lasted less than a year. The lead will sag and the lithium takes the load. If everything is sized properly and the correct voltage for the lithium pack is chosen, you'd be fine.


ga2500ev


> The discharge rate isn't the issue. The discharge capacity is. Lead is killed when it is deeply discharged.


As I understand it, both will adversely affect the Lead. High discharge rates reduce effective capacity. Deep discharge directly affects cycle life. Reduced capacity inevitably results in deeper discharging. So lets say we size our Lead for 50% DOD and supplement with lithium to reduce discharge rate. Geeze, sounds like we're talking multi-vitamins now 

Truly, I don't know if any of this is even worth pursuing. All this fiddling around; its probably better to just save up for more lithium. If this setup worked to any advantage, I have to believe more people would be doing it. Very interesting discussion though! Thanks everyone!


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## Ziggythewiz (May 16, 2010)

TruEnergy said:


> Ziggythewiz, I'll be interested to see the results. Especially under cruising vs accelerating conditions. Not sure if you have the internal resistance numbers for your packs, but it would provide a good comparison.
> 
> Truly, I don't know if any of this is even worth pursuing. All this fiddling around; its probably better to just save up for more lithium.


I'll certainly post results when I have them. Don't hold your breath. My ultimate goals are to get the car up to 144V (from 120) and on lithium. The total expense for that will be $6-7K as I need to upgrade my charger and controller as well as the batteries. With the approach I have in mind I can start with a DIY charger to charge the booster pack, and get some cells, which gets me about $1K closer to my goal while enjoying the benefits of that $1K instead of sitting on it. 

Also, the wife apparently thinks the tax return needs to be spent, and I'd rather have some of it go to into the EV than more kitchen furniture.


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## TruEnergy (Apr 6, 2009)

Ah yes, the "accountants" often have their own agendas 

Looks like this concept has already been commercialized. No idea what the costs are, but they do use a custom DC/DC converter to manage energy sources. Multi-Flex from Indy Power Systems.


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## Ziggythewiz (May 16, 2010)

Hmmm...new idea...instead of waiting till I build a charger to implement this, maybe I can just charge the lithium chunk in parallel and have it's contactor cut out as the lead enters gas mode...


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## Ziggythewiz (May 16, 2010)

I'm getting setup to do my experiment. JLD404 is in place so I can get reading on the full pack for now, and monitor the lithium branch when installed.

Contactor is on the way and cells should be soon.


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## HYPRDRV (Aug 20, 2009)

I've been monitoring this string in hopes it will answer my questions about a boat. I currently have AGM's for a propulsion pack at 144V. I plan on going to LiFePo4's for that pack in the near future. In addition I have a HOUSE bank of 3 AGM's that is charged from the Propulsion Bank through a 144V to 12V charger. I'm still trying to rap my head around the LiFePo4's and how they work so I'm not sure if there is anything I need to be concerned about with either pack. I know that the discharge rates on the House Bank are much lower than the Propulsion bank but even that is only at a total of 60A max. Is there anything I need to be concerned about?

Thanks,
Steve


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## Ziggythewiz (May 16, 2010)

Contactor arrived earlier this week and cells arrived today, so I should be able to start my experiment this coming week. I still need to get a few more meters to keep tabs on everything.

New thread here.


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