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Floodie / Lithium hybrid battery experiment

40181 Views 93 Replies 16 Participants Last post by  dougingraham
I'm starting an experiment to test the effects of using lithium LiFePO4 cells in parallel with cheapo lead acid batteries.

Lithiums are 40 AH Calbs, and they'll be boosting 29HMs (formerly known as 29DC) and GC8s. My current frankenpack consists of 3 29HMs and 11 GC8s.

Phase 1 of FLHE will put 8 calbs in parallel with 2 29HMs with a JLD404 to monitor AH usage and control charging. The calbs will be charged in parallel with the floodies until approx entering gassing phase where the JLD will cut the lithium contactor while the floodies finish their cycle. 1 29HM will remain unboosted as a control.

Phase 2 will add 8 calbs in parallel with 3 GC8s and tested as above.

The experiment will try to gain info about how the current sharing works out as well as how lead cycle life can be prolonged with the aid of a lithium booster.

A successful experiment would demonstrate an increase in lead cycle life sufficient to justify the cost of the lithium booster.


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Good to hear the interest. I probably won't bother geting more data for now on the HM29's as I'd rather drive 'em into the ground. Should have phase 2 up (GC8's) in a couple weeks after being out of town.
Destroyed and replaced 5 batteries as planned. Phase 2 is now good to go and I should have data tomorrow (GC8 behavior, boosted and non). Phase 3 is on the way :)
I wish I had the testing equipment (and an EV!) to do some real world testing like this!!! Good work Ziggythewiz!

For what its worth, I did a simple discharge simulation.

12V Pb 18mΩ
12V LiFePO4 6mΩ
R1 10Ω
R2 1Ω
R3 0.01Ω
Switch 1 'on' at 1s (0.91Ω parallel)
Switch 2 'on' at 3s (0.0099Ω parallel)

At low loads, the two chemistries share current contribution. At higher loads, the LiFePO4 contributes more - limited by its lower IR. I don't have detailed cell models, but this should explain why the Pb voltage sag was less. Being able to log individual pack discharge current and total current should show a similar trend. The question is the rate of power consumption. At relatively "low" loads, they will contribute a similar amount. Under "high" loads the lithium should contribute more. Low and high are very relative because if you never actually reach the "high" part - both chemistries will continue to contribute evenly.


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Interesting sim. I don't suppose there's a mechanism to make the voltages sources behave like batteries (voltage decreases with runtime/SOC)?

I don't have detailed cell models, but this should explain why the Pb voltage sag was less.
By less sag I mean the boosted lead sags far less than non-boosted because it carries less than half as much current. That was an assumption going in and one of the goals of phase 3 is to see how cycle life is affected (for the 29HMs as I have no control data for GC8s) by lowering the amp demands on the lead pack.

I'm still analyzing the data from phase 2. Just finished a page of calcs and realized I biffed some formulas, so now I'm questioning the rest of it :p

I have found that the amp sharing is very SOC dependent. With a higher SOC (where I want to run) the lithium will carry 75% and at a lower SOC they can share even 50/50 (what I'd like :p). I need to squeeze my grey matter and see if there's a cell count that will feed me cake, at least for my typical commute.

I'm really slow crunching numbers as I'm trying to get the garage in order for new cells arriving this week :) Then phase 3 begins! I expect the full hybrid pack to add ~13-17 miles to my range (currently 18-34 miles).
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Indeed a more detailed battery model would help simulate your findings much more accurately. I have read some university papers where they attempted to create PSpice models of lead batteries. Very difficult and very specific to the brand, internal construction, capacity, and materials used.

It might be possible to create one from something like a PL6 log. If the logs are generated at different discharge rates.

Do you know your total amperage draw? If so, I could program identical pack sizes that you are using and iterate through some load values to get an idea of the current distribution. But since the distribution seems to vary with SOC, you will be faced with finding a "close enough" sharing solution. Let me know if there is anything specific you'd like me to try simulate. I will also continue searching for some battery models.
Some years ago I run a very similar experiment making it even more complicated.
Firstly I wanted to test an hibrid life 4S pack made with A123 cells and TCL cells in paralell that did not had any problem to work and passed all the test but there is no much benefit to do this this in order to gain power unless ther is a control.

That battery was left on my garage and endend in parallel with the 12V lead battery of my IC car.
Happened that I was going on holidays and the Lead battery decided to do weak start the same morning I was leaving so I just screwd the Life battery in a run and for holidays we left...
It finally was instaled under the hood without BMS (I checked it every month or so) for a year, until I bought a new lead battery (you know there is always more interesting things to do...)

No problems so far with the sistem, actually the Life battery was taking care of most of the job due the weakness of the other battery, and it is quite small around 12-14Ah.
I still have it around and seems to be find, anyway a test will be necesary to prove that it is still ok.
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Not familiar with TCLs. Is that just a brand?
It is an big electronics OM manufacturer in China they produce lithium cells as well.
New cells arrived. I pulled the booster packs from the car and everything's just about fully charged. I need to finish drilling and grinding my busbars so I can do a 4S10P final charge then 42P to sit and balance.

I ran some numbers and found my typical commute voltage drop is ~140 -> 134.5V
I want to run the booster pack between 90 and 30% SOC, which corresponds to 3.33 -> 3.2 VPC. With 42 cells that's 139.86 -> 134.4


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Booster pack fully charged and balancing.


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you are missing something here... if you really wanna think green, let's think about batteries recycling, and for lithium it is not possile yet, so LA batteries are really green when you know that almost 97% of it can be recycling
but what are the recycling cost? the silicon is also recyclable but using acids and very dangerous products for environment...

You can't think that you are saving the planet if you are killing it in other place
sorry if I have bothered you, I just really care about environment, and I keep thinking it is a delicate topic about using any kind of battery.

I wouldn't disturb you any more...
sorry if I have bothered you, I just really care about environment, and I keep thinking it is a delicate topic about using any kind of battery.

I wouldn't disturb you any more...
If nothing else there's very little lithium in one of these batteries, they're not all that toxic, and contain largely copper and aluminum by weight in the foils and terminals. I bet that you could find a local scrap yard that would take them for the aluminum and copper content alone.

Anyway. Back on topic. Love reading about these types of real world experiments. Keep up the good work.
Got the booster pack loaded up last weekend and finally got the instrumentation connected enough to make the FLHB operational today. Taking it easy until I get a few more meters connected to keep an eye on things.

One benefit I hadn't really considered before is the reduced peukert from taking the load off the floodies. They averaged ~25A this morning, so I should be able to get a much higher % of sticker out of 'em compared to drawing at 80A. Will have to do a range test in a few weeks to see how much it helps.
Charged higher than I meant to so cells were resting at 3.38 instead of 3.3 where I want 'em.

High SOC = slutty batteries...they put out like crazy.

I have my other JLD in now so I can see what's going on, the booster carried 85% of the load, with the floodies just along for the ride and getting charged whenever I let off the pedal. I drove chunks on the booster only to try and knock 'em down but it didn't do much. After a 6 mile drive the boosters were still too high to bother charging.

Also noticed when using only the lithium the current ramps up almost instanty instead of taking a few seconds. Not sure why that is; will have to investigate in a week or two.
Interesting results. Sounds like the Lithium may be "backed" my the lead acid? Perhaps they are acting as a buffer against catastrophic drain ?

All conjecture on my part but I'm waiting for your reports with baited breath!
The lithium booster pack has enough juice for my regular commute (just), so I expect the lead to just share the current load to keep the C rate down on both, but for days I have to run between offices or do errands I expect the booster to do most of the peak work while being fed by the floodies while under peak.

I think the booster's JLD may be misconfigured, exaggerating the extreme results reported above, so I'll have to fix that and see how things look tomorrow.
After charging the floodies but not the booster and shaving a little juice here and there I ended up with a 5:6 F:L current distribution and 0 cross current at rest. That's sitting at 136.2V (3.24 vplc).
which chemistry can handle high drain better?
which chemistry can handle high drain better?
lead sags more under high load, and suffers from peukart's.
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