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.
Floodie / Lithium hybrid battery experiment
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.
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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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.
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'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
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). 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).
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
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
). 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).
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
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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