DIY Electric Car Forums banner

Floodie / Lithium hybrid battery experiment

40178 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.


See less See more
1 - 20 of 94 Posts
poitrsko: not sure what you mean by flood calb flood. I'll post a circuit diagram later to better explain my plan

pete: I'll be using the lead charger I currently have. They'll charge in parallel to mostly offset the unbalancing caused by discharging in parallel, and the JLD will cut them out before they get too high.

I probably want them to charge to about 3.5V/cell (14V on the lead they're boosting) so they'll rest around 3.3. Since they have to match the lead they'll probably live at a high 3.2-3.3 all the time.

I want to do a DIY lithium charger someday, but likely not until just before switching to full lithium.
Here's a schematic of the planned setup


See less See more
Yes, the plan is to have the contactor cut out when the cells are at a voltage that will let them rest equal to the lead's resting voltage. I'm sure it will take some tweaking.

One of the points of this is to see how things behave in parallel. As for upgrades, series is not even an option without either two new chargers or a new charger and motor controller.

I've had some repairs that set me back some, so I still need better baseline records, and I decided I need some more meters before I'm ready to go.
I have a JLD404 for measuring amps through the CALBs, and I'll compare that to the crappy westach reading the full pack. I'll also have a bunch of cheap DVMs on individual batteries/groups.
System's been good to go for about a week. Just need the rain to stop or find the time to get my wipers fixed so I can start getting data. Some areas got 17" yesterday.


See less See more
So...I've finally managed to squeeze a few commutes in between the thunderstorms.

Before starting the experiment, the floodies (HM29) measured at ~12 mΩ. The CALBs measure at 6 mΩ. So far, current sharing seems to be close to expected based on those numbers, with the CALBs passing 65%

With the batteries typically within 1/5th of a volt when connecting or coming off a cruise, current between strings starts around 10A, and decreases to ~5A within a few seconds, then tapering down to 2 within a minute or two. I never gave it a chance to fully equalize, will have to see how long that takes.

With my current charge level the CALBs were almost always feeding the floodies, though it was running backwards at least once. I need to tweak the charge level to try to minimize that.

Voltage sag for the boosted batteries was dramatically improved.

I really need another JLD or two to get better data, and will look into accessing the data port for some automated logging as well.
Thanks, I'll have to rework my monitor panel when I get another JLD. Will need some better tools so I'm not having to 'cut' the plastic with my grinder again.
Thanks. I do need to look into that or a celllogish method to store the data. My meters are great for watching, but it's a a bit of work to take samples from a video.

The JLD404's awesome, after having it for months I don't know how I ever drove without it. Mine's a bit gimpy, so I need to send it in for replacement, but I may get another one as well, haven't decided. It's only $70 from the vendor, $100 if you count the shunt and a DC-DC if you want that. It can do logging as well, but I haven't messed with that yet.
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 :)
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).
See less See more
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


See less See more
Booster pack fully charged and balancing.


See less See more
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.
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).
Lithium can take higher C rates, but the floodies have over 3x the (sticker) capacity. I want them to share somewhere between 5:5 and 2.5:5 F:L. 3:5 would be ideal.
I see...and it's that's lead's weakness....what's Lithium's?
Just $$$ and potential damage if overcharged/discharged. In my setup the lead makes it impossible to overdischarge the lithium (without trying) and the JLDs will prevent overcharge.
1 - 20 of 94 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.