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Floodie / Lithium hybrid battery experiment

40177 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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I like experiments like this. The idea may go against conventional wisdom, but you have made some thoughtful approximations and it seems like it may work for you.

My idea was to have complete battery modules containing any number of cells of the same chemistry, and including all the BMS and charging and protection circuitry in the module, and also boosting (or bucking) the voltage so that the output is a consistent value, such as 144V. Each module would be individually rated for a certain kW-Hr and could have built-in displays showing the approximate state of charge and cycle data and expected end-of-life. But such a device would need a very efficient DC-DC converter or buck-boost circuit. It might be useful for small vehicles where you might be able to use one 2 kW-Hr pack with 320 VDC output for a 2 HP riding mower or small tractor with a 3-phase motor.

Keep up the good work. Your monitor panel is impressive! ;)
Have you considered using a PIC or other microcontroller with multiple A/D channels to do the monitoring? It could interface to an LCD display and/or it could connect to a Windows program vis serial port or USB to display the data and log everything to a data file for later analysis. Here is what I have done:

It uses quad op-amps as differential amplifiers so it can read voltages and currents without worrying about the ground reference. I don't have the circuit in good form but I'm willing to share details and source code. The PIC code is written in C and the Windows GUI uses Borland Delphi, but you can also use Hyperterm or any other serial port terminal application. However, for a nice display, you will want something a bit better.

I wasn't sure what the JLD was but I found this:

That is a nice meter but for $175 it's a bit much. If you don't mind a few hours of breadboarding you can build something like I made for less than $50 or so.
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I may very well do something similar if and when I build a road-going EV. But I plan to use SLAs instead of FLAs, and I intend to make a 250-320V battery pack with a three-phase 230VAC motor and VFD. I can get 12V 12Ah SLAs for about $20 each, including delivery, so that is about $0.14/Wh (although probably closer to $0.25/Wh including Peukert). They are 12 lb each (1 lb/Ah), compared to 0.6 lb/Ah for FLA:

The cost for these FLAs is $85 or $0.067/Wh. For my purposes, I would need at least 20 of these for 240 VDC, which would be 26.4 kWh and about $1600. The weight would be 1300 lb which is a bit much but probably manageable especially if installed in a truck. If I can run at 350 wH/m at 40 MPH I would be pulling 14kW (18.6 HP) or 58A from the 240V pack, so with Peukert I would have a true 58 Ah or 1 hour of driving at 40 MPH or 40 miles (but probably 30 miles to be safe).

To get about the same performance with LiFePO4 I would need 80 x 60Ah cells which I might be able to get for $100 each including delivery, so $8000. They are about 7lb each for 560lb total. They would also need three times as many high-current interconnects, as well as a more sophisticated BMS, which adds maybe another 50 lb and $800. So 600 lb and $8600.

If I made a combination with 50 Ah FLAs and 30Ah LiFePO4, I would probably spend $4300+$800 or $5100, and weight would be about 650+300 = 950 lb. There is also the complexity factor with two different chemistries.

As for long-term cost, the Lithium cells might last 10 years, and the FLAs 2.5 years, so that makes the lead system $6400 vs $8600. If you factor in the recycle salvage value of lead at $0.27/lb, the cost of a set of FLAs drops $350 to $1250/set or $5000 for 10 years.

I think LiFePO4 needs to drop to about 1/2 its present cost, and then the numbers look a lot better. I don't know if it really makes sense to use the combination at this point, especially for a high voltage pack.
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The EVTV dual diode may be better because you can use both of them, while the one on eBay is two diodes connected as a half-bridge. The problem with diodes is that they conduct only in one direction, so each battery pack can drive the controller, but they can't charge each other, and regen will not work. It might be better to use a pair of big MOSFETs or IGBTs so the intrinsic freewheeling diode can steer the current out of the packs, and the gates of the devices can be activated for charging as desired. With MOSFETs, when the gate drive is applied, current can flow in either direction so it may be more efficient at lower current levels where the voltage drop from RdsOn is less than the diode drop. ;)
Today I just happened to pass by a local BatteriesPlus store and I asked them what their price would be for 12V 12Ah SLA batteries such as I recently got on eBay for about $22 each including shipping. I think theirs were about $49/1 and the best they could do for 20 pieces was $35 each. But their 8Ah batteries would be just $16.50 each. So, for my tractor, I could get 240V 8Ah or 1.92 kWh for $330 plus $20 to make the governor happy, so just about $350. I have demonstrated that my small riding mower with me aboard will run at 24V 15A or 360 watts, so I may be able to expect 1 HP or 750 watts to go faster or climb hills or do some work, and at that level I'd draw about 3 amps (0.4C) Peukert says I'll have 5.1 Ah and I should get a run time of about 1.5 hours. That seems pretty good. :)

If and when I get back to my project (after my scheduled hip replacement April 22), I'll start a build thread. But this seems like a pretty good deal at $0.17/Wh (more realistically about $0.25 with tax and Peukert). The batteries have a 1 year guarantee and should be fine for occasional use, and I think they weigh about 5.25 lb each and an equivalent on eBay is about $17.50. But the batteries from BatteriesPlus are made in USA rather than China so I feel better about that. :D

For an electric car as an adjunct to lithium cells, the 55 Ah deep cycle battery might be appropriate, and at a list price of $150 it's not bad at $0.23/Wh. In quantity they are probably much less, maybe under $100, or close to the smaller battery's $0.17/Wh. These are 42.5 lb so a 240V 55Ah 13.2 kWh pack would be 850 lb and about $2000. ;)

EDIT: I found out that the Werker brand from BatteriesPlus may be produced by Deka/East Penn but also could be from elsewhere, including some Mexican sources. There are some local reps for Deka/East Penn.

Their factory is about 2 hours north of me in Lyons, PA.,+MD+21030&daddr=Lyon+Station,+PA&hl=en&sll=40.187267,-75.311279&sspn=2.135889,5.218506&geocode=FYFvWgId7IFu-ylngO2kZxLIiTEDNpvSwWL1mg%3BFfe0aQIdggd8-ynF9kpUf9PFiTG6EDsTNxblAw&oq=21030&mra=ls&t=m&z=9
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