HV Battery Headway 38120HP LiFePo4 70S pack

HOLD ON TO YOUR LUG NUTS:
GOOD NEWS EVERYONE!
I picked up 75 "USED" LiFePo4 cells 38120HP from battery hookup. 70 cells for the pack and 5 spares.
The holders are poor and limit construction to a vertical array 5 x 14. Because of the configuration, extensive wiring changes were needed. With that in mind, I used another complete salvaged pack. As the compression clamp is no longer needed, the rods and 1 end plate were deleted. I lined the bottom of the frame assembly with FR4 2mm (blank PCB material, no copper or one side only) and a cutting pad on top of that. The cutting pad adds insulation, durability and cushioning. Inside edges of the frame were lined with 1x2 PVC trim board. One side needed about a saw blades width trimmed to fit the pack snuggly. Cannot speak to the burning of these materials should the worst happen, it is what I had on hand... The voltage sense harness needs to have the wires extended as the sensing posts will be on top and on the bottom of the pack. A new Batt (-) cable is needed, I used a length of #6 welding wire. The old negative wire and battery post was repurposed for use on the safety plug, which required salvaging the crimped terminal inside the safety plug socket. (not Fun) Also needed another run of #6 wire for the positive battery post. The new #6 wires needed new crimp terminals installed. The pack is held in place using 3 one inch cargo straps each rated 100-300lbs. The cargo straps are held with sailing 1" footman loop stainless anchors. Each anchor was tapped with an M6 cobalt tap and M6 bolts beneath the frame to hold them in place. The fit of the footman loop is perfect for the holes used to secure each of the NiMh blades. The top frame assembly uses more of the cutting pad for insulation and a couple rubber pads where the + & - HV battery posts are in close proximity to the metal. Some pool noodle foam was used to manage the air flow. The metal end plate has a teflon sheet RTV'd to it and some door 7 window foam strips to cushion against the batteries and also control air flow. The battery bus bar configuration is somewhat convoluted to get a shunt between array 11 and 12 for the service plug on top of the pack. Battery assembly weighs ~24kg, the whole pack is about 70% the original weight. Battery hookup said all of these batteries were 80-90% or greater of the new spec 8Ah. I tested a random sampling and was in agreement. I wired all the batteries in parallel and charged them over a 2 day period to 3.3V, how ever long it took for minimal current draw on the power supply. That yielded about 16.5v per 5 cell array, good range for the Prius to assume a valid SOC. Installed the pack and powered ON in accessory mode, everything is running AC as well and Dr. Prius App looks happy, batteries show <0.1v difference. On to READY... relays click ON and load PSST sound, smell of smoke. One battery failed under heavy load...this happened 3 times. 2 cells got very hot and one cell shorted out venting gas. Was not pretty and I was less than impressed. I pushed on, replacing the faulty cells then 2 others showed to be warmer than the others by 8C and Dr. Prius says 80.89% life. Once again, dismantle the pack and replace the 2 cells. My spares are gone...but the sucker works now! Has been up and down the mountain here dozens of times and the pack is tolerating the cycling. I've taken the pack out once to rebalance some cells and today I still have a few more to correct but knock on wood, promising so far... I am attributing the balancing drifting to poorly matched used cells. So looks like I will have to pamper the pack a while. I recommend NEW well matched cells... I'm on a crap pension so I have what I have and taking an exchange rate rip didn't help... The best array would be laid horizontally and stacked 3 high similar to the bamboo sticks NiMh from you know, "over there". That would have kept the wiring the same. Problem is the plastic holders. None available for that configuration, able to bolt to the metal frame and securely hold cells bolted end to end. I did talk to someone "over there" whether anything will come of it... If I had a 3D printer, I could have come up with something better. I think a dummy cell would be needed to clean up the layout, 3x2. Anyway, have a look see. I'll try to answer questions and post more pics when I sort them out. Cheers

 

200A, 80A charge ;o)

batteryhookup.com/products/used-headway-38120-hp-3-2v-8ah-lifepo4-battery

 

Batteries had been parallel charged to 3.2v then assembled into the pack. The maximum voltage the LiFe can charge at is 4.2V but it only adds 1% capacity from 3.65V, so they spec 3.65V and minimum 2.5V(worst case). Never saw the battery go down to 12V. The car complained when it got to 7.8V. Then about 7.4V it lit up alarm lights and would not start. Turning it off and then back to READY it started up. ECU will keep the 70S LIFe in a comfortable range relative to the NiMh specs. I didn't see >90Amps charge with the Dr. Prius app, limits of the polling I guess. Hopefully it can handle the brief extremes. Dr. Prius group is selling a LiFe pack ~2KUS. I expect they are using similar strategy with 5S blocks, no clue what cells the use. Anyway, all experimental. I have a Meanwell LED driver coming tomorrow, more experiments...

 

Hi Admittedly, I am pampering it, seeing 40-60A with ~80A peak regen and charging is the weakest part of it. It is rated to 200A continuous discharge according to one spec, another one says 120A pulse! I am not confident on a highway run yet. I am curious as to what cells Dr. Prius uses in their LiFe solution.... fingers crossedP

 

Yes I did go through that list, very informative albeit scary on regen, thanks. Hopefully it is a short duration pulse.... I found the H-Assistant not H-Reporter. My initial woes (3 bad smokey cells) were no where near those levels for them to baulk the way they did. Just cheap-used-unmatched cells. I undoubtedly will be pulling the critter out many more times, at least it is not the back buster it was.

 

No worries, should be in a happy voltage range as far as the Prius S/W is concerned. Regen maybe biggest issue. Supercaps, may work but shoe horning it into the car would be a problem, at least 2x the size. Trying to keep it stock... Converted my old grid tie charger H/W-S/W to use the MEAN WELL LED driver that arrived today. I just put it on the original NiMh pack for now, set to stop charging at 240V. Will check in a hour...cheers

 

Thats a far more comprehensive spec! I may well be on the edge... I need to move the temp sensors to the output side of the airflow. That should be the worst case condition. No way to monitor the whole pack. The fan is set to run all the time, hopefully that will help plus we have cooled off considerably from our record heat, drought and wild fire summer. 16C and rain today. I will pull the pack today for some balancing, move sensors and put in the grid tie PS harness.

 

Agreed if space is not an issue. Not two separate packs in parallel but integrated where each pack is 35S2P and put in series. Double the height perhaps (custom boxes), stacked back on itself keeping power lines short. Extend the existing V sense harness, temp sensors and safety plug.

I used sweethome 3d to make rough models. This is the pack (basically), showing top bus bar pattern and pink tops highlight the V sense points. Bare in mind, along the centre, those are the even numbered point (2,4,6,8,10,12) which are on the bottom side of the pack. Positive post is upper left and Negative post is upper right. Sense wires start (#1) at Negative post and end (#15) on the Positive post. SW won't allow underside view, can't show bottom bus bars... Site does not allow SH3D files, stuck with Jpegs...cheers

 

Batts were pretty close so I didn't pull the pack.
Got the grid tie working.
Meanwell driver runs through my old grid tie PS.
It manages the output, no battery no output and cut off is at 240v for now.
Hermetic relay flaked out, put an exercise routine in on startup to clean the contacts.
Relay provides the mechanical isolation, it switches on first if the batt voltage is over 180v.
Then a mosfet turns on to supply charge power. We'll see how that goes.