Adding Extra Battery Power to FFE

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Sep 28, 2020
Hi All,

I am new to this Forum but I have been working in PHEV and EV's for years. I just got a 2013 FFE. So far I have added a class 2 trailer hitch for my bike rake and a small trailer I take to hardware stores . I also had Linear Logic send me the prototype Scan Gauge board which was $25 plus shipping. Next I plan on adding extra battery power using the same method that SEFS used for the Chamdeo charger. I figure I can fit about 30kw in the trunk of Dow Kokum cells that I acquired from Oakland University in Rochester, MI. If successful, I will share the results. Shooting for 200 mile range!!!
So I worked on my 2013 FFE this weekend and added 7kw as a proof of concept and the car took the extra power with no issues. I tied into the main positive behind the seat and ran a main negative "Back to the Future 3 style" from the main Negative on the TCM out of the hood and through the back window because I live in Florida and it's been raining for days and my garage is a one car with nowhere to work. I ran 2 - 150 amp DC circuit breakers to spilt the aux. pack to "safer" voltages and run a third circuit breaker separating the main pack, before the tie in relay. I used a set of Tyco 12 HV relays to control the power feed. When I turned on the system, my FFE prototype scan gauge showed 80 amp going in at 1st and leveled off to 50. The surplus gauge on the left side of the dash started adding miles shortly after I turned on the relay and I added 5 miles as if I was at a charger while one leaves the vehicle running. I was curious if the car would throw a DTC code while moving and had my tow dolly ready if it did, but no problems. I have the 150 amp dc circuit breaker before the relays as a fail safe, so if the car is under heavy torque, it will automatically disconnect the aux. battery. So the FFE will accept additional power using the charge dump method pioneered by Cal Cars for the Prius. Now I just need to run a more permanent negative cable from the front of the car and add more batteries. If you are going to try this, "I highly recommend that you have a qualified electrician help you" as high voltage will kill you!! Be sure to add the proper circuit breakers as well. Your charger needs to galvanically isolated as the car will throw a hard code if is sees a path from the HV side to ground which cheap chargers will let happen (plus it's dangerous for you). The good news is that up to the GVWR of the weight car, you can add that weight in batteries. I plan on adding 30kw which is around 450# or the weight of 2 robust grown ups. So big success!!!!! I figure I will end up somewhere between 175-200 miles based on my driving style. At least I can get to the MCO airport (without stopping to charge) and back which was the original goal.
Good afternoon!
Can I have a photo?
I am planning an extra battery too!
What elements are you going to use to assemble an additional 30kW battery?
I had thought about a similar project but I was leery of the rear springs being able to hold up the extra weight. I'm interested to see how this works out.

I posted 4 pics on IMGUR(see link above). One of the car after the weight was added. I will add some extra coil springs or Air shocks long term (Similar to Plug-In Prius projects.) Pic of the temporary battery setup. The negative HV lead coming out of the hood and going in the rear door. And one of the tie in with a new aluminum plate on the TCM. Hopefully the links works - it did when I posted this.

On the element question: I will be using 74 Dow Kokum cells (batched 16 per block - 67# each) that are 11inch X 11inch X12inch and I will use (2X)28 - A123 cells after I detach the factory BMS and add my own. It should add around 450#s to get an extra 30kw or so. More than enough for me. Frankly, I have not needed more than the OEM battery so far. More curious if it could be done.

As far as Chademo, that has been done already on another thread (as I am sure you are aware) and the parts are for sale. In my area, there are only 2 Chademo chargers and they are broken 120% of the If I want CCS, I would just buy a 17 or 18 FFE as they are around the $10k mark these days

Hope that helps
This bodes well for the genset trailer idea I was throwing around.

Thinking of repackaging the SOBDMs Sefs used for the 30kW charger into a portable configuration that could be fed from a 20kW generator head and tapped into the DC bus. It would allow "hybrid" operation on the highway or could just be a portable 30kW charger to use on mains rather than running the generator.
I wuold like to revive this thread as i have some questions. I'm electrician automation worker and just bought 2014 ffe. It drives just fine, but i am concerned about how to renew it's battery. Did you just connected external battery dc output to inner battery dc output in parralel? You have to use seperate charger for additional battery? Does your packs have some BCM? It would be nice to buy battery pack from leaf or zoe and make it work in FFE.
The onboard charger monitors the individual cell voltages of the stock pack and has thresholds for highest max and lowest min value. If you put another pack on in parallel there's no inherent reason it couldn't charge in parallel but the onboard charger will not account for any of it's behaviors. So if the additional pack has cells that are charged past their target voltage but the stock pack has not, that charger will keep on going.

So you should attempt to match the cell voltages (similar chemistry) and the same number in series. You could pretty easily setup some basic monitoring and a second contactor to disconnect the supplementary pack if it tries to go too high or low. A separate charger would let you tailor it to those cells and let you charge in parallel. Lot of options.
Thanks for great info about charging. I still need confirmation, that supplementary battery is connected in parralel with original battery? I can not believe it's so simple. Voltages should be around the same, or supplementary pack has to have higher voltage? If that is true, as long as my pack is alive, I can extend it's capacity to normal range.
A supplementary pack would operate connected in parallel. You want to get them close to the same voltage but they don't need to be exact. They will equalize as they are being used which may make your range indicator go up if the new pack is higher and starts to "charge" the original or lower if it draws the original down. But that's just indicating the state of charge for the pack the car can directly monitor rather than the combined capacity of the two.
i would like to know your opinion on an aux battery consisting of LiFePo4 cells but with a bms and same end voltage so the onboard charger would be able to charge it but the aux battery could also be charged separately with a second j1772 or dcfc connector as well
i know that the different chemistries have different discharge/charge rates etc so im simply looking for what others thoughts are on mixing chemistries
By discharge rate, you mean voltage versus state of charge, yeah? That shouldn't be a problem during actual use so long as neither pack operates outside their nominal cell max/min, but that could be a nightmare to manage. Could also preclude using the on board charger to fill the supplementary pack (or even regen outside a certain state of charge range).

I'd personally try to match chemistry, anything else just creates compounding problems to manage.
i dont like the orig chemistry as much as LiFePo4 but i was thinking it wouldnt be a problem to mix the chemistries esp since im going to have a separate bms for the aux bat
If they don't have the same state of charge voltage curve, you would need to restrict your use to the least extreme limit for charge and discharge.

Say that one has a full charge cell voltage of 4.2V and the other is 4.1V, you would not want to charge the first past 4.1V or you'll immediately be overvolting the second when they are put on the same bus.

It's not anything insurmountable, but you basically end up needing to build an entire battery system that also has to coordinate with what's already there.

Document what you do, chances are there isn't much help others can offer.
Im building a pack that is the same pack voltage but the per cell voltage is different hence the need for a bms

im hoping to make a separate battery can bus and send the car only one pack at a time or both if desired