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LFP batt installed in-place of 7ah aux batt -- Power draw analysis

HammaMan

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I've replaced my aux batt under the rear seat with a 100ah lithium iron phosphate. This batt is in parallel with the under-hood AGM. The LFP batt has a BMS on it that allows for live power flow (bi-directional) down to 1 watt of resolution. I will record data to the best of my ability. This post will be updated with quite a bit of information including....
- Power usage upon vehicle shutoff w/ 20 second and 120s headlight run
- Power used when a lock / unlock command is sent via app
- Power used when approach lighting is activated
- Overnight / 24hr sitting
- and..... what conditions outside of those should be included?

My truck is a powerboost, but the usage data should be relevant for the behavior of most trucks as it's not unique to the powerboost.

Interesting points about this arrangement -- The charged LFP batt's resting voltage based on the parameters I've programmed into the BMS is 13.4v. This is a float voltage for the AGM so it doesn't take any energy unless its not charged to begin with. The LFP batt will charge like a beast, up to 90a, very fast. The powerboost will put up to 15.2v on the 12v system to charge the batts and put out 220a at idle using its DC/DC converter. Once the LFP is 'full' per my settings, the BMS cuts off current inflow while allowing current to exit due to the manner in which the mosfets work. They work similar in practice to a diode, without the additional loss. I've done this because AGMs don't charge for shit on the top of their curve whereas the LFP will eat loads of current until it's ~85% full. This 'little' LFP batt has more reserve / usable energy than both of the truck's factory batteries. About twice as much in-fact.

The post will be updated, anything you'd like to see tested?

--Energy 'costs'--
(total energy used from no load on BMS, to denoted action, and back to no load)

1.31ah - Key off w/ 120 seconds of headlights on (approach truck, welcome lights on, unlock door, hit key on accessory, key off immediately, walk away and lock door)

1ah on the nose - Approach w/ welcome lighting enabled, open door for 2 minutes w/ running board deployed, close door walking away, 10 seconds later push lock button

.45 ah -- Approach close enough to trigger welcome lighting

.40 ah --12hrs overnight with no user 'inputs' or 'wakeups'

.14 ah --Fordpass app remote lock command via cell

.13 ah -- Without approaching truck, push lock button on FOB (truck was locked). This is something you'd do to confirm you've locked the vehicle
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Mszczewski

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Would love to see photos of the install and a detailed parts listing.
 

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Photos would be great. Did the new battery fit in the OEM location? Current draw when the ignition is on ACC would be interesting because it might be possible to eliminate the battery charger when programming modules within certain limits. It might be difficult to determine, but it would be interesting to when or if in normal operation of the F150 this battery is used.
 

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The condition I would study is what happens when all the batteries are dead.. and you start the truck. This would be max amps, which you already said you saw 90 amperes on the circuit which is what one would expect as LifePO4 are low impedance batteries in that size. many LifePO4 batteries have ratings for the BMS so you might check that. I would also check the alternator - so that it does not fry itself. They are built to do terrific amperes... but they don't have a great duty cycle and charging a 100 amp LifePO4 will take some time. 90 amps is also a lot of conductor to the the back of the seat from the alternator. Mine has some heavy wire, but it think is 6 AWG at the biggest. For 90 amps that might not do and obviously you want a dedicated negative lead. bottom line, I think the life of the alternative will be reduced. good luck.
 
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HammaMan

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The condition I would study is what happens when all the batteries are dead.. and you start the truck. This would be max amps, which you already said you saw 90 amperes on the circuit which is what one would expect as LifePO4 are low impedance batteries in that size. many LifePO4 batteries have ratings for the BMS so you might check that. I would also check the alternator - so that it does not fry itself. They are built to do terrific amperes... but they don't have a great duty cycle and charging a 100 amp LifePO4 will take some time. 90 amps is also a lot of conductor to the the back of the seat from the alternator. Mine has some heavy wire, but it think is 6 AWG at the biggest. For 90 amps that might not do and obviously you want a dedicated negative lead. bottom line, I think the life of the alternative will be reduced. good luck.
The PB has a water cooled alternator --- well it's a DC to DC converter, it takes the 280v of the HVB and steps it down to 15v. It's able to deliver 220a continuously because of the water cooling (the DC/DC converter, the motors inverter, and the HVB have a dedicated cooling circuit that can tap the AC compressor for additional cooling if needed -- it too is HVDC). When the gas pedal is depressed even slightly, the starter generator comes into play and it's 280a. Under acceleration the DC/DC quickly idles to divert all power to the e-motor. It comes back online working with the starter generator and has 500a of total generation capability when no longer accelerating -- it's got loads of 12v to spare.

Once I have all of the data in-hand I'll run it against what the other trims and their alternators can do. Ford clearly publishes this data including their output at idle. I suspect other trims aux batt is like the PB's unless the 2kw PPOB is spec'd, that uses twin alternators and twin aux batts. I could make a separate setup specifically for them as they have the same area to work with. For those w/ the aux batt alone and the 400w inverter, take a look at your batt. The wiring on the PB for that batt is 6ga with a 125a fuse at both ends of it. I peaked it at 105 amps for 10 minutes to check for thermal load and the wire wasn't but 60f (had a 280a LFP in it for max loading). I don't have it fully mounted right now, I put 24" 8ga 'jumpers' in place to act as the limiting factor. The BMS has loads of variables and allows you to basically set a duty cycle if the batt requires high amps due to being discharged. Given the 6ga wire run, combined with v.droop due to the current, it will settle at a 'happy' medium if the voltage from the alternator is only 14.4 or so, it'd only be pulling about 50a which is completely safe for all trims.

One of the variables that can be set to limit charging current is to have the battery shutoff its discharge once voltage gets to whatever is appropriate (as in it won't let the LFP get too low where the super high current would be needed). It can also be configured to charge for 30 seconds and stop for 30 seconds (or any combo thereof), but I don't think it's needed if things are sized appropriately. There's also additional ports on the BMS for things like an external switch. Before realizing the AGM wouldn't drain the LFP if left in parallel and they'd just happily float at ~13.3v, I had already designed an elaborate method for turning the discharge (when current leaves battery to vehicle) on whenever the illumination circuit would come on, and then continue to run for another 10 minutes to basically only take current from the LFP while keeping the AGM charged. Keep in mind that the AUX batt floats from the under hood AGM when the vehicle's starter is turning over the engine. This keeps the computers happy as they've still got a nice stable power supply that's not being interfered with the high-amp starter. As such the LFP aux has nothing to do with starting. But what it does do is keep that under hood AGM completely full with a really nice 13v surface charge that starts the truck right up.

The main reason for the early post was to get a discussion going. My goal is to also swap out my MME's shitty 35ah battery that just can't handle updates with the car always going into low power mode. My trim has the same 220a DC/DC converter the powerboost does, so quadrupling its reserve capacity while using the same space would prevent the low power mode from ever occurring while also allowing 2hr update sessions with all of the cooling pumps running (MME consumes 30a of current during updates because all of the pumps turn on).

I'm just happy to see I didn't need the elaborate setup. I've got powered running boards and one thing I've noticed is that they're far more snappier having a nice 13.3v to use vs the AGM's that'd drop down to ~12.5v on cool night.
 

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Are you utilizing the current sensor from the 7.5ah aux battery on your new LFP?
 

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@HammaMan . Although it might be difficult to test, I’d be interested to see if an LFP auxiliary battery is able to continue to perform its intended function in subzero conditions.
 
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@HammaMan . Although it might be difficult to test, I’d be interested to see if an LFP auxiliary battery is able to continue to perform its intended function in subzero conditions.
LFP can discharge down to a cell temp of -20c and won't charge until the batt's temp is 0c. The BMS has a heater circuit to allow it to self-heat. The cells are wrapped in a heating element like a small seat heater, and are insulated (twin temp probes - in the center of the bank and the edge). I'm in talks w/ a BMS manufacturer to get me a custom firmware so it can be tailored to all environments. For example in cold climates while the batt is getting charged it will heat itself up. It'll be 6 months or longer before I can get around to do cold soak tests. It's not really applicable to me in the SE, though we do get some single digit temps at times.
 

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LFP can discharge down to a cell temp of -20c and won't charge until the batt's temp is 0c. The BMS has a heater circuit to allow it to self-heat. The cells are wrapped in a heating element like a small seat heater, and are insulated (twin temp probes - in the center of the bank and the edge). I'm in talks w/ a BMS manufacturer to get me a custom firmware so it can be tailored to all environments. For example in cold climates while the batt is getting charged it will heat itself up. It'll be 6 months or longer before I can get around to do cold soak tests. It's not really applicable to me in the SE, though we do get some single digit temps at times.
Unfortunately, the conditions that the aux battery would be subject to in my truck would be quite a bit harsher and it would need to be able to perform not in just sub freezing temperatures (0 C) but also subzero temperatures (0 F). I have a pair of Battle Borns with internal heaters on my travel trailer and have operated them successfully down to about 20 F. Below that, camping season is over and I store them indoors for the coldest 2-3 months of winter. So, I haven’t had occasion to test them in harsher conditions (although BB claims they can continue to discharge even at 0 F with heaters). Avoiding the harshest cold is not an option for my truck. For a lithium aux alternative to be feasible, the aux would need to be able to continue to function (both charge and discharge) below 0 F—a tall order.
 

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Would love to see photos of the install and a detailed parts listing.
100 AH LiFePo4 batteries are not that much larger than the current led acid battery loacted under the seat. They are around 6.5 X 7.5 X 11 in size. There's plenty of room for them under the seat but at $3-500 retail for me at least the cost doesn't justify any possible benefits swapping to one may provide. It'd be far cheaper and potentially safer to install a 100 AH deep cycle gel AGM battery back there for around $100 instead that are about the same size. Not a big fan of having that large of a LiFePo4 battery in the cab for a safety reasons. There's no possible issue with thermal run-away on a sealed gel AGM unit like lithium that if it goes into thermal run-away, while rare will emit very hazardous compounds like hydrogen cyanide and cobalt. Not particularly desirable things to have filling up an enclosed space with me or my kids in there.
 

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HammaMan

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Unfortunately, the conditions that the aux battery would be subject to in my truck would be quite a bit harsher and it would need to be able to perform not in just sub freezing temperatures (0 C) but also subzero temperatures (0 F). I have a pair of Battle Borns with internal heaters on my travel trailer and have operated them successfully down to about 20 F. Below that, camping season is over and I store them indoors for the coldest 2-3 months of winter. So, I haven’t had occasion to test them in harsher conditions (although BB claims they can continue to discharge even at 0 F with heaters). Avoiding the harshest cold is not an option for my truck. For a lithium aux alternative to be feasible, the aux would need to be able to continue to function (both charge and discharge) below 0 F—a tall order.
It really comes down to your variables. If you used your truck once a week sitting outside in sub-freezing temps, yeah, wouldn't be for you. Keep in mind the battle borns aren't fully insulated (at least not the ones I got to play with). The battle born heaters aren't programmed in the same way the truck's would be. This is why I want a 'custom' BMS. With the right logic, if it's had to run the heater, in its own little insulated box, once hit 60% SOC while charging, the heater would remain on raising the entire batt temp up to 45-50c or so (speculation until tested), which should last about 48 hours before it got to 0c triggering the heater (if desired). What does all this mean for usability -- not sure yet.

I haven't run the truck for 2 days, I've had the doors open for a total of 3 hours (2 rear exterior lights stay on when open post interior light shutoff). I've done a combo of opening the doors and triggering the welcome lighting about 2 dozen times over 2 days. I've pulled 21ah out of the LFP during this time and the truck's voltage is still sitting at 13.3v. Welcome lighting still works, every time and the screens both turn on and greet me. With the AGM's being 100% full charged, just 1/2 of what I've done would have dropped their voltage to 12.4v or so and low power mode would have triggered or be imminent one. I'm LOVING this upgrade and hope to have something to share with everyone soon.
 
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EricR

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100 AH LiFePo4 batteries are not that much larger than the current led acid battery loacted under the seat. They are around 6.5 X 7.5 X 11 in size. There's plenty of room for them under the seat but at $3-500 retail for me at least the cost doesn't justify any possible benefits swapping to one may provide. It'd be far cheaper and potentially safer to install a 100 AH deep cycle gel AGM battery back there for around $100 instead that are about the same size. Not a big fan of having that large of a LiFePo4 battery in the cab for a safety reasons. There's no possible issue with thermal run-away on a sealed gel AGM unit like lithium that if it goes into thermal run-away, while rare will emit very hazardous compounds like hydrogen cyanide and cobalt. Not particularly desirable things to have filling up an enclosed space with me or my kids in there.
Yes, but @HammaMan lives life outside of the specs.

:LOL:
 
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100 AH LiFePo4 batteries are not that much larger than the current led acid battery loacted under the seat. They are around 6.5 X 7.5 X 11 in size. There's plenty of room for them under the seat but at $3-500 retail for me at least the cost doesn't justify any possible benefits swapping to one may provide. It'd be far cheaper and potentially safer to install a 100 AH deep cycle gel AGM battery back there for around $100 instead that are about the same size. Not a big fan of having that large of a LiFePo4 battery in the cab for a safety reasons. There's no possible issue with thermal run-away on a sealed gel AGM unit like lithium that if it goes into thermal run-away, while rare will emit very hazardous compounds like hydrogen cyanide and cobalt. Not particularly desirable things to have filling up an enclosed space with me or my kids in there.
LFP's don't runaway. I don't think you understand the chemistry. There's a reason they're transitioning EVs to LFP. It's a MUCH safer chemistry, isn't subject to thermal runaway, doesn't catch fire on puncture, etc... - LFP is a less toxic battery than AGM as well, which can outgas hydrogen.

As for the battery itself, it's got a dedicated BMS with no less than 50 variables you can control. On dead short it will shut itself off. On over and under temp it will shut off. I don't often tell someone they have no clue what they're talking about, but you sir, have no clue what you're talking about.

https://en.wikipedia.org/wiki/Lithium_iron_phosphate

I've got several of these particular cells as I'm a registered reseller of the brand (no, I don't sell batts, I just use a lot of them in projects). I've got about $200 into the cells and $60 into the BMS. This is a LIFETIME battery and its performance in terms of what I want from my vehicle blows the AGMs out of the water. It's not even close. My truck will never again go into 'low-power' mode and I can use far more energy on the 12v system without issue than I could ever know what to do with. I've reprogramed the power ports to not shut off allowing me to charge devices w/ out wondering the SOC of the 12v system.
 
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Mszczewski

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@HammaMan did you ever get around to finishing this testing in such a way that you would be comfortable doing a write up?
 
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I'll play with this other batt to see if it's a good fit. The issue with easy solutions is the possibility that there isn't temperature protection on
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