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Testing an Aux batt solution...

HammaMan

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I've been looking for a lower cost option to share in regards to getting rid of the battery / sleep issues and will update next week on how everything came together. Will create photos and what's required exactly to do it but for under $200 and an hour the aux batt should be able to be replaced entirely and everyone have a happy truck :)
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@HammaMan I know you’ve discussed progress on this project using a LFP on some other threads but I may have missed what your final recommendations were. Can you summarize? Also, do you think something as simple as adding a second 7.5 ah AGM auxiliary battery in parallel would have any benefit to reducing the PB battery sleep issue or would the current BMS just eat those extra AH ?
 
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HammaMan

HammaMan

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@HammaMan I know you’ve discussed progress on this project using a LFP on some other threads but I may have missed what your final recommendations were. Can you summarize? Also, do you think something as simple as adding a second 7.5 ah AGM auxiliary battery in parallel would have any benefit to reducing the PB battery sleep issue or would the current BMS just eat those extra AH ?
I picked up a 'slim' 30ah LFP on amazon to test. It was so out of balance that it took 5 days charging at .2ah to get it to balance due to using resistance clamping on the higher voltage cells. It would end charging at 13.7v when I got it, for reference peak is 14.6v. Due to its basic BMS design and being that far out of balance, I never posted about it because the odds of someone having the means to first perform a week long top balance charge at .2a and voltage limiting to 14.6v is very slim.

No it wouldn't eventually equalize if just installed as is out of balance due to the ability of the truck to get cells to over-volt and therefore killing charging entirely as the BMS shut it off. I was able to get another aux batt tray and get the batt to fit into it after modifying its internal plastic structure. The BMS is also not properly programmed against its rated specs. It's supposed to be 30a discharge and 20a charge. I found it to allow 60a charging which could kill the BMS (the cheapie in the LFP) -- don't know, didn't test it to failure. I did put it in the truck for a week and it worked fine as it should. It did what the larger LFPs do and brought the under hood AGM up to 100% SOC as the 12v system when off settles into the 13.3v range. A safe float voltage for AGM batteries.

However due to the truck's desire to try and get the under-hood AGM down to a lower state of charge, when driving or operating the vehicle in any conditions, it would simply eat all of the energy in the LFP to power the truck's 12v system unless the key fob was in the truck and the HVAC blower on a setting of 5 or higher. Only then would it disregard its BMS logic to eat up as much of the 12v batts that it could (sans supplying 6a of current from the DC/DC, for some unk reason). The LFP can be brought down to 10v, but the second a battery of that resistance is fed voltage at such a low SOC, it will eat as much amperage that it's fed. The aux batt circuit is a 6ga wire with 125a fuses at both ends of it. I have no reservations in allowing the circuit to pull 100a sustained, but not left unchecked to cook fuses of unk price / and the work to replace them. Didn't bother to price / check what's required to replace them as I've done such on other vehicles and know it's not worth killing them.

A smart BMS that can truly throttle charging current are considered more 'specialty' as it requires additional logic to implement from the manufacturer. One work around is to have a BMS with lots of settings where the parameters can be set to basically cycle 2 seconds on, 10 off, and that would eventually, safely, bring the batt up to a voltage where the amperage is okay. The high amperage draw can be limited with a programable BMS (what I use for my standard setup) by setting the low-voltage limit to ~3.1v which will never let its state of charge / cell voltage to get to a point where high amperage charging becomes a factor.

The TLDR is that to use LFP for aux, you must be ok with 100% SOC on under-hood AGM, be willing to use blower level 5 for charging it, and understand that if sync sleeps with the LFP in place, it's wise to first install a standard battery charger for ~30mins to get the cells out of the fuse-popping-current-zone. Below is the charge curve for a LFP cell. When its voltage is in that dip which is its last 10% or so of capacity, it can eat a lot of current due to the voltage delta. So long as it's not allowed to get that low, the amperage will be okay for the circuit.

Ford F-150 Testing an Aux batt solution... 1689283747583


Because of said variables, I'm not willing to post how / what I used to perform putting the LFP into the truck at the risk of someone not understanding the variables and risk popping one of the 125a fuses. I have a 110ah LFP unit I built myself for my truck and I'm more than happy with. It's got substantial 12v reserve. I've got a lot of other things going on right now that I don't have more time to devote to the project, but I'm learning the ins and outs of creating my own controllers and would like to offer solutions in the future. I'd been in discussion with a chinese manufacturer regarding possibly having such a BMS made absent my own circuit design input, but things aren't looking good right now for manufacturing in china. One of the companies I was speaking with in regards to modifying one of their products has already folded.

One of the limitations of LFP tech in general shows up in regards to low temps. Most cells can't charge below freezing (0c) and can't discharge below -20c. That's not really a big deal if a battery is built with that in mind as a little insulation and a heating element with good logic behind the BMS can take care of that, especially utilizing the battery itself as a thermal storage device. That's a concept that gets truly lost in translation and I wouldn't trust a 3rd party such as discussed to write the logic required to understand that when conditions are below freezing, heating the battery up to 55c can provide an extended period of time before it would need to start using the heater to maintain a 0c temp so that when the vehicle is started it can take full charge. Typically LFP batt heaters are used to first bring the batt up to temp so that safe charging can occur.

While I haven't looked into the logic of LFP EVs, I suspect the logic discussed isn't lost on designers, particularly around charging when the climate is cold and using the battery's own mass to store additional heat from a charging session.
 

Samson16

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but things aren't looking good right now for manufacturing in china. One of the companies I was speaking with in regards to modifying one of their products has already folded.
Fascinating effort sir. I'm sorry for you but not sorry in general that manufacturing in China may have plateaued.
 

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Thanks very much for taking the time to explain! The BMS on the PB side is quite a challenge.

So is it safe to say if someone changed out the existing 7.5 ah aux AGM to say a 2Oa AGM ( it would be a tight fit in existing tray) would it provide any benefit at all ?
 

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I've been looking for a lower cost option to share in regards to getting rid of the battery / sleep issues and will update next week on how everything came together. Will create photos and what's required exactly to do it but for under $200 and an hour the aux batt should be able to be replaced entirely and everyone have a happy truck :)
$225. Duralast Platinum H7 to replace OEM battery. Problem solved.

All the BMS voodoo in the world won't help if the battery has gone to sh*t, which quite a few OEM batteries (including mine) seem to have done.
 

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$225. Duralast Platinum H7 to replace OEM battery. Problem solved.

All the BMS voodoo in the world won't help if the battery has gone to sh*t, which quite a few OEM batteries (including mine) seem to have done.
Are you talking about replacing the battery under the rear passenger side or the battery in the engine bay? I will need to do the same, even my dealership told me the other day that the batteries Ford uses are complete poop
 

RickBullotta

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Are you talking about replacing the battery under the rear passenger side or the battery in the engine bay? I will need to do the same, even my dealership told me the other day that the batteries Ford uses are complete poop
The main battery in the engine bay. The theory (mostly anecdotal) is that many of these batteries sat in a low state of charge for a while waiting for parts during the supply chain challenges, and that while they may test OK, they are actually not performing properly or to capacity. Again, just subjective, but there are many, many people who have solved their shutdown/sleep issues simply by replacing the main 12V battery.
 

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I drive short distances so I connect it to my NOCO trickle charger every Sunday evening and receive a new battery every Monday morning. 😂

Ford F-150 Testing an Aux batt solution... IMG_6933
 

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HammaMan

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Okay, here's the cheapie I've been testing. I have an older one that I wasn't too impressed with as it came from the factory. The cells were way out of balance and it had no cold weather charging protection. They went OOS for many months and I'm guessing they may have used a newer BMS. Just bought another one to test how it comes in terms of cell balance.

My first one, the BMS was shutting off at a charge voltage of 13.8v or so, when it shouldn't stop accepting charge current until 14.6v. That means 1 cell was overvolting prematurely because it wasn't put together with cells of similar voltage. These can't ship with a charge greater than 30% and LFP has a really flat 10% to 90% voltage curve so you can't really get to balance these until voltage gets higher up in the curve. These has a cheap BMS and the first one seemed to simply clamp the higher cells to a very low power resistor only capable of clamping .2 amps. This means you need to either do a low-power initial charge of a few days, or under normal usage conditions it could take months before it's able to balance itself.

This exact battery fits into the battery tray, but the tray needs to be modified for it to fit as it's got little areas in it designed to hold 1 or 2 of the 7ah AGMs. It's not difficult to do. I found another one of these trays on ebay for $50 delivered to keep the factory tray on-hand. The reason the BMS in this unit needs to be fully tested is to protect the 2 125a fuses on the 4ga run between the battery and the BCMC. It's fused at both ends. I've seen this peak at 60 amps and want to be sure OCP kicks in before it has any threat to the fuses (upon the testing of others, the voltage droops enough under higher draw that the under-hood begins to take up some of the load)

This is LFP chemistry, and despite its 30ah rating, this little battery can more than 4x the amount of usable capacity before any low voltage shenanigans present themselves. It will however keep your under-hood AGM at 100% SOC constantly. The BMS itself cannot cope with the under-hood always being at 100% SOC and will try to consume the 12v batts to bring down the SOC under all conditions but 1. To run an LFP batt on the 12v bus, you must use the HVAC blower setting 5 trick to over-ride the BMS and charge the LFP batt.

Furthermore, Charging LFP batts below freezing needs much lower amperage else it can lower its lifespan. This is "common internet lore" and there just isn't any real-world testing that someone has done to produce meaningful data that I've been able to come across. I'm in the south, I don't daily drive the PB, and just don't have the conditions to test this long term because these batteries have such a long life. They're made to run at least 3,000 full-to-dead charge cycles before they hit 80% capacity. Then there's at least another 3,000 of the same cycling before it hits 60% capacity. I mean even being daily driven, there's not even 20% of the capacity being used, and even if 20% capacity could be used being daily driven, we're still talking decades to degrade the damn thing.

There are some reports of people using LFPs outdoors below freezing for years including charging. Assuming the worst case that 90% life span degradation takes place with below freezing charging, it could still be a decade of life this little batt provides. That's enough for now I guess.

PS: I haven't tried to just put the batt in without using the blower 5 trick to see if normal operation of the truck is sufficient. It could be as the truck does up the voltage regularly for various things outside of the blower 5 trick. I don't daily drive the truck to test such. Right now it gets driven once or twice per week so I'm more interested in having maximum reserve capacity.
 
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HammaMan

HammaMan

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Went ahead and ordered a few things for more testing. Got this charger to see if it could properly top balance the batt as ordered -- it may just come better balanced than what I got a year ago.

Ford F-150 Testing an Aux batt solution... 1705159850108

Ford F-150 Testing an Aux batt solution... 1705159895528
 

scott011422

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Hamma, How are you charging the LEP? Did you find a BMS that will charge the battery while under load?
 
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Hamma, How are you charging the LEP? Did you find a BMS that will charge the battery while under load?
It just needs the voltage. Due to lithium's nature, it gobbles up energy when its present. This is why the HVAC blower setting 5 is needed to prevent the truck from trying to consume the 12v batts when it sees the battery's SOC above what it believes it should be, operating voltage drops down into the 12s. Even if you have AGMs in the truck and charge them to 100%, within a short amount of time it will have consumed them to get their SOC to where IT thinks they should be. HVAC blower 5 w/ fob in truck will always keep the bus voltage high.
 

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Thats nice. No wonder you are having such good luck with the LEP battery then. Fan 5 is great for keeping the voltage up, But still won't charge the AGM if there isn't any amperage behind it. I'm not finding any patterns with the cold weather like I could in the warm. I'm not sure what the truck is looking for but it seems the rules change every week lol!

During the warm months the truck will NEVER charge the AGM unless the voltage is 12.49 or less at startup. I have hundreds of captures showing this.

Now that its cold, Sometimes its 12.29, 12.39, it varies.

All this at fan setting 5.

I ordered a DiamondBack HD cover the other day. Really tempted on putting a flexible solar charger on it. I'm always parked in the sun when its out.

I wish there were some variables we could change.

So very frustrating.
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