Testing an Aux batt solution...

[wolfman1]

Somewhere around 1/4” but I just used stuff I had in my garage, so I just remember that it fit 4awg.

I also got the X2 battery. How did you go about making sure it was balanced? The app doesn't show each cell, so I wasn't sure if I just needed to keep it on the charger at a very low rate for a few days or not.

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[HammaMan]

Only way to balance them fully is to trickle charge them at very low amperage. Need a benchtop power supply to do this.

 

[Snakebitten]

I also got the X2 battery. How did you go about making sure it was balanced? The app doesn't show each cell, so I wasn't sure if I just needed to keep it on the charger at a very low rate for a few days or not.

If you can charge the 12V LFP until it doesn't eat any more amps, and then it will rest at ~13.6V, then it's pretty balanced.

That's 3.4v for each cell in the 4 cell pack.

You can balance it by charging at 14.4 Volts (3.6V x 4) but at a teeny tiny amperage of say .025amps so the BMS resistors can bleed off the highest charged cell(s)

I hope I worded that properly, but it's what I did following HammaMan instructions. He was correct about the cheap Chinese LFP battery being shipped unbalanced. That X2 battery may be far better balanced and have a higher quality BMS than the cheaper LFP I used.

 

[Jmitchelltfo]

I also got the X2 battery. How did you go about making sure it was balanced? The app doesn't show each cell, so I wasn't sure if I just needed to keep it on the charger at a very low rate for a few days or not.

3 amp charger was all I had.

It has been working great. Time will tell if it is worth the extra money though.

 

[HammaMan]

For this application it could be easily argued that cell balance is irrelevant since the batteries aren't being cycled. This application keeps them well within their primary curves. The only issue I could see from imbalanced cells is that fan 5 will keep the voltage high enough that 1 fully charged cell can shut down charging prematurely. If 1 hits 3.65v and 3 others are at 3.3v, charging will shut down at just 13.6v on the 12v bus.

So if you're having unusually low voltage issues and can't hold above 13.2v just 20 minutes after powering down the truck, something is up and the first thing I'd look at is top balancing the battery. I can't speak to the logic of the BMS in your battery, but typically the resistors don't start clamping until higher voltages. A cheap benchtop power supply is really the only way I can think of to top balance. One of my 30ah LFPs took ~7ah of current to top balance which was resulting in a sub 13v resting state on the 12v bus.

To further clarify my truck's behavior w/ fan 5. If it's been sitting a few days, it will run mid 14s on voltage. After a few minutes it will eventually settle around 14.2-14.4v. Since my LFP is top balanced, it pretty much fully charges and then sits there floating at the indicated voltage until shutdown.

If you daily drive and don't have a bench top power supply, I suggest when driving away from your home, use fan 3 or lower. When driving to home, use fan 5. That will cycle the batt hopefully enough to trigger clamping. It may take a long time to fully top balance, but after a few months you should see it resting higher and higher.

To take this a step further you can current limit / droop the voltage by using ~18" of 10ga wire. This reduces ampacity and reduces current. When I was playing with a 280ah battery I had to use ~2.5 feet of 8 gauge to keep it below 100 amps. These techniques enter a caution zone and shouldn't be used unless you understand what's going on. This should never be used to power anything from the battery -- furthermore I don't know where your BMS will trip OCP. If you have resistors and a constant voltage power supply capable of 14.6v or higher, you can use resistors to trickle charge.

 

[Tank]

About 2 years ago I desiged a mod to fix this issue.
...which entailed replacing the stick 7.5ah Aux battery with a 14ah battery that fits in the stock location..
Hundreds of people have done my mod in the last 2 years, works perfectly..

 

[HammaMan]

AGM and LFPs aren't comparable in terms of what it does for the 12v bus.

LFP adds well over 20ah of reserve capacity before touching the starting batt that's sitting at 100%. If you take 20ah out of the factory config even w a 14ah AGM aux, you're down into 11.x volt range and modules are sleeping. It takes 20ah before I hit 12.8v.

 

[RyanStroeder]

About 2 years ago I desiged a mod to fix this issue.
...which entailed replacing the stick 7.5ah Aux battery with a 14ah battery that fits in the stock location..
Hundreds of people have done my mod in the last 2 years, works perfectly..

Thank you, Tank! I will add this to my powerboost summary thread!

 

[Jmitchelltfo]

About 2 years ago I desiged a mod to fix this issue.
...which entailed replacing the stick 7.5ah Aux battery with a 14ah battery that fits in the stock location..
Hundreds of people have done my mod in the last 2 years, works perfectly..

I don’t know if you run a battery monitor, but it’s been super informative since I installed mine a couple weeks ago.

This would be one of the biggest differences between a decently sized LFP battery vs the AGM.
Mine has a resting voltage of 13.25 and even on the rare occasion that the starter gets utilized the main battery will never get close to 12 volts. Keep in mind that my main battery has never been replaced……so I’d say that is pretty good.

 

[Shane150]

AGM and LFPs aren't comparable in terms of what it does for the 12v bus.

LFP adds well over 20ah of reserve capacity before touching the starting batt that's sitting at 100%. If you take 20ah out of the factory config even w a 14ah AGM aux, you're down into 11.x volt range and modules are sleeping. It takes 20ah before I hit 12.8v.

What could potentially go wrong if I use a LFP in colder climate? Where I am, it is not cold for extended period of time but there are nights that it will drop below -4F.

 

[Shane150]

If you can charge the 12V LFP until it doesn't eat any more amps, and then it will rest at ~13.6V, then it's pretty balanced.

That's 3.4v for each cell in the 4 cell pack.

You can balance it by charging at 14.4 Volts (3.6V x 4) but at a teeny tiny amperage of say .025amps so the BMS resistors can bleed off the highest charged cell(s)

I hope I worded that properly, but it's what I did following HammaMan instructions. He was correct about the cheap Chinese LFP battery being shipped unbalanced. That X2 battery may be far better balanced and have a higher quality BMS than the cheaper LFP I used.

If I purchase a LFP, I would like to balance it but I am not familiar how to do it. What setting would I have to set the charger at?

Below is the charger I have in mind.

https://www.amazon.ca/Adjustable-Sw...8-1-spons&sp_csd=d2lkZ2V0TmFtZT1zcF9hdGY&th=1

 

[RyanStroeder]

What could potentially go wrong if I use a LFP in colder climate? Where I am, it is not cold for extended period of time but there are nights that it will drop below -4F.

I am also interested in a response to this. I would hope that it would simply have internal shutoffs to prevent charging. Considering it would be wired in parallel, I would guess that it is simply disconnects itself until temperature warm up sufficiently...

 

[hatallica]

What could potentially go wrong if I use a LFP in colder climate? Where I am, it is not cold for extended period of time but there are nights that it will drop below -4F.

Below freezing, capacity dips a bit. This is a fairly minor issue.

More importantly, the charging rate must be drastically reduced (0.1C or lower) to avoid damage. The truck won't regulate this, so the battery must protect itself. My understanding is that typical Battery Management Systems will simply stop charging at freezing temperatures. Eco-Worthy has been shown on the forum, so here is their take: no charge below 32F and no discharge below -4F.

Self-heating LFP are a thing, though I stopped investigating at this level of complexity.

 

[RyanStroeder]

I've started to look for cold temp rated LFP's... This one pops up, but it's looking the dimensions is going to end the conversation...

https://www.relionbattery.com/products/lithium/rb20-lt

Edit: The discharge curves are actually terrible below 0 deg C/ 32 F - I'm no longer considering this as a low temp option:
https://www.delcity.net/images/linedrawings/RELiON-Data-Sheet_RB20-LT.pdf?v=1689689664430

 

[Davexxxx]

What I would like to understand, is the wide inconsistencies in our trucks.

Other than never being stranded, I had all the same warnings and shut downs others have experienced. And they did eventually become chronic (daily, or near so).

My truck frequently sits for a week at a time and nearly as frequently, the only interruption from that week, to the next, would be a single, 16 mile round trip.

Still on both OEM batts.

Fan speed 5 had no effect that I could discern.

The only thing that did work, was the BMS reset, immediately after giving a full charge, directly to the engine battery posts.

Poof. All problems gone, never to return.

Why mine but not others?

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