Questions about AGM -> LFP

[JonMN]

Originally Posted by Urlauber

When it comes to placing the LFP batteries, is there anything fundamentally different from AGM APART FROM TEMP LIMITS?

Are they intrinsically more fragile and prone to explode when there's some splashing?

Stuffing them into the same carrier that holds the AGM underneath the camper makes some sense wrt cabling and such.

Again, I realize they can't be used/charged when frozen, and excessive heat cuts into their lifespan.

If I do go ahead with a change, I am going to do just this. I will check the spec sheets, but some have really good Enclosure Protection ratings (dust/rain). Enduro, for example, is rated at a really good IP65 and operates from -4 to 130F.

[booster]

Originally Posted by JonMN

If I do go ahead with a change, I am going to do just this. I will check the spec sheets, but some have really good Enclosure Protection ratings (dust/rain). Enduro, for example, is rated at a really good IP65 and operates from -4 to 130F.

Those are pretty typical specs these days but as I mentioned we are hearing a lot about not getting that hot. Their cutoffs are really high/low, also, and much higher than recommended operation ranges.


They don't say what grade cells they are on not much in reviews that could be truly believed as not bought and paid for.


What worries me is the huge amount of "sponsered" ads that are in the Google search for them as it often is related to less the top line products and companies from what I have seen.


Here is a link to a forum discussing them a bit and of interest is the post the mentions the founder and his other ventures,


https://diysolarforum.com/threads/en...tteries.24473/


Gut feel is that they are probably just generic sealed marine batteries from one of the several same lower end suppliers, but have no solid proof of that at all.


Nearly all lithium batteries have good initial ratings on them by the buyers, but that doesn't give an idea of longer term durability as far as I know or cycle life.

[Davydd]

Originally Posted by booster

Nearly all lithium batteries have good initial ratings on them by the buyers, but that doesn't give an idea of longer term durability as far as I know or cycle life.

After 6 years of lithium batteries outside under the van I had no detectable drop off. With 4,000 cycles I was never concerned about longevity. That would be 11 years of using 80% of your batteries energy every single day which is never going to happen. When you are driving the ventilation is greater than any ducted method can provide. Inside not much of an issue because you would not be able to stand the heat yourself. Heat may lessen the life of lithium batteries but they don't kill them. I'd be concerned, yes, if I stored my van in Tucson outside in the summer on a asphalt surface with batteries under or inside the van. In Minnesota it would never be an issue.

Cold can destroy lithium batteries so you better have heat, while using or in storage if you ever get down to -4F. That is unquestioned in Minnesota. That means heating pads powered by shore power, batteries with enough power to self heat with the heating pads while underway, or inside heated storage as the main methods.

[booster]

Re the ventilation while driving.



Yes, you have lots of air moving over the batteries, but it is all very hot air, some off pavement that might be 150*F and much of air coming under the front is air that went through the radiator and over the engine, then all around the transmission and rear axle if rear drive. Our rear axle runs at about 150* and the batteries will get to the aforementioned 120* even when not running anything or being charged, just from the hot air going over them.

[Urlauber]

Last Summer camping at Devils Garden in Arches NP I was wondering 🤔 about the temperature of the black asphalt campsite parking spot. With air temperature 107 🌡 it was much hotter for sure, at least upon arrival.

At that spot there's no hookup so I would have to use the battery, although during the hottest hours, we ran the genny for A/C.

Would worry me with LFP. In a few years, when we don't have to go during Summer vacations, things will improve as we wouldn't pick the hottest season.

[avanti]

Our rig has numerous temperature sensors throughout the vehicle, including several underneath the van, inside the battery compartment, and the batteries themselves. The automation system will record them continuously and save the data for two weeks. Once I get things sorted, I will be able to produce some interesting graphs.

[phantomjock]

Originally Posted by avanti

Our rig has numerous temperature sensors throughout the vehicle, including several underneath the van, inside the battery compartment, and the batteries themselves. The automation system will record them continuously and save the data for two weeks. Once I get things sorted, I will be able to produce some interesting graphs.

YES INDEED! I would like to know which system(s) you are recording with. I did something similar effort (on the sailboat) for the various locations in the freezer. A super cheep USB recorder did the job. The challenge--it was one point survey - not multiple locations, so I had to "self-validate" things like OAT, use rate(open close) etc. This might not have the capacity you have described. ~OTOH - a 10 pack is less than $200 bucks~ This unit is not the same - but similar:

I'd like to trial a device for the under chassis batteries and the engine bay.
RECOMMENDATIONS?

[avanti]

Originally Posted by phantomjock

YES INDEED! I would like to know which system(s) you are recording with. I did something similar effort (on the sailboat) for the various locations in the freezer. A super cheep USB recorder did the job. The challenge--it was one point survey - not multiple locations, so I had to "self-validate" things like OAT, use rate(open close) etc. This might not have the capacity you have described. ~OTOH - a 10 pack is less than $200 bucks~ This unit is not the same - but similar:

I'd like to trial a device for the under chassis batteries and the engine bay.
RECOMMENDATIONS?

Home Assistant (by default) records everything and saves it for two weeks--every temperature, location, weather report, light switch, fridge current consumption, and so on. Runs on a Raspberry Pi and storage is on an SSD.

HA supports many off the shelf temperature sensors, but I build my own with an ESP-32 and Dallas 1-wire sensors. An ESP node costs maybe $15, and sensors a just a couple of dollars each (and you can have as many as you like). I realize that this is a bit geeky for some tastes.

I have temperature sensors in the fridge, freezer, and behind the fridge. I also record current consumption of the fridge and freezer. I am looking forward to seeing those data.

For details, see my "Van Automation" thread.

[Urlauber]

I added a BMPro Temp sensor and placed it underneath right where the battery is. However, that provides just a momentary data point without any logging.

[MsNomer]

"I will say, unless you desire high battery capacity of more than 400ah or more (mine were 800ah an 576ah) you are wasting your time and money considering lithium ion. That's just my opinion. The weight advantage and the higher capacity in a smaller profile is the advantage other than a longer lifetime. "

Davydd, you are ignoring the reasons we switched from AGM to lithium.

1. The ability to use high-draw appliances such as microwave at low SOC.

2. The flat charging curve.

3. The irrelevance of 100% charge.

When we switched from 200Ah AGM to 300Ah lithium in the same space, we more than quintupled the available capacity.

[Urlauber]

Originally Posted by MsNomer

"I will say, unless you desire high battery capacity of more than 400ah or more (mine were 800ah an 576ah) you are wasting your time and money considering lithium ion. That's just my opinion. The weight advantage and the higher capacity in a smaller profile is the advantage other than a longer lifetime. "

Davydd, you are ignoring the reasons we switched from AGM to lithium.

1. The ability to use high-draw appliances such as microwave at low SOC.

2. The flat charging curve.

3. The irrelevance of 100% charge.

When we switched from 200Ah AGM to 300Ah lithium in the same space, we more than quintupled the available capacity.

Exactly. All these advantages apply whether you want 100Ah or 8000Ah of capacity.

In my case/mind, dumping two AGM batteries will reduce the weight from ~150lb to 28lb if I go with a single 100Ah. Still pondering that, need to see exactly how long a fully charged 100Ah battery will last me. If it is 2 full days I think it will be enough as MOST of the time solar will offset my usage and if the apocalypse hits and it is totally dark for a few days I can always use the genny.

[Urlauber]

Just thought I'd update with where I currently am with this (still completely theoretical) project...

A few things I need to still decide...

1) Battery - go with a bottom of the barrel $300 (GRFLIFJGADFETC) or a mid-grade $550 (SOK)? Unsure about the cells inside some of those cheapos, may be used, difficult to verify since the sealed box is always shiny on the outside, and only time tells.

2) Battery placement - reuse the under-carriage battery tray, or put it somewhere inside? One requires additional wiring and (scarce) room, the other risks exposure which could cut into the life span. Maybe use a protective box? Add some ducting like avanti?

3) What to do with the existing Trojan AGM batteries? Worthless for resale, even though new they are rather expensive. So I can ride them for a bit longer, maybe build some sort of power bank in the garage for power outages, etc.

And some things I have pretty much set my mind on...

1) A single 100Ah battery to get my Lithium adventures started. Should cover me 80%, for the rest I have a generator, as well as a separate Power Station. Also, there are two battery trays underneath, with existing wiring, easy to double the capacity and go parallel with two of 'em if needed.

2) Bluetooth app directly from the battery, at least initially, to get direct data of cell voltages (balancing), charging and discharge current, etc. I will probably add a shunt based monitor as well and see how closely they match.

3) Disconnect the alternator charging, but maintain the Emergency Start switch to connect the House and Chassis batteries in case of a discharged Chassis battery or the need for additional oomph to start the generator.

4) The 200 peak amps of the LFP BMS should be enough to start the generator, but see 3).

5) Keep the existing converter and solar controller for starters and see how it goes (charging-wise). I see myself using the converter rarely, with most energy provided via the solar panel.

[GeorgeRa]

Originally Posted by MsNomer

"I will say, unless you desire high battery capacity of more than 400ah or more (mine were 800ah an 576ah) you are wasting your time and money considering lithium ion. That's just my opinion. The weight advantage and the higher capacity in a smaller profile is the advantage other than a longer lifetime. "

Davydd, you are ignoring the reasons we switched from AGM to lithium.

1. The ability to use high-draw appliances such as microwave at low SOC.

2. The flat charging curve.

3. The irrelevance of 100% charge.

When we switched from 200Ah AGM to 300Ah lithium in the same space, we more than quintupled the available capacity.

I am struggling with your 5-fold math, please explain. 200Ah (about 150Ah) to 300Ah (about 270Ah) ratio is not 5. Perhaps you change voltage and compare 12 V to 48 V Ah.

[MsNomer]

AGM: Only the top 25% of capacity was useful to us because, even with Lifelines, the voltage dropped so low by 75% SOC that we couldn't use the microwave or any other high-draw appliance. 25% of 200Ah = 50 useful AH.

LiFePO4: The entire capacity is available. I used a conservative 250Ah of the available 300Ah, which is 5 x the useful 50Ah of the AGM.

Then to add insult to misery, that 50Ah of the AGM, being at the top of the charging curve, took forever to replenish. It took longer to replenish that 50Ah than it now takes to replenish fairly depleted lithiums.

[GallenH]

Originally Posted by MsNomer

AGM: Only the top 25% of capacity was useful to us because, even with Lifelines, the voltage dropped so low by 75% SOC that we couldn't use the microwave or any other high-draw appliance. 25% of 200Ah = 50 useful AH.

Interesting. So when you're running a microwave (through an inverter, right?) it doesn't work when battery power drops. Didn't know that. Is it because the drop takes you below a specific voltage? I don't understand why the lithiums would work when they fall below that voltage. Isn't the inverter just looking at incoming voltage? Confused.

[booster]

Originally Posted by GallenH

Interesting. So when you're running a microwave (through an inverter, right?) it doesn't work when battery power drops. Didn't know that. Is it because the drop takes you below a specific voltage? I don't understand why the lithiums would work when they fall below that voltage. Isn't the inverter just looking at incoming voltage? Confused.

The 12v input current can pull down the input voltage to low enough to trip the inverter low voltage input shutdown switch and that ends the inverting.


A lot depends on how conservative you are with the low voltage input trigger point. Some keep it quite high at 11.2v or higher and others are set at 10.5v. At the lower settings you can go deeper into the SOC of the batteries before the voltage drops that far under load.


Lithium batteries give up their charge easier so the voltage doesn't drop near as much as the same load causes on lead acid batteries.

[GeorgeRa]

Originally Posted by MsNomer

AGM: Only the top 25% of capacity was useful to us because, even with Lifelines, the voltage dropped so low by 75% SOC that we couldn't use the microwave or any other high-draw appliance. 25% of 200Ah = 50 useful AH.

LiFePO4: The entire capacity is available. I used a conservative 250Ah of the available 300Ah, which is 5 x the useful 50Ah of the AGM.

Then to add insult to misery, that 50Ah of the AGM, being at the top of the charging curve, took forever to replenish. It took longer to replenish that 50Ah than it now takes to replenish fairly depleted lithiums.

I am glad that new battery is working for you. I have 230Ah AGMs and it is a border line for a small 600W microwave which draws about 85-90ADC. If you would increase your battery to 300Ah AGM your results could be similar. 5-fold comparison is a little like my 5l ICE car accelerates 5 times faster then a 1l ICE car.

[GallenH]

Originally Posted by booster

The 12v input current can pull down the input voltage to low enough to trip the inverter low voltage input shutdown switch and that ends the inverting.


A lot depends on how conservative you are with the low voltage input trigger point. Some keep it quite high at 11.2v or higher and others are set at 10.5v. At the lower settings you can go deeper into the SOC of the batteries before the voltage drops that far under load.


Lithium batteries give up their charge easier so the voltage doesn't drop near as much as the same load causes on lead acid batteries.

I see. MsNomers comparisons then have more to do with the use of high draw appliances working off the inverter coupled with his upgrade from 200AH to 300AH. So if use of my microwave was restricted to when I'm on shore power this really isn't a factor, right? Well, what I mean is that if I go from 200AH AGM (100AH at 50%) to 300AH of Lithium (240AH at 80%) I would get, with my use pattern, an increased capacity of 2.4x. Is that correct thinking?

[booster]

Originally Posted by GallenH

I see. MsNomers comparisons then have more to do with the use of high draw appliances working off the inverter coupled with his upgrade from 200AH to 300AH. So if use of my microwave was restricted to when I'm on shore power this really isn't a factor, right? Well, what I mean is that if I go from 200AH AGM (100AH at 50%) to 300AH of Lithium (240AH at 80%) I would get, with my use pattern, an increased capacity of 2.4x. Is that correct thinking?

The pretty much covers it. The high amp draw is what makes the usable lower with AGM than lithium, but only while the high amps are being drawn. The amount of power they both lose is the same so at low loads you would still get the full capacity, minus cushion, from the AGM.


All of this is based on you getting 100% full on every recharge, however, and that is very difficult to do. Most lead acid batteries systems don't get full unless they are driven a long time or have solar that has enough capacity and time to top of the charge,

[Urlauber]

I thought one of the LFP battery advantages is that the full capacity is available. While it would be advantageous for maximum lifespan to not always completely discharge them, it is perfectly fine to do so.

Note - I know over-discharging them is deadly and should be prevented by the BMS.

How did we arrive at the 80% figure?