LFP on Shore Power with Inverter/charger?

[BFL13]

An inverter/charger requires that you have a battery connected (or some 12v source) so it will supply any 12v to the RV. (Unlike a converter that will do 12v with no battery)

Some say not to float an LFP. If you choose not to float yours, what do you do when on shore power? You can't isolate the battery and run 12v off the charger in the inverter/charger since it would be dead.

You could just not enable the charger, and run 120v off shore power pass through---or can you? Does 120v pass-through happen with no 12v to the inverter/charger?--- And just cycle the LFP for your 12v, thus not floating it.

What do folks do in that situation?

[BFL13]

Makes sense to me.

How can you tell you are still above 50% SOC? What settings are you using for "full"? Is that with the smart shunt?

The Video here shows how to set it up including the full capacity. scroll down to the video.

http://www.wegosolar.com/products.php?product=SMART-SHUNT-Victron-Energy-all-in-one-battery-Monitor

[jaycocreek]

Sometimes we tend to over think things...I can remember back when I ran a battery until the tv screen started to shrink,then I charged it..lol..Never new better!..Now things are quite different in the way I use my batteries....

Right now my battery is going on the 7th day of running my Engel compressor fridge/freezer and the SOC is above 50%,something I couldn't do with my $200 agm nor could I put 50ah back into it in less than 3 hours,something I was after for boondocking which is 100% what I do...The weight of 32lbs is quite manageable compared to over double that for a lead acid of comparable size which is important if the wife needs to do anything with the battery...I also use it in a smart battery box in my truck camper that also serves as a step lol..and I can bring it in the house with ease to run whatever if the power goes out...So yes,I'm quite happy I made the change to Lithium for those reasons...

As for exact numbers for the Victron SOC or Voltage to SOC or exact amp hours,I don't really care as long as I have a guide to approximate numbers and the good thing is,if I somehow run it until the BMS shuts it down,it's really no big deal with lifepo4 cells...

As it turns out with the failing Bluetooth and the partial refund,I feel good about the price I paid for a 120ah lifepo4 battery and especially the support/2 day shipping and no tax...

[BFL13]

https://www.lynxbattery.com/lithiumbatteriesrv

They say the 120AH is "nominal" so the real 20hr rate capacity could be that 113AH IF they are full at resting 13.6v like the BBs. I don't know.

You could get the battery as full as it can get, and wait till next day to get the resting voltage, and divide the 1536 by that to get the AH to use as "full" with a monitor.

The charging voltage is 30a, which would be their recommended for long life I suppose. You can use higher amp charging to save gen time if that is more important than max lifetime cycles.

Their sales blurb says "four times the power", but it is clear that they mean "energy" , not "power". Their Forbes link guy has a "power density" notion and an "energy density" idea too.

He has the energy density being what saves weight (correct) and that is what the blurb probably means by "four times---". Tried to make sense of that before, but since the LFP is only 1/3 the weight of an AGM same AH, it is hard to follow. Might not include casing and BMS etc, just the cells?

EDIT--105AH AGM =66 lbs. Lynx 120AH = 35 lbs so where is the energy density "four times" ? It is only half the weight. (another thing we are not supposed to ask about? )

"Power density" seems to be like CCA the way he uses it, so he just means higher power density means more power (I guess)

Near as I can tell, you are not supposed to worry about all that, and just use the battery, but stay above that lower knee, playing it safe by staying higher above the lower knee, since your monitor is only going to be a rough guide to the SOC. ? YMMV.

[jaycocreek]

For those watt hours I mentioned,I was just going off the sheet they sent my for my battery..Being old school,I don't care(fully understand) most of it..lol

[BFL13]

Steve, thanks for the clarification. I was using CCA because it is the only thing I can think of with battery ratings that are a measure of its power. FWC said a battery's power is its max current at its nominal voltage (if I got that right) so 800CCA is twice the power of 400CCA.

I don't know where an RVer cares about power as such. Ads saying a battery has "twice the power" got me wondering what that is supposed to mean. Seems to be "Sales" talk. ?

That Odyssey 31 hybrid battery that allows a high draw makes that claim, and ISTR LFP ads saying that too.

Another puzzle is how they do AH with LFPs, but that only matters to those who operate them trying to keep track of usage while camping if they even do that.

EG, The blurbs say don't use Peukert, but still say the LFP is 100AH because they ran it down at 100 amps in 1 hour so that is 100AH. Then they sort of dance around saying it also takes 20 hours to run it down at 5 amps, so that is 100AH at the 20 hr rate. But no Peukert here folks! 🙂 It makes your head spin.

Then they start in with the Wh, but use the 12.8 nominal voltage to get the AH. OR----did they get the AH first and then invent the Wh????

In the previous example, it was 1536 Wh and 120 AH at 12.8v

The battery is full at 13.6v so that is where you have to start. Either:

A. the battery is really 1536/13.6 = 113AH , or
B. the battery is really 120AH so x 13.6 = 1632 Wh

Which is it? If you are monitoring by Wh usage or AH usage, I would think that is important for setting up your monitor.

Not a clue. so Steve, what are you going to do for operating your "280AH" battery for setting up a monitor? Just curious on my part, but other LFPers might be interested. ?

[StirCrazy]

BFL13 wrote:
Ok one last shot at it. IMO Steve has it wrong by saying "power" has a time component. AFAIK Watts is "power" and no time, while Wh is the "energy", which is over time.

yup I did have a brain fart. I apoligise for that, but thats isn't what the main point of my post was about. it was about you trying to use CCA as some sort of power capacity for the battery. first of all why are you using a starting battery in your rv? and second the definition of CCA is

Cold cranking amps (CCA)
Starter batteries, also known as SLI (starter light ignition) are marked with CCA. The number indicates the current in ampere that the battery can deliver at –18°C (0°F). American and European norms differ slightly.

AH if we assume that the voltage is 12.0V then makes sence and is great for comparing batteries. when I first started buying batteries there was no standard and some would use reserve capacity , some would have AH but not the chart they would pick one rate and other companies would pick a different rate to make there batteries sound better.... it isnt 100% accurate but it gives you a method of comparison. I wouldnt take it for gospal that if we buy a 100 AH lead asid that we are going to get 100 ah out of it as it all depends on how you vary the voltage and current but it is an aproximation of the capacity and as long as we understand that were all good.

Steve

[BFL13]

jaycocreek wrote:
On my battery spec sheet it says (energy-1536 watt hours) but that really doesn't matter to me because I prefer knowing the amp hours over the watt hours,makes it easier for us dummies..lol

Right. 1536/12.8 = 120AH but that 12.8 is "nominal" so you need the "real" voltage to get the "real" AH and the AHs could be any darned thing!

Eg, if 13.6v is "full", then 1536/13.6 = 113AH

So if you had a Trimetric monitor that wants your "AH capacity when full" to be entered so it can keep track from there, you would enter 113, not that 120. Not a clue what your smart shunt wants!

You can fight that out with your monitors and meters, but it has to be tough being an AH man in that strange world. Rather you than me! 🙂

[jaycocreek]

On my battery spec sheet it says (energy-1536 watt hours) but that really doesn't matter to me because I prefer knowing the amp hours over the watt hours,makes it easier for us dummies..lol

[BFL13]

Ok one last shot at it. IMO Steve has it wrong by saying "power" has a time component. AFAIK Watts is "power" and no time, while Wh is the "energy", which is over time.

Watts = volts x amps, and the amps might be said to have a time component with its definition of Coulombs per second, but I don't think that is a time component in "power".

"Capacity" in Wh or AH is clear enough( 200AH vs 100AH at a given rate), and "twice the power" if that means 800 CCA vs 400 CCA.

IMO people are mixing up "power" with "capacity". Should be simple enough to clear that up and end this!

[BFL13]

My plan is to stick with AH and camp same as I always have. You guys can sort out the rest of it. We need a new topic! This thread is dead.

[StirCrazy]

BFL13 wrote:
Steve, IMO you are mixing up power and energy now. Based on what DrewE and FWC said here (scroll down) I think I have it right that CCA is power and how long the batt can keep cranking is to do with its energy.

("Capacity" should be its energy IMO. Not sure you should say "reserve power" either. Maybe somebody can sort that out)

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/30219738/srt/pd/pging/1.cfm

FWC's second para relates to my previous notion too, a low power batt with lots of energy like a deep cycle.

no sir, i belive you are confused, power = work over time or the power triangle in electricity where P=IV (power = Current X Voltage)

not confusing power and energy at all, Like I said power is a amount of work over a spicific period of time or to simplify it how fast you are doing it. Energy is the total amount of work done irregardless of the time it took.

I think you not understanding a lot of the terms leads to your state of confusion resulting in the same questions being asked over and over when multiple people explain them. this is ok, we are all here to learn. for eg, you may think that because my spelling isnt the greatest that I am uneducated so I must know nothing but yet I am a stationary engineer and a mechanical engineer (well 2 courses short on the Mechanical engineering so I dont have my pinky ring.. but I am ok with that 😉

going back to your origianl CCA is nothing but a potential to do work. and having said this it is a potential at a spicifc tempature.

that is what the battery is capable of, not what it is doing. so untill you turn that key it is just a potential to do work.

Steve

[BFL13]

Steve, IMO you are mixing up power and energy now. Based on what DrewE and FWC said here (scroll down) I think I have it right that CCA is power and how long the batt can keep cranking is to do with its energy.

("Capacity" should be its energy IMO. Not sure you should say "reserve power" either. Maybe somebody can sort that out)

https://www.rv.net/forum/index.cfm/fuseaction/thread/tid/30219738/srt/pd/pging/1.cfm

FWC's second para relates to my previous notion too, a low power batt with lots of energy like a deep cycle.

[StirCrazy]

BFL13 wrote:
If I am right that CCA is "power" , then an experienced RVer is looking for a deep cycle battery with LESS power. He stays away from those starting batteries, and sure would not want one with "Twice the Power".

it isnt power. power is watts, it is the potential. you need amps and a voltage to make power and that is applied over a period of time.

starter batteries have less power than say a GC battery, but they are designed to release more over a shorter period of time. so they are good at putting out a short burst at 800 amps. where they heavy design of a GC battery limits the peak discharge but allows a larger reserve. so say a starting battery can do 800 amps for 1 minuit a gc battery may be able to do 150 amps for 30 min.

Steve

[3_tons]

time2roll wrote:
If you like the marketing.... look up the specs.

Ha, Well I’d much rather be camping off grid than ruminating over how it’s all done 🙂

3 tons, microwaving potatoes and squash - lol

[time2roll]

If you like the marketing.... look up the specs.