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?

This is what I do.... right, wrong or indifferent.I set my inverter (hybrid) to loadshare 30a or 50a depending on the power source. I turn off the charger but leave my solar on to charge if needed so the inverter is passing through power, powering everything 120v but the 12v loads are carried by the batteries. When I was doing this it was colder weather so the furnace and misc 12v loads would use roughly 10-15% DoD (50-75ah) solar would top them off and float at 13.6v. This was last spring for a couple months during covid first started and didn't want to stay in hotels for work. Also did this way 5 years ago before doing the boondocking fulltime.Lot of cycles of use with heavy draw items everyday. Past 2 weeks with the heat (90-100f) kicking here in AZ I've been spliting run time of the generator, batteries & solar using the air conditioner. When air conditioner, tv, humidifier and other inverting loads there will be 2-3 hours of 100-175ah inverting, stopping at 60% SOC then do the gen for air conditioner for awhile longer but not using the gen to charge the batteries. By the time morning coffeemaker, microwave use is finished SOC is 40-45% and solar will charge back up by 2pm roughly when I switch the air conditioner back to batteries/ solsr and do it over again. Today started moving north so shouldn't have to do this for a while again. :)

I read some inverters have 2 stage charging. Bulk, absorption and off. At the set point, 12 to 13 volts, the charger repeats the 2 stage.

So the inverter /charger stays 12v powered so it can run the pass through by getting that 12v from the batteries which are being cycled. If you need more 120v than the pass-through has, you get inverter help with the hybrid. Pretty neat!I was thinking you could clamp a small float charger on the inverter/charger's DC terminals to keep it powered up and just isolate the LFPs, not floating them. If you did that with solar it wouldn't work at night.If you had a separate inverter and a converter, instead of an inverter/charger, you would not have this. The converter would supply the 12v with LFPs isolated, not floating.I don't know if there is much penalty in cycles or whatever if you did float the LFPs, but it would be good to have the choice I guess.EDIT--if the inverter/charger has a "no float" option and the charger turns off, how does the inverter stay powered up? You want the battery to not float but that would put a drain on it ?

The best part of this was last spring when a storm blew through and power was out for a couple of days, we didn't even know it till a couple hours later when I went outside to check out the damage and the campground owner came by to apologize for the power lost and not knowing when it would return. It made no difference for us because we always fill the water tank and it a seamless unnoticed event when going from 120v to 12v inverting power and solar to help with the heavy lifting. ;)

Along with the inverter-charger, I still kept the PD charger and can run either source separately or concurrently as a duo... When camper’s not in use, the PD serves as the power supply while the battery stays isolated (at about 50% SOC) via dedicated battery switch...Upon trip departure, solar typically restores battery from say 50% SOC to what’s a ‘user acceptable’ level of charge, or a full charge if need be - a 100% full charge is not needed except for an occasional cell balancing...3 tons’

LFP on Shore Power with Inverter/charger? | Good Sam Community

114 Replies

FWC
Explorer
Apr 21, 2021
I am not sure why you wouldn't trust the %SOC on your monitor - for a Trimetric it is just a linear function of Ah used, so if you trust Ah and have programmed the monitor with your notion of bank size it will give you the same %SOC that you are calculating in your head.

BFL13 wrote:
I would never trust the %SOC of a monitor. I do trust the AH count. I don't have the Trimetric set-up to even read %SOC. I do have an idea of the battery bank's AH size as adjusted for temperature. This matters when camping in ambient 35F temps.

I look at the AH countdown from zero and subtract that in my head from my notion of battery bank size in AH to get an idea of SOC. I know my daily usage. Easy to tell if I need to recharge today or if it can wait till tomorrow.

I have the voltage read-out too. I mostly watch that for estimating SOC, which is also easy with "ordinary" batteries. I cross-check the two SOCs to see if they "match". No big deal, no spoiling of quality camping time.

It is easier in the summer with solar, where you can go for weeks without getting down to where you need to haul out the gen. Do have to keep an eye on the weather forecast for overcast predictions. I do watch for when the batts get to "true full" while on solar, and reset the AH counter. If it doesn't get to true full that day, I just leave the AH counter running. ( I have disabled the auto-reset on the Trimetric like they suggest if you are on solar)

If I had LFPs I would not change my ways, except I would miss having the more "accurate" voltage readings.
FWC
Explorer
Apr 21, 2021
time2roll wrote:
If the battery is cold and loses 30% of the capacity does the counting of AH still add up? If you know the battery is cold the voltage will still be dropping quick in the last 30%.

What ever system you have is but a guide. Keep your wits about you and all will be fine.

Yes the Ah counting still works even at low temperatures. The Ah used are still the Ah used, and these are not based on voltage. Better Ah counters (eg Victron) with a temperature sensor can adjust the available capacity based on temperature to provide accurate SOC as well.
steveh27
Explorer
Apr 21, 2021
I just returned from a 4 day turkey hunting camping trip. I had electric at night. My PD4635 convertor charger worked well. PD told me to press in the boost button to get them fully charged, but I did not do that on this trip. When driving the alternator would charge the 2 LiFePo4 batteries. I noticed when the Trimetric reached 14.4 volts the charging stopped. I think that must be from the BMS. The cable from the alternator goes through a battery isolator and then 2 40 amp breakers.
BFL13
Explorer II
Apr 20, 2021
I would never trust the %SOC of a monitor. I do trust the AH count. I don't have the Trimetric set-up to even read %SOC. I do have an idea of the battery bank's AH size as adjusted for temperature. This matters when camping in ambient 35F temps.

I look at the AH countdown from zero and subtract that in my head from my notion of battery bank size in AH to get an idea of SOC. I know my daily usage. Easy to tell if I need to recharge today or if it can wait till tomorrow.

I have the voltage read-out too. I mostly watch that for estimating SOC, which is also easy with "ordinary" batteries. I cross-check the two SOCs to see if they "match". No big deal, no spoiling of quality camping time.

It is easier in the summer with solar, where you can go for weeks without getting down to where you need to haul out the gen. Do have to keep an eye on the weather forecast for overcast predictions. I do watch for when the batts get to "true full" while on solar, and reset the AH counter. If it doesn't get to true full that day, I just leave the AH counter running. ( I have disabled the auto-reset on the Trimetric like they suggest if you are on solar)

If I had LFPs I would not change my ways, except I would miss having the more "accurate" voltage readings.
time2roll
Nomad
Apr 20, 2021
FWC wrote:
Coulomb counters/Ah meters work very well (when configured properly), and can easily track the battery SOC to 10% or so, which is plenty accurate for RV use. I am not sure why this is causing so much concern.

If you know the temperature of your LiFePO4 batteries, and the loads, you can probably get an estimate within 20% - 40% using voltage, but it is much more complicated than just glancing at your Ah meter.

I know folks like to fuss over their power systems (it is a hobby unto itself), but the point of a well configured system is the you don't need to be constantly thinking about it, it just does it't thing in the background. If you are running a decent size battery system of any chemistry, and Ah meter seems like a no-brainer, you can glance at it every once in while to make sure everything is OK, no need for tables, maths etc.
If the battery is cold and loses 30% of the capacity does the counting of AH still add up? If you know the battery is cold the voltage will still be dropping quick in the last 30%.

What ever system you have is but a guide. Keep your wits about you and all will be fine.
jaycocreek
Explorer II
Apr 20, 2021
BFL13 wrote:
FWC has shown how temperature changes the LFP voltage so much that you can't really use the voltage/SOC table if I understand him on that. I don't know if you can use a temp/voltage table and allow for the temp so you get "close enough".

The main thing you want to know while camping is whether you need to haul out the gen today or can it wait till tomorrow to do a recharge. You need your SOC now to decide that based on your planned usage between now and tomorrow. Solar is part of that decision of course.

"Close enough" is where the accuracy of the voltage reading matters. An AH counting monitor would be a better guide IMO, with your estimated adjusted for temp, low load, "resting" voltage as a rough cross-check.

So far I have found what StirCrazy said to be fairly accurate on voltage...Going on 9 days running my Engel fridge/freezer set at 35 degree's...And note the accuracy of the dumb voltage meter..LOL
FWC
Explorer
Apr 20, 2021
Coulomb counters/Ah meters work very well (when configured properly), and can easily track the battery SOC to 10% or so, which is plenty accurate for RV use. I am not sure why this is causing so much concern.

If you know the temperature of your LiFePO4 batteries, and the loads, you can probably get an estimate within 20% - 40% using voltage, but it is much more complicated than just glancing at your Ah meter.

I know folks like to fuss over their power systems (it is a hobby unto itself), but the point of a well configured system is the you don't need to be constantly thinking about it, it just does it't thing in the background. If you are running a decent size battery system of any chemistry, and Ah meter seems like a no-brainer, you can glance at it every once in while to make sure everything is OK, no need for tables, maths etc.
BFL13
Explorer II
Apr 20, 2021
FWC has shown how temperature changes the LFP voltage so much that you can't really use the voltage/SOC table if I understand him on that. I don't know if you can use a temp/voltage table and allow for the temp so you get "close enough".

The main thing you want to know while camping is whether you need to haul out the gen today or can it wait till tomorrow to do a recharge. You need your SOC now to decide that based on your planned usage between now and tomorrow. Solar is part of that decision of course.

"Close enough" is where the accuracy of the voltage reading matters. An AH counting monitor would be a better guide IMO, with your estimated adjusted for temp, low load, "resting" voltage as a rough cross-check.
pianotuna
Nomad III
Apr 20, 2021
StirCrazy wrote:
pianotuna wrote:
Why not just write the seller/maker?

Who is the most 'senior' user of Li here? (i.e. longest use)

I have had a cell phone for 30 years ;)

probably not me, I have been playing with small 30AH batteries for about 2 years now but thats it.

Steve

You certainly enjoy obfuscation. And your cell phone from 30 years ago was NOT Li but more likely nickle metal hydride or perhaps ni cad.

Who has had a house bank that consists of Li formulation for the longest period of time?
jaycocreek
Explorer II
Apr 20, 2021
hold up therebig guy, yes you can use voltage in 10% aproximations

I believe this although my smart shunt voltage is slightly off because of any load I may have but the voltage meter that came on my battery box has been spot on voltage wise..So far I could actually come pretty close to actual voltage if I only used the voltage meter on my smart battery box,I have to let the smart shunt rest without a load to get a good reading even with just the Engel fridge/freezer cycling the voltage is lower...