4 X 6v vs. 2 x lithium – page 13 – irv2 forums grade 9 electricity worksheets

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My requirements/use: 6 person family on a multi-month trip 60% will have hookups with the rest being semi remote bits of peace or empty parking lot overnights. It has a generator, but don’t want to run it for 4-5hrs at a time while lead acids float to full. I am looking at starting with two 12V 100ah lifepo4 drop in replacements from Starkpower https://starkpower.com/product/12-volt-100ah-battery and upgrading to a more robust inverter with a substantial charger like the Victron Multiplus 3000 https://starkpower.com/product/multi…verter-charger. Not knowing our daily power needs makes this difficult, but I would rather start this adventure off right. Also having tools, a house, and address to ship things to will make it easier. 200ah of mostly usable battery capacity with much faster charging from alternator, generator or shore power seems like a big bonus. Adding solar is phase 2 and will be added if I find it is needed.

RV Specs: Class A gas, 5500 Onan, Giant Residential Fridge (don’t know the amp draw yet), 1500w Microwave, 1200w Induction Stove, Eaton 1800w True Sine Inverter, 2 6v Batteries (from manufacturer and assumed to be very low quality), Battery Charger is unknown, but from what I have read 5-6hrs on Gen to get up to 100%.

My requirements/use: 6 person family on a multi-month trip 60% will have hookups with the rest being semi remote bits of peace or empty parking lot overnights. It has a generator, but don’t want to run it for 4-5hrs at a time while lead acids float to full. I am looking at starting with two 12V 100ah lifepo4 drop in replacements from Starkpower https://starkpower.com/product/12-volt-100ah-battery and upgrading to a more robust inverter with a substantial charger like the Victron Multiplus 3000 https://starkpower.com/product/multi…verter-charger. Not knowing our daily power needs makes this difficult, but I would rather start this adventure off right. Also having tools, a house, and address to ship things to will make it easier. 200ah of mostly usable battery capacity with much faster charging from alternator, generator or shore power seems like a big bonus. Adding solar is phase 2 and will be added if I find it is needed.

RV Specs: Class A gas, 5500 Onan, Giant Residential Fridge (don’t know the amp draw yet), 1500w Microwave, 1200w Induction Stove, Eaton 1800w True Sine Inverter, 2 6v Batteries (from manufacturer and assumed to be very low quality), Battery Charger is unknown, but from what I have read 5-6hrs on Gen to get up to 100%.

UPDATE: I now know where the ampere hours were going when my SOC meter was reading 100% and charging went on and on. It was charging the battery!! The problem was the SOC meter had drifted off and was reading high by 20%. It was telling me I was at 100% when I was only at 80%. I read some more on charging LFP and determined that 1) I was not getting my LFP up to 100%, and 2) the SOC meter was useless as an indicator of charge unless it had been recently calibrated by a full charge (it handn’t).

So, I let the solar run and eventually battery voltage did rise! I didn’t try to get to 14.6V with my modest solar, but had no trouble getting to 14.4V so probably could have gotten to 14.6V. It’s a 300AH battery and indeed I put about 60AH into it after the SOC meter hit 100% to get to 14.4V. Even with less than 10 amps into the 300 AH battery, I was able to get to 14.4V. The SOC meter started counting backwards from that point and surely was telling me 80% where it used to say 100%.

I don’t know how often the SOC meter must be calibrated via a full charge (to 14.4 or 14.6V) but I had gone through a lot of partial cycles without getting a full charge and apparently that did let the SOC meter drift up to 100% when I was actually at 80%.

Since the above experience and learning process, I have gotten the Lifeblue up to 14.6V with very modest solar output; less than 10 amps. It really doesn’t take long to get from 14.4V to 14.6V even at 10 amps. It seems the battery is very close to 100% at 14.4V.

I have four 100W Renogy panels in series. I’ve seen over 300W a few times but that’s rare. So I can produce up to about 22 amps (300W at 13.5V) on a good day. That might get a 100AH LFP above 14V but only gets my 300AH up to about 13.8V (the claimed float voltage). Might also work for 200AH but I doubt that. And that’s mid-day; as the sun drops, current drops and I’m charging away at 10-15 amps and maybe 13.5V. That’s just fine for the LFP where an AH in is an AH of added charge. This is my solar controller.

It has a "user" profile that lets me skip the absorption stage and set the bulk to float trigger voltage and the float voltage. But, as I noted, these don’t do any good because there isn’t enough current to get to the trigger and if I set the float at 13.8 the charging continues at 10-15 amps right past 100% SOC.

The issue is that the voltage of an LFP is a function of the charge current more than the SOC — unless you’re charging current is substantial (well above 50 amps in my case). And even then the voltage moves only 0.3V from zero current to 15A (max on a typical solar day).

I have a typical propane/electric RV fridge. I have run it on the solar when the sun was really good (developing over 300W) and the battery was fully charged. The fridge takes right at 300W. I’ve also run the 600W water heater on the inverter when the sun was good (300W from the sun and 300W from the battery). These were just manual experiments though. Normally we are not in the RV during the day so can’t monitor such use. In fact, unless there’s plenty of room in the battery for a day’s solar production, we turn the solar off when we leave for the day.

UPDATE: See my post just minutes ago. Things I said in the above post are wrong. My mistake was believing the SOC meter. Turns out it was reading high by 20%. And I simply needed to let the solar run until the LFP voltage started rising, indicating 100% charge. Indeed, it does not take much current to get the LFP to 14.4V or higher. It just takes time … and realizing that the SOC meter will be correct and calibrated only if the battery is pushed up to 100% charge (as indicated by the voltage). It’s unnerving watching the meter sit at 100% for another 60AH of charge, but that did the trick. It now reads 100% only if I get voltage up to 14.4 or above. And probably will until I have inclement weather and go through a lot of cycles never hitting 100% … but now I know that that causes the SOC meter to read high.