Lithium Batteries

pnichols wrote:

StirCrazy wrote:

pnichols wrote:

An integrating ammeter type battery monitor for an LiFePO4 based RV system can be an expensive kindof toy, like so many things that we think we need nowadays. These type ammeters need to be calibrated relative to the actual battery(ies) that you're expecting it to monitor SOC accurately, and they should be recalibrated every once in a while to maintain their SOC accuracy as the capacity of the battery bank declines over time.

mine cost a whole 40 bucks cdn. it doesnt care about the voltage it reads amps in/out. the solar controler and the converter worry about the voltage. it will tell you the voltage also but the battery capacity is set by me when I first hook it up at full charge.

Steve

That sounds like a regular ammeter - I have one of those too, mounted permanently in the coach - that shows how much current is flowing INTO or OUT OF the coach batteries at any point in time.

Since the current lithium RV batteries have an output voltage that sags so very little as they run down, it's very tricky knowing how low they're getting merely by taking a look at their output voltage - unlike lead acid batteries (AGM or wet acid) in which their output voltage declines enough so as to be a good indicator of when to charge them.

What's needed is a meter that shows more than instantaneous amps going in or out of the batteries. An integrating ammeter keeps track of up all the amps that have left the battery over time since the last charge, and then indicates how many amp hours of storage are left in the batteries (assuming you keep the integrating ammeter calibrated periodically). That's the best way to tell when you need to charge the batteries without having to rely on estimating based on how much their output voltage has declined.

I'm not sure I'd "trust" a true integrating ammeter to remain accurate or continue working over the years that cost only $40. I certainly wouldn't - considering what lithium RV batteries cost up front - I wouldn't risk it.

That's one of the reasons (among other performance characteristics close to or exceeding lithium) why drop-in silicon dioxide (SiO2) batteries for RV use look good to me so far - their voltage sags enough as they discharge so as to not need to add a high quality integrating ammeter cost to their purchase cost.

Let me know how the SI batteries do at mid SOC and running a microwave for 12 minutes before having your inverter shutdown do to low voltage.
Here is from this morning with some readings, I didn't record the 12 cup coffee maker time that was used at 0630, roughly 10 minutes drawing 83a.
I've used it like this at 30% SOC, I guess this is the disadvantage you might have been speaking of in prior post?
Edit- Is that they still keep powering high draw items at lower SOCs



I'll stick to lfp.

Day 1 installed 4/13/16, fulltime use.

Days bonndocking
2016_ 200 of 261 days
2017_ 365
2018_ 365
2019_ 344 of 365 days
2020_ 187 as of Sept 11 out of 254 days.

As of 9/11/20
1,461 (boondocked) of 1,610 days.