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.

it shows remaing AH so it is what you are talking about. it is also rated for Li AGM LA batteries.. lighium dont realy have a flat curve either, some may as in flashlight batteries but the ones we are looking at are fully charges at 12.4V and 20% at 11.9, so yes it is more shallow but it is still linier and readable.

Steve