Surely given the preponderance of PV charging , Victron could update the BMV712 or the Victron connect app to show battery discharge recharge info in Wh as opposed to Ah. For example I can’t immediately reconcile how much of the PV generation ( in Wh) has gone to battery as opposed to the loads. Sure I can do an approximate conversion from Wh to Ah at a nominal system voltage , but it’s not as accurate as the BMV computing Wh based on the actual voltage.
Maybe as a configurable option, but not at the expense of AH.
And wh ratings are really only used in lithium batteries. You wont find it for lead acid and other types because of voltage curves. So too variable for consistency over all battery types and for calculating.
Easiest to say 100ah I discharged 50ah and have replaced 30ah. So now at 80ah.
The issue is variable voltage the issue is comparing Wh from the panels with Wh consumed by the batteries and by extension Wh consumed by the boat.
There no reason the BMV can’t report in Wh.
Ah has nothing to do with voltage it’s just columb counting , Wh is a more accurate reflection as it encompasses voltage variation over the time period
Ah ratings for batteries is an entirely arbitrary construction based on a set discharge for a set time. Wh could equally be used.
At best, irrespective of units, it will be a reasonable guess.
I had the same issue and I'm using total energy charged / discharged (which the BMV reports in kWh) to compare to PV history data. I don't know if it's a good solution because it's not clear to me what those numbers mean (are they at the input or output of the charge efficiency estimator?), it'd be nice to have better documentation.
The main problem with those kinds of comparisons, is the system losses are difficult to track. All systems have different amounts of losses due to the way install was done wiring crimping length or ambient temps etc. And often users are shocked at the differences.
It depends on what you're trying to do, in my case system losses are just part of the load and not a problem at all. It's still useful to know that X amount of energy from the panels nets me on average Y into the battery if I'm trying to decide for example when I need to turn on a trickle charger.
The BMV shows Kw but not KWh afaik
It’s a shame the bmv doesn’t report daily kWh usage. It would then be possible to compare different generators directly
comments about Wh fundementalky don’t realise it’s much more accurate then Ah as it tracks system voltage
System voltage is always changing, whether because it is being raised by charge or dropped under load. So too variable to have it as a base calculation if you are wanting consistent accurate readings with history. It would end up being a ballpark calculated amount.
An interesting article that helps get a grip on the difference between the two mathods of measurement.
The commentary in that linkin article comes down firmly on using kWh .
People saying Wh are too variable miss the point , to calculate Wh correctly yiu have to sample voltage , so let’s say you sample every 100mS. Now your Wh calculation is only assuming voltage stays the same for 100 mS. In contrast , Ah has no idea what’s happening to voltage
Secondly this idea that Ah in to a battery is similar to Ah out is of course nonsense charge efficiency affects capacity restored , If I return 100Ah , I don’t get 100Ah back out , ( I do but at a lower SOC) any coulumb counter will rapidly get out of sync over a few days unless reset by 100 % charge triggers. At least Wh fatefully reflects the fact that energy store has an inefficiency.
Ah largely got used because it was easy to measure whereas Wh is awkward. Once battery manufacturers speced capacity in Ah ( a spec that entirely flatters batteries by the way ) then we then to use Ah as a “ proxy “ for Wh ( by assuming a fixed nominal voltage ( which itself is fiction )
All battery energy counting is fraught with inaccuracy , just that Ah is actually worse
