On 26 Feb 2016 at 22:06, rayfellow via EV wrote: > The one that gets me are the RV (recreation vehicle) salesmen when talking > about the house battery capacity will refer to it as 100 - or 200 - amp hours.
I don't know much about RVs, but I don't understand what's wrong with stating battery capacity as amp hours. That's a standard measure of battery capacity, no? > Knowing that they're talking about a 12v system, I believe the math > would be 100 amp hours at 12v would be 1.2 KWh's. Do I have this right? Roughly. But it seems to me that to get an accurate measure of capacity in watt-hours (or kWh), you'd have to track the voltage during the discharge. At the start of discharge of a fully charged battery, the voltage may be more than 12 volts; it depends on the load and battery internal resistance. When the voltage under load falls to 10.5v the battery is considered flat. So during discharge, the voltage is constantly falling. That changes the power calculation each instant. To determine watt-hours capacity you have to monitor and record the amp-hours withdrawn, and the voltage over time. The easier way is to measure watt-hours capacity with a true watt-hour meter. Also, don't forget that actual USABLE capacity of a battery depends on how much current you need from it. Batteries aren't quite as straighforward or simple as they appear, eh? David Roden - Akron, Ohio, USA EVDL Administrator = = = = = = = = = = = = = = = = = = = = = = = = = = = = = EVDL Information: http://www.evdl.org/help/ = = = = = = = = = = = = = = = = = = = = = = = = = = = = = Note: mail sent to "evpost" and "etpost" addresses will not reach me. To send a private message, please obtain my email address from the webpage http://www.evdl.org/help/ . = = = = = = = = = = = = = = = = = = = = = = = = = = = = = _______________________________________________ UNSUBSCRIBE: http://www.evdl.org/help/index.html#usub http://lists.evdl.org/listinfo.cgi/ev-evdl.org Read EVAngel's EV News at http://evdl.org/evln/ Please discuss EV drag racing at NEDRA (http://groups.yahoo.com/group/NEDRA)
