Larry - You are right. Amp-hours on its own doesn't really mean much at all.
Except, of course, that most modern EVs have battery/traction packs in the
~300V bracket and most batteries used in such vehicles have cell voltages in
~3-4V range so, depending on the context, an Ah rating gives the
That is right, Kilo Watt Hours is the proper trom for total energy quanity.
the voltage and the ampere hours are terms best quantified by the system
design engineer. If you are qualified to design you understand the ratios
of voltage and maximum current draw versus the demand of the load. As well
[mailto:ev-boun...@lists.evdl.org] On Behalf Of Larry Gales via
EV
Sent: Tuesday, July 08, 2014 11:18 PM
To: ev@lists.evdl.org
Subject: [EVDL] Question about amp-hr
I know that watts = amps * volts, and watt-hours (wh) is a measure of
energy, but over and over again I hear people talking about EV
Cor van de Water wrote:
Reason is that Li-Ion batteries are sized by Ah
so it is normal to say what size (Ah) battery cells you have,
if you want to indicate which version cells are in your pack,
but if you want to tell the energy in the pack then it only
makes sense if you tell (or know)
I know that watts = amps * volts, and watt-hours (wh) is a measure of
energy, but over and over again I hear people talking about EV batteries in
terms of amp-hours. What does that mean if you don't know the voltage?
1000 amp-hr is not impressive if the voltage is, say, 0.1 volts. Is
Larry,
YMMV. The energy capacity, Amp Hrs, of a cell is very useful and you need
to know the nominal cell voltage to go very far with it. Indeed you can
get 200AmpHr at 3.2 V, no problem, as an example.
2 cells in parallel gets you the sum of amp hrs at the nominal voltage. 2
cells in series
Heck, to draw 10uV at 1000A would be an interesting application. In any event
you are right. 1000Ah rating only makes sense as a power value if you know the
battery so you know then that 1000Ah is really 12,000Wh for a 12v nominal
battery. What people mostly like to know about EV batteries
People talk in amp-hours because it's easy and/or they're being sloppy.
Batteries are sold in standardized packages (1 cell @ 3.6V for lithium, 3 or 6
cells at 6V or 12V for lead) at which amp-hours is the metric used to
differentiate different capacities. But when you build a big series
