T&T: AMPs question

[Arild Jensen]

> -----Original Message-----
> From:  Peter Bennett

> However, for the load test, I'd try
> to put enough load on the batteries to discharge them in 20 - 30 hours
> (the AH spec is based on a 20 hour discharge.)  That would require
> drawing about 30 amps.
>
> I suspect that the load test mentioned by JSpence tests the ability to
> deliver a high current, as for starting, and won't determine the AH
> capacity.


REPLY
Peter is correct.  Furthermore the "industry standard" test requires
repeated tests to determine what the actual discharge current has to be for
the battery to reach full discharge in 20 hours.

A slightly less accurate but more easily done test is to discharge the
battery at a known rate (pick 10a or 20A) and measure elapsed time from full
to empty.  Although not as accurate it does come close.


Of course the dedicated battery meters like the Link 10 and similar
offerings from several manufacturers is the best way.
Xantrex still sells the Link 10 but now has several other meters either
stand alone or integrated in their inverter/charger products. BEP now has a
model as does Victron and Mastervolt.
A company called Mid-Tronics makes a battery capacity meter for an instant
snap reading. This technology is used in many of the dealership battery test
equipment and some batteries even incorporate an abbreviated circuit into
the battery top itself.
Pulsetech now sells a rebranded model of the Midtronic instrument as part of
their product lineup for battery dealers.

Something to consider is the fact apparent amp hour capacity does vary
depending on the actual load current.
Research done by a Mr. Peukert  a long time ago established the calculations
needed to correctly compute the A-H remaining  for a given discharge rate.
At 1A discharge the 100A-H battery may run 150 hours or more but at 50A it
may not even run two hours.  The relationship is not linear. Which is why
the link 10 and similar products are expensive. Its actually a miniature
computer.


As always YMMV  < grin>

Arild