Michael Ross via EV wrote:
Is it easy to create exactly 10 amps? (not rhetorical)
Don't many chargers vary a good bit depending on the load the work into?
In which case, you need to have a second instrument for the current
measurement, and it needs to be sufficiently accurate and steady.
I measure four wire resistance all the time for temperature measurements
using platinum RTDs and thermistors. It is the only way to go for
accuracy.
My main point is to know and understand if your instrument is up to the
task.
If you need high precision, then you will indeed need good equipment.
However, if the goal is just to find bad/weak connections, then a 10% or
even 20% measurement accuracy is sufficient. In most cases, the
*difference* in resistance between connections is the important point.
For example, I'll use a battery charger that has a built-in ammeter.
That ammeter is probably no better than 10% accuracy. I'll charge the
pack as a whole, and quickly connect my meter probes across the posts at
each end of my inter-cell jumpers, looking for any that have an
unusually high resistance.
If I need higher precision, I also have a Simpson 1699 micro-ohmmeter.
It's basically an accurate 1 amp current source, a DC amplifier that can
read voltages down into the microvolts, and a meter with 6 ranges
calibrated in milli-ohms.
--
The principal defect in a storage battery is its modesty. It does not
spark, creak, groan, nor slow down under overload. It does not rotate.
It works where it is, and will silently work up to the point of
destruction without making any audible or visible signs of distress.
-- Electrical Review, 1902
--
Lee Hart's EV projects are at http://www.sunrise-ev.com/LeesEVs.htm
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