Electricky Dicky wrote:
On Wed, 03 May 2006 11:55:39 GMT, chuck wrote:
Electricky Dicky wrote:
On 2 May 2006 06:21:06 -0700, "Andina Marie" wrote:
Carl wrote:
Hi Nigel,
When you have batteries arranged this way you need to be very careful
that they charge and discharge in balance. Otherwise you end up with
voltage variations between the pairs that leads to early failure (I
know - it seems odd). Your positive lead should connect first to one
pair and the negative first to the other pair.
Here's a diagram of correct wiring from the high end german battery
supplier - Sonnenschein.
http://www.sonnenschein.org/Really%20FAQ's.htm
Carl
That is a common but unfounded myth.
With appropriate jumpers between the parallel batteries, the voltage
difference caused by cables entering/exiting from the same side are
less than 0.001 volts which is far less than internal battery
incongruities and will have zero effect on the battery life.
If the two batteries were separated by a considerable distance, say 10
feet, and the jumpers between them were smaller than the starter motor
cables, in that case one battery would tend to be used slightly more
than the other but only during heavy loads. As soon as the load is
removed, the batteries will equalize within a few seconds.
Andina Marie
I completely and utterly disagree!!!!!
Richard
Nb "Pound Eater" Parkend G+S
The actual voltage drop will depend on actual wire size and length. In
the case of #4 wire, which is probably a worst case example, the voltage
drop due to a one foot length difference (two feet round trip) would be
on the order of 0.040 volts at 100 amps. That difference is really
insignificant since it represents only initial charging current, and
ultimately the battery will be charged and discharged at a much lower
current. At 1.0 amps and #0 wire, the voltage difference is 0.0002 volts
(two feet). In the end, the difference should be less than differences
in the characteristics of individual batteries, as was stated.
With what specific part do you completely and utterly disagree, Richard?
Chuck
The bit about "myth" and the inference that there is no need to
connect "cross corners".
If you have the time take a look at
http://www.smartgauge.co.uk/batt_con.html
This article discusses the situation with facts.
The article is UK based so metric cable sizes. To assist our colonial
friends, 35mm2 is slightly larger than 2AWG.
I will be interested to see comments.
Richard
Nb "Pound Eater" Parkend G+S
Thanks for the reply, Richard.
A couple of points.
I think the article you referenced confirms the data I provided on wire
resistance. It is a bit naive, however, in assuming a constant and
uniform internal resistance among the batteries. Internal resistance
varies with the age and condition of the battery and non-linearly with
the amount of current being drawn from the battery. Variations of
internal resistance between the cells of 8% seem to be common among new,
similar batteries and the added wire resistance to the farther battery
in the case of "corners not crossed" is only about 7.5% of the battery's
assumed internal resistance. Battery manufacturers want to see internal
resistances increase by 50% before replacement under warranty,
suggesting that increases of as much as 45% are within normal variances!
See:
http://www.batteryuniversity.com/print-parttwo-42A.htm
Does internal resistance reveal battery capacity?
Real batteries are not easy to model. For example, even if there is a
difference in each battery's contribution to a particular load, the
battery providing the greater contribution will more rapidly see an
increase in its internal resistance, thus enabling the other battery to
increase its contribution.
Except in extreme cases, the method of connection is not too important.
Chuck