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Hugh,<br>
Let me give it a shot. My apologies about noting only solar charge
controllers - I forgot that the sun is a rarity where you live.<br>
<br>
The return amps affects only the transition from absorption to
float. If, while the voltage remains up at the bulk/absorption
setpoint, the charge controller's current necessary to maintain this
voltage drops below a programmed threshold, the charge controller's
logic determines that the battery is full and transitions to float.
That's all. Rule of thumb is that the current threshold is about 2%
of battery capacity.<br>
<br>
It's a nice feature, but can bite the system owner as the batteries
age and require a higher current to overcome increased internal
resistance. If the absorption time has been set long (as is typical
with "opportunity charging" recommended with PV systems - use all
you can when you can get it) the float transition current setpoint
is no longer reached and water consumption goes way up, leading to
unexpectedly low water levels in the cells.<br>
<br>
Re the other question - how a charge controller senses load - it
simply adjusts current during absorption and float to respond to
voltage dips that are proportional to load. In other words, it tries
to maintain programmed setpoint voltage by allowing more current
through. The Solar Boost products actually used an external shunt
option, tying to the Kelvin terminals on the shunt to measure
current and allow compensatory current; a dip switch controlled
internal/external sensing. Modern digital controllers apparently
rely solely on voltage variations.<br>
<br>
Allan<br>
<br>
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<font face="Times New Roman, Times, serif"><b>Allan Sindelar</b></font><br>
<small><a href="mailto:Allan@positiveenergysolar.com"><font
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<span style="font-size: 10pt;">NABCEP Certified Photovoltaic
Installer<br>
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<b>Positive Energy, Inc.</b><br>
3201 Calle Marie<br>
Santa Fe, New Mexico 87507<br>
<b>505 424-1112</b><br>
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<br>
On 4/24/2011 11:43 AM, Hugh wrote:
<blockquote cite="mid:p06230906c9da1134a514@%5B192.168.1.3%5D"
type="cite">At 08:22 -0600 24/4/11, Allan Sindelar wrote:
<br>
<blockquote type="cite"> if I understand your reference to
transition current as a transition to float, several charge
controllers have that feature.
<br>
</blockquote>
<br>
I imagine they are solar charge controllers. Diversion charge
controllers as used on wind and hydro systems do not have access
to the battery current to measure it. I am not sure how the solar
ones can 'know' the battery charge current without knowing the
load current (to inverter) but maybe there is a controller with an
external shunt or something? I'd like to hear about that.
<br>
<br>
thanks for any further pointers...
<br>
</blockquote>
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