Tri-Metric program question [RE-wrenches]

[Allan Sindelar]

Wrenches,
We have been including a Tri-Metric monitor with our Outback
grid-tie-with-battery-backup systems, so that the homeowner has some sort of
state-of-charge indication during an outage. We have learned to be selective
about whether to include a Mate as well, as it's not as user-friendly for
our typical non-technical grid-tie customer.

The issue is that the Tri-Met is fundamentally designed for off-grid use,
and uses charged-voltage and charged-current parameters to reset the monitor
on a regular basis. As the PS1 keeps the batteries in float, the Tri-Met can
develop an accumulated error that is only reset after a grid outage and
recharge cycle, which could be months at a time. We have seen this happen,
where the % of full slowly drifts down over days or weeks.

I called Ralph Heise about this, and he had suggestions, but no clear
answers - in fact he is looking for ideas that have worked too. He suggested
the following two ideas, which make sense in theory:
1. Set the charged voltage parameter below the float voltage (far enough
below to accommodate the effect of hot-weather temperature compensation -
say 52.4V if float is at 53.6 - and set the charged current setpoint just
above the float current - 1 or 2A, I would guess. This keeps the monitor
reading 100% while in float, and the combination of voltage and current
settings would prevent premature resetting based on voltage-above-float
alone.
2. Set the charge efficiency factor unrealistically high - say at 100% - so
that this keeps the % reading at 100% while in float. This would make the %
reading slightly high during outage cycling, but it could be easily reset
each charge cycle.

Has any Wrench out there come up with a good solution? How would you set up
a TriMet for this application? Or otherwise, how do you address the bigger
issue of a monitor that is used only during an outage?

Thanks in advance,
Allan at Positive Energy


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