Tri-Metric program question [RE-wrenches]

Mick Abraham mick at abrahamsolar.com
Tue Oct 10 07:42:15 PDT 2006


Here's an off-the-wall idea for Allan's Tri-Metric issue: So long as the 
grid is up and running, the end user doesn't need any battery state of 
charge information at all, so: A SPST normally closed relay with a 
120vAC coil could interrupt the DC positive going to the meter so long 
as the grid power is energizing the relay coil. 

If the grid goes dark, the deadman relay would power up the meter, and 
the TM-2020 always displays 100% when it's first powered up. TM-2020 
program settings are retained even with no power to the meter (but I 
don't know if that's permanent non-volatile memory).

Here's an advantage: the end user can confirm grid blackout status by 
noting that the Tri-metric is lit up. Here's a (possibly huge) 
disadvantage: if the grid comes up briefly then goes back out, this 
would reset the TM back to 100% which may falsely mislead the end user. 
Therefore, this suggestion is worth considering if the blackout pattern 
tends to be off, staying off, then on for a long time. If the balckout 
pattern tends to be off for awhile, then briefly on, then off again, 
this suggestion injects a new batch of problems.

Just thinking outside the box, 

Mick Abraham

Allan Sindelar wrote:
> 
> 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
> 



Abraham Solar Equipment
Pagosa Springs, CO
www.abrahamsolar.com


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