Tri-Metric program question [RE-wrenches]

Tue Oct 10 07:03:49 PDT 2006

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Hi Alan,

I am surprised that no one else mentioned this, as it used to be a 
constant issue for my battery backup/grid tied systems. Maybe you and I 
are the only ones that run into this issue??

I use the Link-10 (E-meter) because it is easier for my customers to 
read a red/yellow/green bar graph display then numbers. Eventually (we 
can hope) charge controller manufacturers will add amp hour metering to 
their units so FINALLY the charge controller and meter will always be in 
sync with each other.

Because of our horrible grid reliability in the winter when storms roll 
through, most of my grid tied system incorporate battery back up. What 
used to happen to me with the old grid tied SW systems (and to a much 
less degree with FX systems), was the inverter constantly pulses tiny 
charge/discharge currents into the batteries. As you know, the amp hour 
meter treats charge and discharge currents differently so over time, 
these +/- current pulses result in the meter erroneously accruing a 
negative battery SOC reading.

If you are having problems with the amp hour meter on a grid, tied, 
battery based system, try raising the float voltage slightly on the 
inverter/charge controller. Yes, it will slightly lower the efficiency 
and cause the batteries to consume a bit more water, but the slightly 
additional charge current will offset the discharge pulses and keep the 
meter on track... also from what I have read, slightly overcharging wet 
cell lead acid batteries does more good than harm. I have also found 
that a few charge/discharge cycles will get the meter to recalculate 
battery efficiency higher (the e-meter starts out a default of 90%) so 
the +/- pulses are treated closer to being equal.

Hope this helps.

Todd

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
>  
>

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