E-meters [RE-wrenches]

[Todd Cory, Bald Mt. Solar]

I have a grid tied system and have dealt with the e-meter drift in between grid
outages. The main thing is to make sure the meter does not accumulate a false
negative AH reading. Here is what I have discovered...

The TRACE SW 4024 while floating the batteries pulses both positive AND negative
current into the batteries. The e-meter (or any other AH meter) does not count
current going in and out of the battery equally. It counts discharge more or
less accurately, but depending on what it thinks the battery efficiency is, it
will count amp hours back up slower than what is actually happening.

The trick is to get things set up so the meter does not accumulate a negative
reading or when the grid does go down the meter will be hopelessly inaccurate.
If it is doing this, I get the customer to cycle the batteries which usually
resets the e-meters calculation of battery efficiency so this does not happen.
If negative AH's still are adding up, I tweak the float voltage set point up a
bit higher.

I have found an additional problem though with seasonal swings in battery
temperature as the SW will accommodate temperature with a higher or lower float
voltage. So sometimes the meter will be fine until the summer when the batteries
are hotter and the float voltage adjusts itself to aa lower point. More recent
versions of the SW series than my "oldie" have eliminated the ability to adjust
the volts/degree for temp compensation. So it is always very tricky to get the
AH meter synchronized with the rest of the system accurately. This can actually
be a huge pain in the butt... as if the metering is not accurate it is really
quite worthless.

IMO, the main problem here (again) is actually with the inverters charger. If it
only pulsed positive current into the batteries everything would be fine...
however in a grid interactive mode it constantly swings current both ways. This
probably also accounts for the high (NOT) efficiency of this beast when
configured in "sell" mode.

Not to open the subject again... BUT if Trace was to bestow us with a unit with
software that was "smart" enough to shut itself OFF when it was not needed (ahem
"silent sell"), this problem with the metering could also be eliminated, not to
mention the horrible waste of some 28 amp hours (@ 26.4 volts) a day in
inefficiently wasted power.

Stepping off my soapbox again...

Todd Cory



- - - - - - -
To send a message:
 RE-wrenches at topica.com

The archive of previous messages: 
 http://www.topica.com/lists/RE-wrenches/

To unsubscribe send a message to: 
 RE-wrenches-unsubscribe at topica.com

To check out the other RE-Wrench participants:
 www.mrsharkey.com/wrenches/index.html

Hosted by Home Power magazine: 
 www.homepower.com

For info contact list moderator by email:
 michael.welch at homepower.com

___________________________________________________________
T O P I C A  http://www.topica.com/t/17
Newsletters, Tips and Discussions on Your Favorite Topics