Hi All,
I've searched a lot for this particular issue and can't seem to see anyone else having it so I thought I would ask here. In a nutshell:
*I have two Classic 250's connected w/ follow me (one solar, one hydro) on a 48 V system.
*My absorb voltage is set for 57.6
when I start to go to absorb (around noon yesterday) neither unit seems to reach the absorb voltage, instead they get to about 56.9, 57 and then start the absorb counter (and throttling back the solar); The classic displays this voltage, even though the absorb voltage is set to kick in at 57.6
the offset is minor but I can't figure out the cause and I seem to remember on my previous 12 V config that it would actually hit the absorb on the nose.
*whiz bang jr is attached, but I set everything to timer for this recent test
any thoughts?
Thank you
Eben
Quote from: ebenbayer on July 13, 2014, 07:56:28 AM
*My absorb voltage is set for 57.6
when I start to go to absorb (around noon yesterday) neither unit seems to reach the absorb voltage, instead they get to about 59.8, 60 and then start the absorb counter (and throttling back the solar)
How long does he voltage stay elevated? I mean is this a transient "overshoot"? Any chance you have automatic equalization turned on? Any chance of a high resistance connection somewhere between the controller and the battery?
--vtMaps
Thanks for the reply!
I made a serious typo which is misleading-- i get to 56.9 (not 59.8 ) so am coming up a little shy when the absorption counter starts (not overshooting)
I've got good connections to battery and otherwise all the volts at various charging rates match up very closely. Issue at hand is the classic seems to think it should be absorbing even when it shows it is beneath the set point (by about .5-.75 V)
any other thoughts?
Eben
Quote from: ebenbayer on July 13, 2014, 01:32:10 PM
I made a serious typo which is misleading-- i get to 56.9 (not 59.8 ) so am coming up a little shy when the absorption counter starts (not overshooting)
<snip>
Issue at hand is the classic seems to think it should be absorbing even when it shows it is beneath the set point (by about .5-.75 V)
Sounds pretty normal that you should not reach the set point at this time of year in the northern hemisphere.
Are your batteries warm? If so, the Classic is doing exactly what it should to protect your batteries from overcharging... or even going into thermal runaway. You do have a remote battery sensor, don't you?
--vtMaps
Hi vtMaps,
I think I have enough power to hit my set point because if do an EQ the voltage will keep rising.
I do have the remote battery sensor installed, it was reading 30 C (~86 F) during this time period. My charge rate is on the low size for bank (720 amp hours) so I haven't seen them get too warm, yet.
Am I reading you correctly though that the ~.5-.75v offset to the low side is the result of the classic compensating charge voltage for 5 or so C? for a delta C of 5 that would line up at about .6 volts or right what im seeing.
Seems to make sense.
Thanks for the info!
Eben
You can see just what the Classic is using for temperature compensated voltage level.
To view this, go to the CHARGE menu then the T-comp menu and press the SOFT-RIGHT
key (upper right) that is labeled via the LCD as "VIEW" and it will show you the temperature
compensated target voltage.
Might be it.
Yes if the battery is 30c thats 5c over the "neutral" point. So with -5mv per degree c per cell you have
24 cells * 5 degrees c * 5mv = 600mv or 0.6 volts
Ryan
Thanks All! Sounds like its narrowed down. Ill confirm on the unit itself later this week. Seems clear in retrospect :)