Charging volts higher than programmed

[Wxboy]

After a long day of good sunshine and no problems from the Classic the sun was going down and the Classic dropped out of Absorb so I shut the inverter off to reduce the very small load I had on and get the voltage back up for a few minutes.  The absorb voltage is set to 14.7, tcomp is set at -2.5 and the batt temp was 10 degrees C, float set at 13.5.  When I shut the inverter off it did reduce the load enough to increase the voltage but instead of going to 15.0, which is what it's been running with the temp at 10 degrees, it went to 15.2 and the status said Float.  So the Classic was running too high for absorb and way too high for float.  I should also mention that the watts were showing zero at the time and 12 on the Trimetric.  To add to that I went in to tweaks and adjusted battery volts by +.1 and the Classic started charging at 15.3V, still showing FLOAT.  Then I tweaked to +.2 the Classic went to 15.4, +.3 gave me 15.5.  I then tweaked to -.1 and it dropped to 15.1.  I checked the battery voltage with a meter and it was going up and down with the adjustments. 

End amps were set at .5 so the Classic went to Float because it was showing zero watts/amps even when it was outputting 12 watts.  Typically my Classic reads a little high on watts in the morning and low in the evening until it resets itself by resting and coming out of resting.  So I understand why it went to Float but why was the float voltage higher than the absorb voltage set point?  On top of that why does tweaking the battery voltage change the charging point?  Maybe the sun and moon were aligned to cause everything to go wrong at once but at a minimum it appears that the battery voltage tweaks is doing something it shouldn't(at least on my unit). 

I'm sure someone will say that .5 amps to too low but I set it there so that it would stay in absorb for the full time set on the timer.  The bank running at the time is a 136 ah agm bank. 

I was going to see how long the Classic would behave this way but light levels were dropping fast so after 5-10 minutes the voltage dropped because there wasn't enough power coming from the panels to maintain the voltage.  It did stay in Float at 15.2 volts for at least 5 minutes and I believe it would have stayed there for longer if the light levels allowed it. 

1042 MNGP
1181 Classic

[Halfcrazy]

Well if the Classic was showing 0 watts it sure sounds like a surface charge that just had not bleed off yet? I am not sure what else to point at but I do not think it would be the Classic. It should now the battery is to high at some point and actually show "Bat over V" on the display.

Ryan

[Wxboy]

Ryan, I guess I didn't go a very good job describing it if it sounded like a surface charge condition.  I don't want to say anything negative about the product so I'll just call tech support if I see this happen again. 

[boB]

Sounds like maybe when you removed the inverter load, the Classic shot up a couple tenths of a volt and (coincidentally?)
then when it went to Float, the surface charge kept it there and of course the Classic output current would go to 0.0 amps
while it is dropping to Float.  (the Classic really should go to "silent" mode during this time)

But what is the MAXimum allowed Absorb voltage for those AGM batteries ? Also, do you have the MAXimum temp compensated
voltage limit set in the CHARGE/LIMITS menu ?

What was the polarity on the Trimetric wattage or current reading ?  Could it have  been negative which might be
the idle draw of the Classic at that time ?

12 watts of discrepancy is 0.1 amps at 12V and is at the bottom of the resolution for the Classic and maybe the Trimetric, too.

When you tweak the battery voltage reading UP, the actual regulated voltage should go down (with a separate meter)

The Float voltage  can't be set higher than the Absorb voltage.  When the Classic is right at the point of
load and no load it is common to see some jumping around of the voltage so that's probably what was
causing that.

Also, to keep the Classic in Absorb as long as the timer is set to, turn down the Ending Amps to 0.0 amps,
that way it won't end Absorb early.  At such a light load and small battery bank, it might just be ending
absorb because it is bouncing around and surface charging so easily ?

boB

PS...   You don't have a second charging source, do you ?

[Wxboy]

Hi Bob, here are some answers to your questions.

I don't have a second charging source. 

The Trimetric was set to read watts and it was actually reading 12.2.  It will read all the way down to less than 1 watt.  It was reading positive not negative.

I do agree that when I took off the load it could have bounced up to 15.2 but in my opinion it wasn't a surface charge that was holding it there.  Any time I've ever reduced the charging source on the batteries the voltage starts to drop pretty much immediately and this was holding for several minutes.  The fact that adjusting the voltage offset increased the voltage of the batteries seems to back me up on that. 

I agree with you that when tweaking the voltage reading up the actual battery voltage should drop and that's what I was trying to accomplish but that wasn't what was happening. 

I had the charge limit set at 15.2 volts. 
Today I am doing an experiment with the tweaks and the voltage limit so I can't wait to get home to see what happened.

[niel]

are you sure you have the battery temp compensation at 2.5mv as it sounds like it may be at 5mv?

[boB]

are you sure you have the battery temp compensation at 2.5mv as it sounds like it may be at 5mv?

Whatever the temperature is and this setting is set to, the LIMITS menu should give
an absolute limit to the charge voltage.

Another menu to view is in the T-Comp menu under VIEW...  It will show you
the temperature compensated battery target voltage the Classic is trying
to get the batteries to.

Check that VIEW when this is happening and tell us what that voltage is displaying.

Thanks,
boB

[Wxboy]

niel, I am sure that it is set at -2.5. 

boB, if this happens again I will be sure to check that but since I haven't seen this happen before I have a feeling I won't see it happen again.  I'm glad you mentioned this because I didn't know you could see what the Classic is targeting at the current temp.