Quick Voltage Question

[Tons001]

Quick question about using the battery tweaks on the Classic. If I use the tweaks menu to adjust the battery voltage after resting for a couple hours to match using my Fluke, then it is too high with the Classic reaches absorb. If I tweak it back to zero while at absorb, it puts out the correct voltage to the battery. This leads me to believe that I should not tweak it at all so that the charging voltage is correct. Thoughts?

[TomW]

Tons001;

A common problem mostly due to voltage drop in the cables during high current throughput.

I have 2X Classics.and the only time they actually agree on voltage is when both are resting or in other words when virtually no current is flowing through either Classic or equal current.

It is either accurate at rest or at X load but not both.

Tom

[boB]

Tons001;

A common problem mostly due to voltage drop in the cables during high current throughput.

I have 2X Classics.and the only time they actually agree on voltage is when both are resting or in other words when virtually no current is flowing through either Classic or equal current.

It is either accurate at rest or at X load but not both.

Tom

Is the voltage drop unequal or is the readout at the terminals not reading right at some current ?

What if the resting voltage is higher than at other times ?  Do they still agree ?

boB

[TomW]

Is the voltage drop unequal or is the readout at the terminals not reading right at some current ?

What if the resting voltage is higher than at other times ?  Do they still agree ?

boB

boB;

@rest they agree more or less but my system is never actually at rest. Always a load and often charge current flowing in one or both while drawing power feeding loads with the inverters (Stacked OB FX's into a PSX-240 Autotransformer).  I set them up once @ rest and just let them sort it out on their own. I can see upwards of 50 amps from solar regularly and over 50 on wind occasionally so a.2 volt offset at full power seems reasonable?

Perhaps larger cables should have been sourced but I figure its reads 99.3% of actual even under heavy charging and that is acceptable.

Thoughts? Did I miss the mark here and it is not somewhat common to not be accurate through the range?

Tom

[boB]

Is the voltage drop unequal or is the readout at the terminals not reading right at some current ?

What if the resting voltage is higher than at other times ?  Do they still agree ?

boB

boB;

@rest they agree more or less but my system is never actually at rest. Always a load and often charge current flowing in one or both while drawing power feeding loads with the inverters (Stacked OB FX's into a PSX-240 Autotransformer).  I set them up once @ rest and just let them sort it out on their own. I can see upwards of 50 amps from solar regularly and over 50 on wind occasionally so a.2 volt offset at full power seems reasonable?

Perhaps larger cables should have been sourced but I figure its reads 99.3% of actual even under heavy charging and that is acceptable.

Thoughts? Did I miss the mark here and it is not somewhat common to not be accurate through the range?

Tom

Only  0.2V off ?   That should be just fine.  I wouldn't worry about that, even if you could make it better I
wouldn't do anything to change it myself.

[mofawayesu]

May I jump in on this topic?  I just setup my Classic 150/epanel setup on a 12v system and I'm seeing similar voltage differences - around .2 v difference at rest (it reads low) while under charge (~30-50A) it reads accurately.  If this was line loss, I would have expected the reverse - accurate at rest, inaccurate under load.  I took my meter the other day when it was almost at rest, and found that a tweak of .2 was necessary for Vbatt and .7 (!) for Vpanel.  I reset the offsets to zero though after noting that it was then inaccurate under higher charge rates.

A similar (related?) issue I'm seeing is that the Classic is not regulating accurately to the bulk/float settings.  Currently bulk is set to 14.4 and looking at the peak voltage in the daily history, it went as high as 14.6.  A similar problem with float voltages.  Is this normal? 

Mike

10 x SP70, 2xSP80, Outback FX2012, 4 x Deka L16, Classic 150, e-panel

[Tons001]

A similar (related?) issue I'm seeing is that the Classic is not regulating accurately to the bulk/float settings.  Currently bulk is set to 14.4 and looking at the peak voltage in the daily history, it went as high as 14.6.  A similar problem with float voltages.  Is this normal?

Are you using a t-comp setting? That was the part of the puzzle I was forgetting about. My batteries are in the basement which is a pretty consistent 65 degrees so the Classic was raising the voltage to try and get the batteries up to 77 degrees. If it really bothers you, you can either disable t-comp or lower your voltage limit to 14.4 in the charge settings.

[mofawayesu]

I'm using T-comp, but the batteries are sitting around 28-30 deg. C, so if anything I would have expected the batt voltage to drop, not rise.  Peak voltages today were only .1v above the setting, which is better, but my previous controller never wandered above the setpoints.  I'm still figuring out all the settings on the Classic though, so maybe I'm missing something else....

[zoneblue]

After checking for cable loss, you have to be a bit careful about what grade of meter you use.
The average DMM, and entry level flukes are only 0.8% + n counts. At 24v thats upwards of 0.3V.

I recently splashed on a 0.1% meter and the classic here now reads bang on, unadjusted. My other 4 meters had a quarter volt spread, it was driving me nuts.

[boB]

A temporary spike to 0.2 volts over the set point is nothing to worry about at all.

You would rather it did not stay there all day of course.

Do you have anything else charging the batteries besides the Classic ?

Also, the PV input voltage being off 0.7 volts is also nothing to worry about, but
is actually not too far off.  The PV voltage is only used for tracking mainly but
you calibrated it to be better so that's fine.

boB

[mofawayesu]

No, the Classic is the only thing charging the batteries.  And it only blips up over the set point from time to time - of course with my previous CC there was no way to see if it ever went over - it had no logging features - so my perception that it never went over before is based on the fact that I never saw it on the SOC meter.

I'll admit that my meter is of the cheap variety, but it lines up pretty well with the voltages reported by the Outback Mate.  For all that, I'm sure it's not entirely accurate either.  I still find it odd though at low load/no charge, the Classic reports the system voltage .2-.3 lower than the both my meter and Mate.  Other ideas there?

Thanks all!

[Tons001]

I did find that my meters were driving me nuts. The $100 Sperry DMM seems to be more in line with how the Classic reads voltage vs. the $500 Fluke DMM which always read .2-4v higher than the Classic and Trimetric. I went back to the cheaper of the two. I will say that the Fluke is the only thing I will use to meter DC amperage though.

[Resthome]

Even the Fluke meters need to be calibrated.

[zoneblue]

... of course with my previous CC there was no way to see if it ever went over - it had no logging features - so my perception that it never went over before is based on the fact that I never saw it on the SOC meter.

Sometimes what you dont know doesnt hurt you. But once you know theres no goin back!