Battery voltage: From where is it coming?

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JRHill
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Battery voltage: From where is it coming?

Post by JRHill »

Maybe this is a stupid question but I have asked myself this several times in the past. Whether Optics or the Mate3x's various screens you see the 'somewhat' instantaneous battery voltages. Whether from that particular component or from the FNDC who would know?

The reason this just came up is I just adjusted the VFXR's calibration. I expected to see a corresponding change in any display that reported the inverter's measure of battery voltage. Not that I saw. So the calibration offset only affects programmed voltages for various functions? And if you don't have a FNDC and the devices' various voltages vary, which one wins for what is shown on the Mate3x or Optics?
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Re: Battery voltage: From where is it coming?

Post by raysun »

The reported voltages come from the various devices.

The "System" voltage, shown under the battery icon in OpticsRE, is reported from the FNDC. If no FNDC, then the Mate reports it.

The inverters report voltages from their internal voltmeter.

The FlexMax charge controllers report voltages from their internal voltmeters.
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Re: Battery voltage: From where is it coming?

Post by jsmith »

Page 20 of the FM100-AFCI Owner's Manual, in describing the function of it's battery sense terminals, states the following:

"IMPORTANT:
The MATE3s system display shows the overall system voltage as measured at the battery terminals of various devices. (See Figure 27 on page 35.) This voltage is used for generator starting and other functions.
 If no other devices are present, it will show the reading of the FLEXmax 100. Unless:
 If OutBack inverters are present, the inverter voltage replaces the FLEXmax 100 as the
system voltage reading. Unless:
 If the FLEXmax 100 Battery Sense terminals are in use, this reading replaces the inverter or the regular charge controller readings as the system voltage. Unless:
 The FLEXnet DC Battery Monitor is the highest priority and will replace the Battery Sense reading as the system voltage.
The Battery Sense reading is still shown on the Charge Controller screen (see Figure 28 on page 36). This reading is still used to adjust the FLEXmax 100 charging."

The two figures referred to are the following:
Screen Shot 2022-01-19 at 7.24.05 PM.png
Screen Shot 2022-01-19 at 7.26.54 PM.png
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Mike Curran
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Re: Battery voltage: From where is it coming?

Post by Mike Curran »

Thanks JSmith. I wish Outback had provided this info sooner.
https://ei.tigoenergy.com/p/pZXn7SZQyO45
https://enlighten.enphaseenergy.com/public/systems/Hctc107221
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Re: Battery voltage: From where is it coming?

Post by raysun »

Of course, the order of precedence described in the FM100 manual is unique to systems with an FM100 installed.

What's consistent across all systems is the FNDC voltage will be displayed in all configurations where it is present.

Absent the FM100's battery sense readings, it does get a bit more hazy. It would be good that it be documented in one of the Mate guides, but I don't find it listed.
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Re: Battery voltage: From where is it coming?

Post by JRHill »

From Mr Raysun: "Yes, there's an app note kicking around on calibrating the FNDC. I lived with one miscalibrated for about 4 years because I never got around to addressing the hassle of calibrating."

Well I'm there today and will get it done. Two different Flukes - I'll split the difference between the two different models but its silly as the delta is less than than any OB calibration. I CANT FIND THAT DOC. And I can't find the thread with whatever search terms.

I have to get this done. Now that I have matched up the VFXR and the FM80 battery voltages as close as possible, the FNDC is still .3+ higher. This can't be. I'll Cal the FNDC today but I can't find the OP Doc or the thread.
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Re: Battery voltage: From where is it coming?

Post by raysun »

Sent you an email with the doc attached.
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Re: Battery voltage: From where is it coming?

Post by JRHill »

raysun wrote: Thu Jan 20, 2022 10:29 am Of course, the order of precedence described in the FM100 manual is unique to systems with an FM100 installed.

What's consistent across all systems is the FNDC voltage will be displayed in all configurations where it is present.

Absent the FM100's battery sense readings, it does get a bit more hazy. It would be good that it be documented in one of the Mate guides, but I don't find it listed.
Since I now have a noticeable difference between the VFXR and FM80 (which are calibrated to one another, VFR taking precedence since I had to choose and it is the new boy), the FM100 post from jsmith is true for my system. So the logic seems to be similar. I have to dial in the FNDC and then cal the inverter and FM to the FNDC.

The DW s rolling her eyes at me....
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Re: Battery voltage: From where is it coming?

Post by jsmith »

Outback now publishes the FNDC calibration instructions on the last page of the FNDC Overview Guide:

https://www.outbackpower.com/downloads/ ... _guide.pdf
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Re: Battery voltage: From where is it coming?

Post by raysun »

Since I now have a noticeable difference between the VFXR and FM80 (which are calibrated to one another, VFR taking precedence since I had to choose and it is the new boy), the FM100 post from jsmith is true for my system. So the logic seems to be similar. I have to dial in the FNDC and then cal the inverter and FM to the FNDC.
Not to put too fine a point on it, but all the devices should be calibrated to the battery voltage at their input terminals.

For the FlexMax 60 or 80 the calibration should be done without PV input, and when there is little to no load on the battery.

The inverter should be calibrated with little or no load as well. I usually bypass the inverter / battery, supplying house loads from the generator during inverter calibration.

Likewise, the FNDC calibration adjustment is very sensitive. Its best undertaken when the battery voltage is not a moving target.
20220120_091940.jpg
A capture when the inverter and charge controller voltages happened to align. Due to the 0.4V inverter resolution, this is not always the case. The FNDC is off by 0.1V but recalibration is low priority for me, as the only reference to is is used by Charged Voltage.
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Re: Battery voltage: From where is it coming?

Post by raysun »

One very tangential side note: During Bulk charging, the FlexMax charge controllers measured voltage at the Bat +/- terminals will be higher than the voltage measured at the Battery Pos/Neg terminals. Mine measures +0.2V. I believe this is the controller "pushing" the voltage to cause charge current to flow.

I haven't measured, but assume the inverter chargers do the same thing.
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Re: Battery voltage: From where is it coming?

Post by pss »

The only accurate battery voltage you can rely on is that measured directly from your terminals and that measured directly on the terminal input of the inverter. That value is reported on the Mate 3S. Otherwise, all of the voltages reported whether from FNDC or charge controller may not be entirely accurate. Hmm.
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Re: Battery voltage: From where is it coming?

Post by raysun »

pss wrote: Thu Jan 20, 2022 12:11 pm The only accurate battery voltage you can rely on is that measured directly from your terminals and that measured directly on the terminal input of the inverter. That value is reported on the Mate 3S.
The inverter voltage as reported on the Mate? IME, for a 48V inverter the reported voltage can vary as much as +/-0.4V from actual measurements at the terminals. That's after it has been calibrated (if need be.)
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Re: Battery voltage: From where is it coming?

Post by JRHill »

All I can say is this is not for the layman (FNDC Calibration). I had to drill into EVERYTHING. Mostly the FNDC and I adjusted it several times before I realized I was going in the wrong direction. 1/16th of a turn and watch, again and again. Then I got it. Then the FXR and FM80. Then back to the FNDC. Then back to the FXR and FM. A few more times and they were like democrats and republicans having a party. They all were working together!
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Re: Battery voltage: From where is it coming?

Post by JRHill »

I think the FM80 is the republican, the inverter the democrat and the FNDC the independent.

But I don't want to get political....
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