Outback Users: Minimum Bank Voltage- Outback Mate or FNDC

Surfpath · September 2013

I guess I could just use my voltmeter, but......

I'm trying to determine where on my Outback flexpower panel I will find an accurate bank voltage. Although I take SG's frequently, I also have been using the "Minimum Voltage" on the Charge Controller summary screen. It's the value just below "Max voltage." But in the Mate (under System, DC, then Batt, I think) it also lists Battery System Min Voltage. Usually the latter is quite a lot higher than the minimum the CC reports.

For the past In my naivety am I confusing battery voltage (Mate) with panel voltage (CC)?

Should I be going with the Mate?

Perhaps this should be a beginners corner question:-)

vtmaps · September 2013

Re: Outback Users: Minimum Bank Voltage- Outback Mate or FNDC

Surfpath wrote: »

I'm trying to determine where on my Outback flexpower panel I will find an accurate bank voltage.

The voltage readout on the summary screen of the Mate is pretty good. Sometimes it varies by 0.1 volt from my trimetric, but I'm not sure which is correct.

--vtMaps

ps. what's going on with your yamaha generator?

RandomJoe · September 2013

Re: Outback Users: Minimum Bank Voltage- Outback Mate or FNDC

I don't think I've ever had more than a few tenths difference between the CC and FNDC voltage readings. The CC can be adjusted, get a good meter and make sure it's reading right. The FNDC is supposed to be a much more accurate device, being dedicated to battery monitoring. It is also attached directly to the battery whereas the CC is measuring at its DC output terminals.

How does the Flexpower 1 panel connect to the batteries? If there is only a single pair of wires to the battery bank, i.e. the CC shares wiring to the battery bank with the inverter, any voltage drop induced by heavy current to the inverter will be seen by the CC. In my case I have two separate feeds to the bank, one for the CC and one for the inverter, so only the inverter "sees" any voltage drop due to wiring at high load.

Surfpath · September 2013

Re: Outback Users: Minimum Bank Voltage- Outback Mate or FNDC

RandomJoe wrote: »

I don't think I've ever had more than a few tenths difference between the CC and FNDC voltage readings. The CC can be adjusted, get a good meter and make sure it's reading right. The FNDC is supposed to be a much more accurate device, being dedicated to battery monitoring. It is also attached directly to the battery whereas the CC is measuring at its DC output terminals.

How does the Flexpower 1 panel connect to the batteries? If there is only a single pair of wires to the battery bank, i.e. the CC shares wiring to the battery bank with the inverter, any voltage drop induced by heavy current to the inverter will be seen by the CC. In my case I have two separate feeds to the bank, one for the CC and one for the inverter, so only the inverter "sees" any voltage drop due to wiring at high load.

Good question. Yes, there is a single pair of wires to the bank. The neg is attached to the CC and the positive to a post in the chassis of the FP (by the big DC breaker I believe).

You are correct, the FNDC connects directly to the bank using two of its squiggly wires which connect to these aforementioned battery leads. I presume the Mate reports the Bank's voltage using the FNDC and its connection.

I see significantly higher minimum bank voltages on my Mate (again I am only interested in minimum voltages for the day - I presume this will be recorded sometime in the earliesh morning before bulk kicks in). An example is that I will see 49.1 on the CC's "MIN" readout, but 49.5 within the Mate's "DC" menu. Again I hope I am comparing apples to apples and not misunderstanding what the CC is reporting as MIN voltage.

I'll have to borrow the wife's camera and take a few snaps of what I'm talking about. I'll also take a voltmeter reading directly from the bank. Picture is worth a 1000 words.

Surfpath · September 2013

Re: Outback Users: Minimum Bank Voltage- Outback Mate or FNDC

vtmaps wrote: »

The voltage readout on the summary screen of the Mate is pretty good. Sometimes it varies by 0.1 volt from my trimetric, but I'm not sure which is correct.

--vtMaps

ps. what's going on with your yamaha generator?

VT I am still in no man's land with the genny. No progress from the dealer at all (2 months?). Very busy now, can't stay on top of it. On rainy days we turn off the fridge and go into outback search (drop consumption from 3.5kwh to about 2). Make up for it later when the sunshine returns. Luckily no multiple days of cloud. We've been fortunate. Nine month old generator (I like the generator, a little big though) but not very helpful service.

Surfpath · September 2013

Re: Outback Users: Minimum Bank Voltage- Outback Mate or FNDC

Sorry folks no photos (or voltmeter reading yet).... but the readouts are straightforward and, of course, the CC and the Mate speak to each other so I just read the Mate at 11pm last night:

1) STATUS/DC/Batt
Battery Min Today 49.8v

2) STATUS/CC/Log2
Today Battery
Min 49.3v

So can someone explain to this novice the difference between these Battery Minimums?

Again, I perform SG's regulary and rely on them for SOC determinations. It's just I'd like to know where to find an accurate minimum bank voltage.

vtmaps · September 2013

Re: Outback Users: Minimum Bank Voltage- Outback Mate or FNDC

Surfpath wrote: »

So can someone explain to this novice the difference between these Battery Minimums?

I don't know the answer... I don't have a FNDC. But I will speculate....:cool:

I can see three directions to pursue:

1) temperature compensation... is one of those values the actual voltage and the other value is the temp compensated voltage?

2) Data sampling rate... charge controller logs voltage at a different rate than the FNDC.
When the daily minimum reflects a voltage sag due to a load with a large start-up surge, the minimum is very brief and different data loggers will see it differently depending on their sampling rate.

3) If the minimums do reflect large surges, then wiring may be a factor. The CC gets its idea of battery voltage from somewhere within itself. The FNDC gets its idea of battery voltage on the battery side of the charge controller cables. Any resistance in those cables, their connections, or their circuit breakers will manifest itself as a voltage drop which is proportional to current through the cable.

--vtMaps

NorthGuy · September 2013

Re: Outback Users: Minimum Bank Voltage- Outback Mate or FNDC

vtmaps wrote: »

I don't know the answer... I don't have a FNDC. But I will speculate....:cool:

I can see three directions to pursue:

I don't have FNDC neither. I agree to these three probable causes and I want to add one more:

4. The precision of measurement may be such that this result can be explained solely by measurement errors.

Outback Users: Minimum Bank Voltage- Outback Mate or FNDC

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