Why does my solar not charge to 100%?

[Raul]

Thats interesting I went with series as it seemed to be the majority way of fitting it (YouTube videos)
If I change this to parallel my amps will go up, would need to check what the amp rating is for the panels, also instead of a cumulative 3 X 175 watts I will only get a single 175amp I am currently running 6mm cables from the panels to the controller, would I need to beef these up?

If it’s a short run, 3-4m then at 24a you will have a loss at full power, about 2,65%. That’s all 3 in parallel. If you think you have no shade then leave it as it is.

 

[autorouter]

If I change this to parallel my amps will go up, would need to check what the amp rating is for the panels, also instead of a cumulative 3 X 175 watts I will only get a single 175amp

You get 3 x 175W whichever way you wire them. Watts = volts x amps. In series you get 3x the voltage but the same amps through each one. In parallel you get 3x the amps, but the same voltage across each one. When multiplied, you get the same result.

For series wiring you have to check the max voltage for the controller is not exceeded. Your 68V is well within the range of 150V for the Victron 150/35 controller.

For parallel wiring, you need to check that the total amps doesn't cause excessive voltage drop (ie less than 3% of the panel voltage, about 19V), using a voltage drop chart or calculator for the length and cross-sectional area of the wiring.

 

[autorouter]

duplicate post

 

[Raul]

The trade off is that series connection will be much better in low light/off season and have reduced resistive losses due to lower currents. Parallel tends to have better performance in partial shading, although this depends on the design of the bypass diodes. In reality, all panels are a combination of series and parallel connections.

There has been extensive testing on this parallel vs series. Much comes down to equipment quality, design of the system, quality of connections, crimps etc, and most important dc converter type.
A German institute has tested various charge controllers at different voltage inputs, and concluded that, most efficient conversion was a battery voltage times 1,5-1,7. The higher the incoming was, the more losses the converter had. It was advised that IF you can design and keep the incoming at battery voltage times 1,5 , the converters will performed best. Of course, there are situations where high voltage has the advantage. Specially when the panels are in the back garden away from the conversion point.

 

[DuxDeluxe]

Sounds like the controller needs recalabrating to the battery.
I would say the battery is fully charged hence no input from solar when nothing turned on.
Switch stuff on and put a drain on the battery which is then being charged by solar.

My thoughts exactly PJ

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[cmcardle75]

There has been extensive testing on this parallel vs series. Much comes down to equipment quality, design of the system, quality of connections, crimps etc, and most important dc converter type.
A German institute has tested various charge controllers at different voltage inputs, and concluded that, most efficient conversion was a battery voltage times 1,5-1,7. The higher the incoming was, the more losses the converter had. It was advised that IF you can design and keep the incoming at battery voltage times 1,5 , the converters will performed best. Of course, there are situations where high voltage has the advantage. Specially when the panels are in the back garden away from the conversion point.

I'm not sure that make sense. The input and output voltages and currents are nominally independent from each other. Series has the indisputable advantage of reducing cabling resistive losses. Cheap panels with inadequete bypass do suffer connected in series in partial shading.

Most of the other differences will depend on controller design. However, the most common MPPT controllers are unable to boost voltage, so will achieve better efficiency in low light (i.e. morning, evening and shoulder season) from the higher voltages than series connection will achieve. This is not fundamental, though. It is quite possible to design an efficient MPPT controller that would take a nominal 12V (i.e. 20V) parallel panel array and charge a 48V battery even in twilight, however slowly.

 

[Raul]

If you really want to see results get testing, I’m sure you love it. Cable los is easily corrected, but more interesting show me a buck boost solar controller with a wide range mppt. The only place you will se such type of converter is on hydro and wind, and they are several hundreds into thousands. They run totally diferent algorithms that’s not suitable for tracking insolation. Also you forget one thing, solar panels are NOT a voltage source, you can have same 50w out of the panel array configured at 100 or 20v. The controller will receive same watts with different task if at 100v incoming vs 20v. You figure out where is more work done, to push out 13-14v. We are talking rock bottom 12v systems here, not 24 or 48v where the voltage gets chopped once or twice max.

 

[Southdowns]

Morning all, thank you for all the comments, I have to admit I have got a bit lost with some of the technical knowledge.
So I could change the set up to parallel or I could leave it in series.
I will have to think about it.
Thank you again.
Ian

 

[autorouter]

If you want to try switching between series and parallel, you can get 2-to-1 or 3-to-1 adapters for the standard MC4 solar connectors. Depending on the layout you might need some short lengths of wire to connect them. The controller can handle series and parallel connections. The connectors are weatherproof, and lock together. If you're getting some adapters, you could get an unlocking tool as well. It's possible to manage without, but it makes life easier.

However I think there's a distinct possibility that this series/parallel question is not the real problem. But without doing further testing and taking some voltage/amps measurements of the panels, perhaps separately, it's a bit difficult to track down.

 

[Southdowns]

However I think there's a distinct possibility that this series/parallel question is not the real problem. But without doing further testing and taking some voltage/amps measurements of the panels, perhaps separately, it's a bit difficult to track down.

Yes, I am not sure either. I am grateful to everyone who has taken the time to have a think about my problem.
Series or parallel, either are proven ways of connecting solar panels and the Victron controller I have, I would assume should be handle either?
I am definitely generating watts and I don't seem to have a shortage of solar its just not seeing the monitor go back up to 100% or close to it that is bugging me, especially when during the day we were out and about and the minimal items were on, so plenty of time for it to recharge.

The app on my phone was showing high watts when we turned things on and when we turned these off the watts went down often to zero. So I am again assuming that my battery was full and the controller said "no more thank you"

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[Raul]

Post your controller settings and the battery monitor settings. They may be out and not synchronising.

 

[Southdowns]

Here we go, hope this is what you need

 

[Southdowns]

This was the original setting AGM spiral

 

[Raul]

absorbtion time? It should be 6 to 8 hrs. The controller will work it out if needs to be held for that time or less. Depending on the wake up voltage. But you need to set a max time.
Toggle the expert mode to enable the full settings.

 

[DBK]

Morning all, thank you for all the comments, I have to admit I have got a bit lost with some of the technical knowledge.
So I could change the set up to parallel or I could leave it in series.
I will have to think about it.
Thank you again.
Ian

I don't think you will notice any difference in the real world. But unless their advice has changed since I fitted mine Victron recommend series connection. Changing also won't sort out the issue you started this Thread about.

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[Southdowns]

It was on 6 but now pushed it up to 8.
Do I need to do anything with the equalisation voltage? Lenny HB suggested turning it off?

 

[Raul]

Just disable it. And make sure the equalisation voltage is below float voltage, just in case you activate it manually by mistake.

 

[cmcardle75]

As for the 100% detection, that is part of the battery monitor configuration. It might be set to require a voltage higher than your configured float, which is why it isn't detecting full charge.

 

[Southdowns]

Just disable it. And make sure the equalisation voltage is below float voltage, just in case you activate it manually by mistake.

Done that, thank you for persevering with this. Could only take the voltage down to 8v which is below the float. Now need to test it, currently raining here and the monitor is showing 100% from the weekend drive. I will update when I have tried it.

 

[Southdowns]

It might be set to require a voltage higher than your configured float, which is why it isn't detecting full charge.

Is that what I have just done with the equalisation voltage? Just checking in case you meant something else?

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[cmcardle75]

No, it is the setting within the BMV712. This has 100% detection, which depends on sensing a high voltage for a defined period with low current. It is possible that your existing B2B/split relay/mains chargers provide significantly higher voltages when fully charged and the BMV712 is successfully calibrating to 100%. However, your more gentle settings for the MPPT might not be firing off the detection.

If your battery monitor doesn't have Bluetooth, you'll need the manual to find out how to check/adjust the settings using the screen and buttons.

However, you mentioned the BMV712, which should have Bluetooth smart features built in. I have a BMV-702 and had to have a add a dongle to get Bluetooth. If you do have Bluetooth, add it to your Victron app and do it that way!

 

[cmcardle75]

No, it is the setting within the BMV712. This has 100% detection, which depends on sensing a high voltage for a defined period with low current. It is possible that your existing B2B/split relay/mains chargers provide significantly higher voltages when fully charged and the BMV712 is successfully calibrating to 100%. However, your more gentle settings for the MPPT might not be firing off the detection.

If your battery monitor doesn't have Bluetooth, you'll need the manual to find out how to check/adjust the settings using the screen and buttons.

However, you mentioned the BMV712, which should have Bluetooth smart features built in. I have a BMV-702 and had to have a add a dongle to get Bluetooth. If you do have Bluetooth, add it to your Victron app and do it that way!

For example, mine has a "charged voltage" of 13.7V, "tail current" of 4% and a "charged detection time" of "7 minutes". This means it will jump to 100% if the voltage stays over 13.7V for 7 minutes with no more than 4% (of 300A) charge current. (I should probably reduce the 4%).

I suggest reading section 2.2 & 2.3 of the following:

https://www.victronenergy.com/upload/documents/Manual-BMV-700-700H-702-712-EN-NL-FR-DE-ES-SE.pdf

 

[Southdowns]

Sorry my fault, I have the BMV 700 not the 712. I am reading the manual at the moment and blowing my mind with all the different settings.
So I have a float voltage of 13.8V (Is that the charged voltage?) the 4% is the default and the detection time has a default of 3 minutes, but I am guessing this should be a bit higher otherwise it will keep trying to sync too often?

A question though if I have read everything correctly my absorption voltage is 14.7v, will the monitor confuse this with the charged voltage. Or am I confusing my voltages?

 

[Southdowns]

Just read the charged voltage needs to be 0.2v or 0.3v below the float. So may have answered my own question

 

[cmcardle75]

Just read the charged voltage needs to be 0.2v or 0.3v below the float. So may have answered my own question

Indeed. Whilst the high absorbption would be detected, it might not go below the tail current for long enough before dropping to float. Best to have the detection voltage below the float.

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[Southdowns]

Thank you, just made the adjustment, set it to 13.5v
Will let you know the results next time we are out and about

 

[cmcardle75]

Thank you, just made the adjustment, set it to 13.5v
Will let you know the results next time we are out and about

Hopefully that will do the trick! You can also consider getting the add-on Bluetooth dongle if you like to play with these things!

 

[Southdowns]

I would get the dongle but my wife thinks I am already obsessed and another app on the phone might be a bridge too far. LOL

 

[nabsim]

I would get the dongle but my wife thinks I am already obsessed and another app on the phone might be a bridge too far. LOL

It’s the same app just shows extra devices

 

[nabsim]

I have never had AGM battery’s so only know the little I have read about them, from what I read though they take a long time to get to 100% SOC don’t they? Or am I confusing them with Gel? Could part of the problem be it’s dropping off around the 85% SoC then slowly filling up? Although the drive home wouldn’t do it if that was it so I am probably confusing myself

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