question

kcrtechy avatar image
kcrtechy asked

Charging pattern of a 250/85 MPPT Smart solar reg

I am very curious as to why this new 250/85 solar reg commences charging and ramps up the output to effectively follow the load and then suddenly there is a "click " from the regulator and the output drops to zero.

Is this normal as it is NOTHING like I have ever experienced with a charger being either a Mains unit or a solar regulator as every one I have ever come across effectively follows the load. This is going from Float mode to a 1000 watt load on a 24V bank. It goes up to 38A @26V and suddenly stops, waits for a while and then restarts WHY is it so??

PV Solar Input is 170V O/C charging a 24V Lithium battery (LiFePo4 type). PV volts drop to around 150V on load so the regulator is NOT being fed with an excessive voltage.


We are using this to maintain a 2200watt Victron inverter to power our community radio studios so we do NOT have to rely upon an erratic AC mains supply with frequent short breaks which upset the various computers and modems we use.

MPPT SmartSolar
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klim8skeptic avatar image klim8skeptic ♦ commented ·

@KCRtechy This is going from Float mode to a 1000 watt load on a 24V bank. It goes up to 38A @26V and suddenly stops, waits for a while and then restarts

It is normal for the output of the mppt to go to zero at the end of the absorption stage, before the battery voltage drops a bit to the float voltage. The mppt will then ramp output up to match load currents to keep the battery at the float voltage.

Another thing to look at regarding the "click". The mppt has a relay that can be programmed to close once the mppt goes to float or storage. Something to check.

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Alex Pescaru avatar image
Alex Pescaru answered ·

The tracker is periodically searching for maximum point.

During that process it will go through the whole Voltage - Current curve to determine the maximum power point. That mean that will also be at the point of current = 0, voltage = VOC.

Which is your PV configuration? How many panels with which VOC? Meaning the Maximum Total VOC ?

Because also the max VOC must be below eight times battery voltage...

And now, with lower temperatures, that max VOC of, you said 170V, corrected with temperature, could be very close to the 24*8 = 192V max.


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kcrtechy avatar image kcrtechy commented ·

Alex,

The PV volt O/C is 180V max at full sun and 170V as the sun goes off the panels. The array is a series paralled setup of 8 x 400Watt Bi Facial 45V PV O/C panels being arranged 4 in series and then both lots in parallel down to the regulator.

Maybe its only a Victron way of doing things but other MPPT regs I have been involved with have NEVER suddenly ceased charging and then restarted like this one is doing and I have yet to observe what it does in FULL SUN so maybe it will behave differently in full sun.

Will check that out next time I am over there. Where these panels are in Australia LOW temperatures are uncommon as currently for example we have just had a 41C day and in winter time I have yet to see any temp under 6C.

We chose the 250/85 unit as we originally had a all in one inverter/solar reg & mains charger and it needed over 150V to function on the solar array so we are stuck with that config as it is.

We dumped the all in one inverter unit as I found we had quite audible noise being injected into the program output from our studio desks which ceased as soon as the solar array was switched off. Close investigation showed that the Negative leg of the solar array was DIRECTLY connected to the OUTGOING 230V Neutral which here in Australia is grounded.

But on looking at the Neutral with a CRO there was substantial noise on that Neutral which somehow managed to get past the various power supplies in the studio setups and become JUST audible during quiet program sections and NOTHING I could do would stop it.

With the 250/85 solar reg there is NOW NO noise in our outgoing program as there is now NO connection between the AC Neutral and the solar Neg side. We MIGHT ground the 24V Neg side IF it does NOT introduce rubbish into our program...yet to try that as early days re-jigging the entire setup which has been a PIA re-arranging wiring and the like.

So we dumped the all in one inverter and purchased Victron 24 volt x 2200 watt inverter and a Victron smart 30A battery charger controlled by a BMV 700 to switch that on should the 24V bank get low SOC (during the night for example or periods of low solar during the day) and the Inverter runs 24/7 powering the studio gear and some essential lighting plus ALL the station computers and server and modems etc.

Right now I am simply load testing the setup with a1000 watt dummy load and seeing how they all interact. The Mains 30A battery charger works fine and the Clicking sound is coming from the solar reg as it shuts down by the look of it and restarts and maybe that will not be a problem once we put the system on line but it seems VERY ODD to me to function like that.

The end result we are aiming for is that any AC mains breaks DO NOT put us OFF AIR.

Lindsay

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Alex Pescaru avatar image Alex Pescaru commented ·

Hi @KCRtechy

Thank you for your detailed answer.

Indeed, the high frequency type inverters have no galvanic separation between PV negative and the neutral output. This because the negative PV goes up to the H brigde from the inverter's final stage and from there through the PWM sinewave switches to the neutral earth.

As for the 250/85, it could have indeed, a problem.

I didn't realized that you may be in the Australia where now is the middle of the summer and the temperatures are not so low how are here in Constanta.

Indeed, a modular design with a separate MPPT charger + Mains Charger + Battery + Inverter topology will produce a more clear output. And also much easier to handle and repair.

Did you tried to switch off that mains 30A battery charger and to remain only with the MPPT to see if it will supply the inverter with all the power necessary for the load? Of course, the battery will remain connected. Who knows, maybe the 250/85 is somehow disturbed by that mains 30A charger.

Are all the Victron devices connected between each other over VE bus or VE CAN?

Meaning could the mains charger and the solar charger share tasks and power for the battery and/or inverter?

Alex

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kcrtechy avatar image kcrtechy Alex Pescaru commented ·

Alex,

When I was testing the solar reg the mains charger was OFF. It will be a rare occasion that the solar and Mains charge are on together anyway.

None of the Victron devices are interconnected by either VE Bus or VE Can. So far I have only used the Bluetooth option and I really do not wish to setup a complicated system. Am trying to keep it as simple as possible as I am the ONLY tech at the station and other volunteers show NO interest in keeping the place On Air.

Dunno what they will do when I pass on !!!

Lindsay

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JohnC avatar image
JohnC answered ·

@KCRtechy

I'm curious too. You say this happens in Float mode. That means the batteries are effectively full, So why then would the mppt shutting off cause AC failure?

If that clicking was actually the battery bms 'shutting the gate', then this would explain both the AC loss and the mppt output loss.

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kcrtechy avatar image kcrtechy commented ·
John,

Maybe I have confused you as the MPPT reg shutting down DOES NOT interrupt the Inverter output.

When the batteries are FULLand thing are in Float mode the solar reg MUST supply what our studio load actually is as the Victron inverter is running 24/7 with NO connection to the mains at all.

We just use the mains to top up the battery bank during periods of LOW solar or during the night should the equipment load for drag the batteries down when there are NO Presenters On Air and the computer is outputting audio from the server music files. That is interspersed with News Bulletins on the hour every hour which are downloaded and scheduled to play out on the hour automatically and that in total is around a 400 watt load.

So from 8pm most nights until 7am most days the place runs on auto pilot effectively and with 270AH of 24V battery backup that should be enough to carry us through until sun up next day. If not the Victron 30A charger will top up the bank to whatever SOC we have set it at...currently ON @ 65% SOC and OFF @ 80% SOC.

The clicking IS coming from the 250/85 solar reg and happens each time the output goes to ZERO and then it slowly comes back which in practice MIGHT work OK as at the moment I am simply load testing the setup BEFORE I put the studios online with it all.

Avoiding any program interruptions by doing it that way.

The LiFePo4 batteries do have Inbuilt BMS and disconnect at 11V on each battery and when that happens there is NO noise..no idea how it is done as all inside the cases..they just go OPEN circuit for a while and then come back on line after a couple of minutes which took me by surprise when I first experienced that.

Lindsay

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