Zwy
Solar Wizard
2S compares to 3P is 1/3 less wattage. Keep up now, I thought you were a Photon Sorcerer.
Growatt 24V SPF 3000TL LVM – 3kW 120Vac Stackable Inverter 2kW MPPT Charge Controller Split Phase
- Thread starter DouglasPHill
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DouglasPHill
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- May 24, 2021
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Again everyone, thank you. My head is spinning. Please correct me here: for illustration one panel = open circuit voltage 37.4, max power voltage 30.2 (I don't know the difference) and max current 8.43amps hence 30.2x8.43amp = 255W
So if I put 2s I get 60.4 volts at 8.43 amps which is 509W (round numbers here. 3p I get 30.2 at 25amps = 763W
The controller appears ok with up to 80amps. And both the 60.4 volts and the 30.2 volts are in the voltage range.(I think)
If I use 8gauge wire I should be good to go 3P. (They dropped off the panels yesterday )
So if I put 2s I get 60.4 volts at 8.43 amps which is 509W (round numbers here. 3p I get 30.2 at 25amps = 763W
The controller appears ok with up to 80amps. And both the 60.4 volts and the 30.2 volts are in the voltage range.(I think)
If I use 8gauge wire I should be good to go 3P. (They dropped off the panels yesterday )
Zwy
Solar Wizard
You always use VOC which in your case is 37.4. If you went 2S you would see VOC at 74.8. 3S would be 112.2 but with low temps you could exceed the rated PV range upper limit of 115V. Could it damage the CC? Possibly, even though the max rated PV voltage is 145V.
3P is probably the best choice but there are always some cons/pros. One, CC's like to see voltage 5V above battery voltage before it begins charging. If you have full sun for 4 hours or more a day, not a problem depending on battery size and usage. Low light conditions you might see charging begin until later in the day. But if you have any panel shaded, 3P is still the best choice. With panels in series, you could see very low amps coming from PV array if one panel is shaded.
You will be fine with 8 ga wire up to about 20 feet length. 25 feet would put you just over 3% voltage drop.
3P is probably the best choice but there are always some cons/pros. One, CC's like to see voltage 5V above battery voltage before it begins charging. If you have full sun for 4 hours or more a day, not a problem depending on battery size and usage. Low light conditions you might see charging begin until later in the day. But if you have any panel shaded, 3P is still the best choice. With panels in series, you could see very low amps coming from PV array if one panel is shaded.
You will be fine with 8 ga wire up to about 20 feet length. 25 feet would put you just over 3% voltage drop.
DouglasPHill
New Member
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- May 24, 2021
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As always time goes by before I can continue work. I know this is really stupid but I couldn't figure out how to provide 12volt dc if my batteries are 24 volts. I had assumed the growatt would have a 12volt dc output. But now I'm thinking you take the AC output out of the growatt and run that to another appliance that creates clean 12 volt dc. Is that correct? Correct that the growatt doesn't do it and need another appliance to do it?
If it is done a different way, please explain. Thank you.
If it is done a different way, please explain. Thank you.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
Correct, the Growatt will not do it.
You have two options:
1) As you say, put an AC->12V supply in.
2) Put a 24V-12V buck converter in.
I would lean toward option 2 because it is going to be more efficient.
Victron has some good ones:
DC-DC converters - Victron Energy
Victron Energy's DC-DC converters are useful if you do not have a suitable voltage device. Ensure that voltage is converted now.
Rednecktek
Solar Wizard
I had the same issue needing to provide 12v from my 24v system, so I picked up a 60a buck transformer to feed it all.
Zwy
Solar Wizard
You just need a 24V to 12V buck converter. You won't need the inverter on at all to run the 12V system.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
That looks like a nice unit.
One question: Are there any control inputs? Is there any way to tell it to shut down if the voltage gets too low?
It is not mandatory, but I like to have a Low Voltage disconnect on the DC loads. That way there are two levels of defense: The BMS and the Low Voltage Disconnect.
Rednecktek
Solar Wizard
Not on those units, they're just a simple transformer. You'll have to rely on something like a shunt or your BMS or the inverter to tell you when it's too low, but you're still going to have to deal with it manually unless you get some creative equipment involved.
FilterGuy
Solar Engineering Consultant - EG4 and Consumers
That is what I like about the Victron buck converters; they have built in Low Voltage Disconnect..... but I sure don't like the price of the Victrons.
BTW: This may be a bit picky, but technically a DC-DC buck converter is not a transformer
Rednecktek
Solar Wizard
It will be once I get the Decepticon sticker on it.
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