If there is a BMS, why do I need a solar panel controller?

ynot said:

we see folks running big parallel packs with no BMS

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I'm glad you are getting the information you require and that is good. That's what this board is all about. I was not trying to be snide or enigmatic with my first answer but it does in essence boil down to voltage. You see initially solar panels were matched to batteries so you could hook a bunch of them up in parallel get your 14.8 to 15 volts and charge a bunch of deep cycle flooded cell 12V batteries in parallel and everything was good. Many were 6V in series to get the 12V. Inverters were 12 volt, copper was cheap as you needed to run some serious 00 or even 000 cable to support the amperage.
Well things have changed. Panels now run at ≈ 30 to 40 volts and we now wire them in series (Usually 3s) which increases the voltage to ≈100 to 120 volts. The benefit of this is that we get to use smaller wire as the amperage is reduced, With a Solar controller we can recoup that amperage by convert the voltage to a usable 48V and thus increasing the amperage with a minimal loss. My initial comment should have included wattage with the voltage. Wattage is the final product of all the work done by the voltage and amperage. 12V x 100 Amps =1200W, 48V x 25A =1200W and 120V x 10A = 1200W
I can get the same amount of work done '1200W' with each scenario the only thing changes is voltage which allows us, if we increase it, to use less amperage.
What does that have to do with a BMS and solar controller you ask. Assuming you have 4500W of solar panels on your roof and you want to utilize the output to charge a 12V battery bank you would have a current of 375A that is a wire size(in copper) of 600 which is just a bit over an inch in diameter. Just imagine the circuit breaker! Kind of ludicrous right? So what if we take that 4500W and increase the voltage to 100V? Now we have a manageable 45 Amps of current.
We can run 1 array of 3 panels in series X 6 and combine them all into an AWG 6 run. We can even split the array if we have an easterly and westerly attitude and just run (4) AWG 10 wires.
That leaves us with 100V just waiting to be hooked up to something. The BMS isn't going to allow that voltage is way to high unless you are running a 100V or so battery. The problem is that your solar output won't be consistent and the BMS has no way to regulate it. In comes the charge controller. It can take that 100V and 45A regulate it and turn it into something more manageable as in 48V at 93.75A. So we have reduced our primary wire size to AWG 10 and now we just need AWG 3 if we run at 100% for the secondary wiring. The BMS is now happy with a consistent voltage and can make sure each pack stays in balance with the others.
I would like to see the folks than run big parallel packs without a BMS. Pictures please.
Wolf

I'm glad you are getting the information you require and that is good. That's what this board is all about. I was not trying to be snide or enigmatic with my first answer but it does in essence boil down to voltage. You see initially solar panels were matched to batteries so you could hook a bunch of them up in parallel get your 14.8 to 15 volts and charge a bunch of deep cycle flooded cell 12V batteries in parallel and everything was good. Many were 6V in series to get the 12V. Inverters were 12 volt, copper was cheap as you needed to run some serious 00 or even 000 cable to support the amperage.Well things have changed. Panels now run at ≈ 30 to 40 volts and we now wire them in series (Usually 3s) which increases the voltage to ≈100 to 120 volts. The benefit of this is that we get to use smaller wire as the amperage is reduced, With a Solar controller we can recoup that amperage by convert the voltage to a usable 48V and thus increasing the amperage with a minimal loss. My initial comment should have included wattage with the voltage. Wattage is the final product of all the work done by the voltage and amperage. 12V x 100 Amps =1200W, 48V x 25A =1200W and 120V x 10A = 1200WI can get the same amount of work done '1200W' with each scenario the only thing changes is voltage which allows us, if we increase it, to use less amperage.What does that have to do with a BMS and solar controller you ask. Assuming you have 4500W of solar panels on your roof and you want to utilize the output to charge a 12V battery bank you would have a current of 375A that is a wire size(in copper) of 600 which is just a bit over an inch in diameter. Just imagine the circuit breaker! Kind of ludicrous right? So what if we take that 4500W and increase the voltage to 100V? Now we have a manageable 45 Amps of current.We can run 1 array of 3 panels in series X 6 and combine them all into an AWG 6 run. We can even split the array if we have an easterly and westerly attitude and just run (4) AWG 10 wires.That leaves us with 100V just waiting to be hooked up to something. The BMS isn't going to allow that voltage is way to high unless you are running a 100V or so battery. The problem is that your solar output won't be consistent and the BMS has no way to regulate it. In comes the charge controller. It can take that 100V and 45A regulate it and turn it into something more manageable as in 48V at 93.75A. So we have reduced our primary wire size to AWG 10 and now we just need AWG 3 if we run at 100% for the secondary wiring. The BMS is now happy with a consistent voltage and can make sure each pack stays in balance with the others.I would like to see thethan run big parallel packs without a BMS. Pictures please.Wolf