Forum Discussion
412 Replies
smkettner wrote:
jrnymn7 wrote:
Salvo,
Are you saying, because of its buck converter, if a small enough load is applied, during abs or float, the MPPT controller does not need to kick into full blown mppt mode, because the bucker itself can handle the increased demand? But if the load is too much for the bucker to handle, then it will kick back into full blown mppt mode?
Controller is just trying to hold the set voltage.
Controller will switch back and forth between MPPT and PWM as needed to hold the voltage.
Not really a big deal.
Same as your vehicle using cruise control downshifts as needed to make power to go up a hill.
Vehicle is just trying to hold the set speed.
Unless I'm mistaken, Jim has seen his amperage rise and fall, without the controller switching between pwm and mppt. This indicates there is available power for the controller to use, without having to switch to mppt. That seems to be the mystery to be solved. It must have something to do with the buck converter.
Like with your analogy, on a not so steep hill, engine revs/power may indeed increase, but it can maintain speed without actually shifting gears.
In float, I can see the load just using the surplus current; Isc minus float current; but with a large enough load, at some point more current is required... above and beyond Isc. Jim sees currents above Isc while the controller is still in pwm mode. So the controller is apparently getting extra power from the array, without utilizing its 'maximum power' tracking ability.- SMK, yes, there is nothing to be gained, but apparently there is something to be lost if the bank can still accept 16.4a (tapering), but only 8.2a are available, due to the series wiring.
jrnymn7 wrote:
Salvo,
Are you saying, because of its buck converter, if a small enough load is applied, during abs or float, the MPPT controller does not need to kick into full blown mppt mode, because the bucker itself can handle the increased demand? But if the load is too much for the bucker to handle, then it will kick back into full blown mppt mode?
Controller is just trying to hold the set voltage.
Controller will switch back and forth between MPPT and PWM as needed to hold the voltage.
Not really a big deal.
Same as your vehicle using cruise control downshifts as needed to make power to go up a hill.
Vehicle is just trying to hold the set speed.- Salvo,
Are you saying, because of its buck converter, if a small enough load is applied, during abs or float, the MPPT controller does not need to kick into full blown mppt mode, because the bucker itself can handle the increased demand? But if the load is too much for the bucker to handle, then it will kick back into full blown mppt mode?
In other words, with a small added load, the available power at the present power point on the curve is sufficient, so the bucker can just use that available power, but a larger added load forces the controller to search for more available power along the curve? - A MPPT controller switches to PWM mode after float for two reasons. There is no longer the loss with the battery being at a higher voltage and the battery could not accept the additional current anyways. The extra current is still there, just not being used to charge with.
Also, with the 12v's in series the Isc stays the same as with one panel but the voltage doubles. That excess voltage creates extra amps even in float IF you pull a load. Again my panels that have a Isc of 10a produce 16a out of the controller even in float. - That's not quite correct. There's no advantage using mppt over pwm when in absorb or float mode. mppt has on average a 5% advantage in boost mode. Since mppt uses a buck regulator in its topology, it can operate in pwm mode while the panel voltage is higher than Vbat.
jrnymn7 wrote:
Correct me if I'm wrong,
It has been said, when using an MPPT controller, once Vabs Setpoint is reached, the controller operates in pwm mode only. If so, there would be a distinct disadvantage to using 12v panels in series with an MPPT controller. - ^^^ once the battery is in Absorption mode you will not gain any benefit from series/parallel/MPPT/PWM. Once the battery is a Vabs it does not matter how the power is generated because no matter the configuration there is excess available power.
- RE; Panel Wiring and MPPT:
Correct me if I'm wrong,
It has been said, when using an MPPT controller, once Vabs Setpoint is reached, the controller operates in pwm mode only. If so, there would be a distinct disadvantage to using 12v panels in series with an MPPT controller.
Assuming ideal conditions, and using two 140w panels with specs of 7.9a Imp, 17.7v Vmp, and 8.2 Isc, and using a Vabs Setpoint of 14.8v:
If wired in parallel:
While in mppt mode, bulk charging at an average of say 14v (13.2-14.8), average current would be 20a (280w/14v).
Just before switching to pwm mode, bulk charging current would be at 18.9a (280w/14.8v).
As it switches into pwm mode, current would drop to 16.4a (2x Isc), and amps would taper from there.
If wired in series:
While in mppt mode, bulk charging at an average of say 14v, average current would be 20a (280w / 14v)... Same as with parallel wiring.
Just before switching to pwm mode, bulk charging current would be at 18.9a (280w/14.8v)... Same as with parallel wiring.
However, as it switches into pwm mode, current would drop to only 8.2a (1x Isc), and amps would taper from there. So if abs charging continued for any significant length of time, there would be significant losses. - I agree 24 or 48 volts would be the route to follow for the battery bank.
Method 3 on the smart gauge site for the wiring. I.E. equal length cables from all jars to a buss. correctly interconnecting multiple twelve volt batteries
With 24 batteries that works out to six "strings" of four jars, assuming each jar is 12 volts. Voltage at the buss is 48. - Exactly, at 24 volt the MS TS-MPPT-30 would be perfect.
