MPPT Controller Explanation For Dummies

[noelex 77]

Originally Posted by colemj

So it seems that MPPT is unlikely to be useful if your system spends much of a day in absorption mode, regardless of how efficiently you reached that point.

Yes, spot on.
If the controller is maintaining regulation voltage (absorption, or float) then power is being thrown away, so there is no advantage to MPPT and many controllers will disable the MPPT circuitry. (Although the MPPT controller will reach this state slightly sooner, so the the batteries may finish the day at slightly higher SOC)

On beauty of MPPT controllers is the benefit is greatest when you need it most, when the batteries are not hitting regulation, the battery voltage is low, and temperatures are cold (which raises the Vmp)

[tartansail]

For those with smaller capacity panels, another purported advantage for some of the MPPT controllers is that they will bump the voltage (at the expense of current per Ohm's Law) and still provide some juice when the panel is putting out less than the battery voltage as can happen with heat or partial shading. The Genasun is supposed to do this, but I have no way of testing whether it works with the panels I'm using.

[noelex 77]

Originally Posted by tartansail

For those with smaller capacity panels, another purported advantage for some of the MPPT controllers is that they will bump the voltage (at the expense of current per Ohm's Law) and still provide some juice when the panel is putting out less than the battery voltage as can happen with heat or partial shading. The Genasun is supposed to do this, but I have no way of testing whether it works with the panels I'm using.

There are very few MPPT controllers that will do this. Genasun make one as you say, but its primary purpose is to use low voltage panels, such as the Solbian panels.

For normal panels, under low light, solar panel voltage stays above battery voltage to very low levels of illumination. The batteries stop charging because the panels cannot produce any current, rather than not enough voltage.
Boosting voltage at the end/beginning of the day makes very little difference to the power output and the self consumption of the circuitry necessary to boost voltage means there is a net loss. This is why even expensive MPPT controllers don't boost voltage.

[tartansail]

Originally Posted by noelex 77

There are very few MPPT controllers that will do this. Genasun make one as you say, but its primary purpose is to use low voltage panels, such as the Solbian panels.

Under low light solar panel voltage stays above battery voltage to very low levels of illumination. The batteries stop charging because the panels cannot produce any current, rather than not enough voltage.
Boosting voltage at the end/beginning of the day makes very little difference to the power output and the self consumption of the circuitry necessary to boost voltage means there is a net loss. This is why even expensive MPPT controllers don't boost voltage.

Thanks for the clarification. Is the same true of heat and shading (i.e. less amps, not less voltage)?

[noelex 77]

Originally Posted by tartansail

Thanks for the clarification. Is the same true of heat and shading (i.e. less amps, not less voltage)?

Heat no.
One reson solar panels are made with 36 cells and and apparently very high voltage is to make sure the Vmp is always above the battery voltage.

Shade yes.
In some circumstances boosting the voltage can recover power when the panel voltage has dropped below the battery voltage.

[s/v Jedi]

I'm starting to think the confusion is caused by people buying "MPPT" controllers off eBay which are nothing more than re-labeled PWM controllers or worse. Because it is nice and cheap. After that experience, they will now be experts claiming that MPPT is snake oil, while in reality they have been conned and don't even realize it, or can't accept it.

Every electronics engineer learns how to calculate and build impedance matching networks in the first year. A MPPT controller is just that: an impedance matching network that can deal with a dynamic environment like solar arrays on boats. Only ignorants will claim matching impedance is a myth or don't realize this is what real MPPT controllers do.

It is like using 50 Ohm coax instead of 75 Ohm coax for your VHF. Will it work with 75 Ohm coax? sure it will. Is it smart? no.....

[colemj]

Originally Posted by goboatingnow

Panel voltage doesnt change much based on illumination , current capacity does. What you are seeing is the benefits of moving the Vo closer to Vmp ( any improvement helps). thats the advantage of voltage conversion, never mind the Mpp tracking part.

Dave

Yes, I didn't express that well, but meant the Vmp is too high at that illumination (which the PWM can't accommodate).

Mark

[colemj]

Originally Posted by s/v Jedi

I'm starting to think the confusion is caused by people buying "MPPT" controllers off eBay which are nothing more than re-labeled PWM controllers or worse. Because it is nice and cheap. After that experience, they will now be experts claiming that MPPT is snake oil, while in reality they have been conned and don't even realize it, or can't accept it.

There may be more to it than that. I have seen numerous burned out MPPT's in the past 5 years - some of them almost setting the boat on fire (one did! ). All of them were BZ or Bluesky controllers. Those people are also now anti-MPPT - particularly the Bluesky people after dealing with their customer service.

Mark

[s/v Jedi]

Originally Posted by colemj

There may be more to it than that. I have seen numerous burned out MPPT's in the past 5 years - some of them almost setting the boat on fire (one did! ). All of them were BZ or Bluesky controllers. Those people are also now anti-MPPT - particularly the Bluesky people after dealing with their customer service.

Mark

Aha! I never trusted BlueSky. Makes sense.

[endoftheroad]

Genasun warranty 5 years.
Genasun sells from their factory $170
I got mine solar chandlry $143

my point is, 2.quality pieces of equipment for less than $300 including shipping. that includes a 5-year warranty. well I don't even think a laptop has that warranty. so why the argument of MPPT controller not lasting long?
sorry typing from the phone

[noelex 77]

Originally Posted by s/v Jedi

I'm starting to think the confusion is caused by people buying "MPPT" controllers off eBay which are nothing more than re-labeled PWM controllers or worse. Because it is nice and cheap.

I agree. There are some terrible controllers out there. Get a good PWM controller in presence to a cheap MPPT controller. At these lower price levels look for something that can be set to appropriate set points for your battery, or even better is fully adjustable.
If you want MPPT at a moderate price Genasun and Rogue are two brands of reasonably priced controllers that are also suitable for smaller systems.
For larger systems Outback and Midnite.

If you can fit more panels, with the cheap cost of solar, this is often the best way for the maximum power for your dollar.

[colemj]

Originally Posted by endoftheroad

Genasun warranty 5 years.
Genasun sells from their factory $170
I got mine solar chandlry $143

my point is, 2.quality pieces of equipment for less than $300 including shipping. that includes a 5-year warranty. well I don't even think a laptop has that warranty. so why the argument of MPPT controller not lasting long?
sorry typing from the phone

Inexpensive and cheap are different things. I don't think anyone has argued MPPT's not lasting long, or Genasun being cheap.

Mark

[endoftheroad]

Originally Posted by colemj

There may be more to it than that. I have seen numerous burned out MPPT's in the past 5 years - some of them almost setting the boat on fire (one did! ). All of them were BZ or Bluesky controllers. Those people are also now anti-MPPT - particularly the Bluesky people after dealing with their customer service.

Mark

Sorry, I misunderstood your post.
I thought you were saying mppts were short lived. my fault.

[T1 Terry]

Let's look at the numbers instead of percentages to get a true perspective of what you will gain for your hard earned $$. A 400w system, average PWM into lead acid batteries, 70% efficiency, genuine average charging voltage around 13v, 5 hrs peak sun, 400 x 70% x 5 /13 = 107 Ah, if the boost charging (no current limiting) runs for the full day, this would be a very rare occurrence, so half the day? 3 peak sun hrs, 400 x 70% x 3 / 13 = 64Ah.
Allowing for a 10% efficiency improvement with the MPPT controller, 400 x 80% x 3 / 13 = 73Ah, a gain of 9Ah before current cut back occurred. In reality, this would mean the controller would simply drop into current control condition earlier. How much earlier? 400w x 80% /13 = an instant current of 24.6 amps, 24.6 Ah if continuous for an hr, 0.41Ah per min, so the extra 9Ah would mean the controller dropped into current control mode 22mins before the PWM controller did, woopty do, does that sound like value for money? I doubt the PWM would be limited to the 70% efficiency over the 3 hrs and I doubt the MPPT could maintain the 80% efficiency over the 3 hr period, even the 22 mins could be an exaggerated figure.

T1 Terry

[noelex 77]

If regulating much of the day MPPT is of very little, or no value.

If your panels are capable of producing 107 AHrs with a PWM regulator, but you are only using about 64AHrs a day then switching to a MPPT is going to produce no benefit.

The value of MPPT comes when you are consuming more than you can produce with a PWM controller. If you can fit more panels this is usually more cost effective, but for many yachts this is not practical, and the modest extra production available with a MPPT regulator becomes attractive.