MPPT solar charge controller recommendation?

Great thread for those looking for controllers (like me) but I still can't decide ... :?

towpro wrote:
I have had -48 in a Phone switch light me up more than once. (but the old party line switch ring generators hit you even harder).

I have also seen the results of someone cutting hot wires in the Central Office, grounding they out in the process, sparks fly, blades on cutters melt.

Likewise on the -48v from a PBX.

I also have a pair of side cutters with a nice 12 gauge notch in them from my not checking a circuit prior to cutting....and trusting a co-worker who said the breaker was off.....

I've worked on 300v (high current, aka, 80-90 amp) DC circuits before. Fortunately I never bit myself; that stuff is almost too scary to be messing with.

I have had -48 in a Phone switch light me up more than once. (but the old party line switch ring generators hit you even harder).

I have also seen the results of someone cutting hot wires in the Central Office, grounding they out in the process, sparks fly, blades on cutters melt.

Boatycall wrote:

DWeikert wrote:
If the panel you select has a peak voltage closer to 14v, then you lose the advantages of MPPT and may as well go with PWM. On the other hand, as the panel voltage increases the greater the advantages of an MPPT controller.

100% Correct.

Let me see if I can help explain a little better. As a lot of you know, I'm an Electrical Engineer by day, TC'er by weekend.

First, you have to understand what "Watts" actually is. It is a simple math equation, not a direct measurement -

Watts = Voltage x Amperage. or the age old P=IxE.
Also worth noting, this conversion can be used for running your microwave off a 12v inverter. (There's other formulas involving watts, but lets use this one for now). If you buy a watt-meter, like a Kill-O-Watt, it's measuring volts and amps, then displaying the two multiplied.

Let's do a real -world example--
You want 200 watts solar. You found a great deal on a 200w panel, it's voltage is 20 volts, it's output current is 10amps, hence 200 watts.

**Here's the problem**
Sure, it's 200 watts, but it's output current is 10 amps. A PWM controller will NEVER give you more than those 10 amps - and that's in a perfect lab-controlled world. Real world, probably 8.5-9amps, but for now, we'll say 10.
Pulse Width Modulation is nothing more than a fancy high speed on-off switch - that's how it regulates charge - on or off pulses, at a very high speed, varying in duty cycle. Dead battery - no pulses, full on duty cycle, 10 amps. Closer to full battery, the charge pulses become shorter in time, until finally you go into float mode with just very short pulses.

**Here's where MPPT comes in**
Your 200 watt panel puts out 10 amps @ 20v. MPPT does a voltage step down/amperage step up conversion. It drops 20v to 14.4, and by doing so, amperage gets converted UP to 13.8amps (in a mathematically perfect controller anyway.)
As the battery voltage comes up, the charge is of course regulated like your 12v converter until it finally goes into trickle charge mode.

**So - the moral of the story**

If you're going to go PWM - you need a LOW VOLTAGE panel.
Advantage to low-voltage panel--
* can use a much cheaper PWN controller
Disadvantages -
* Needs larger wire to handle full current of panel and minimize loss to due to wire resistance.
* Needs much more sunlight before it attains charge because you must get the panel voltage over 14 before it will actually charge.

**If you're going to go MPPT, you need high voltage panels, or panels wired in series.
Advantage to high voltage panels--
*Charging will start at a much lower light level - if you use 46volt panels in series, 92vmax, it takes very little light to make 92v of solar to cross over 14v and begin charging.
*Much smaller wire needed - high voltage panels are low in amperage, high in voltage, less loss due to wire resistance.

Disadvantage -
* needs a more expensive MPPT controller
* Be careful installing them, install them inside a garage, not outdoors. 46Vdc can bite you, ask me how I know.

Nice explanation.
Now I need to ask, how do you know that 46Vdc can bite you? LOL
The world wonders.

Boatycall wrote:

DWeikert wrote:
If the panel you select has a peak voltage closer to 14v, then you lose the advantages of MPPT and may as well go with PWM. On the other hand, as the panel voltage increases the greater the advantages of an MPPT controller.

100% Correct.

Let me see if I can help explain a little better. As a lot of you know, I'm an Electrical Engineer by day, TC'er by weekend.

First, you have to understand what "Watts" actually is. It is a simple math equation, not a direct measurement -

Watts = Voltage x Amperage. or the age old P=IxE.
Also worth noting, this conversion can be used for running your microwave off a 12v inverter. (There's other formulas involving watts, but lets use this one for now). If you buy a watt-meter, like a Kill-O-Watt, it's measuring volts and amps, then displaying the two multiplied.

Let's do a real -world example--
You want 200 watts solar. You found a great deal on a 200w panel, it's voltage is 20 volts, it's output current is 10amps, hence 200 watts.

**Here's the problem**
Sure, it's 200 watts, but it's output current is 10 amps. A PWM controller will NEVER give you more than those 10 amps - and that's in a perfect lab-controlled world. Real world, probably 8.5-9amps, but for now, we'll say 10.
Pulse Width Modulation is nothing more than a fancy high speed on-off switch - that's how it regulates charge - on or off pulses, at a very high speed, varying in duty cycle. Dead battery - no pulses, full on duty cycle, 10 amps. Closer to full battery, the charge pulses become shorter in time, until finally you go into float mode with just very short pulses.

**Here's where MPPT comes in**
Your 200 watt panel puts out 10 amps @ 20v. MPPT does a voltage step down/amperage step up conversion. It drops 20v to 14.4, and by doing so, amperage gets converted UP to 13.8amps (in a mathematically perfect controller anyway.)
As the battery voltage comes up, the charge is of course regulated like your 12v converter until it finally goes into trickle charge mode.

**So - the moral of the story**

If you're going to go PWM - you need a LOW VOLTAGE panel.
Advantage to low-voltage panel--
* can use a much cheaper PWN controller
Disadvantages -
* Needs larger wire to handle full current of panel and minimize loss to due to wire resistance.
* Needs much more sunlight before it attains charge because you must get the panel voltage over 14 before it will actually charge.

**If you're going to go MPPT, you need high voltage panels, or panels wired in series.
Advantage to high voltage panels--
*Charging will start at a much lower light level - if you use 46volt panels in series, 92vmax, it takes very little light to make 92v of solar to cross over 14v and begin charging.
*Much smaller wire needed - high voltage panels are low in amperage, high in voltage, less loss due to wire resistance.

Disadvantage -
* needs a more expensive MPPT controller
* Be careful installing them, install them inside a garage, not outdoors. 46Vdc can bite you, ask me how I know.

Pretty hard to argue with the facts.

pianotuna wrote:
What ever controller technology is used it is important that it be temperature compensated with a probe on the battery bank. It should also have adjustable set points. That may eliminate elcheapo controller.

+1 on this.

The beauty of the Bogart and MS SunSaver (linked above) is that not just voltage is adjustable but also the time in absorption can be programmed to match the changing battery state of charge.

In storage you probably don't want 2+ hours of absorption every day.

In use 2 hours may not be enough. Some controllers drop to float right at the bulk set point so absorption is done very slow at float voltage.

Spend the money on a good controller. Read the manual and charge profiles before you click and buy.

DWeikert wrote:
If the panel you select has a peak voltage closer to 14v, then you lose the advantages of MPPT and may as well go with PWM. On the other hand, as the panel voltage increases the greater the advantages of an MPPT controller.

100% Correct.

Let me see if I can help explain a little better. As a lot of you know, I'm an Electrical Engineer by day, TC'er by weekend.

First, you have to understand what "Watts" actually is. It is a simple math equation, not a direct measurement -

Watts = Voltage x Amperage. or the age old P=IxE.
Also worth noting, this conversion can be used for running your microwave off a 12v inverter. (There's other formulas involving watts, but lets use this one for now). If you buy a watt-meter, like a Kill-O-Watt, it's measuring volts and amps, then displaying the two multiplied.

Let's do a real -world example--
You want 200 watts solar. You found a great deal on a 200w panel, it's voltage is 20 volts, it's output current is 10amps, hence 200 watts.

**Here's the problem**
Sure, it's 200 watts, but it's output current is 10 amps. A PWM controller will NEVER give you more than those 10 amps - and that's in a perfect lab-controlled world. Real world, probably 8.5-9amps, but for now, we'll say 10.
Pulse Width Modulation is nothing more than a fancy high speed on-off switch - that's how it regulates charge - on or off pulses, at a very high speed, varying in duty cycle. Dead battery - no pulses, full on duty cycle, 10 amps. Closer to full battery, the charge pulses become shorter in time, until finally you go into float mode with just very short pulses.

**Here's where MPPT comes in**
Your 200 watt panel puts out 10 amps @ 20v. MPPT does a voltage step down/amperage step up conversion. It drops 20v to 14.4, and by doing so, amperage gets converted UP to 13.8amps (in a mathematically perfect controller anyway.)
As the battery voltage comes up, the charge is of course regulated like your 12v converter until it finally goes into trickle charge mode.

**So - the moral of the story**

If you're going to go PWM - you need a LOW VOLTAGE panel.
Advantage to low-voltage panel--
* can use a much cheaper PWN controller
Disadvantages -
* Needs larger wire to handle full current of panel and minimize loss to due to wire resistance.
* Needs much more sunlight before it attains charge because you must get the panel voltage over 14 before it will actually charge.

**If you're going to go MPPT, you need high voltage panels, or panels wired in series.
Advantage to high voltage panels--
*Charging will start at a much lower light level - if you use 46volt panels in series, 92vmax, it takes very little light to make 92v of solar to cross over 14v and begin charging.
*Much smaller wire needed - high voltage panels are low in amperage, high in voltage, less loss due to wire resistance.

Disadvantage -
* needs a more expensive MPPT controller
* Be careful installing them, install them inside a garage, not outdoors. 46Vdc can bite you, ask me how I know.

Jfet wrote:
I tend to agree that PWM is better for systems close to the battery voltage. With 200 watts of 20V panels, I would probably go with a PWM controller for the price and lower tare. With our 1100 watts of 60V panels into a 24V battery, there was no question, MPPT all the way.

I think even MidNite is making a PWM controller soon, and they only make top notch stuff. I do like the MidNite Kid 30 amp MPPT controller because the tare is only around 6 watts and the conversion efficiency is in the high 90s.

My panels are only 17.7v and the MPPT controller gives me roughly 25% more current into the batteries than the panels supply. A 20v panel is going to provide that much more charging current. IMHO anything above ~16v from the panel makes MPPT worthwhile.

I tend to agree that PWM is better for systems close to the battery voltage. With 200 watts of 20V panels, I would probably go with a PWM controller for the price and lower tare. With our 1100 watts of 60V panels into a 24V battery, there was no question, MPPT all the way.

I think even MidNite is making a PWM controller soon, and they only make top notch stuff. I do like the MidNite Kid 30 amp MPPT controller because the tare is only around 6 watts and the conversion efficiency is in the high 90s.