MPPT Controller Explanation For Dummies

[sailorchic34]

Originally Posted by Maine Sail

The most critical aspect is to be sure that temp compensation has been 100% disabled. Some cheaper MPPT's used "ambient" temp sensing of the air around the controller even without an external temp sensor connected. This needs to be able to be turned off if charging Li banks...

Hum...The temperature compensation in the solar controller, that is the ambient ones (not the battery post mounted ones) are there to control the power transistors power input to keep them from going into thermal runaway and frying. Manufacturers imply its for the battery's but its actually a feed back control to keep the power mosfets from running away. They are somewhat sensitive to temperature, that is internal circuit temperature in the same way lithium is sensitive to water vapor.

[foggysail]

Originally Posted by sailorchic34

As to lithium,to my mind using a battery material that burns / explodes er.. that is highly reactive with water vapor contact, may not be prudent in a marine environment. Look at the fun the 787 had. The USPS will NOT ship lithium phone batteries by air anymore. Something about a fire on a 747 cargo plane or two...

AWE CHICK!!! Here we are getting ready for the 4th which is right around the corner and you don't want that flash bang excitement?

[Maine Sail]

Originally Posted by sailorchic34

Hum...The temperature compensation in the solar controller, that is the ambient ones (not the battery post mounted ones) are there to control the power transistors power input to keep them from going into thermal runaway and frying. Manufacturers imply its for the battery's but its actually a feed back control to keep the power mosfets from running away. They are somewhat sensitive to temperature, that is internal circuit temperature in the same way lithium is sensitive to water vapor.

If it is a battery temp compensation sensor mounted to the controller they adjust battery voltage based on "ambient" temps at or around the controller. Voltage limits go up when it gets cold and voltage goes down when it gets hot.. Many controllers do this so you need to be wary of what you are buying.

This has been an issue on many a solar install I have worked on. I really dislike controllers that don't allow you to disable temp sensing or offer an external sensor option so you can physically mount it to the batteries to get accurate temp compensation.

Here is a summary from just one controller that does this:

"NOTE: The use of a Remote Temperature Sensor is strongly recommended. Controller location, air flow, and system power can drastically affect the local temperature sensor reading. A RTS will provide optimal charging performance.

7 - Local Temperature Sensor
Measures ambient temperature. Battery regulation is adjusted based on ambient temperature unless an optional RTS is installed."


Unless your controller is sandwiched in between a couple of batteries ambient temp compensation is often a poor choice on boats and if using a controller like this with Li you will need to figure out how or if you can disable it altogether.

[s/v Jedi]

Originally Posted by endoftheroad

As I mentioned I'm a greenhorn regarding solar and electrical but it seems my Genasuns mppt's each dedicated to a sole panel are rockin the house (boat).

They are rockin the boat See what happens, I told you the naysayers were gonna be jealous about your kit

Now you need to find ways to use more power, like connecting that fridge

[Nicholson58]

Originally Posted by endoftheroad

Wikipedia Definition;
Maximum power point tracking - Wikipedia, the free encyclopedia

Can someone simplify?

I can't over-emphasize how useful you will find this site below. Very long read. I re-read it once or twice a year. On the OP - MPPT will help you only if you install panels with open circuit voatage substantially higher than your charge voltage. The 'extra' unusable power at the excessive voltage is reduced to the desired voltage at higher amps. My panels are 54 VDC open circut for my 24 VDC batteries. 54 would ruin the batteries and the MPPT can convert high volts/low amps to lower volts/higher amps.

HandyBob's Blog « Making off grid RV electrical systems work

[s/v Jedi]

Originally Posted by Nicholson58

The 'extra' unusable power at the excessive voltage is reduced to the desired voltage at higher amps. My panels are 54 VDC open circut for my 24 VDC batteries. 54 would ruin the batteries and the MPPT can convert high volts/low amps to lower volts/higher amps.

I'll give this a go: The 54V panels would not destroy your batteries so quick. What happens is that they will start transferring power to the battery because their voltage is (much) higher. However, as the current ramps up, the voltage will be pulled down because the batteries can take much more current than the panels can supply. This will stabilize at the battery voltage without ill effects.

The trouble comes when the batteries become fully charged, at which point the voltage will start rising more and more, eventually boiling the batteries out.

But before that happens, the panels operate around that 28V charge voltage. The panel power output is not optimal at that voltage because it will be higher output at say 35V. This is where the MPPT controller helps, as it will find that point of maximum power transfer so that it sponges up all the panels can give and it uses that as a source for charging your batteries with the proper algorithms for that.

So, the fact that you can use high voltage panels is a secondary benefit of an MPPT controller. The primary benefit is the higher efficiency. I have noticed about 25% extra production as compared to no controller at all. This is with the Outback Flex60.

We lived for many years without a controller because our batteries are never full when we live aboard. Now that we leave the boat in the summer, they do become fully charged and I installed a controller to keep it under control

[nimblemotors]

I don't know if this is any simpler, but..

power = amps * volts, if you extract too many amps from a solar panel, it reduces the voltage, making the total power (amps * volts) less than if you didn't extract so many amps. A MPPT finds the max power by adjusting the amps until it discovers the max power available.

This is not really specific to charging a battery.

[foggysail]

Originally Posted by Nicholson58

I can't over-emphasize how useful you will find this site below. Very long read. I re-read it once or twice a year. On the OP - MPPT will help you only if you install panels with open circuit voatage substantially higher than your charge voltage. The 'extra' unusable power at the excessive voltage is reduced to the desired voltage at higher amps. My panels are 54 VDC open circut for my 24 VDC batteries. 54 would ruin the batteries and the MPPT can convert high volts/low amps to lower volts/higher amps.

HandyBob's Blog « Making off grid RV electrical systems work

I don't find fault with your post, its just a little incomplete. A pulse width modulated controller designed to work over your expected voltage range will easily provide the desired power transfer from your panels to your batteries. As others such as MailSails explained the MPPT will in addition to providing power transfer will do so in a manner where the panels operate at maximum efficiency.

[familycruisers]

Originally Posted by sailorchic34

I should note that my $26 PWM controller also charges my batteries by noon in the summer. 230 watts solar and 65 ish amps a day, including a 3 cf 120V fridge. To me the added cost of a MPPT controller was not justifiable for my small loads.

I should note that we did have a blue sky controller on the Florida boat, but I generally only saw 10 ish percent gain. When panels were $600 each it made sense to go mppt. But with cheap panels its not always the best bang for the buck. Least wise for the $500- $600 a month people anyway.

As to lithium,to my mind using a battery material that burns / explodes er.. that is highly reactive with water vapor contact, may not be prudent in a marine environment. Look at the fun the 787 had. The USPS will NOT ship lithium phone batteries by air anymore. Something about a fire on a 747 cargo plane or two...

Different battery tech. Lifepo4 is very safe and non reactive. You can puncture a fully charged cell and out won't ignite. Now LiPo, those are scary. We use and have been using this tech for years in the hobby industry. Actually, the maine industry could learn a few things from the hobby world. Such as cell taps for balancing and individual cell monitoring.

[endoftheroad]

Originally Posted by s/v Jedi

They are rockin the boat See what happens, I told you the naysayers were gonna be jealous about your kit

Now you need to find ways to use more power, like connecting that fridge

I have the fridge connected, I just enjoyed a cold cup of almond milk. yumm....
I bought this new to me sailboat 1.5 yrs ago and wasn't even sure if the fridge worked. It's awesome, compressor kicks on about every 1hr10 mins for about 20 mins run time. coolmatic/waeco/bd35f compressor, very small effecient unit that keeps my well insulated icebox nice and cold at 2/3rd setting.

Momma is very happy and impressed she thinks I'm a knowlegable old salty sailor.
We won't tell her different.

Nicolson58, thanks for the link, i'm enjoying it and will save it.

endoftheroad

[sailorchic34]

Originally Posted by Maine Sail

If it is a battery temp compensation sensor mounted to the controller they adjust battery voltage based on "ambient" temps at or around the controller. Voltage limits go up when it gets cold and voltage goes down when it gets hot.. Many controllers do this so you need to be wary of what you are buying.

This has been an issue on many a solar install I have worked on. I really dislike controllers that don't allow you to disable temp sensing or offer an external sensor option so you can physically mount it to the batteries to get accurate temp compensation.

Here is a summary from just one controller that does this:

"NOTE: The use of a Remote Temperature Sensor is strongly recommended. Controller location, air flow, and system power can drastically affect the local temperature sensor reading. A RTS will provide optimal charging performance.

7 - Local Temperature Sensor
Measures ambient temperature. Battery regulation is adjusted based on ambient temperature unless an optional RTS is installed."


Unless your controller is sandwiched in between a couple of batteries ambient temp compensation is often a poor choice on boats and if using a controller like this with Li you will need to figure out how or if you can disable it altogether.

Oh agree completely that the ambient temperature is useless for controlling battery charge. The effect does limit battery charge in warmer temperatures,

The reason for the temperature sensor is to limit current through the mosfet power transistor so as to limit circuit temperature which effects resistance and there for current through the power mosfet. Uncontrolled the power transistor can at high ambient temperature go into thermal runaway and burn out rather quickky, in seconds actually. The temperature compensation controls this and keeps the power transistors from premature failure.

Its the power Mosfets that of course control the current and voltage with MPPT, to the batteries. So yes it does limit charge current to the batteries, but that is secondary to the primary effect of preventing thermal runaway in the power mosfets in the controllers.

Marketing would have you believe its there just for the batteries, but the reality is its there to keep the controller from burning up under high temp and load.

[Nicholson58]

Originally Posted by s/v Jedi

I'll give this a go: The 54V panels would not destroy your batteries so quick. What happens is that they will start transferring power to the battery because their voltage is (much) higher. However, as the current ramps up, the voltage will be pulled down because the batteries can take much more current than the panels can supply. This will stabilize at the battery voltage without ill effects.

The trouble comes when the batteries become fully charged, at which point the voltage will start rising more and more, eventually boiling the batteries out.

But before that happens, the panels operate around that 28V charge voltage. The panel power output is not optimal at that voltage because it will be higher output at say 35V. This is where the MPPT controller helps, as it will find that point of maximum power transfer so that it sponges up all the panels can give and it uses that as a source for charging your batteries with the proper algorithms for that.


So, the fact that you can use high voltage panels is a secondary benefit of an MPPT controller. The primary benefit is the higher efficiency. I have noticed about 25% extra production as compared to no controller at all. This is with the Outback Flex60.

We lived for many years without a controller because our batteries are never full when we live aboard. Now that we leave the boat in the summer, they do become fully charged and I installed a controller to keep it under control

As you note - the short of it is - With 4000 bucks in batteries, I use the MPPT and its ability to operate as a proper multistage charge controller AND to gain the extra value from the high voltage panels.


BTW for those people challenged, DO read Handy Bobs blog. ALSO. Volts times amps = watts. V*A=W Watts is power. Assume for a civen solar condition that Watts is constant. Using the equation, reducing the volts increases the amps. More amps is better. This is what the MPPT does with high voltage panels.

[goboatingnow]

Originally Posted by foggysail

I don't find fault with your post, its just a little incomplete. A pulse width modulated controller designed to work over your expected voltage range will easily provide the desired power transfer from your panels to your batteries. As others such as MailSails explained the MPPT will in addition to providing power transfer will do so in a manner where the panels operate at maximum efficiency.

Lets just recap

PWM solar controllers ( bang bang ) work by rapidly connecting and disconnecting the panel from the battery. It works because PV panels are primarily current sources and hence have quite large output resistance. If the panel operating point is significantly removed from the battery voltage , then by pulling the panel to the battery voltage will result in serious inefficiencies , especially if the operating point should be many volts higher.

PWM solar controllers are really a terrible way to use PV panels. Note a PWM controller does not do any voltage conversion

Now back to MPPT .

Its important to seperate two things in a modern mppt charger

( a) maximum power point tracking

( b) voltage conversion


A PV panel will generate a optimum power output for a given illumination, that power points moves with sunlight levels and panel operating temperature. Ie there is a specific voltage/output current that maximises the PV panel output. This is because a PV panel does not have a truly linear relationship between output power and voltage , ie halving the voltage does not result in doubling of the current. There is a sweet spot on the curve. mPPt algorithms search , locate and then track that point as the variables change. Hence they maximise the panel output.

Voltage conversion is a additional feature, this is merely a switched mode power supply , a bit like the one on your mains charger ( you know the one that accepts anything from 90vac to 240 vac) , is this regard the voltage conversions doing the sane thing, providing a stable output voltage to charge the battery , even though as a results of the MPPT ( and of illumination levels ) the input voltage is all over the place.

mPPT is only valuable where you are actually drawing 80% or more of the panels available power, otherwise the panel will never be at the Vmp operating point anyway. The voltage conversion function of course is very useful as it allows you to use unmatched or higher voltage panels and not suffer the efficiency loss every time the PWM controller straps them to the battery voltage!!

Where panels are being operated close to their maximum , mppt gives real gains , approaching 20% , nor is the issue of standby current an issue in modern designs. Of yiu can afford it, mppt is always better.


Note the output of a switched mode PWM converter is pure DC , not to be confused with PWM solar chargers.
Dave

[bobofthenorth]

This point may already have been covered and I just missed it. If so I apologize for plowing old ground.

I used MPPT on my install so that I could wire my panels in series. That in turn allowed me to run significantly smaller gauge wiring from the panels to the controller. I routinely see well in excess off 100 volts input to the controller. I don't remember the exact numbers but I used either 6 or 8 AWG for a roughly 50 foot run.

[endoftheroad]

Its starting to make some sense to me.
Good stuff!