MPPT controller vs PWM

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Denek

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Hi all.
Our boat is going out onto it’s swinging mooring next week and I want to fit a solar panel to keep the batteries topped up. We will mostly be weekending to start but will need to fit more panels when we start longer cruising next year.
Can someone please explain the difference between the controllers above and the benefits of each.

Thanks
 
As I understand it...
To put energy into your battery, the voltage coming from your panel has to be higher than the voltage the battery is already at.
MPPT uses a sort of transformer to trade current for voltage and means that even if you don't have all that much actual energy available, it will still boost it up to a high enough voltage to give you some charging.
Therefore MPPT will give you the maximum out of your panels, and be the best way of getting the last few percent of charge into your batteries.

The main downside is that MPPT costs more than other charging systems. I believe there is also some minor power loss due to the voltage change.

For smaller setups you are usually OK with a cheaper PWM charger, even if it's not quite as efficient. You could spent the extra money on a second solar panel, or a bigger battery, etc, and that would be better value. But MPPT is the way to go for large systems.
 
As Kelpie said MPPT will charge your batteries faster but they are more expensive.
Solar panels have a trade off between current and voltage, the actual trade depends on the amount of light falling on them so you cant just set some value. If you take all the current they can supply you will have a very low voltage from them, since power = volts * amps then you have low power. Conversely if you let the voltage rise by not taking much current you also have low power.
What MPPT does is load the cells in such a way that you get the maximum power available at any given time. Thus the name Maximum Power Point Tracking
PWM, on the other hand rapidly connect/ disconnect the cells directly to the battery at an on/off ratio such that you dont exceed proper battery voltages.
 
Or maybe a little simpler, with a solar panel connected straight to the battery the voltage will be down round 13/14v or ghere abouts depending on state of charge. Solar panels work more efficiently at a higher voltage so the mppt makes the solar panel think it's connected to a battery at around 18v so works more efficiently, maybe 15/20% more amps will go into the battery. The mppt constantly hunts around for the most efficient voltage. Pwm just stops the voltage at the battery go too high. Victron bluesolar are great regulators, well worth the money.
 
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Thanks guys.
Sounds like PWM will be ok to start with at least. When we start sailing longer distances and times we will look again but I think I will order the 50w panel kit with PWM. Another quick question. And recommend adhesives to stick the panel down?
 
Denek said:
Sounds like PWM will be ok to start with at least. When we start sailing longer distances and times we will look again but I think I will order the 50w panel kit with PWM.
Click to expand...

That's exactly what I've done for the last three years. You can get about 5A max from a 100W panel using a PWM controller, which is plenty for keeping even quite a big bank topped up. Of course the current will reduce if it isn't brilliant sunshine and the panel is only at an angle to the sun.

Don't undersize your wiring. A bit of voltage drop between the controller and the battery has more effect than you might think on how much current you can get into the battery.

Can't help on the adhesive I'm afraid.
 
Switched from PWM to MPPT a couple of years ago. One big advantage of an advanced MPPT controller is that is customisable. You can regulate the charging voltage, float voltage and so on. These values need to be changed depending your battery technology (Gel, LiFePO4,..) and usage. When set correctly these features can prolong your battery life. Considering how much a decent battery goes for it would be wise not to skimp on the only thing that keeps it healthy, the controller.
 
Denek said:
Thanks guys.
Sounds like PWM will be ok to start with at least. When we start sailing longer distances and times we will look again but I think I will order the 50w panel kit with PWM. Another quick question. And recommend adhesives to stick the panel down?
Click to expand...

For fifty quid, why not get a basic, good make, MPPT?

https://www.bimblesolar.com/offgrid/mppt/BUDGETTracer2210CN?sort=p.price&order=ASC

I was really frustrated when I had a 100w panel through a PWM, and often toyed with MPPT.

In the end I upgraded to 500w of solar and a 40A MPPT
 
miha90 said:
Switched from PWM to MPPT a couple of years ago. One big advantage of an advanced MPPT controller is that is customisable. You can regulate the charging voltage, float voltage and so on. These values need to be changed depending your battery technology (Gel, LiFePO4,..) and usage. When set correctly these features can prolong your battery life. Considering how much a decent battery goes for it would be wise not to skimp on the only thing that keeps it healthy, the controller.
Click to expand...

ITYWF this also applies to good PWM controllers
 
I started off with a PWM last year but was disappointed by its performance. Once I changed to a MPPT the charging of the two AGM batteries was significantly more efficient under similar conditions, if the figures on the battery monitor are anything to go by.
 
lpdsn said:
Patented by Wallace & Gromit.
Click to expand...
:) :)

DCFqXqsXkAAKcRU.jpg
 
My 2d worth, I have two 80w panels in parallel going into a dual output PWM controller feeding a 120ah and a 240ah bank. Typically I spend 3-6 days at a time on anchor / sailing and the battery banks cope well so I have never felt the need to change the controller to a MPPT.
If you go for a PWM controller and have two battery banks buy a dual output controller, mine is a Photonic DB1024 (10A) they also have a 2024 (20A). They can be programmed to supply different percentage of available charge to each bank and puts all the charge to one bank if the other is fully charged.
 
For the last 4 years we have had a Chinese 100w panel and dual battery PWM contolller. No only has this kept our batteries fully charged when on the mooring, but it completely replenishes the power we use when at anchor. Even with the fridge on 24/7, it still puts more into the batteries during the day than the fridge takes out over 24 hrs, and what the lights and telly use in the evening.
 
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