Mppt solar charge controller ?

[noelex]

Some of the cheap solar controllers do allow discharge at night, but for most panels the effect is not dramatic.

Of more significance is that many have a poor charging algorithm. Some do not even have PWM circuitry, but rather use the older on/off or bang/bang method of controlling the charge current (even if labeled PWM or even MPPT). These charging faults will not discharge the battery, but the amount of energy recovered from the panels can be very small and can shorten the battery life significantly.

However, there are some good, cheap PWM controllers available. If on a very tight budget, a PWM controller is generally better than a cheap MPPT controller. A good MPPT controller is better again, but a MPPT controller has to track correctly and perform the voltage conversion efficiently. This takes reasonably sophisticated circuitry that the cheap MPPT controllers often lack. So if on a very tight budget look for a good PWM controller rather than a poor MPPT controller (providing you are using “12v” panels in parallel).

 

[croc9968]

Sorry to hijack the thread a little but I'm looking to set a cheap solar set up for day sailing around the North East (awaiting jokes on lack of sun etc etc)....would the Dokio and Victron be a fairly good, cost effective set up?

 

[peteK]

The self consumption of a mppt controller I looked at was 60ma so stayed with my pwm at around 6ma as only have small panels and batteries.

 

[Pete7]

Sorry to hijack the thread a little but I'm looking to set a cheap solar set up for day sailing around the North East (awaiting jokes on lack of sun etc etc)....would the Dokio and Victron be a fairly good, cost effective set up?

No.

The Victron used to control say a 100w Dokio panel would be very nice and allow for some expansion but a simple PWM contoller would be much more cost effective if that was the main goal. However, if the budget can stretch that little bit more then longer term I think you will find the Victron a better buy. The difference in price is a couple of takeaway meals and soon forgotten. The performance and ease of monitoring the solar charging with a Victron will be an interest should last many years giving maximum performance.

The Dokio are cheap solar panels in a reasonably strong nylon cloth bag that folds, is light weight and reasonably cost effective. However, there is no way I would leave it outside exposed to the elements as I do with our 300w rigid solar panel which is mounted on an arch. The Dokio is very much for us at anchor or in harbour if there is no shore power etc in good conditions. In strong wind or rain, get it inside quick. That said being able to move the panel to face the sun several times a day and instantly measure the improvement on the Victron bluetooth app means that it generates fare more than a fixed panel of the same size. Direction and tilt makes a huge difference. Sadly the best bang for buck isn't there in small solar panel range. You can buy a 300w rigid solar panel cheaper than 100w budget Dokio.

Dokio aren't the only supplier, there are others rebadged by Bimble and Lensun or Photonic Universe have some more up market folding panels. I did have to make a warranty claim on a Lensun panel after the super duper EFTE layers claimed to be far better than cheaper panels failed in 18 months in a UK climate.

12V 120W portable folding solar panel with SunPower Cells - lightweight, High Performance cells, perfect for Hymer , T5 , Caravans etc

Thanks for our European client’s bulk order 100pcs flexible solar panels and 100pcs 100w folding solar panels – Lensun Solar Panel – Lensunsolar

12V solar panels charging kits for caravans, motorhomes, boats, yachts, marine

 

[noelex]

The self consumption of a mppt controller I looked at was 60ma so stayed with my pwm at around 6ma as only have small panels and batteries.

It is a good point. The MPPT controllers do have significantly higher self consumption. The better models “go to sleep”, turning off some unnecessary functions at night, but many are higher than 60ma even in sleep mode.

When “awake” and running, the self consumption can be in the range of a few watts for some of the larger models.

Especially with a small solar array (or one controller per panel on a larger array) it is important to try and pick a solar controller with low self consumption. Good voltage conversion efficiency (if MPPT) is also imprtant as is accurate and fast tracking. Unfortunately the manual does not always list the self consumption and when they do, the specification is a non realistic best case and not what is found in practice most of the time. The best way is to measure this yourself, but this is not always practical before buying. Victron and Genasun are two brands that stand out for low self consumption MPPT controllers, but I am sure there are many others.

 

[TiggerToo]

Maybe this is a silly question: would one classify the Marlec HRDi as an MPPT?

https://www.marlec.co.uk/wp-content/uploads/2015/10/HRDi-Manual-SM-347B.pdf

 

[ianj99]

Maybe this is a silly question: would one classify the Marlec HRDi as an MPPT?

https://www.marlec.co.uk/wp-content/uploads/2015/10/HRDi-Manual-SM-347B.pdf

It states "It uses Pulse Width Modulation " on page 2.

 

[ianj99]

I think the main benefit of an mppt controller is when you have two panels in series. The controller can then still provide a good charge in low light because the total voltage is well above the 14-15 needed at the battery terminal.
I did use a Victron 75/15 on the boat with a 100watt semi flexible panel and then moved it to my camper which had two, 100watt panels (Amazon) in series. Even on a dull day in the depths of winter, they still provided enough to run the lights.

I replaced the Victron with the pwm controller supplied with the panels so I will find out in a week or so, how well the domestic battery has been maintained over the last 9 months.

 

[TiggerToo]

It states "It uses Pulse Width Modulation " on page 2.

what does that mean?

 

[ianj99]

what does that mean?

PWM is a way of controlling current by switching it on and off. The ratio of on to off (duty cycle) changes the average current - e.g. equal on and off means 50% of the max current will flow and so on.
So in the context of solar charging, the panel output can be controlled so the battery is not overcharged. A good PWM controller could be as good as a MPPT controller but many of the cheap Chinese ones are crude and not very effective. (they don't adhere to the usual 3 stage charging process)

 

[TernVI]

PWM and MPPT are not mutually exclusive.
An MPPT controller is using some sort of regulation, which may be PWM, to track the maximum power of the panel.
Many really cheap controllers are not really PWM, they are just a switch.
PWM 'implies' a DC-DC converter, which should convert the panel volts to battery volts, a respectable circuit does this with enough efficiency that you get more current out than goes in. IT will also generally allow the panel volts to be much higher than the battery volts, with good efficiency. e.g. 35-38V of panels and 12V batteries with maybe 95% power efficiency.

Confusingly, the cheap Chinese ones which all look much the same, are not all the same. My mate has an old version of the ebay Chinese thing which is indeed making an effort at tracking the max power point of the panels, and putting out more current at 14V than the panels put in at 17V.

Likewise, people like Victron change their firmware more often than their underwear, you can't be sure any two units are the same.

However, the big thing for many yacht installations is to make sure the charging regime is good for the batteries.
It's best to understand how the controller will behave and be sure it will not overcharge if the boat is not used for days or weeks. The best settings for living onboard 24/7 may be wrong for weekend sailing. Many people with boats and motorhomes are shortening their battery life with high float voltages and long periods of unwanted daily 'boost' charging.

 

[ianj99]

PWM 'implies' a DC-DC converter, which should convert the panel volts to battery volts, a respectable circuit does this with enough efficiency that you get more current out than goes in. IT will also generally allow the panel volts to be much higher than the battery volts, with good efficiency. e.g. 35-38V of panels and 12V batteries with maybe 95% power efficiency.

No, MPPT controllers have a DC-DC converter which is why they work better with two panels in series.

PWM controllers do not need a DC-DC converter, they can control the current by varying the duty cycle. If any do have a DC-DC converter they won't be the cheap Chinese type, and might as well use MPPT technology.

 

[PaulRainbow]

Likewise, people like Victron change their firmware more often than their underwear, you can't be sure any two units are the same.

Of course you can, just keep the firmware updated. My solar controller and SmartShunt are connected to my onboard PC and they are both fully up to date, as is the Victron connect software. Even without the PC they will keep up to date by installing the app' on a phone or tablet (if the devices have Bluetooth).

 

[TernVI]

No, MPPT controllers have a DC-DC converter which is why they work better with two panels in series.

PWM controllers do not need a DC-DC converter, they can control the current by varying the duty cycle. If any do have a DC-DC converter they won't be the cheap Chinese type, and might as well use MPPT technology.

You sound a bit confused TBH.
People were using DC-DC converters between solar panels and batteries long before MPPT came along.
A simple way is to guess a good panel voltage and control the DC-DC to avoid driving the panel below that.
That's just a few analogue components, while proper MPPT is a lot more involved, generally using an IC designed for the job or a microprocessor.
MPPT charger-controllers are old hat really, we've been using MPPT for each panel for some years now, lots of systems use MPPT at cell level within the panels, which can make amazing differences in partial shade conditions or when panels are not all aligned the same way.

 

[ianj99]

You sound a bit confused TBH.
People were using DC-DC converters between solar panels and batteries long before MPPT came along.
A simple way is to guess a good panel voltage and control the DC-DC to avoid driving the panel below that.
That's just a few analogue components, while proper MPPT is a lot more involved, generally using an IC designed for the job or a microprocessor.
MPPT charger-controllers are old hat really, we've been using MPPT for each panel for some years now, lots of systems use MPPT at cell level within the panels, which can make amazing differences in partial shade conditions or when panels are not all aligned the same way.

Not confused. I'm sure there are PWM controllers that contain a DC-DC converter, but the ones I have come across haven't. They were cheap Chinese ones so were crude and not much use.
MPPT controllers also use PWM to regulate the output but they just give a better result than a cheap PWM thanks for their Dc-Dc converter.
The OP asked what the difference was.
I've never come across a panel with a built in controller of any sort.

The OP may find Victron's explanations helpful:
Which solar charge controller: PWM or MPPT? | Victron Energy