Solar Panel MPPT Charger

[noelex]

In practice, in Greece it has been considerably higher than the figure you quote, the makers claim up to 40%. It is, of course, far more effective where you have lots of sun.

MPPT is most effective when its cold, the batteries are flat which is not the conditions you are likely to see in Greece, so your results should be a good average representation.

There are independent tests on the advantage of MPPT regulators in domestic solar installations and these report a 10% gain overall.
There are various reasons why MPPT is likely to perform worse on a boat solar array than a domestic situation. So all the evidence I can find points to 10% as optimistic.

I am interested in some real world data from boats its sadly lacking.

Charles, how did you measure the improvement?

The manufacturers claims can largely be ignored. The most common claim is “Up to 35% improvement”. This is true given ideal conditions for MPPT conversion, but there are times when the losses in the voltage conversion mean the MPPT regulator is loosing power. To discover the real improvement the gains and losses must be added up to come up with an average.

 

[charles_reed]

MPPT is most effective when its cold, the batteries are flat which is not the conditions you are likely to see in Greece, so your results should be a good average representation.

There are independent tests on the advantage of MPPT regulators in domestic solar installations and these report a 10% gain overall.
There are various reasons why MPPT is likely to perform worse on a boat solar array than a domestic situation. So all the evidence I can find points to 10% as optimistic.

I am interested in some real world data from boats its sadly lacking.

Charles, how did you measure the improvement?

The manufacturers claims can largely be ignored. The most common claim is “Up to 35% improvement”. This is true given ideal conditions for MPPT conversion, but there are times when the losses in the voltage conversion mean the MPPT regulator is loosing power. To discover the real improvement the gains and losses must be added up to come up with an average.

Crudely - before fitting controller 4 days @ anchor from fully charged (12.6v under load) to 50% charge (12.0v under load), voltmeter terminated.
After MPPT 5 days to same points.

2 x 105 AH sealed batteries, charge from motor, Adverc smart controller 14.6v on high voltage cycle.
PV panels 2 x 50 watt nominal in 1st case 12v nominal, Parallel; in 2nd case 24v, series, into MPPT.

 

[noelex]

Crudely - before fitting controller 4 days @ anchor from fully charged (12.6v under load) to 50% charge (12.0v under load), voltmeter terminated.
After MPPT 5 days to same points.

2 x 105 AH sealed batteries, charge from motor, Adverc smart controller 14.6v on high voltage cycle.
PV panels 2 x 50 watt nominal in 1st case 12v nominal, Parallel; in 2nd case 24v, series, into MPPT.

Thanks for letting me know. It certainly looks like you gained a bit with the MPPT, but probably a bit too crude to determine how much.
I am still hoping someone will do a detailed comparison.
I would love the gain to be more as some extra power would always be welcome, but I just cannot see its possible.

 

[nigelmercier]

I think adjusting the software controlling the microcontroller is beyond the capabilities of most yachtsmen. But if you could explain how you would go about making the adjustments that would be great. It makes the regulator far more useful.
For example if I wanted to reset the boost voltage to 14.7V how is that done? What interface is used ?

To reprogram the PIC microcontroller, you have to have a programmer. These can be bought for about £20, or get someone else who has one (me for instance) to program it for you. Alternatively, I could supply custom PICs at cost.

 

[noelex]

To reprogram the PIC microcontroller, you have to have a programmer. These can be bought for about £20, or get someone else who has one (me for instance) to program it for you. Alternatively, I could supply custom PICs at cost.

OK thanks
Making the points adjustable, even with difficulty, makes the controller more attractive.
It also introduces the possibility of disabling the regulation (by setting the threshold high) and using a central PWR with a mppt controller for each of the panels.
The only other problem is I suspect the MPPT in this unit is not the most efficient.

 

[properjob]

Solar MPPT Charger Kits

I think they are available but only for lead acid batteries.
http://www.jaycar.com.au
CAT. NO. KC5500

Alan.

Has anyone built one of these kits ?

I have built one and am setting it up before installing it, but I'm having difficulty in finding out the required temperature compensation value in mV/°C for my batteries. This figure is required to complete the setup procedure.

My batteries are Merlin PowerPack which are Lead/Calcium/Acid, Maintenance Free, Semi Sealed. Similar to the old Delco Voyager, the Delphi and the Lead Calcium Vetus types.
I have looked at spec sheets for all of these types with no results, does anybody have any clues as to where I might find this info ?

 

[ccscott49]

In practice, in Greece it has been considerably higher than the figure you quote, the makers claim up to 40%. It is, of course, far more effective where you have lots of sun.

Charles, which controller do you have and will it run a 24 volt system? I have the old type controller and want to update. Thanks for any help/input.

 

[jdy]

Has anyone built one of these kits ?

I have built one and am setting it up before installing it, but I'm having difficulty in finding out the required temperature compensation value in mV/°C for my batteries.

Caveat - Im not an electronics/computer engineer, just a hobby DIYer.

I have built the Jaycar kit (based on the 2011 edition of Silicon Chip magazine mentioned earlier in the thread). I used 20 Mv/deg C as the compensation value as an average ball park figure as I couldnt find any spec sheets for my battery either.

Observations: The charging and control of charging seems to work really rather well - and if you fiddle with the software and reprogram the 16F88 chip you can change how long it is in absorption mode etc or reset float voltages.

I recently updated the unit in the light of changes to the design that were published in Issue 282 of the above mag (2012). This changed the diodes and MOSFET to lower the power losses. It also added tweaks to the software allowing you to optionally select bulk charge to automatically come on in the morning, plus an option to revert straight back to float if a load drew down an otherwise full battery momentarily -saves sitting in absorption mode if you dont need to. These options are selected with links, or you can comment out a couple of lines of code and get same result in software. No changes to PCB required so you can use the older kit and buy the newer diodes.

I like the charging control - seems to work quite well. However. I'm less impressed with the efficiency - in that amps in from the panel often equal amps out to the battery, and MPPT ought to be able to realise some improvement under ideal bench test conditions.

From what I can see from some prodding about with meters and scopes, the MPPT PWM algorithm controlling the MOSFET is not always picking an ideal duty cycle. Am going to experiment further with manually setting the cycle to see what it can do in best case conditions - to work out whether the limitations are the losses in the electronics, or a less than perfect algorithm. My hunch so far is that it is the latter...

Sorry - long post! Hopefully of interest to some. And if anyone is also experimenting with this kit, or the PIC 16F88 and MPPT PWM, I'd be very keen to compare notes.

Jon