Solar Controller for Low Voltage Panels? Not Victron!

[s/v Jedi]

A current that much lower for series connection… unless something is broken this must be the array current, not the battery charge current.

[marty9876]

Originally Posted by Msailor

I'm hopeful that other sailors (those who can't wire in series) have dealt with low voltage panels and have found controllers to do the job. Any suggestions?

Note, new solar panels is not now an option. Thanks for any ideas.

Check out Morningstar - that’s what I went with after all my research

https://www.morningstarcorp.com/wp-c...er-mppt-en.pdf

Note the fine print: **PV Voltage must be greater than Vbattery + 1 Volt to start chargin

I’m assuming, it was a few years ago, that’s the spec that pushed me to that controller

[Msailor]

Thanks Marty, appreciate the Morningstar info. Looking at their spec sheets, seems that all their MPPT controllers have the 1 V differential requirement for charge starting. They reference "PV voltage" for the differential. The question of course, is whether that's panel VOC or something else, like panel VOC minus voltage drop from connection to the controller. But it does seem that Morningstar's start requirement is easier to reach than Victron's.

[marty9876]

Originally Posted by Msailor

Thanks Marty, appreciate the Morningstar info. Looking at their spec sheets, seems that all their MPPT controllers have the 1 V differential requirement for charge starting. They reference "PV voltage" for the differential. The question of course, is whether that's panel VOC or something else, like panel VOC minus voltage drop from connection to the controller. But it does seem that Morningstar's start requirement is easier to reach than Victron's.

Reading through this thread, a few times, makes me think I'm still not 100% getting all concepts here in play. I still might be mixing up, or not understanding, which is being used or the impacts of Vmp vs. Voc from a controller standpoint

That said, I can say the Morningstar controller works with a pair of flex panels in parallel with the following specs:

Specification:
Optimal power [Pmax]: 100W
Working voltage [Vmp]: 18V
Working current [Imp]: 5.56A
Short circuit current [Isc]: 5.8A
Open circuit voltage [Voc]: 20V

[Msailor]

Agreed this stuff is difficult to fully understand. Solar panels do seem to come with good info about VOC--which is fixed and you can easily verify with a voltmeter. They also give you good info about the target voltage, MP, for getting maximum power.

Seems all MPPT controllers use a voltage differential as a requirement for battery charge starting, but that info seems to hard to find--and hard to understand because of undefined terms for one of the numbers in the differential arithmetic, that for panel voltage. So consumers like me (and perhaps you), think its panel VOC, when its not. When its undefined, I call it voltage drop. Noelex says its what the controller does to get maximum power, and so its deliberate voltage adjustment on the panel side (as opposed to voltage regulation on the battery side).

As your experience compares to mine, seems pretty clear low voltage panel systems like ours do better with low differentials, and so Morningstar will be better than Victron. Even though there may be other factors particular to different controllers affecting charging, because panel VOC will diminish over time and a high differential system will stop charging well before a low differential system, a high differential controller is not for me. Thanks again for your input.

[bcboomer]

Ocean Planet Energy did an article about controllers. They said that the only 2 controllers that actually boost are Genasun GVB & Western WMarine10.
Take a look at their site and see if they will do the trick for you.

Unfortunately that article came out after I bought Blue Sky Energy "boost" controllers that don't actually boost low voltage.

[s/v Jedi]

It’s a non issue. Just compare Voc with Vmp and you will find a 15-20% gap between the two. If your Vop is too close to the battery charge current, you are not going to get the rated output from your panels and you require a so-called boost-controller, which does dc-dc conversion to boost output voltage up.

[hpeer]

Dead simple, mercury wetted contacts, long life, relatively cheap.

I am not using because I moved to high voltage panels.

Not trying to sell, just what I have used.

[Msailor]

Originally Posted by bcboomer

Ocean Planet Energy did an article about controllers. They said that the only 2 controllers that actually boost are Genasun GVB & Western WMarine10.

Take a look at their site and see if they will do the trick for you.



Unfortunately that article came out after I bought Blue Sky Energy "boost" controllers that don't actually boost low voltage.

Thanks for the post! I was unaware of the "boost" type controller.

[Msailor]

Originally Posted by hpeer

Dead simple, mercury wetted contacts, long life, relatively cheap.



I am not using because I moved to high voltage panels.



Not trying to sell, just what I have used.

Interesting controller. Seems to have a different approach to battery charging than the three stages I'm familiar with. Thanks for the reply.

[sailingharry]

Mppt controllers are good, and the m stands for maximum power. But as you have discovered, they do require a bit of extra voltage to get them going.


It is worth noting that the power gain by using MPPT becomes more noticeable as the maximum power voltage gets higher and higher than the battery voltage. If the maximum power voltage is say, 15v, a direct connection to the battery is probably more efficient than any controller.


With that concept in mind, you may be well served by a PWN controller. It has no surcharge requirement, and provides the efficiency of a direct connection -- but without the power gains of an MPPT controller at midday. In your installation, that compromise may or may not be significant.

[CarinaPDX]

Originally Posted by hpeer

Dead simple, mercury wetted contacts, long life, relatively cheap.

I am not using because I moved to high voltage panels.

Not trying to sell, just what I have used.

I have used this controller for a couple of decades with my wind generator. It is a simple, robust PWM controller.

It is my opinion that for smaller 12V PV systems a PWM controller is preferable to MPPT. Instead of spending the extra money on MPPT for a modest efficiency improvement, spending towards larger, or more, panels will have a greater yield. The OP's 300 watts is large enough to preference MPPT but should be fine with PWM as well. In series and thus higher voltages MPPT is of course advantageous, and allows for smaller cabling. (When switching from series to parallel the cabling must be re-evaluated for the higher current produced at the lower voltage - too many 12V systems have significant voltage drop in the wires.)

I am surprised at the significant drop in Voc over just a few years. I don't think that this is normal behavior for quality panels, but haven't ever tested mine for Voc after installation. Once set up the system has functioned just fine. I am switching to a Morningstar dual output PWM controller (for my two battery banks) from a single output controller with dual Schottky diodes on the output (as part of an overall cleaning-up of the electrical system).

Greg

[noelex 77]

Originally Posted by CarinaPDX

It is a simple, robust PWM controller.

The NC25A-12 is not a PWM controller. It is a simpler so called bang/bang controller. There is no multistage algorithm, nor any ability to maintain a voltage set point like a PWM controller.

The algorithm will turn on charging until a set voltage is reached and then it will stop all charging until another set point is reached.

[hpeer]

Nolex,

I believe you are correct, and also as Carina said, it is good for simple installations where the supply voltage is say 14 to maybe 20 volts. I switched them for MPPT when I upgraded my panels.

In fact it was the mfgr. of this NC25A controller that suggested I use MPPT controllers.

It would likely work well for a wind generator that pits out rectified DC. Like my Aero6Gen ir maybe a D400.

[CarinaPDX]

Originally Posted by noelex 77

The NC25A-12 is not a PWM controller. It is a simpler so called bang/bang controller. There is no multistage algorithm, nor any ability to maintain a voltage set point like a PWM controller.

The algorithm will turn on charging until a set voltage is reached and then it will stop all charging until another set point is reached.

Thanks for the clarification; I hadn't made the distinction. This is definitely "bang-bang" as the on/off cycle is quiet long and with a wind gen quite noticeable. IIRC it was recommended by the wind gen manufacturer (early AirMarine unit).

Greg