Solar Controller Question

[Rick D]

I'm going to ramble a bit before I get to the point. I was considering replacing my three-stage solar regulator with a Blue Sky system since it has had some rave reviews. But, now I'm wondering if I should just remove the one I have to go direct?

I have three 25 amp/day flexible solar panels which I put on the bimini only when I am at on the hook or on my mooring for more than a day or two. The average amp draw on the boat is six amps, so the panels basically handle the load during the day but don't provide any surplus. On 400 amps house capacity I run the generator when it gets down to -160 to-180-ish and quit when it gets up to -80 to-60. The point is that the batteries are rarely up past 80-ish %. and the draw is pretty consistent over 24 hours. The solar panels probably are worth 50 amps a day real world and the consumption about 100-140 amps in 24 hours (gross).

So, what got me asking the question is that I understand the Blue Sky reconfigures the charge profile to more accurately reflect the small solar input into larger banks by essentially allowing a longer higher voltage input. That made me wonder if I even need a regulator considering my typical battery state, the size of the bank and the output of the panels. It seems to me I am cutting my own charge ability by using a controller to start with. Maybe I could run a bypass switch and keep it tho.

What do you think? What haven't I considered here?

 

[Stu Jackson]

Rick, my experience is that the batteries acceptance rate is going to be the controlling factor once you get up past the 80-90% anyway, so the charging between 50% and 80-90% can't go much above the source which is less than the acceptance anyway. The choice you have is simple: more capacity or longer time to charge. Sounds like you're taking good car of your bank. Recent advice, I believe I posted here earlier with a link, is to also remember to completely charge the bank regularly if you can plug in.

 

[Capn Dave]

You almost got it Rick

The MPPT controllers BlueSky among others, don't really use low voltage better. All solar panels put out more voltage than 12 volts. It is morel like in the 17-19 volt range. What BlueSky and others do is take the high voltage and instead burning off the excess with a restive load, electronically drop the voltage to 12V and increase the output amperage of the panels. So what in effect you are pumping more amps back into your batteries.
In reality it is a little more complicated that that, but you get the idea.

Fair Winds

Cap'n Dave

 

[Rick D]

I'm Not Sure I Got It Dave, But...

...does it make a difference to the charge current at say 60% whether it is a stepped down voltage or a raw 19 volts? Are you telling me that the voltage must be stepped down even at that percentage of discharge to be worthwhile? Rick D.

 

[Stu Jackson]

Rick,

It's not so much stepped down to be worthwhile, but controlled to avoid overcooking the batteries with too high a voltage. I'm still not sure where and how they convert the voltage into additional amperage, but I'd like to be able to first understand it, and then see if it matters, because if it's only a few amps, then my point about battery acceptance comes into play and the result is that you'd be paying $$ for something that may, that's may, be only marginally better than what you already have.

 

[Capn Dave]

Ahoy Rick

In a word no. It does not step down the charge current. It drops the voltage to a useable level inturn increasing the amperage, instead of just burning off the extra volts.
Amps is what you want to feed the batteries.
Solar charge controllers regulate the solar cells output to keep from overcharging the batteries. In turn the cheap charge controllers waste as much as 30% of the solar panels output
I hope I understand your question correctly.

Fair Winds

Cap'n Dave

 

[Rick D]

OK, I think I Got It Dave...(and Stu)...

...and now I have to consider if that conversion would make a material difference at the end of the day. The breathless quotations I have seen claim this to be almost as good as adding another panel. For me, that would just about be a wash in terms of dollars, but the increase of efficiency sorta warms my heart and biases me to the Blue Sky- type unit.

 

[shorty]

I think 25 watts, not amps

If your panels are small enough to fit three on the bimini, you probably have 25 watt, not amp, panels. They would be 2 amps each.

 

[Bob S]

Forgive me for my ignorance!

Does anyone make an smart regulator that can also be used to control a solar panel's output? It just appears to me we are spending money to regulate the alternator output and again for the solar panel's output. Why can't they be combined into one unit?

 

[walt]

I think this was already answered but Ill add a little detail. Solor panels are basically "current output" and will put out the same current regardless of the voltage load. For example, a panel which puts out the rated 1 amp at 18 volts (ie, 18 watts) still puts out 1 amp when connected to a 12 volt battery (ie, now only 12 watts).

The MPPT controller uses power switching to maintian the input from the solar panel at its optimunim power point - ie, 18 volts and in the example, 1 amp. But the output of the MPPT controller maintains most of the input power so if the 18 watts were maintained, the output would be 12 volts but the current would be 1.5 amps ( ie, 18 watts output = 12v * 1.5 amps). These are ideal numbers, you normally get less.

I have one of these (not on a boat) and and it effectively gives about 15% more current than a non MPPT controller in my setup (160 watts of panels). Cost wise, you have to compare the additional cost of the MPPT controller to simply adding 15% more panel. On a boat where space is limited, the MPPT controller possibly becomes more attractive.

 

[GuyT]

Re: Forgive me for my ignorance!

Two different animals bsmith.
An alternator has a field winding and the strength is adjusted to regulate the output of a 3 phase winding which is sent to a rectifier.
A solar controller adjusts the output of the panel by regulating through a max tracker or a simple linear regulator that limits the output voltage.
The technology and circuitry are completely different and therefore not able to be combined. Good idea though!

 

[walt]

Ive owned three different types of solar controllers that worked differently. The oldest one uses a form of pulse width control when it starts to regulate the charge to the battery but it does this by shorting the panel voltage to ground. This was the best way many years ago when only bipolar transistors were available.

The newer simple ones uses a FET which simply connects the pannel to the battery and acts like a low impedance switch. When regulation is needed, the FET is switched on/off (ie, pulsed).

The third is the MPPT controller mentioned - much more complicated.

My old Honda BF8 outboard has an alternator but no regulator and I think this is still common in smaller outboards. The alternator current is not that high but you could still damage a battery by overcharging (but you would likely have to try awful hard). I thought about using a solar charge regulator for either a large panel I have or the outboard but using the solar charge regulator for the outboard would be a bad idea since most likely its the type with the FET which switches on and off. The switching off of course is the same as disconneting a running alternator from the battery and the alternator coill creates a large voltage spike. Normally, this can damage the rectifiers in the alternator but in this case, it would also likely damage the FET in the solar controller. So no regulator at the moment on the old Honda BF8 outboard..

 

[newly anonymous]

link to a Practical Sailor article relevant to this discussion

www.blueskyenergyinc.com/pdf/Practical%20Sailor%20PDF%20-%20Blue%20Sky%20Energy.pdf

 

[Bill Roosa6491]

State of the art solar controls

Hi Guys
The Blue Sky controller works like a transformer for DC. It supplies a fake load that maximizes the output (watts) of the solar panel (19 volts X whatever amps). It then converts this to something like 13.6ish volts to charge the batteries. The extra wattage you see operating at (the panel) 19 volts vs battery voltage depends on the size of the panel. The formula is:
Wattage increase = new wattage - old wattage
or
Delta W = 19 volts * x amps - 12 volts * x amps
where x is the amp rating of the panel
or
Delta W = (19-12)* x amps
7 watts for each amp the panel is capable of producing
That means 7/13.6= 0.51 amps on a "1" amp panel or 151% increase!!!
this all assumes that your panels are the "36-cell" type and can produce 19 volts when cooking at 110F under the blazing tropical sun. Most panels are not 36-cell and have VERY significant voltage drop off with rising temperature.