solar charge controller?

Maine Sail · Aug 8, 2011

That type of controller is anything but fast as they are what's referred to as a "shunting" type. What this means is that when the battery voltage has risen to 14.2 volts the regulator shuts off and when the voltage drops back to 13 volts it kicks back on. It can take as much as 40+ minutes on some batteries, especially AGM's and some thick plate deep cycle batts, to drop back below 13 volts so much of your peak sun hours are wasted with a shunting type controller.

There is lots of wasted charging time with these types of regulators. If you have the time, as in many days or weeks, they work fine but a true three stage controller with PWM will generally charge faster as they do not shunt when they hit a voltage threshold they just keep charging via fast pulses and then go into float mode and never shut off.

For basic regulators I like the Morningstar controllers. The Pro Star 15 is a great one that won't break the bank. If you search you can find one for as little as $75.00-$85.00. for a small MPPT I like the Genasun controllers..

walt · Aug 9, 2011

A little different explanation on the "shunting" types of regulators..

Back in the "stone age", all solar regulators did was mostly prevent the over charging of the battery (and that is pretty much all you need in this case). The transistors which were available made it most economical to shut off the solar panel by "shunting" the panel to ground with a diode to the battery that basically disconnected the battery when the panel was shunted. There is nothing wrong with doing this - the panel is a constant current output and shunting it does no damage and there is little power dissipated in the shunt since the voltage is very low (power is voltage times current). Nothing wrong with shunting - it’s just old technology.

The newer "pulse width modulated" (PWM) controllers use a different type of transistor (FET) which basically connects or disconnects the panel to the battery. The cheap Morningstar regulators are this type.

With either shunt or PWM, something is sensing battery voltage and controlling whether the panel is connected to the battery or not. I know with the Morning star controllers, this switching happens at a high rate - I’ve looked at it with a scope. But this switching could also happen at a high rate with a shunting type regulator. If the one you bought is "slow", it must be that the circuit design is very old as there isn’t any cost savings to making the switching slow.

Id say you are mostly fine with the one you picked - I think you will find that 50 watts of solar is more than you need especially if your outboard has a charger. If you have more power than you need, the main purpose of the controller is to limit over charging of the battery - the one you have will do a fine job of this.

Hookup.. for these less expensive type of solar charge controllers, you want the wire between the controller to the battery as short as possible because any voltage drop in this run tricks the controller into thinking the battery voltage is higher than it really is - and the charge controller shuts off too soon.

Also, I know all the Morningstar PWM have temperature sensors as battery charging is definitely temperature sensitive so putting the charge controller close the battery means that it has a better idea of what temperature the battery is actually at.

The run between the charge controller and the panel is just not very sensitive with less expensive charge controllers. Reason is that the controller is simply connecting the battery straight to the panel and the panel voltage drops from its open circuit voltage to the battery voltage. The current is constant from the panel - so voltage drop in the wire generally doesn’t matter (until it’s a few volts - but you would have to use some very small wire to get this). Not caring much about the wire between the panel and controller ONLY applies to these cheaper PWM or shunt controllers. With MPPT, the loss in this wire does matter..

FYI, as mentioned, I think the controller you have will probably work just fine mostly since I think you generally will have excess power from the panel.. After four years of always adding more power, I ended up with a 40 watt panel and an outboard charger and just have way more power than I need even for a one week trip…

Maine Sail · Aug 9, 2011

doehunter said:
Main Sail,
Please excuse my ignorance here but I don't understand.
Let's say I start with a low battery that has just barely over 12 volts. Will my controller make it slow to get up to 14.7 volts?

What controller do you have that goes to 14.7 volts? Your Sunforce goes to 14.2V. There are only two and sometimes three stages of charging. Your Sunforce will do two stages BULK and ABSORPTION.

Bulk - Any point below the controllers set point voltage. In the case of the Sunforce it is a 14.2V absorption voltage. Until the Sunforce controller hits 14.2 volts it is always on.

Absorption - This is any point in charging where the battery has risen to 14.2 volts and the controller is "limiting" this voltage to 14.2 volts from there on. This usually occurs at about 80% state of charge leaving the last 20% to go. Many older shunting regulators simply turn off when the battery hits absorption voltage / 14.2V and have varying levels of re-start voltage. The Sunforce is about 13 volts to kick back on.

Float - An additional reduced voltage limit stage.

It is the time period between the on voltage (13.0V) and the off voltage (14.2) where your charging times are extended as the surface charge can take a while to dissipate. I have timed this on multiple occasions and some shunters are faster than others. The inexpensive Sunforce is one of the slowest I've seen and the Flex Charge units are about the fastest.

We need to remember that these shunters are normally designed for off grid applications where the batteries almost always have a load on them. This drops the surface charge of the batteries back to 13V very quickly so the controller can go back into "ON" on mode. On a boat however, when left unattended, like when on a mooring, we normally have zero load and the surface charge with some batteries can take as long as 40 minutes to drop back to the 13 volt ON point but 1-15 minutes is more the norm. That is 1-40 minutes of your few hours per day of precious sun time when your controller is in the OFF mode.. As the batteries near full they come up to 14.2 volts faster and faster and then shut off more frequently and the wait for them to turn back on begins with each rise to 14.2 volts.

doehunter said:
Then after it gets there, I thought it was supposed to shut off. When the battery gets back down to 13 volts, isn't that still pretty much a fully charged battery?
I guess I didn't follow the shunting thing.
Jim

When you hit the "absorption voltage" of 14.2 volts, or what ever the controller is set at, this is usually at about 75-85% state of charge, not full, and you still have a long way to go. 13V is well above fully charged but that is only a "surface charge" which can take a while to dissipate with no loads attached.. If you let that battery sit for 24 hours and measured the open circuit voltage you'd see the real state of charge.

I have done this exact upgrade from the inexpensive Sunforce to the Morningstar PS-15 and the boat was back to 100% state of charge in an average of 2 days vs. an average of 5-6 days. Same panel, same wiring, different controller. Both controllers get you there but a PWM controller will almost always do it faster in a marine application when no loads are present.

For shunting regulators the Flex Charge units are fairly fast as the on/off differential voltage seems to be much narrower and they tend to act more like a PWM than a shunting unit...

walt · Aug 9, 2011

The cheap solar charge controllers are difficult to tell if they are working or not. I have one (cheapest one morningstar sells) that was kicking around for a few years including my son playing with it for a while. To tell if it was working or not, I had to take it into the "lab" at work and hook up some power supplies, resistors and a scope and then I could see it doing its business (could see the switching). Albert Fischer who post here sometimes went through the process of trying to figure out if his was working or not on the trailer sailor forum - have no idea where that thread is but it went through some process to look at things.

Maine sail, your data is correct (and good that you contribute here) but I just want to point out that the "shunt" type of controller doesn’t need to be slow. The only reason they are is that any design using the shunt is probably on the order of 20 years old now and back then the "control" likely had to be done with analog circuits so slow was cheaper. New ones likely use very inexpensive microcontrollers and the it’s very simple to have the micro sense the battery voltage and implement any charge algorithm you can define. The actual switching of the shunt can be very fast..

Sumner · Aug 9, 2011

walt said:
A little different explanation on the "shunting" types of regulators.................. I think you generally will have excess power from the panel.. After four years of always adding more power, I ended up with a 40 watt panel and an outboard charger and just have way more power than I need even for a one week trip…

Hey Walt welcome back and a great explanation of the different type of controllers. I didn't even know about the shunt type I thought there was just the PWM and MPPT. I'm wondering if Jim's isn't a PWM since it is new.

Jim for a 12 volt battery to take a charge it has to be presented with over 12 volts. Your car alternator is doing this all the time. Most of them charge at between 14.0 and 14.3 volts also when the battery needs it.

How big of a panel does someone needs is a question with out a good generic answer. You need one to fit your needs. A 40...

http://purplesagetradingpost.com/sumner/macgregor/outside-22.html

....helped us, but no where near meet our needs with my CPAP machine and the frig that we now would never give up and our computer/chartplotter usage. With it we still ran the gen-set ...

http://purplesagetradingpost.com/sumner/macgregor/outside-15.html

...15-30 minutes a day. 180 watts...

http://purplesagetradingpost.com/sumner/macgregor2/outside-33.html

...now takes care of 90%-95% of our needs and we only have to run the gen-set occasionally now. Since we broke a panel on the last trip we have replaced it with a 100 watt panel for a total of 200 watts now.

It also depends on how long you go out, 1-3 days and you can have a net loss on the battery/batteries and make it home and charge them up again. You getting past 3 days is a different story. Unless you are using the outboard quite a bit, and it has an alternator, chances are, unless you aren't using much electricity you will fall behind with even a 40 watt panel. Especially if the sun conditions are not good.

The confusing part for me was the controller types and which one would work best for our needs. Like Walt said the PWM, the most common and cheapest, just connects the panel to the battery and does this in an off/on manner. Now here is where it gets confusing and you have to take your time to get through this part, at least I have had to.

Let's take say the 40 watt panel that we have in our array that is very typical of about any 40 watt panel. We know that Watts = Amps X Volts and from that know that Amps = Watts/Volts. From that it would be easy to surmise that our 40 watt panel puts out 3.33 amps (40 watts/ 12 volts = 3.33 amps).

That won't work as if you look at the panel specs it says that its max. amperage is 2.33 amps and the max voltage is 17.2 volts. So did they lie telling us that it is a 40 watt panel? No because 2.33 amps X 17.2 volts = 40 watts, so it is a 40 watt panel. Now the problem is that when we hook it to the discharged 12 volt battery with the PWM controller it is at 12 volts. So we still have the panel putting out 2.33 amps, like Walt said, but 2.33 amps X the 12 volts now means the panel is only 28 watts (2.33 X 12). So we just lost about 30% of our wattage.

If you look at the adds for the MPPT controllers they claim they can 'potentially' produce 30% more to the battery than a PWM. How they do that is that they take that 17.2 volts at 2.33 amps and convert it down, so that what the battery gets is now 3.33 amps at 12 volts. The 3.33 amps X 12 Volts = 40 watts. So they do more than just connect the panel to the battery they convert the amperage side to your benefit.

As the battery becomes charged their benefits diminish. If you are out multiple days and using the battery up and it is low in the morning (12 volts or less) then the MPPT can make your solar panel look to be 30% larger than the PWM. We chose the MPPT for this reason and also that we are limited to how much solar we can physically mount on the boat and want to maximize what we have.

For most people that go out 1-3 days the MPPT probably isn't worth the extra money. I will say though that panel prices are coming way down and since a 60 watt panel doesn't take up much more space than a 40 if you are thinking solar maybe think about a 60. Places like Solar Blvd....

http://www.solarblvd.com/Solar-Pane...60-Watt-12-Volt-Solar-Panel/product_info.html

..have them for as low as $159. When looking at panels be sure and get what they call a 12 volt panel. The specs will say it has a voltage between 17 and 18 volts. For instance they now have a 60 watt panel for only $99 on their site, but it is a 48 volt and is not going to work in our application.

Go solar and if you want a better explanation of PWM vs. MPPT go here....

http://windsun.com/ChargeControls/MPPT.htm

Sum

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walt · Aug 9, 2011

Just an option.. but a few of the guys here (Chris, Albert F., Mike B. are ones I remember) have a fairly simple set up with a 20 to 40 watt panel that clamps to the rear rail. The nice thing about this install is that you can rotate the panel but also (important..), it’s easy to remove the panel for either travel or day sailing. Too bad there wasn’t an easy way for these guys to put pictures of their panel install on this forum...

Interesting that at the Lake Havasu even last Feb, there were about 130 trailerable sailboats there. I was the ONLY boat that had a solar panel on while sailing (and mine is removable..). Sumner has the Cadillac install for longer term cruising if that’s your boat use. I just use ice for the few days per year that I need to keep food cold instead of a fridge – WAY simplifies the boat power requirements.

FYI, your stereo probably uses 1 to 2 amps (I get too much audio distortion much past 2 amps so don’t go past that), I think the auto pilots also use 1 to 2 amps depending on boat balance and swell.. Led lights are in the noise.

FourPoints · Aug 9, 2011

I had the same exact sunforce controller when I hooked up my panel this spring, My batteries were a little over 50% charged (reading right around 12-12.2v) when I installed everything, and after 3 weeks of good sun with little to no load on them, I found that the batteries were still only testing around 75% charged according to the hydrometer. That is when I started digging into the differences in how the charge controllers worked and found that the sunforce was actually preventing the batteries from fully charging by turning off as soon as the surface charge reached 14.2v, and never allowing much charge to be absorbed. The self discharge of the batteries was almost equal to what I was actually inputting through the sunforce controller, and in the end I wasn't really charging much of anything.

I went with the Genasun GV-4 (http://www.genasun.com/gv-4.shtml) on Maine Sail's reccomendation (I beleive he actually has a genasun, not a morningstar on his boat), partly because I don't have enough room to install a large panel so I needed to get all the juice I could out of what I have (12w), and the MPPT gives me a nice boost in the mornings.

I checked on everything a couple days after hooking it up, and found the batteries were sitting at float stage and the hydrometer was indicating full charge. Every time I have checked the batteries since installing the GV-4, they are sitting at float stage and fully charged within a day or two of getting back at the docks from going out for the weekend, and no matter what I seem to do power wise at the dock they are always recharged the next day (and no, I don't have a shore power chargeing system).

In short, the sunforce is half worthless and get rid of it, replace it with a good controller and you will be very happy with the decision.

Maine Sail · Aug 9, 2011

walt said:
Maine sail, your data is correct (and good that you contribute here) but I just want to point out that the "shunt" type of controller doesn’t need to be slow. The only reason they are is that any design using the shunt is probably on the order of 20 years old now and back then the "control" likely had to be done with analog circuits so slow was cheaper. New ones likely use very inexpensive microcontrollers and the it’s very simple to have the micro sense the battery voltage and implement any charge algorithm you can define. The actual switching of the shunt can be very fast..

That is not what makes them slow it is the differential between on and off voltages and the time it takes for an unloaded battery to drop from OFF voltage of 14.2V to the ON voltage of 13.0V...

Some AGM and thick plate batts will hold surface charges slightly above 13.1V -13.3V for a long time. Until the battery voltage drops back to 13 volts the controller won't turn back on. It is not how fast it switches on when 13 volts is attained, that is very fast, but in how long it takes the bank to self discharge back to 13 volts that is the issue.

A controller that had an OFF at 14.2 but an ON at 13.8v would be much faster than one that turns off at 14.2 and back on at 13.0V. Batts won't stick at 13.8 for very long but can cling to voltages above 13.0V for a while..

Maine Sail · Aug 9, 2011

FourPoints said:
I had the same exact sunforce controller when I hooked up my panel this spring, My batteries were a little over 50% charged (reading right around 12-12.2v) when I installed everything, and after 3 weeks of good sun with little to no load on them, I found that the batteries were still only testing around 75% charged according to the hydrometer. That is when I started digging into the differences in how the charge controllers worked and found that the sunforce was actually preventing the batteries from fully charging by turning off as soon as the surface charge reached 14.2v, and never allowing much charge to be absorbed. The self discharge of the batteries was almost equal to what I was actually inputting through the sunforce controller, and in the end I wasn't really charging much of anything.

I went with the Genasun GV-4 (http://www.genasun.com/gv-4.shtml) on Maine Sail's reccomendation (I beleive he actually has a genasun, not a morningstar on his boat), partly because I don't have enough room to install a large panel so I needed to get all the juice I could out of what I have (12w), and the MPPT gives me a nice boost in the mornings.

I checked on everything a couple days after hooking it up, and found the batteries were sitting at float stage and the hydrometer was indicating full charge. Every time I have checked the batteries since installing the GV-4, they are sitting at float stage and fully charged within a day or two of getting back at the docks from going out for the weekend, and no matter what I seem to do power wise at the dock they are always recharged the next day (and no, I don't have a shore power chargeing system).

In short, the sunforce is half worthless and get rid of it, replace it with a good controller and you will be very happy with the decision.

I am glad that worked out for you!! Never did read the final result but I know how poor performing those Sunfoce units are. Just spent a few hours working on a Sabre 34 with a Sunforce and the boat has been on the mooring for two weeks with two group 27's and a group 24 starter. She has a 50W polycrystalline panel. The batteries are at 84% SOC...... Enough Said.. I have seen this time and time again with the Sunforce shunter and some other cheap controllers.

The Genasun MPPT controllers are the only controllers specifically designed for small panels and they work wonders.. The big guys, Blue Sky & Morningstar don't work nearly as well without voltages into the 20's... I normally don't install a Blue Sky or Morningstar MPPT until I get to over 180 watts of panel.

timebandit · Aug 9, 2011

I think this explains why the on and off chargers don't work well.

I learned a lot from this, thanks MS.

http://www.pbase.com/mainecruising/battery_state_of_charge

walt · Aug 10, 2011

Doehunter, you can hook up the panels either way.. seems simpler just to go with a single controller.

I don’t think the point here was that "on/off" charge controllers don’t work well. The point was that the Sunforce controller doesn’t work well. It does what it claims - keep the panel from overcharging the battery.. I would bet that design is at least 20 years old and they just keep cranking it out..

It’s not the method of how a controller switches (shunt or PWM), it’s the algorithm used - ie, when the controller choses to charge or not charge. The Sunforce uses a poor/ obsolete algorithm. I’ve been using the Morningstar Sunsaver PWM controllers with small panels - been completely happy with them (but never measured batteries with the hydrometer - I do have a charge monitor however). The Morningstar sunsavers give you some additional options at fairly low cost. The one I have has a light control output that I can program to turn on a 12 volt output depending on day and night (it uses the panel to tell when it is day and night) – cost about $55 for 10 amp model. I use this to run some anchoring lights on a mooring. They have another model which will independently charge two batteries from one panel. Prices range from $40 to $60, I think the two battery model is about $80.

The GV-4 is pretty slick - no extra features but its MPPT so gives about an extra 10 to 20% charge compared to the Morningstar sunsavers (assuming the charging algorithms are comparable – I think a reasonable assumption). This looks like a good option for trailerable sailboats.. Pay a little more - just over $100.

Sumner · Aug 10, 2011

doehunter said:
I have a 50 watt panel mounted permanent.
I have a 2nd that could be used as a spare, or a secondary.
Is it better to get a controller sized for the 50 watt and another one for the spare, or get set up for the pair of them even though I might not hardly ever use the secondary panel?

Get one that will take some expansion. One thing you need to watch is that if You go with an MPPT charge controller you can have multiple panels, but to get the best use from the charge controller the best thing is if all the panels are the same.

The next best thing is that they have the same voltage and hopefully are made with the same type of cells. I talked to a tech at Blue Sky yesterday about the panels we have on the Mac as they are a 40, a 60 and now a 100. They all have the same working voltage, which is called Vmp, of 17.2 volts and are of the same cell type, Q cells.

He said that we were fine and that the MPPT contoller would still give us better performance over a PWM controller. If you are buying a panel the seller should have the panels specs. The other important one to look at is the Isc which is the short circuit current in amps. Add up the Isc amps for the panels you have or that you are getting and then look and see if the charge controller can handle that many amps.

The last thing is that since the MPPT can manipulate the current you need to look at the Imp for the panel/panels. That is the maximum power current in amps generated by the panel. Add that up for the panel/panels and and it should be no more than 70% of the output amperage of the charge controller. For instance I'm using a Blue Sky 2512iX that is rated at 25 amps. It will output up to 25 amps. So 25 amps X .7 is 17.5 amps. I want to make sure that the panels I'm using don't have a combined amperage output over 17.5 or I'll just be wasting that which is over the 17.5 as the controller will limit it to 25 amps when it reaches that.

It all sounds kind of complicated, but if I can help someone I'll be glad to. The controller MS recommended looks like a good one, but if you plan on adding on to your array in the future you might want to spend a little more money now for a controller that has more capacity,

Sum

Our Endeavour 37

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walt · Aug 10, 2011

best use from the charge controller the best thing is if all the panels are the same.

Sumner, yup for the MPPT controller since the maximum power point can be different for different panels and the MPPT controller is continually searching for the maximum power point. If all panels are identical, it will find the optimum.

But for the PWM controllers (such as the morningstar sunsavers), the currents from the different panels simply add together. You can mix panels sizes all you want - no problem, no tradeoff.

MPPT controllers are also more sensitive to wire runs between the charge controller and panel. The "heat issue" with panels also mostly applies to MPPT controllers since the panel voltage is much more sensitive to temperature compared to panel current.

Sumner · Aug 10, 2011

walt said:
...Sumner, yup for the MPPT controller since the maximum power point can be different for different panels and the MPPT controller is continually searching for the maximum power point. If all panels are identical, it will find the optimum. .....

The tech said that if you had one panel that puts out 16 volts and another 17 and another 19 volts then the voltages will average and you will be wasting the potential output of the panels above the average. If I understood him right.

The thing that has been/was hard for me to understand is that with the MPPT controller it actually manipulates the current and can make it higher than the panels output amperage. The PWM is stuck with just passing on the panels amperage to the battery. That is a big benefit when the battery is low like in our situation cruising on a day to day basis where the battery ends up low in the morning and and needs to be re-charged each day.

If someone goes out for 1-3 days and the battery goes low and then they come in and the boat sits to the next weekend the PWM charger is going to do a good job of having the battery ready to go the next weekend,

Sum

Our Endeavour 37

Our Trips to Utah, Idaho, Canada, Florida

Our MacGregor S Pages

Mac-Venture Links

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