Which MPPT Solar Controller?

[willardj]

Originally Posted by Rhian

I am just about to fit new solar panels, 4 x 135 watt, and am wondering which controller to purchase.

I have been advised to use an MPPT controller as they are more efficient but not sure which one to use. Currently looking at the Bluesky solar boost 3024iL and the Morningstar Tri-star TS-MPPT-45.

We have a 12v system and are wondering if the 40 amp models will be big enough and if anybody has any experience of these 2 models or can recommend any others.

Thanks in advance!

Just starting with the math 4x 135w = 540w / 12v = 45a. So you can see how you will be right at the high end of the limits. but when you add in the loss from the inverter, wire and so forth it should be fine. The Mornstar Tristar 45 and Tristar 60 are great cc's. Midnite has a new Classic lite model out now about the same price as the TS 60 but it is a 96a at 12v.

[colemj]

Originally Posted by willardj

Just starting with the math 4x 135w = 540w / 12v = 45a.

A 12V panel output would be insufficient to charge batteries.

The open circuit voltage on nominal 12V panels is ~17V, so the math would be 540w/17V = ~31amps. The rating for controllers is the input amperage, even though the output may be higher.

The 45A version of any of the controllers listed will be fine. If you plan to ever add panels in the future, get the 60A version.

Mark

[willardj]

Originally Posted by colemj

A 12V panel output would be insufficient to charge batteries.

The open circuit voltage on nominal 12V panels is ~17V, so the math would be 540w/17V = ~31amps. The rating for controllers is the input amperage, even though the output may be higher.

The 45A version of any of the controllers listed will be fine. If you plan to ever add panels in the future, get the 60A version.

Mark

True each batt type have diff charging requirements but you do have to take into account that your batts may get that low and you don't want your cc working at it's limits even if it is for a short period of time. Lead acid 14.6-14.8, sealed 14.1 range, agm's 14.5 range i think.

[colemj]

Originally Posted by willardj

True each batt type have diff charging requirements but you do have to take into account that your batts may get that low and you don't want your cc working at it's limits even if it is for a short period of time. Lead acid 14.6-14.8, sealed 14.1 range, agm's 14.5 range i think.

I don't understand. The panels can only put out ~31amps no matter what state of charge the battery is in. The battery can't "pull" more amps out of them. Even with an MPPT and operating the panels in series in unshaded overhead sun, the panels will not put out close to 45amps. The controller limits are input limits and have no relation to the battery type or its recommended charging voltage. The charge controller will be happy to operate within its specifications for as many hours per day as available to it.

Mark

[jeremiason]

Originally Posted by willardj

True each batt type have diff charging requirements but you do have to take into account that your batts may get that low and you don't want your cc working at it's limits even if it is for a short period of time. Lead acid 14.6-14.8, sealed 14.1 range, agm's 14.5 range i think.

I am not an electrician, but I can read a guage...

Right now my 795 watts of solar panels, run in series are producing about 30 amps of current from the panels to the Blue Sky controller at 36-48 volts.

The output to the batteries is producing 40-42 amps at 13.9 volts.

That is with direct sunlight down here in Panama

[noelex 77]

Originally Posted by jeremiason

I am not an electrician, but I can read a guage...

Right now my 795 watts of solar panels, run in series are producing about 30 amps of current from the panels to the Blue Sky controller at 36-48 volts.

The output to the batteries is producing 40-42 amps at 13.9 volts.

That is with direct sunlight down here in Panama

Be careful of the gauges on MPPT controllers they often exaggerate the gain. If you measure the actual input and output voltages and current they are usually a bit different.
There is always some error in every measurement, but they they almost universally exaggerate the gain.

BTW There is something wrong with the figures 30amps from the panels @ 36-48v is about 1,200w which is not possible from 795w of panels and would give much more than 40-42A @ 13.9v after voltage conversion.

[jeremiason]

Originally Posted by noelex 77

Be careful of the gauges on MPPT controllers they often exaggerate the gain. If you measure the actual input and output voltages and current they are usually a bit different.
There is always some error in every measurement, but they they almost universally exaggerate the gain.

BTW There is something wrong with the figures 30amps from the panels @ 36-48v is about 1,200w which is not possible from 795w of panels and would give much more than 40-42A @ 13.9v after voltage conversion.

The output on the Blue Sky Controller read out is accurate when compared to Xantrex Battery Monitor. When I first set up the panels, they were inputing about 48-52 volts to the controller as read on a voltage meter, I haven't measured since then, because they are working and can only rely on the COntrollers read out to determine Current flow.

OK, like I said I am not a electrical tech, I take your word on the formula... As I said that is what the gauges read... "Solar Panel Current 25" and "Output Charge Current 42".

Just a stupid question though.... aren't solar panels the same as batteries... In series, you half the amps but twice the voltage?

Also a solar guy once told me that mixing sizes of panels will reduce voltage output to the controller drastically.... Due to this I was going to remove the 85 watt panels on the dodger when I added the four 135 watt panels over the bimini.

I experimented with the configuration and disconnected the three 85 watt panels (all three in series) from the controller and ran the 4 - 135 watts panels only (two panels paired each in series)... During this they made about 25-28 amps on their own and 40-43 output to batteries when combined with the 85 watt panels.

The system has been working for over a year now with no problems.

[willardj]

Originally Posted by colemj

I don't understand. The panels can only put out ~31amps no matter what state of charge the battery is in. The battery can't "pull" more amps out of them. Even with an MPPT and operating the panels in series in unshaded overhead sun, the panels will not put out close to 45amps. The controller limits are input limits and have no relation to the battery type or its recommended charging voltage. The charge controller will be happy to operate within its specifications for as many hours per day as available to it.

Mark

Ohm's Law: Amps = Volts / Ohms
Power Formula: Watts = Volts * Amps

Here is how I came up with my #'s. 4x 135w = 540w / 12v = 45a. Ok but I see where you are saying that each panel puts out a bit under 7.75a x 4 = 31a and with a regular pwm cc I would go with that then again with an MPPT controller its different. But first stay with this for a sec. That 8a or so these panels put out is at 19-22v. Now let get back to the mppt. The mppt will take that 135w panel of say 21v and 8a and make 12v (min side) and 11.25a (x's 4 = 45a) by using the extra voltage to make more ampage. (as voltage goes down ampage goes up). Also have to remember that solar puts out more power in the cooler part of the year not the hottest. If I am off my mistake but by the way the math comes out to me and from my 145w 22v @ 7.6a panel that I have gotten 11a out of. I am always up to learn more so help me if I'm wrong.

[noelex 77]

Originally Posted by jeremiason

The output on the Blue Sky Controller read out is accurate when compared to Xantrex Battery Monitor. When I first set up the panels, they were inputing about 48-52 volts to the controller as read on a voltage meter, I haven't measured since then, because they are working and can only rely on the COntrollers read out to determine Current flow.
.

You can measure the input voltage and current quite easily if you want to. Using a multimeter to measure the input voltage and a clamp on multimeter to measure input current is easy. A clamp on multimeter is a great tool to have.

Originally Posted by jeremiason

OK, like I said I am not a electrical tech, I take your word on the formula... As I said that is what the gauges read... "Solar Panel Current 25" and "Output Charge Current 42".

Just a stupid question though.... aren't solar panels the same as batteries... In series, you half the amps but twice the voltage?
.

MPPT regulators convert the voltage, trading volts for amps. Your formula is correct so an input of 10A @ 24v should become an output of 20A @ 12v. This assumes 100% conversion and in practice their will be some loss, but not much.

Using this formula in your previous example of 30A @ 36-48v if this was correct it should become about 90A @13.9v.

30A@36-48v is wrong because it means your panels would be producing 1200w which is not possible. It's probably a simple mistake with the input voltage or current.

[btrayfors]

Tom:

Two batteries in series: double the voltage, keep the same amperage

Two batteries in parallel: double the amperage, keep the same voltage.

Examples:

1. two 225AH T-105 6-volt golf-cart batteries in series = 225AH @ 12VDC

2. two 225AH T-105 6-volt golf-cart batteries in parallel = 450AH @ 6VDC

Since we're talking here about solar panels, the nominal open circuit (OC) voltage of "12V solar panels" is about 17VDC.

So....

Two of them in series = OC voltage of 34VDC

Two of them in parallel = OC voltage of 17VDC

In my experience, some series connection of solar panels is highly desirable, because of better performance in low-light situations, and more effective use of MPPT controllers.

Note than many new large solar panels have 40VDC OC voltage ratings.

Bill

[colemj]

Originally Posted by willardj

Ohm's Law: Amps = Volts / Ohms
Power Formula: Watts = Volts * Amps

Here is how I came up with my #'s. 4x 135w = 540w / 12v = 45a. Ok but I see where you are saying that each panel puts out a bit under 7.75a x 4 = 31a and with a regular pwm cc I would go with that then again with an MPPT controller its different. But first stay with this for a sec. That 8a or so these panels put out is at 19-22v. Now let get back to the mppt. The mppt will take that 135w panel of say 21v and 8a and make 12v (min side) and 11.25a (x's 4 = 45a) by using the extra voltage to make more ampage. (as voltage goes down ampage goes up). Also have to remember that solar puts out more power in the cooler part of the year not the hottest. If I am off my mistake but by the way the math comes out to me and from my 145w 22v @ 7.6a panel that I have gotten 11a out of. I am always up to learn more so help me if I'm wrong.

I don't think I have a problem with your equations or calculations, but with some of the inputs and assumptions. The connected panels will never produce amperage at 12V because the battery voltage is higher than that unless you have a completely dead battery. They will only produce amperage when the voltage goes above that of the batteries and, by the manufacturer's specification, will produce a maximum voltage of ~17V and ~8amps (for the 130W panels). This is usually at a mild temp (~70F), and actual output can increase a bit at colder temps. I think we agree on that.

Now an MPPT controller can convert that extra voltage into output amps at a lower voltage. However, the specification that is important is the INPUT amperage, not the OUTPUT capabilities. The highest amperage input is fixed by the design of the panel and is given in the manufacturer spec. Although that spec can be exceeded for a cooler panel, it is most likely that if your panel is cooler than 70F, then you are probably in a latitude where you won't experience direct overhead sunlight and won't get full output.

Mark

[willardj]

Originally Posted by colemj

I don't think I have a problem with your equations or calculations, but with some of the inputs and assumptions. The connected panels will never produce amperage at 12V because the battery voltage is higher than that unless you have a completely dead battery. They will only produce amperage when the voltage goes above that of the batteries and, by the manufacturer's specification, will produce a maximum voltage of ~17V and ~8amps (for the 130W panels). This is usually at a mild temp (~70F), and actual output can increase a bit at colder temps. I think we agree on that.

Now an MPPT controller can convert that extra voltage into output amps at a lower voltage. However, the specification that is important is the INPUT amperage, not the OUTPUT capabilities. The highest amperage input is fixed by the design of the panel and is given in the manufacturer spec. Although that spec can be exceeded for a cooler panel, it is most likely that if your panel is cooler than 70F, then you are probably in a latitude where you won't experience direct overhead sunlight and won't get full output.

Mark

Ok think I see where you are coming from. Input side. The tristar 45 can handle I think 150v in and would assume 45+ (31a of these panels) amps in but my thing is why would you want to put more in than you could get out? Think the best way to run 4- 135's would be 2 strings series then parallel which would give something like 40v and 16a going in to the cc. If you were moving 40v and 16a thru #10 wire for say 20' to stay under 2%v drop. If they were all parrallel voltage stays low say 19-22v ampage goes up to 31a or so the voltage drop jumps to 7.4% in that same #10 20' piece of wire so wire size would have to increase to #4 which jacks cost up.

[noelex 77]

To solve confusion with solar thinking in terms of watts is always helpful. A panel will rarely put into the battery more than is watt rating would suggest.if you look at some of the numbers you are using in watts it becomes clear that they are unrealistic.

Originally Posted by willardj

. That 8a or so these panels put out is at 19-22v..

8x20.5v=164w (from a 135w panel!)

Originally Posted by willardj

make 12v (min side) and 11.25a (x's 4 = 45a) by using the extra voltage to make more ampage..

11.25A @12v=135w so this is possible under ideal conditions ( which would have to be significantly better than the standard test conditions to make up for losses in the wiring, voltage conversion and controller) but how often are you going to see a boat battery at only 12v with a charge voltage of 11A?. Even so this is just within the specs of the controller.

Originally Posted by willardj

If I am off my mistake but by the way the math comes out to me and from my 145w 22v @ 7.6a panel that I have gotten 11a out of.

11A with a 145w would be 10.2A with a 135w solar panel of the same efficiency. This would be 41A for 4 panels, which is still lower than the controlers 45A limit.

There is nothing in these numbers which indicate the Morginstar 45A controler would not be suitable other than the theoretical case of 8A @ 20.5v which would involve the panel having an output into the batteries ( after the wiring and controler losses) of 164w which is unrealistic or a 135w panel.

[GeoPowers]

You know, I love this forum- it lets me talk "solar geek" to like-minded folks so my wife doesn't have to put up with my jibber-jabber.

[willardj]

Originally Posted by noelex 77

To solve confusion with solar thinking in terms of watts is always helpful. A panel will rarely put into the battery more than is watt rating would suggest.if you look at some of the numbers you are using in watts it becomes clear that they are unrealistic.


8x20.5v=164w (from a 135w panel!)

isc and voc#'s is why the wattage is off.


11.25A @12v=135w so this is possible under ideal conditions ( which would have to be significantly better than the standard test conditions to make up for losses in the wiring, voltage conversion and controller) but how often are you going to see a boat battery at only 12v with a charge voltage of 11A?. Even so this is just within the specs of the controller.

Your right this was about 1030am on a cool day in my field with a batt I ran down good n low. not on my boat but was doable.



11A with a 145w would be 10.2A with a 135w solar panel of the same efficiency. This would be 41A for 4 panels, which is still lower than the controlers 45A limit.

I'm not saying anything bad about that controller if I was going to run those four panels the Tristar 45 would probably be my choice aswell.

There is nothing in these numbers which indicate the Morginstar 45A controler would not be suitable other than the theoretical case of 8A @ 20.5v which would involve the panel having an output into the batteries ( after the wiring and controler losses) of 164w which is unrealistic or a 135w panel.

Agree