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Old 20-03-2018, 17:41   #1
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Which Controller

I have four 50 watt panels wired in Serial on my boat. I need a controller but have had very mixed recommendations from two different manufacturers. One wants to sell me a 100/35 MPPT controller and the other a 100/15 MPPT. There is a major price difference. Which is correct and why?

The panels specs are :.
4 panels Wired in serial
Optimal power [Pmax]: 50W
Working voltage [Vmp]: 18V
Working current [Imp]: 2.7A
Short-circuit current [Isc]: 2.9A
Open-circuit voltage [Voc]: 20V
Dimensions: 570*540*2.5mm/22*21*0.09inch
Air resistance: 50psf (2400 pascals)
Snow resistance: 113psf (5400 pascals)
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Old 20-03-2018, 17:48   #2
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Re: Which Controller

If you wired your panels in "series" as you say, and not in parallel, then you have created a 48V 50W panel bank, which requires a quite small controller. The 100/15 is more than adequate.

Because you have a Tartan 37, I would imagine that you do not have a 48V battery system. This means that you should wire your panels in "Parallel," creating a 12V 200W panel bank. This would require a 12V 15A controller of your choice.
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Old 21-03-2018, 04:38   #3
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Re: Which Controller

I have been told by the manufacture of the panels and a number of others have suggested Series as the output is a combination of Voltage and wattage. If wattage goes up twofold and voltage down by half then the result is the same. The advantage is because the controller has a input voltage threshold and in lower light (sunrise and sunset) the controller will start operation earlier and thus increase daily total output. (This is my understanding of this and why I was considering Series connection - I may be wrong)
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Old 21-03-2018, 04:46   #4
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Re: Which Controller

The 100/15 is adequate for your setup.

18x4=72 volts (less than 100)

2.9x4=11.6 amps (less than 15 amps)
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Old 21-03-2018, 04:58   #5
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Re: Which Controller

Using your panels in series only multiplies the voltage. It DOES NOT multiply your Watts/Amps.

MPPT controllers are not magic boxes that can somehow make solar panels capable of more output than their rating. They are more efficient than PWM regulators, will not somehow convert your 48V 50W panel bank into a powerhouse solar charging set-up.

The MPPT controller uses the excess voltage to create efficiencies where the PWM wastes the excess voltage.

But WATTS are WATTS. In series your solar bank cannot produce more than 50W per hour. In parallel your solar bank can put in up to 200W per hour.
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Old 21-03-2018, 05:03   #6
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Re: Which Controller

So am I to understand that in Series I am losing power and that I would be better of wiring in Parallel and using a larger controller? What size controller would I need in that case? I am also confused in what the sizing means
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Old 21-03-2018, 05:21   #7
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Re: Which Controller

Quote:
Originally Posted by SailsWithFists View Post
Using your panels in series only multiplies the voltage. It DOES NOT multiply your Watts/Amps.

MPPT controllers are not magic boxes that can somehow make solar panels capable of more output than their rating. They are more efficient than PWM regulators, will not somehow convert your 48V 50W panel bank into a powerhouse solar charging set-up.

The MPPT controller uses the excess voltage to create efficiencies where the PWM wastes the excess voltage.

But WATTS are WATTS. In series your solar bank cannot produce more than 50W per hour. In parallel your solar bank can put in up to 200W per hour.


The victron MPPT controller lists the amps as max, either from the PV array or to the battery. So those four panels tied together will still create 200 watts. And 200 watts at 12 volts is just over 15 amps (16.6). However you’re not charging at 12 volts, nor will all 4 panels be operating in optimal conditions.

So as pertains to the original question the 100/15 will be just fine.

But if you really want to play it safe, upgrade the controller.
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Old 21-03-2018, 05:42   #8
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Re: Which Controller

So does Parallel or Serial make a difference to the resulting charging capability?
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Old 21-03-2018, 06:05   #9
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Re: Which Controller

Quote:
Originally Posted by Steve O View Post
So am I to understand that in Series I am losing power and that I would be better of wiring in Parallel and using a larger controller? What size controller would I need in that case? I am also confused in what the sizing means
By putting your panels in series, you will not be able to produce more than 50W @ 72VDC. You have a 12VDC system, so the controller will reduce the voltage to 14.1V (Gel) 14.5V (AGM) or 14.6V (flooded) and provide a maximum of 50W.

In parallel, your solar panel bank is capable of 200W @ 18VDC (11.6A @ 14.6VDC regulated), so you can use any 12/24V regulator with a 15A rating.



Quote:
Originally Posted by Sailmonkey View Post
The victron MPPT controller lists the amps as max, either from the PV array or to the battery. So those four panels tied together will still create 200 watts. And 200 watts at 12 volts is just over 15 amps (16.6). However you’re not charging at 12 volts, nor will all 4 panels be operating in optimal conditions.

So as pertains to the original question the 100/15 will be just fine.

But if you really want to play it safe, upgrade the controller.
No. The Victron is listing the maximum Volts and Amps it can control. It absolutely cannot make a 48V 50W panel array produce 200W.

I even called Victron to confirm, and they assured me they do not sell magic beans that can defy the laws of physics.
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Old 21-03-2018, 06:33   #10
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Re: Which Controller

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Originally Posted by SailsWithFists View Post
By putting your panels in series, you will not be able to produce more than 50W @ 72VDC. You have a 12VDC system, so the controller will reduce the voltage to 14.1V (Gel) 14.5V (AGM) or 14.6V (flooded) and provide a maximum of 50W.

In parallel, your solar panel bank is capable of 200W @ 18VDC (11.6A @ 14.6VDC regulated), so you can use any 12/24V regulator with a 15A rating.





No. The Victron is listing the maximum Volts and Amps it can control. It absolutely cannot make a 48V 50W panel array produce 200W.

I even called Victron to confirm, and they assured me they do not sell magic beans that can defy the laws of physics.


You’re incorrect in your understanding. Check out ohms law.

Bring voltS down and amps go up. No magic just math.
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Old 21-03-2018, 06:50   #11
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Re: Which Controller

Quote:
Originally Posted by SailsWithFists View Post
By putting your panels in series, you will not be able to produce more than 50W @ 72VDC. You have a 12VDC system, so the controller will reduce the voltage to 14.1V (Gel) 14.5V (AGM) or 14.6V (flooded) and provide a maximum of 50W.
No, it will provide a maximum of 200W! 2.7A * 72V = ~200W.

Quote:
Originally Posted by SailsWithFists View Post
In parallel, your solar panel bank is capable of 200W @ 18VDC (11.6A @ 14.6VDC regulated), so you can use any 12/24V regulator with a 15A rating.





No. The Victron is listing the maximum Volts and Amps it can control. It absolutely cannot make a 48V 50W panel array produce 200W.

I even called Victron to confirm, and they assured me they do not sell magic beans that can defy the laws of physics.
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Old 21-03-2018, 07:09   #12
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Re: Which Controller

Quote:
Originally Posted by Steve O View Post
I have four 50 watt panels wired in Serial on my boat. I need a controller but have had very mixed recommendations from two different manufacturers. One wants to sell me a 100/35 MPPT controller and the other a 100/15 MPPT. There is a major price difference. Which is correct and why?

The panels specs are :.
4 panels Wired in serial
Working voltage [Vmp]: 18V
Working current [Imp]: 2.7A
For serial: 4*18 = 72V (2.7A)
For parallel: 4*2.7 = 10.8A (18V)

Unless you plan to cool the panels with dry ice and ensure a perfect angle to the Sun, the <100$ 75/15 will serve you perfectly well. If you happen to try the science experiment, get the 100/15 or put the panels in a mixed series-parallel array.
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Old 21-03-2018, 07:24   #13
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Re: Which Controller

I stand corrected!

I finally spoke to the right person at Victron.

The MPPT controller internally converts excess Volts into usable power. Even though the panels wired in series have a maximum of 72VDC @ 2.9A input into the controller, the MPPT internally strips the excess voltage above the charging voltage requirement and spools it into usable power (something I did not know.) Whereas other regulators take excess voltage and shunt it away in various ways as a loss.

Steve O. - wiring in series, and using the MPPT controller allows for shadows/low light charging because the spooled excess voltage is then used to push up the charging voltage as necessary for given conditions. In series, your maximum current is still less than 15A, so the smaller controller will work fine. However, you will not be able to add much more to the system later if you so desire.

I learned something new already today.
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Old 21-03-2018, 07:36   #14
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Re: Which Controller

I would recommend something that has to this point not been put forward.
If you are set on an mppt controller I would recommend actually wire your panels in two banks of series . Giving you two 24v nom. 50 watt panel combinations. Doing three things. first increasing the efficiency of the panels. Second this setup will protect from power losses due to shading. Third it will give you controller redundancy in the event of loss of a controller ( you can wire both sets thru a single controller in series/ parallel )
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Old 21-03-2018, 08:23   #15
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Re: Which Controller

Quote:
Originally Posted by Sailmonkey View Post
The 100/15 is adequate for your setup.

18x4=72 volts (less than 100)

2.9x4=11.6 amps (less than 15 amps)
Wow, some serious miss-conceptions, but the right answer.

Quote:
If you wired your panels in "series" as you say, and not in parallel, then you have created a 48V 50W panel bank, which requires a quite small controller. The 100/15 is more than adequate.

Because you have a Tartan 37, I would imagine that you do not have a 48V battery system. This means that you should wire your panels in "Parallel," creating a 12V 200W panel bank. This would require a 12V 15A controller of your choice.

Some more wrong answers with the right choice.

Lets sort it out:

The controller has some data and some meaning of it.

The 100/15 means the controller has an Voltage INPUT limit of 100V and has an current output limit of 15A.

you have 4 x 50W panels. No mater how you contact them / series / parallel or mixed 2s2p or 2p2s - you always have 200Wp

to the resulting output: we assume an empty battery in bulk charge with a battery voltage of 12V. The maximum wattage on solar would be 12V x 15A = 180W, it is close to the 200W and usually a controller has a over-current protection, it is also unlikely you hit the Wp on all panels in your set up. This power is generated by cold panels (25°C), no clouds at noon with 90° angle to the panels. In reality this never happens. when the voltage rises and the battery is fuller - lets say 14V - the controller can provide 210W (14V x 15A)

So safe there - no issues.

Next one Voltage. When deciding if the Voltage is sufficient you use the Voc for the calculation (the worst case), so 4 * 20V = 80V < 100V - this is OK, enough room.

So yes, it will work in series and it will run to the limits in a 12V setup.
in a 24V battery setup it would even work better (then you could connect up to 360Wp and with 48V up to 720Wp)


A mixed config 2s/2p or 2p2S: only the incoming voltage drops to 40V, the input current doubles from 2.7A to 5.4A, the output current and the power remains the same, but you will have some advantages on shading.

A parallel setup would increase the incoming current to 10.8A and drop the incoming voltage to 18V (mp) -20V (oc), the charging current will be still the same, but you will be most resilient towards shading, also the effect of the weakest panel will not drag down the total performance, because each panel provides the maximum possible output at all times and does not rely on the troughput through the chain of the other panels.

3V above battery voltage is the starting point where MPPT has advantages over PWM, so even in a parallel config you will be slightly better than a PWM controller.
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