Tell me why!

[Mirage Gecko]

Recently posted about wiring up my 2 new 200 Watt panels and got that bit sorted.
So started looking to upgrade my charge controller and research I find tells me I will need a 40 amp controller as a 30 seems good to only about 380w.No problem but there does not seem to be many available to me that cost less than the panels so I read the blurb on the 30s a bit deeper to see if I should chance it and find that if I hook up the panels in series for 24 V then the 30 A controller is good for about 760W.
Why would I spend substantially more money on a 40 at 12v as opposed to bigger range of controllers at much reduced price if I hook up in series.
What is the catch here?
Chris

[noelex 77]

The 760w is assuming you have 24v in and out. You will have 24v in and 12v out. The 30A limit applies to the output. With a 12v battery system and 400w you are unlikely to get 30A often,but it will occasionally happen.

MOST solar controllers will self limit to protect themselves from excess current. If yours does this using your existing controller, while not ideal, is OK, (considering you have nothing else to buy) but check the inbuilt current protection with the manufacturer (or it might say in the handbook).

Edit:
I reread your post and I think I misunderstood. If you do not already have a 30A controller I would buy a larger model. Relying on the controllers self protection mechanism is not ideal especially for a boat where ventilation etc is not always great. You can use 2x20A models as an option.

[Mirage Gecko]

Thanks Noelex
On the boat already is an old PWM that I am unsure of specs .I know this sounds vague but it has been mounted in one of the engine bays and needs quite a bit of surgery to get it and the wiring etc out.
I am OK to buy a new 30 Mppt and have a good range in price and quality to choose from.However the 40s seem limited and out of step in price in comparison the only exception being some of the Chinese models that appear to be suspect if their spec sheets are anything to go by.
Chris
Edit
Just found a 40(Tracer) that is within $ reality so will possibly go this way.

[colemj]

Wait a minute.

First, 400W of nominal 12V panels should be fine on a 30A controller. It will be close to the maximum for the controller, but not exceed it.

Second, I have doubts that your 200W panels are nominal 12V panels. If they are higher voltage like I suspect, you cannot use a PWM controller on them, so your existing controller, as well as the Trace 40 you are considering, will not work. You will need a MPPT controller for these.

Mark

[noelex 77]

Originally Posted by colemj

Wait a minute.

First, 400W of nominal 12V panels should be fine on a 30A controller. It will be close to the maximum for the controller, but not exceed it.

If you look at the specifications for solar controllers they will general have a "recommended maximum solar array size" for 30A controllers this will be below 400w.

This is 760w @ 24v Mirage Geko was referring to. For the same 30A controller on a 12v system it will probably be 380w. So if you use it a 400w array you are exceeding the manufacturers specifications.

A 400w array will certainly produce 30A+ into the batteries under the right conditions but these instances will be rare. Most (but not all) controllers will cut back the current to self protect themselves if the 30A is exceeded. The loss in total output will be very small, but it does create some problems and I would not generally recommend this approach.

There are several problems:

• You are relying on the self protection mechanism
  
  
• If you read the detailed specification the maximum current (30A) is temperature dependent. It is sometimes quoted at 20°C ! At times of maximum solar output the temperature is likely to be high. Where the controller is mounted temperatures can be very high.
  
  
• The self protection mechanism is not sophisticated enough to derate the current based on temperature.
  
  
  So for a reasonable life of the controller at least stick to manufacturers recomended maximium solar array size. A bit of leeway is good idea.
  

[colemj]

Originally Posted by noelex 77

If you look at the specifications for solar controllers they will general have a "recommended maximum solar array size" for 30A controllers this will be below 400w.

The Blue Sky 30A MPPT controller states 400W maximum array, the Victron 30A MPPT states 440W and the Morningstar 30A MMPT states 400W.

There will not be any problem running a 400W array on a 30A controller, and it will not be running in self-protection mode. Yes, leeway is good - if only for future expansion possibilities - but in this case, the OP's array fits fine into the manufacturer's specs and recommendations.

Stating the Wattage and Voltage relationship in different values does not change anything.

Mark

[Mirage Gecko]

Originally Posted by colemj

Wait a minute.

First, 400W of nominal 12V panels should be fine on a 30A controller. It will be close to the maximum for the controller, but not exceed it.

Second, I have doubts that your 200W panels are nominal 12V panels. If they are higher voltage like I suspect, you cannot use a PWM controller on them, so your existing controller, as well as the Trace 40 you are considering, will not work. You will need a MPPT controller for these.

Mark

Mark
Are you suggesting this is not an MPPT

40A MPPT Solar Charge Controller Regulator Tracer MAX PV 100V Input W Meter MT 5 | eBay
Chris

[irwin37]

Please note solar panel output ratings are tested at 68 Deg with exposure to one sun. Thats the equivalent of noon on the equator with the sun directly overhead (1000 watts per meter squared).

It would be very rare for a panel to produce rated output, but it does happen. It can actually produce more then rated output under curtain conditions but again I would not count on it.

30 amps at 13.5 volts is 405 watts so a 30 amp charger should work fine but will limit future expansion. An mppt controller is not required if your panels have a max power voltage of 17.5 volts or less. A pwm controller will work but you will not get full power potential, the panel voltage will be pulled down to near battery voltage. ( IE panel rated at 200 watts with max power voltage of 17.6 and max current of 11.4 amps will only put out 154 watts at 13.5 volts) With a good mppt controller (beware of cheep Chinese mppt controllers) you will get 14.8 amps at rated output, again not likely.

Have I totally confused you yet?

John

[Mirage Gecko]

No John you have not confused me yet but I freely admit I need to re read some posts a number of times before I get it.I have a logistics back ground so tend to try to find simple solutions to complex issues.
However I am continually surprised by opinions that should be facts if people know what they are talking about but not for one minute suggesting this about your comments.
Colemj you have an answer to my question on the Tracer?
Chris

[colemj]

Originally Posted by Mirage Gecko

Mark
Are you suggesting this is not an MPPT

40A MPPT Solar Charge Controller Regulator Tracer MAX PV 100V Input W Meter MT 5 | eBay
Chris

Oops, my fault. I read your post as "TRACE 40" - the Trace 40 PWM controller is one of the most popular and regarded PWM controllers out there.

Now I see you were listing a "TRACER 40", which I know nothing about.

Mark

[colemj]

Originally Posted by Mirage Gecko

However I am continually surprised by opinions that should be facts if people know what they are talking about but not for one minute suggesting this about your comments.

As for my post above saying you will be OK with a 30A controller, that was based on actual manufacturer recommendations for the three I listed - not my opinion.

It is also not opinion that a MPPT controller must be used with panels producing >17-20V.

Mark

[noelex 77]

Originally Posted by colemj

It is also not opinion that a MPPT controller must be used with panels producing >17-20V.

Mark

Just be careful when looking at the specifications. The Voc of "nominal 12v" panels will be around 20-22v (Kyocera panels are often 22.1v) these sort of voltages are OK with a non MPPT controller.

A good way is count the number of cells. "12v" panels will have 36 cells.