why don't Solar controller mfg/sellers use honest ratings

[MrWizard]

example most 30amp controllers are listed at 390w of panels

and 40amp controllers at 500w of panels

but we don't charge batteries at 12.0v we charge at 14v or higher

14v*30 amps 420w output, going to need more than that input

40a*14v 560w output to batteries, controller must handle at 600w input

500w with 17.5 actual output 12v nominal panels only equals 28.57 amps into and thru Controller NOT 40 amps

so will these controllers really handle the rated amps ? which means a much larger array than the stated max

or are they just blowing smoke..uykw

30 amp ? 390/17.5v = 22.28 amps max from the array
so what is it really a 25amp controller ?

30amps charge at 14v =420watts out , 17.5 * 30 = 525 input
you need 525w panels to get 30amps out at 14.0v

this of course does not included mpppt panels although the same mfg/sellers are doing the same thing playing loose with the words

[Empty_Nest__Soo]

I have not looked that much at cheaper controllers, but the lack of a heat sink is one obvious difference. And yes, providing a heat sink at a reasonable cost should be easy. I can’t explain why the market has not offered that.

But how about a Tri-star 45 for $161? http://www.ebay.com/itm/221681616399?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT

Wayne

[MrWizard]

I believe I mentioned several examples of several quality MFG
But 'if' mosfets that handle 25~30 amps can be installed in a $30 controller...
Surely somebody can make something comparable to the $200~$300 controllers for less, and rate it correctly
Looking at the cheap controllers it seems the major thing visibly missing is a quality heat sink
They have no trouble including LCD displays, but they don't include heat sinking fins and current limiting SO you can use enough panels to actually reach the listed output rating
So to find a spare that will handle the 35 amps peak I expect to see someday, (depending on conditions) I'll have to buy one rated at 50 or 60 amps
My Xantrex is a true 40 amp controller, that will handle 60 amp input
A replacement is $200, just may have to go that route, OR maybe a Tracer,

[Empty_Nest__Soo]

It seems to me that this discussion is limited to cheap Chinese-made controllers. As if there are no other choices.

There are solar controllers that will operate at a continuous current equal to (or somewhat greater than) their rated output. Obvious examples are the Bogart SC-2030 and the Morningstar Tri-Star controllers.

But you won’t buy one for $30. That doesn’t mean there are no other choices. Sometimes you get what you pay for.

Wayne

[time2roll]

I don't think NEC regulates any device. Just external connections.
UL or similar lab would approve a device meets specs.

[MrWizard]

Perhaps you are right .. ?

[jrnymn7]

Perhaps it's a bit like comparing a cheapowatt ps to a megawatt or meanwell?

If there's no current limiting protection, then the OP best take care not to go beyond the unit's duty cycle. In fact, many bench power supplies are rated at peak amps, not continuous duty amps. I think it's the megawatt that says right by its connections that it's duty cycle is ~90% of it's rating.

yes, here it is:

S-350-12

In the case of solar charge controllers, perhaps all the mfg would have to add to their literature is "peak" after the amp rating, with an asterisk pointing to a side note regarding the nec compliance of 25%.

[MrWizard]

The reference to applied charge voltage keeps coming into this discussion, with point being batteries charging at 13.x volts not 14v
And that amperage is lower when battery voyage is up
Well !!!
Most of us with solar arrays also have inverters
Some large some small, I have two connected and operating 24/7 and a spare, just in case something happens
Now what do you suppose the output of your solar array is going to be at or near STC when you use that inverter at lunch or brunch
Maybe your camped and the panels are tilted and you just decided to warm up a cup of coffee or makes hot water for soup or tea
Yeah full voltage full amps yield.. Maybe only for a few minutes, and battery voltage will drop but solar input will be max
Do you want 22 amps from your 30 amp controller, are you going to Add another panel to get 30 amps
Maybe you have a 20 amp controller and 200w aka 13 amps, going to buy a 30 amp controller when you add another panel ?, just so you can get 20 amps charge

Yeah I'm flogging the dead horse...I want to get the mental gears turning

We have talked wire size to death and beyond,
But our discussion of controllers has been centered around MPPT vs PWM..
Not quality real world ratings and programming features

[BFL13]

You do need a controller that will handle 30 amps if your array is rated at 24 amps STC.

Mr Wiz says it would be more honest to call that a 24 amp controller. It would be stated in the manual for it that it can do 30 amps for short periods, but it should only be operated at 24 amps continually. Or it could just clip its amps at 24.

In the case of the Solar 30 it does say it can run at 30 amps continually, so it must be able to do more than that for short periods. So if you had an array rated for 24 amps at STC you could run it with a "25" if it was clear that the 25 is 80% of what it can really do.

So for honest ratings, which is more honest for equipment to be named for its "rating"?

A. call it an "80" for its continuous ability, or
B. call it a "100" for what it can really do, and state in its manual it should only be run at 80 continually to comply with the NEC?

What is the real popping amount for a "15a" circuit breaker?

Mr Wiz says "30a worth of panels" but there is no such thing. Panels can do all sorts of amps depending, and are "rated" for one of the situations-STC It is just a WAG to give it a 1.25 margin above STC.

Actually, a 24 amp array at STC could be called "30a worth" so a 30a controller would be a good match.

[MrWizard]

that is true until you have a rainy or overcast morning
that breaks to clear skies later in the day
then the panels climb to max output before getting hot and starting to reduce power output

buying a controller that is amp rated , Not watt limited is what i intend too do

this was a topic i felt deserved discussion

this was not a real concern when controllers were the size and price of
Xantrex, blue sky, morningstar ..etc..

but the Ample supply of smaller ..almost no heat sink .. low priced.. charge controllers has changed the market..especially for the novice shopper/user

and even for the more experienced camper looking to modify or upgrade their solar installation

[NinerBikes]

MrWizard wrote:
you guys think its a safety "derating" tell the consumer to use 3xx max panels
and he can't possibly hit the controller limit

Okay could be ..

BUT ??
other controllers some costing more some about the same
are built with heat sinks and current limiting, and simply clip any over current and pass thru the rated limit..these controllers are truely what they say they are

i dont think a user should have to buy a 45amp controller to control 30amps worth of panels
or a 30amp controller to control 22amps worth of panels

just build it for what it is supposed to do and price it accordingly

I have a 150W solar panel 12v kind. It is rated lsc of 8.8 amps. My RC charge meter has recorded a peak amperage out of that panel of 9.3 amps, on a 65% SOC battery. I'd have no problem putting 2 panels together, but there is no way I'd run the two through my 20 Amp Charge controller that I also use, too close for comfort. I probably would run a pair of 140W panels through the same 20 amp charge controller and not worry of the blue smoke syndrome.

For $33 for a 30 amp charge controller, even if it's 24 amps, derated, go try and build and sell what you want... I am sure there are some high roller RV'ers that will buy bling to show off to their RV buddies. There will also be the low budget travel trailer and camper folks looking to charge cheaply with a value priced charge controller. Pick your price point, and market accordingly.

My thought process it that by the time the sun is at it's 10 AM position, where the panel can make max amps, your batteries are probably at the point where the amp charge rate is dropping off as the voltage increases, if you designed a balanced proper battery pack, solar panel and charge controller system that is properly designed and integrated. That, in essence, lets the marketing people able to cheat a bit on the ratings, most of the recharging is done when the panels aren't aimed directly at the sun, so the panels aren't maxing out until later in the day... at that point the charging rate of the batteries is lower, they are chemically reducing the amount of amps accepted at that point and state of charge.

[time2roll]

So just buy a controller without the strict panel wattage limit.
Read the entire manual before you click and buy.
Don't rely on the quick specifications sheet or marketing materials.
Usually I drop out of the discussion when the primary specification is the price.

[MrWizard]

you guys think its a safety "derating" tell the consumer to use 3xx max panels
and he can't possibly hit the controller limit

Okay could be ..

BUT ??
other controllers some costing more some about the same
are built with heat sinks and current limiting, and simply clip any over current and pass thru the rated limit..these controllers are truely what they say they are

i dont think a user should have to buy a 45amp controller to control 30amps worth of panels
or a 30amp controller to control 22amps worth of panels

just build it for what it is supposed to do and price it accordingly

[BFL13]

This is a typical part in the various solar panel manuals I have seen:

"Under certain conditions, a module may produce
more current or voltage than under its Standard Test
Condition's rated power. As a result, a module’s
open-circuit voltage and short-circuit current under
STC should be multiplied by 1.25 when determining
component voltage ratings, conductor ampacities,
overcurrent device ratings, and the**** size of controls***
connected to the PV output."

(***s added by me) From 3.0 here:

http://www.canadiansolar.com/down/en/Installation_Manual_of_Standard_Solar_Modules%20(UL)_en.pdf

[jrnymn7]

o.k., now I see where you're coming from, thank you! And yes, my brain was still in "mppt mode" when I said 390w /13v = 30a pwm. 😞

------------------

I don't think it wise to discount the possibility that a set of new panels may very well outperform their rated wattage. And other than maybe JiminDenver, the CL Solar King, most folks buy new panels to go along with their new controller purchase, especially when building a new system. So I think it may be quite responsible, on the mfg's part, to adopt a 'better safe than sorry' approach to rating controller wattage limits.

Here are some 135w poly's from 2solar:

• Maximum Power at STC(Pmax): 135Wp

• Maximum Power Voltage(Vmp): 18.12V

• Maximum Power Current(Imp): 7.45A

• Open-circuit Voltage (Voc): 21.80V

• Short-circuit Current (Isc): 7.97A

• Cell Efficiency (%): 15.72

• Module Efficiency (%): 13.61

• Temperature coefficients of Pmax: -0.47%/?

• Temperature coefficients of Voc: -0.38%/?

• Temperature coefficients of Isc: +0.04%/?

• Operating Temperature(?): -40?~+85?

• Nominal operating cell temperature (NOCT): 47±2?



130/135 = .96 x 7.97 (Isc) = 7.67 + 7% = 8.2a x 3 = 24.6a

24.6a + 25% = 30.75a

So I think maybe they have already factored in the nec allowance, as others have suggested? This would certainly be the responsible thing to do, I think. And if an OP has chosen to push 30a thru a 30a pwm, then they are in the wrong, not the manufacturer. And if by pure chance, the mfg got it right by accident, well, I'd consider that a happy accident.

And it in no way violates what is taught on this forum, as in when someone points out to a newbie such as myself, that I need to allow for that extra 25%. In my case, I allowed for even more by going 280w thru a 30a pwm. And I'm glad I did, seeing as I've seen over 18a out of the two 140's... 18a + 25% = 22.5a. If I had gone with a 20a controller, I'd likely have fried it the first season.

I was often told I would likely not see 280w... and I didn't, I saw 300w. 😉

[BFL13]

The 30 amp controller can handle 30 amps. You need that ability when your panel can do 24 amps at STC so you can have the margin for when the panel does more than its ratings.

24 x 1.25 = 30 The panel and the controller are a "system" If you had enough panel to do 30 amps you would need a 30 x 1.25 = 37.5 so a 40 amp controller.

With PWM, you get panel Isc not Imp which has no meaning with PWM.

A 130w panel could have an Isc of 8.2 like my Sharp but some have more and some less Isc per watt at STC.