example most 30amp controllers are listed at 390w of panelsand 40amp controllers at 500w of panelsbut we don't charge batteries at 12.0v we charge at 14v or higher14v*30 amps 420w output, going to need more than that input40a*14v 560w output to batteries, controller must handle at 600w input500w with 17.5 actual output 12v nominal panels only equals 28.57 amps into and thru Controller NOT 40 ampsso will these controllers really handle the rated amps ? which means a much larger array than the stated maxor are they just blowing smoke..uykw30 amp ? 390/17.5v = 22.28 amps max from the arrayso what is it really a 25amp controller ?30amps charge at 14v =420watts out , 17.5 * 30 = 525 inputyou need 525w panels to get 30amps out at 14.0vthis of course does not included mpppt panels although the same mfg/sellers are doing the same thing playing loose with the words

It might have to do with the 1.25 NEC thing.390w would have about 390/130 x 8.2 = 24.6 amps aimed at high sun with PWM and batt v under 13.5v. IV curve says a little less amps above 13.5v till the big drop at 15v.So if you expected 25 amps you should get a controller rated for 1.25 x 25 = 31.25My Solar30 doesn't seem to give the panel watt limit. It says panel voltage limit is 48V and the "rated working current" is 30 ampsMy MPPT 20 amp Eco-Worthy says its Voc limit is 42 or 45 volts (EDIT now they say 50v on their website specs!! Means it can do two 12s in series.) depending which list you read, and its max panel wattage is 300w-12v or 600w-24v.300/130 x 8.2 = 19 amps so that doesn't work for the 1.25 margin, but it is MPPT and might therefore clip its amps so the margin is not required. I know it has a 25 amp fuse on its circuit board so that would be one limit! (had to change that when I made some sparks one time)There was something funny that came up about the Blue Sky controllers having an operating amps less than the named size of the controller in their owner's manual. Can't remember the details.

similar game when inverter and generators list VA not watts.

Transformers are listed in volt amps and that is a certified measurement for inductive devicesAnd slightly off topicWhat I'm saying is they give tWo numbers, and they conflict with each other, you can't get the stated output, if you abide by the stated input

390w / 13.2v = 29.54abulk charging begins in the low 13's and rises... but in the meantime...

Do you know of any solar controller advertising a bulk charge of 13.2vEveryone I look at is 13.8 Or higher, many say 14.1vDrain two 12v batteries in parallelConnect each one to a controllerOne set at 13.2. One set at 14vWhich one it's going to take more amps?If it's a 30 amp.controller,It should handle 30 amps in and out aka thru putIt's not a 30 amp controller if it's limited to 22.xxx amps inputThe Blue Sky 2000e would clip the amps it would put out 25.12I recorded this number many times, it was never a continuous output, but when the 505w worth of panels did their thing the controller did too

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

59 Replies

pianotuna
Nomad III
Jun 27, 2015
Hi Mr Wizard,

I prefer discreet devices, too, but 999 for a 3000 watt psw inverter is pretty good and having the ability to do 30 amps of solar is a definite bonus.
Naio
Explorer II
Jun 27, 2015
pianotuna wrote:
This looks interesting--a combo inverter/charger/solar controller.

inverter charger and solar controller It can accept 30 amps on the solar side.

Cool find. Until I saw the $9oo price tag!

Edit: OIC, that is just what 3000 psw's cost.
MrWizard
Moderator
Jun 27, 2015
thats interesting, i don't think its practical for Rvs, at least not for me
AC charge is too low at 25amps,
i prefer discreet devices, easier to replace an item if some function fails
pianotuna
Nomad III
Jun 27, 2015
This looks interesting--a combo inverter/charger/solar controller.

inverter charger and solar controller It can accept 30 amps on the solar side.
time2roll
Nomad
Jun 27, 2015
http://www.morningstarcorp.com/string-calculator/
MrWizard
Moderator
Jun 27, 2015
I don't think of voltage as being a problem with controllers
In most cases your panels in series is easily under the limit or you know it's over, especially with PWM where parallel is the norm, because you want amps not volts
With MPPT you do need to check that your series arrangement is under the controller limit
BFL13
Explorer II
Jun 27, 2015
It is not 1.25 for voltage as such, but you do have to leave margin in your controller's total Voc input limit for when Voc is higher than rated at STC.

You can calculate that from the coefficient in the panel spec for the coldest you expect to be using it.

Mr Wiz--"working amps" with PWM is Isc NOT the lower Imp figure you would use with MPPT. You would see this if you had tracking panels and checked panel Isc (disconnected) with amps to the battery (connected) --same amps amount.
MrWizard
Moderator
Jun 27, 2015
NEC says use a controller with a rating 25% more than your isc..not working amps which is less than Isc
I don't know how the output would ever reach that point
Unless maybe there was a dead short on the output at STC..?
And even then you could not exceed Isc

And morning star says the controller will handle 130% of the rated input and taper the amps
Which means NEC wants you to use 36amps Isc not the panel working amps for a 45amp controller that the MFG says will handle 58 amps input

Now I believe Morning star, I would have no qualms connecting 700w aka 41amps to that controller

But I would have second thoughts about some of these other controllers
The NEC and controller MFG are not using the same play book

There has got to be done middle ground for quality and price point
How long until the market sorts itself out
time2roll
Nomad
Jun 27, 2015
With 41 amps Isc it would appear you need a PWM controller rated 51.25 amps minimum to meet NEC. That probably puts you at a 60 amp controller.

Those panels in series would need just 45 amp MPPT to meet NEC and not clip the amps. Actually if you rarely see 35 amps a 30 amp MPPT might be fine with minimal clipping. Still meets NEC.

There is no 125% applied to voltage that I am aware of.
MrWizard
Moderator
Jun 27, 2015
what is the "Voltage" ?

again this is MPPT which will convert the volts to amps
for increased output
something that DOES NOT happen using PWM

all the cheap controllers are PWM, even the the 'fake' mppt are PWM
there is no 'overhead' conversion to more amps

smkettner wrote:
Yes this is on p8 of the TS MPPT manual:

To comply with the National Electric Code (NEC), the current rating of the controller must be
equal to or greater than 125% of the solar array’s short circuit current output (Isc). Therefore, the
maximum allowable solar array input to the TriStar MPPT 150V controller for compliance with the
NEC is:
TS-MPPT-30: 24 amps Isc*
TS-MPPT-45: 36 amps Isc*
TS-MPPT-60: 48 amps Isc* *Solar array Isc @ STC

My array Isc is about 8 amps and 675 watts. Maybe another reason to go series.

TS MPPT manual