Solar Panel Connectors

Remember, if you are adding panels that they should all have similar voltage output.

PT, you must have gone to school and learned the "New Math" or some other weird "progressive education" thing.

25% over 16a is 20a. Show your work! ok. 1/4 of 16 is 4 add 4 to 16 and you get 20. Now 20 is 20% over what? Like the non -progressive education text-books said (before they were banned by NDP union teachers)--"The easy solution is left to the student."

EDIT--Blue Sky manual should be followed of course if that is what you have. MorningStar MPPT says go ahead and run it to the rated amps but if you buy more panels than that, you won't get any more amps to the battery, so don't waste your money. Are you sure it is not the same with Blue Sky MPPT?

Hi BFL13,

The "bad math" 16 amps x 125% = 20 amps.

And the Blue Sky MPPT Manual suggests NOT using more than 80%. I don't want to find out the hard way that they are right.

So my 30 amp controller can only accept 307 watts of panels safely.

Because it is MPPT you can not "think" in amps of input--you have to rate it by the watts.

BFL you are confusing clipping the voltage in pwm with amps in an MPPT unit. I think perhaps?

To think of it another way the 20 amp rating is like a fuse. Go beyond it and the fuse fails.

The reason for the derating is often to allow for cloud lensing effects.

Well I don't agree with PT at all on this, which is weird, but is.

Most/all MPPT controllers are designed to run at their rated amps, same as a PWM controller is, without overheating. But the MPPT controller will "clip" the amps, so if the panels crank out more amps the controller just won't let any more through than it is rated for and will not overheat.

So with those MPPT controllers you can ignore the 20% margin rule. However it does mean if you attach more array so that array will produce more amps than the controller is rated for, it means you wasted some money buying panels, or you need a higher amp controller, but at least you will not damage your under-sized controller.

PT also is having a bad math day, by using 25% instead of 20% margin when he says to use only 16a of 20 instead of 16.67 of 20 for a PWM controller.

Expected max amps of 260w is 260/130 x 8.2= 16.4a, so IMO, to meet the 20% margin rule with PWM with a 20a PWM controller, you can go to 260w of array.

With MPPT clipping the amps at 20, you can have as much array as you feel like, but you will still only get 20a to the battery. At "STC" 25C etc, and allowing for 10% MPPT advantage in amps over PWM, you should get value from an array approx 280w.

Hi,

What BFL13 says is true--for PWM controllers. But it is untrue for MPPT controllers. With them to keep the margin of safty 204 watts is the maximum you can use. I regularly see 17 amps from 256 watts of panels. I have seen 21 amps. My system is MPPT based, with a 30 amp controller.

16 amps is all that the 20 amp controller should be expected to handle. Go over that at your peril. You may let the magic blue smoke out.

One rule of thumb is between 60 and 150 watts of panels per 100 amp-hours of storage. The smaller the battery bank the higher the wattage needed (per 100 amp-hours). Here is a link to the rather special spreadsheet which includes an energy audit, that N8GS has created to help size solar battery charging systems!
Solar Spread Sheet N8GS

For a nice explanation of solar, try this link:
Golden rules of solar

IMO you can use the "20a" controller for the 50w plus two 100s.

A solar panel can at times crank out more amps than it is rated for, which rating is done at standard test conditions including 25C temp. The usual recommendation for controller amps rating and fusing of the pos wire from controller to battery is to have a 20% margin.

A "20amp" controller is designed to run at 20 amps without overheating. To have a 20% margin, the panel should be rated at no more than (1/5 more needed so 20 is 6 parts = 3.33a a part ) 16.67a

You use the rated Isc for normal expected max amps. A 100w panel should be 6.3a approx. Your 50 might be half that 3.1 say. So two 100w plus your 50 could get you 12.6 plus 3.1 = 15.7a which is under 16.67a

pianotuna wrote:
Hi,

You need to derate the controller by 25% i.e. it can only handle 16 amps not 20. so maximum safe wattage is about 204 watts.

Why ?

Hi,

You need to derate the controller by 25% i.e. it can only handle 16 amps not 20. so maximum safe wattage is about 204 watts.

This type connector is commonly used in two way radios and can be found in almost any cb shop or ebay. They are known as SAE DC Power connectors.