Author Topic: Solar panel max input voltage for a mppt controller  (Read 2645 times)

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fabieville

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Solar panel max input voltage for a mppt controller
« on: August 11, 2016, 11:18:50 PM »
I am thinking of buying a epsolar mppt controller that supports a 150v maximum input solar voltage. I have (4) 250watt 24v panels with a open circuit voltage of 38v. What I am planning to do is wire all 4 panels in series so that the voltage coming down to the controller will be 152v.

Will the controller still be able to handle that high voltage input which has surpass its max rating by just a meager 2v?

will that 2v or maybe a 3v increase cause any damage to the controller?

Or would the controller would not see the max voltage coming down due to the fact that the battery would be always connected to the controller first which would therefore create a load on the panels and when you check the input voltage it would always drop from the 152v?

In regards to the last question with the battery been connected to the controller first, even when the battery is fully charged the input voltage coming down from the solar panels would rise back to the max or the battery would still create a resistance on the controller so you would never be able to see the 152v coming down from the solar panel while the battery is connected?

Here is a link to it:
http://www.ebay.com/itm/4215BN-EP-Tracer-40A-12V-24V-MPPT-Solar-charger-Controller-regulator-with-MT50-/112008515395?var=&hash=item1a143a4f43:m:mFKPjQdC8AfEqgubMCjk83Q

« Last Edit: August 11, 2016, 11:24:21 PM by fabieville »

DamonHD

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Re: Solar panel max input voltage for a mppt controller
« Reply #1 on: August 11, 2016, 11:26:21 PM »
In cold weather the Voc of the panels will be even higher.  I'd say don't do it.

Rgds

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clockmanFRA

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Re: Solar panel max input voltage for a mppt controller
« Reply #2 on: August 12, 2016, 02:56:44 AM »
Some years ago I investigated the early Tristar MPPT's controllers, they had a voltage limit of 150v.

A few friends had matched their panels to that 150v, however in the Winter months on bright sunny days, the early Tristar MPPT's went PHUT!.

After discussion, and a bit of thought I now use the VOC of the panels at Max 130v, and this gives a bit of leeway with the Tristar's.

I fit the Midnite Classic 200, which as it says can handle 200v, and Midnite has also added a safety margin built in.

Recently with a lot of controllers being made in China, are they really MPPT.?
Everything is possible, just give me time.

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OperaHouse

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Re: Solar panel max input voltage for a mppt controller
« Reply #3 on: August 12, 2016, 09:03:31 PM »
There is a video on the insides at  https://www.youtube.com/watch?v=iWxM7KhmGM4  Not in English but a good teardown of internals.  Appears to be the same as the Renogy Commander. Capacitors will be the weak link in this.  Advise not going over 100V.  Two inductors in series and potted  Hard to tell, but gut feeling is going over 20A is pushing it for long term usage.  Heat sinks on the front appear to be mostly cosmetic.  Heat is sent directly to the back plate AND THE CAPACITORS! Appear to be versions of this that had a plastic cover instead. I would mount it on standoffs to get air circulation behind.  Just a very quick assessment.

OperaHouse

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Re: Solar panel max input voltage for a mppt controller
« Reply #4 on: August 13, 2016, 09:48:38 AM »
At the heart of every MPPT controller is a PWM one.  In simplistic terms, the capacitors store the power of the solar panel to be used later.  As an example, the panel can produce 10A all the time.  With a 50% duty cycle as an example, the FET switches on taking 10A from the panel and 10A from the capacitor bank.  That makes 20A.  When the FET is switched off, the 10A from the panel recharges the capacitor bank.  The inductor also stores energy, but acts to change high voltage low current to low voltage higher current.  Should the capacitor bank lose it's capacity to store a charge, the controller basically becomes a PWM controller.  If the capacitor doesn't short out or explode, you may not even notice the change.

A capacitor rating is more than volts and capacitance.  Like a resistor it has the ability to handle so much current.  It is interesting that people put monster cables on a controller and inside the capacitors have #20 leads.  A capacitor will have a temperature rating, say 85C.  That does not mean the capacitor can run at that temp forever.  Generally the life expectancy is 4,000 hours.  Drop the temperature and it lasts longer.  This is based on the liquid inside evaporating.  No liquid, no capacitance. 

A capacitor will have an internal resistance or ESR.  Considerable current goes in and out.  The weakest point is the attachment of the foil to the lead.  Like a fuse it is easy to pop this open if a bad crimp is made.  It is a chemical device so the purity of the components is critical.  Tear apart a quality capacitor and the foil will have a nice even coating.  Other capacitors can have a blotchy finish.  Even quality manufacturers have had bad runs of capacitors when some minute impurity geys in.  Even the worst capacitor maker can have a run that will last 20 years, but they can't do it consistently.

The market is driven by price.  Delete a few capacitors or use lower cost ones and statistically you can get two or three years of life.  These have to be shipped.  The smaller the enclosure, the more you can get into a container.  That doesn't bode well for heat sensitive devices.  It takes a Herculean effort to get 40A on a circuit board, a custom super thick foil, added metal bars, and extra solder.  It can be done for a short time and that is what they count on.  Pretty hard to get a panels full amperage and that doesn't last for long periods during the day.  And they count on someone having fewer panels than the stated max.

I wouldn't mind having one of these.  The basic electrical design is sound. Some day these will be showing up on ebay broken after 5 years for $20.  Then I can cut a hole int the face and add some extra capacitors.  Check out this video demonstrating heating of capacitors and the advantage of parallel capacitors.  IR imaging shows heating effects.  Bear in mind these are at very small currents.

https://www.eevblog.com/fundamentals/       #742 There are other interesting ones for  learning.