Here is the situation: I have 2 roof top panels (95W GoPower, Imp 5.53, Vmp 17.2) mono and a 100W Windy City (Imp 5.75, Vmp 17.4) poly panel wired in parallel on the roof. No room for more.For low angle winter sun, I add a portable (2 80W panels in parallel) 160W Solar Blvd (Imp 8.88, Vmp 18) mono panel, bypassing the controller. All go to the input of a GoPower PWM controller in the trailer.All panels have bypass diodes, none have blocking diodes.Everything works as expected until the the controller switches to float while still under full sun at which point the controller output drops to under .5 amps going to the batteries (a pair of Interstate 6V). At that point unplugging the portable panel INCREASES the output current of the controller from around .5 amps to a couple of amps. Just before sunset, replugging the portable panel will slightly increase the controller's output.If I connect the portable panel using its controller to the trailer batteries (bypassing the GoPower controller) the same thing happens.Would the higher Vmp of the portable panel cause this? Would blocking diodes help? (Installing them on the rooftop panels would be a major job - easy for the portable.) Since the panels are not in series, do the bypass diodes serve any function? Any suggestions would be appreciated. It isn't a major problem, but one that I'd like to understand.

vermilye wrote:Everything works as expected until the the controller switches to float while still under full sun at which point the controller output drops to under .5 amps going to the batteries (a pair of Interstate 6V). And I would say that is exactly as expected too.What exactly leads you to believe that there IS a problem ??Switching to float implies that the batteries are "full" and don't need the extra current.

Remember the little old lady in the WENDY'S hamburgers ads?In this case it's..."Where's The Volts?"Speaking of one without the other is a perfect example of useless information. :)

vermilye wrote:Would the higher Vmp of the portable panel cause this? Maybe..your Vmps are not that different. But in parallel, the closer your voltages are the better.Afraid I'm not qualified to comment much more.

Sam Spade wrote:vermilye wrote:Everything works as expected until the the controller switches to float while still under full sun at which point the controller output drops to under .5 amps going to the batteries (a pair of Interstate 6V). And I would say that is exactly as expected too.What exactly leads you to believe that there IS a problem ??Switching to float implies that the batteries are "full" and don't need the extra current.The controller "thinks" the batteries are full (indicates 100%) but the TriMetric battery monitor still shows them down by anywhere from 5 - 10 amp hours. I may be pushing it, but I'd like to be able to get the last few amp hours back in the batteries before dark.And, why does the current go up when I unplug the portable? For example, right now at 12:00 the Trimetric says I'm down by 7.82 amp hours & at 96%. The controller is putting out 1.4 amps & 13.6V (float) and says the batteries are at 100%. Unplug the portable, the controller stays at 13.6V but jumps up to 4.1 amps. Why?

Controller dropping to 0.5A is normal. Batteries are near full and controller is switching to Float mode. Increased amps when disconnecting one of parallel panels is odd, especially in Float. I would understand this with series panels - but not in Float.

Bypass / Blocking Diodes | Good Sam Community

Sam_Spade
Explorer
Jan 08, 2016
Salvo wrote:
Forget volts. They do not enter into the picture. Solar is a current source, not voltage source.

As was already pointed out......that's absurd.
Nagrompj
Explorer
Jan 08, 2016
Amps and no volts!

That like water pressure and no water.

So a 100 watt panel is not 17 volts and 5.88 amps
100 / 17 = 5.88
Or is it
100 / 0 volts = ?
Your math don't work! Volts definitely matter.
Salvo
Explorer
Jan 08, 2016
Forget volts. They do not enter into the picture. Solar is a current source, not voltage source.

Nagrompj wrote:
You can't talk about amps and not talk about volts.
Nagrompj
Explorer
Jan 08, 2016
You can't talk about amps and not talk about volts.
Your roof mounted panels are flat on the roof I assume.
If the output voltage of the roof top panels (not the controller) is very close to the needed charging voltage the amps would have to go up.
Ohms law: Volts down, amps up. Volts up, amps down
Your portable panels are pointed to the sun = volts up, amps down. Unplugged = volts down, amps up.
red31
Explorer
Dec 28, 2015
not applicable to OP, informative! "All Morningstar PWM type controllers have a PWM switching frequency of ~300Hz."
Salvo
Explorer
Dec 28, 2015
That doesn't bode well for the TriMetric battery monitor.

Here's the issue with pwm. Let's say the battery wants 2A in float mode. We have 4 panels, each produces 2A. So 4 panels produce 8A. But the battery only needs 2A. Here's where pwm comes into play. The controller shorts panels to battery and 8A charge the battery for a limited time period, which is defined by the duty cycle.

The duty cycle it the ratio of the time the battery sees 8A to the total time of the pwm cycle to produce average 2A.

For 4 panels, duty cycle = 2A / 8A = 25%

For 2 panels, duty cycle = 2A/4A = 50%

If we have only one panel then duty cycle is 100%

Without filtering or some very high speed measurements, it's impossible to measure average current of a 25% duty cycle. The smaller the duty cycle, the greater the error.
pianotuna
Nomad III
Dec 28, 2015
So some sort of period averaging meter would be needed? Or an Oscilloscope?
Salvo
Explorer
Dec 28, 2015
I see, it's a phantom current source that's causing the mystery. Let's add another to your list. 3) the Menahunies are playing jokes on Vermilye.

I'll concede it's possibly not a measurement error if the charge controller is defective or the OP hasn't entirely explained his configuration.

Sam Spade wrote:
Salvo wrote:
LOL, then they're both wrong. If the controller is outputting the exact same voltage in both conditions then the battery MUST get identical current.

If the controller was the ONLY voltage source, that would be true.....but it is NOT the only source in his lash-up.

A couple of us have answered your curiosity question already; let's try again. The extra input that you are connecting is either 1) confusing the controller or 2) adding a current source AFTER the controller where the ammeter is located.
LScamper
Explorer
Dec 28, 2015
Both red31 and Salvo have the correct answer. The problem is that the meter is made to read DC amps. The output of the controller is a pulse of varying width. The meter gets confused with this type of measurement and reads different current even though the average is the same.
Sam_Spade
Explorer
Dec 28, 2015
Salvo wrote:
LOL, then they're both wrong. If the controller is outputting the exact same voltage in both conditions then the battery MUST get identical current.

If the controller was the ONLY voltage source, that would be true.....but it is NOT the only source in his lash-up.

A couple of us have answered your curiosity question already; let's try again. The extra input that you are connecting is either 1) confusing the controller or 2) adding a current source AFTER the controller where the ammeter is located.

Forum Discussion

Bypass / Blocking Diodes

About Technical Issues

Related Content

Solar Panel Shadows and Bypass Diodes

Solar Panels With Bypass Diodes

Leveling Blocks

Solar panels for less than ideal conditions - bypass diodes?

leveling blocks