MPPT vs PWM charge controller in an always cloudy scenario

[Sunking]

Sunking can you tell me what the proper 4-stage settings should be on the TriStar MPPT.

Well yes and no. Problem is 4-stage solar charge controllers cannot really be used. You paid for something that cannot be used effectively. The 4th stage is Equalize which is a controlled overcharge which takes up to 24 hours. Try to find a place on earth with a 24 Sun Hour day. Only way to EQ a battery is with a AC powered battery charger running on either commercial AC power or generator.

OK to answer your question I have to make some caveats here because sure enough some of you will run off and try this without all the facts and destroy your batteries. For this to work your system has to be designed properly where you use 20% or more of your battery capacity daily, and the panel wattage sized to replace that energy daily. IT DOES NOT APPLY TO OCCASIONAL USERS like weekend cabins.

Second the actual voltages vary by manufacture and battery type being either AGM or FLA. So the actual voltages need to come the OWNERS MANUAL. What follows is generic based on either FLA or AGM chemistry.

AGM

Bulk = Absorb = 2.4 to 2.6 Vpc. Lower range in summer warm months, higher in winter.
Float = 2.25 Vpc

FLA

Bulk = Absorb = 2.5 to 2.7. Lower range in summer, higher in winter.
Float = 2.2

[inetdog]

Only way to EQ a battery is with a AC powered battery charger running on either commercial AC power or generator.

You mean my brilliant idea of running the EQ charger off an inverter attached to the batteries during the night won't work?

[Mike90250]

You mean my brilliant idea of running the EQ charger off an inverter attached to the batteries during the night won't work?

It will work Just Fine. (as a heater, till the batteries run down)

[epsgunner]

Ok.. my take on this.. I have JUST hooked up just 2 of my 145w panels.. 18V and 8.05 AMP panels..

I get 20.7 at the combiner and 19.2 to the controller terminals(with a load drawing)..

Watch my video and see how the PWM jumps when I turn off 1 panel then turn it back on..

Each panels only making about 65-70 watts as my cloudy day... and the PWM is regulating the crap out of the incoming volts from the panels.. (this is because my battery is totally shot and was at 9.6VDC this morning when I started).

After 3 hours outside.. it said 4.X amps and 14.4 V going into the battery.. (didn't matter if it was just 1 panel on or 2..)

I turned off the panels at the end and got 13.6 volts and 0 amps for the battery..

I am guessing my PWM controller couldn't get an accurate read because of how it limits the OUTPUT to the battery and as the battery SHOWS full.. its really not..

I know the panels are good and CC is good.. I need to get a good battery that I can really test..

[Sunking]

OK EPSGUNNER I will try to explain what is going on with a PWM controller.

Think of a PWM controller as nothing more than a on/off switch. It regulates it output by turning the switch on/off called duty cycle from 0% (meaning the switch is always off disconnecting the panels form the batteries) to 100% where the panels are connected directly to the batteries. With me so far?

With a PWM controller the Input current = Output current and is the down fall of any serial regulator.

So lets say you have a 12 volt 100 AH battery that is 50% discharged, and you connect a 100 watt panel directly to the battery. A solar panel is a current source, not a voltage source. The spec on the panel is 18 volt Vmp and 5.55 Imp. When connected to a discharge battery the voltage of the panel is pulled down from 18 Vmp to match the battery voltage of around 12.1 volts and is supplying its constant current of 5.55 amps. Do the math 12.1 volts x 5.55 amps = 67 watts. You loose 33% of the panel power

So when you measure the voltage at th einput of a PWM controller and it is approx = to the battery voltage (about 1 volt higher), you know the PWM controller is at 100% duty cycle. As the battery aproaches full charge you will see the voltage from the panels rising up to Voc voltage of say 22 volts. When you reach Voc the PWM is at 0% duty cycle and there is no current flow at Voc.

FWIW use a MPPT controller with the same panel and battery at 50% DOD you will see the input voltage from th epanel @ 18 volts with 5.55 amps. On the output you would see 12.1 volts at 7.85 amps or 95 watts. Interesting huh? That is what a MPPT device does, it tracks Maximum Power Point of the panels.

[epsgunner]

So when you measure the voltage at the input of a PWM controller and it is approx = to the battery voltage (about 1 volt higher), you know the PWM controller is at 100% duty cycle. As the battery aproaches full charge you will see the voltage from the panels rising up to Voc voltage of say 22 volts. When you reach Voc the PWM is at 0% duty cycle and there is no current flow at Voc.

Thats why with 1 panel I was at 17.X VDC at the controller... then when I clicked #2 panel on the voltage jumped to 19.X VDC at the controller..

I had 53% PWM with 2 panels ON.. then with just 1 panel ON it went to 87% PWM..

The watts and amps shown really didn't change except for a minute and then re-leveled..

Why did the PWM % number go UP to 87% (from 53%) when I turned OFF 1 panel??

[inetdog]

Thats why with 1 panel I was at 17.X VDC at the controller... then when I clicked #2 panel on the voltage jumped to 19.X VDC at the controller..
Why did the PWM % number go UP to 87% (from 53%) when I turned OFF 1 panel??

Actually fairly simple to explain:

With one panel, when the "switch" in the modulator was on, a limited amount of current was able to flow. So chopping that current by 87% gave the amount the battery needed
With two panels, the maximum current with the pulse on was higher, so it had to be turned off more of the time to get the same amount of current to the battery.

I1 x 87% ==> what the battery needed to hit target charge voltage.
(I1 + I2) x 53% ==> same current.

[billvon]

I had 53% PWM with 2 panels ON.. then with just 1 panel ON it went to 87% PWM..

The watts and amps shown really didn't change except for a minute and then re-leveled..

Why did the PWM % number go UP to 87% (from 53%) when I turned OFF 1 panel??

Vout=(PWM)*Vin

So when your input voltage goes down your PWM period has to go up to maintain the same output voltage.

[epsgunner]

So if I add my 3rd, 4th, & 5th panel the PWM should almost be at 0%???

[billvon]

So if I add my 3rd, 4th, & 5th panel the PWM should almost be at 0%???

Well, 0% would require an infinite input voltage, so you won't get close to 0%. But if you are at 5 panels you might see a 20% duty cycle.

[epsgunner]

Thanks..

I'm going to try my setup again with a single panel and a GOOD battery (not the junky one that read 9.6 VDC this morning).. maybe I'll get more accurate numbers from it..

[Sunking]

Well, 0% would require an infinite input voltage, so you won't get close to 0%. But if you are at 5 panels you might see a 20% duty cycle.

Well I disagree, if the batteries are fully charged then even with just one panel the duty cycle should be near 0% meaning the batteries are not taking any current because they are full.

At the input of the CC you would see the voltage higher than Vmp of say 18 volts, and just ever so slightly below Voc of say 22 volts. So if th ePWM does go to 0% modulation you will see full Voc input because there is no current flowing. No current flowing in a panel with full sun light is Voltage Open Circuit aka Voc

[epsgunner]

Well I disagree, if the batteries are fully charged then even with just one panel the duty cycle should be near 0% meaning the batteries are not taking any current because they are full.

At the input of the CC you would see the voltage higher than Vmp of say 18 volts, and just ever so slightly below Voc of say 22 volts. So if th ePWM does go to 0% modulation you will see full Voc input because there is no current flowing. No current flowing in a panel with full sun light is Voltage Open Circuit aka Voc

Well I was at 20.7 VOC today.. then with both panels ON I was at 19.2 at the terminals inside the charge controller..

You may be correct.

[billvon]

Well I disagree, if the batteries are fully charged then even with just one panel the duty cycle should be near 0% meaning the batteries are not taking any current because they are full.

Agreed to some extent; you'll only see a proportional PWM number when you are delivering a significant amount of power. When the system is starting to regulate to reduce power you'll see a reduction of PWM below the Vin/Vout ratio. I wouldn't expect it to get close to zero unless the voltage setpoint gets significantly below the battery voltage though (i.e. heavy load, batteries fully charged, sudden reduction of load.) If your PWM value gives you a voltage even slightly below battery voltage you won't see any significant current flow.

[epsgunner]

Last weekend I hit 99% PWM with 14.4 V on the meter and 111 watts.. then it went to BULK mode at 112 watts for the battery reading on the TS-45 meter..

Tommorrow with a good battery (and the sun and 80'F) I should have some real numbers (I hope).

Gonna let it run for 6 hours and see what happens..