BFL13 & PWM

Question

ye ole controller worked as you suggest which is how PWM controller operate AFIK, nothing new to learn.

"A PWM controller is not a DC to DC transformer. The PWM controller is a switch which connects the
solar panel to the battery. When the switch is closed, the panel and the battery will be at nearly the
same voltage. Assuming a discharged battery the initial charge voltage will be around 13 V, and
assuming a voltage loss of 0,5 V over the cabling plus controller, the panel will be at Vpwm = 13,5 V.
The voltage will slowly increase with increasing state of charge of the battery. When absorption
voltage is reached the PWM controller will start to disconnect and reconnect the panel to prevent
overcharge (hence the name: Pulse Width Modulated controller). "

http://www.victronenergy.com/upload/documents/White-paper-Which-solar-charge-controller-PWM-or-MPPT.pdf

one of my fav video is connecting a 21watt light directly to a 20w panel, the panel output is ~6v and the light is dim, part 2 is education also.

https://www.youtube.com/watch?v=JZQEJ33xblE

bfl13 · Answer

Thanks, I think. Need a link to the Xantrex C40 manual, which might explain something.

Got started, sort of.--"dump loads to control battery voltage" ??? Is this what is confusing things?

https://www.windynation.com/cm/Xantrex%20Complete%20Charge%20Controller%20R2.pdf

Found it--didn't help.

http://www.wsetech.com/pdfs/C_series_manual.pdf

I did see red31's graph of what happens with panel voltage after the controller starts controlling, but that rising voltage was said to be from the measuring instrument averaging and not the "real thing" IIRC.

Later I will see if I can get some readings too, but might be a few days though.
---------

From red31's link in the OP, "The input voltage of a PWM controller is, in principle, equal to the voltage of the battery
connected to its output (plus voltage losses in the cabling and controller)."

So howinheck can Mr Wiz get 17v at his "PWM" controller's input? (which he is no doubt seeing--he is not a liar!) We need that C40 manual to see if it explains that.

red31 · Answer

You've done the measurements before!Remember the fake mppt 30? its review shows how input voltage is higher than output due to 'duty cycle' when not needed (bulk), the scope shows it all!!!You need a scope for your educational documentaries !https://www.youtube.com/watch?v=la-gvy0DfJs, about 6:40I don't see any need to understand how EVERY pwm controller operates, but it is fun to measure what is going on at different times.PWM on is batt v - Ipanel, PWM off is Voc - I=0.0A

mexicowanderer · Answer

I like the idea of dumping excess energy to heat water. In the low head hydro systems I have installed (240 vac) excess energy heated 3 50-gallon hot water heaters for resort rental rooms. Augmented by separate propane burners. Nifty utilization of excess energy.

bfl13 · Answer

Just checked my old 130w set- up I sold last year, now over at a neighbour's trailer.

It has a simple "RJ Special" fake MPPT 20a controller (called CM02 or something like that) which is actually a standard PWM and works just fine as such, as RJ reported and we confirmed. (This one is on four 6s and a 130w tilted South, and is doing great on its second summer with him)

Input array terminals-13.55v
Output battery terminals-13.34v

(mid-morning)

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