PWM input voltage, Xantrex C40 test video

red31 wrote:

BFL13 wrote:

Today his battery bank has reached the controller's high voltage set point near 14.3, and the battery side is 14.34v. The array side is 19.10v.

If Voc = 21v that yields ON time of 28.4%

(14.3*.284) + (21*.716) = 19.1v

(Isc(Ipanel @14.3v sun adjusted) *.284)+(Ioc(zero)*.716) = I*.284

Math is happening! :) Actually that 130w panel in the sun usually had a Voc of about 20.3v (rating 21.9v) with the heat, while it was cranking out its rated amps of 8.2 or so.

They have been away for a few days so I got the above reading where there is not much 12v load. I don't know what they leave on when they are away. So his batts ( four 6s) are quite full.

Side note: that is how he can get away with a single tilted South 130 on four 6s and the batts don't go bad on him. He is away enough that they get to true full during the day on those away days (when sunny) the 14.3 float is not losing him much water either. Just right! :)

BTW red31, I used your equation of time/declination graph I printed last December in my post on tilting yesterday. Maybe you could repost that graph in that thread? Thanks.

BFL13 wrote:

Today his battery bank has reached the controller's high voltage set point near 14.3, and the battery side is 14.34v. The array side is 19.10v.

If Voc = 21v that yields ON time of 28.4%

(14.3*.284) + (21*.716) = 19.1v

(Isc(Ipanel @14.3v sun adjusted) *.284)+(Ioc(zero)*.716) = I*.284

Back on limited internet. I just checked my old PWM, 130w set-up that I sold to my camping neighbour last year.

Last week I reported it was in Bulk and ISTR the voltages were maybe 13.6/13.5 or some such (not sure which thread I posted that in) Anyway, it was as expected with the two voltages close.

Today his battery bank has reached the controller's high voltage set point near 14.3, and the battery side is 14.34v. The array side is 19.10v.

red31 wrote:
"PWM or 16.62-13.92 * 16.10a = 43.47 Watts going to heat up controller?
"16.62
controller out
13.92v"

Think about 43.47 Watts going to heat up controller. If you have a series PWM controller and it is in the off state the panel voltage is at V open circuit as you have said. But in the off state the current is zero! With zero current there is no power dissipation (P = V*I) to heat the controller.

Also if you have a shunt type PWM controller and if is in the off state the panel voltage is zero, the panel output is shorted by the controller. With zero voltage there is no power dissipation (P=V*I) to heat the controller. OK there will be a small voltage drop across the shunt switch so there will be a small amount of power dissipation with a shunt controller.

Amps to the battery will taper once battery voltage is held constant, but solar amps can be as many as the array can produce to run other loads too.

It is hard to keep the battery voltage constant with loads running and solar conditions changing all day.

If the loads take all of the available solar amps so the battery gets none, the battery voltage will fall. With loads on and off all day and sometimes taking all the amps and sometimes leaving some for the battery to continue charging, it gets confusing.

You can be in Float with the battery getting a few (tapering) amps and the solar providing some of the rest of its amps to loads. If the loads take all the solar amps plus some from the battery, so the battery voltage falls enough (13.2v being a typical trigger), the controller will re-start Bulk, but that does not necessarily mean the battery will get any more amps just then if the loads are still taking them all.

You can spend a long time in that Float with battery voltage not down to 13.2 yet.

IMO the early morning data Mr Wiz provided shows that the C40 is a normal series PWM controller and after that in the day, there is so much going on at the same time it is confusing the picture.

bare with me for a moment and consider this

according to all the arguments being presented, the controller does not go into PWM and voltage control until bulk set point is reach, at which time amps should be tapering yes ? no ?

my meters show that voltage control commences while amps are still rising as the voltage comes up, and once panel voltage exceeds set point, the amps continue to rise or maintain while set point is maintained and panel voltage rises

now according to all arguments presented..panel input voltage can not rise, unless output voltage is controlled

i'm not debating how voltage is controlled
i'm only saying control takes place (in my case) before everybody else says it should,
control takes place as soon as panel voltage exceeds set point
even though batteries are NOT charged, amps are NOT tapering, the batteries are taking more amps than before control commences
control is IN EFFECT before vtabs ? float condition is reached

Mr Wiz, please read this again from crewzer linked earlier. He does the actual calculation which helps explain the input voltage that you see once Bulk is done.

"PWM controllers like the Morningstar TriStar and the Xantrex C40 limit the bulk-stage array voltage to that of the battery bank. In fact, it’s essentially the battery itself that sets the array voltage.....

"It’s likely that the actual array voltage will operate higher than the battery voltage when the controller is functioning in ...absorb, float, or most of EQ... In this case, the array voltage will be the PWM duty-cycle weighted average of the battery voltage and the array’s Voc.

"For example, if the PWM duty cycle is 50%, the battery voltage is 58 V, and the array Voc is 70 V, then the array’s operating voltage would be (58 V x 50%) + (70 V x 50%) = 64 V...."

This is the same as the other posters and the standard blurbs say too.

there is a lot of talk about "voltage avg"
about voltage being low when controller is pulsed on and high when controller is pulsed off.. do any of you know what that means

it means that 14.xx v is the applied voltage to the system
and that 16.xx~17.xx is the applied panel voltage

stop and think about regular 60Hz 120vac.. where everybody does thee volt-amps aka watts calculations
do you realize that is the RMS voltage aka Relative Mean System volts
that the peak to peak of 120vac is 177vac
that 120v is the Average, what is the"mean" distance of something, another way of saying average

this whole discussion, was because people couldn't believe the panel output was not down to controller output

i provide the readings and the video and still dis-belief

its all about the controller and enough solar watts to supply amps for the batteries

i know what my meters say.. its there for you to see
you try to explain it away as an optical illusion or misunderstanding of whats going on

yet its exactly what i said it is once the panel voltage gets higher than the set point, it starts controlling the output voltage, no matter what level the amps are at..
its that simple
the controller is not wasting any more amps than any other PWM controller
that is irrelevant logic
in my case the blue sky MPPT gave me only a little bit more avg ampHrs with previous panel wattage than the C-40
what has given me a boost and made a change in the charging profile is having more wattage so the Solar can raise voltage earlier

remember..all i did was make a statement in some other thread about an observation of 17v input 14.4v output
i wasn't asking any questions, how or why, i wasn't complaining, and i wasn't bragging,

and the questions started coming ..saying NOT possible...PWM doesn't work that way...etc..

My panel is dumb, operates @ Vbatt+loss or Vbatt+loss / Voc (on/off) to limit amps.
No need to operate at higher v (more watts) without bucking.

Bulk
"13.34v below fuse
Controller out
12.92v"

vout+.42v

"14.04v
controller out
13.64"

Vout+.4v

PWM? or (16.63-14.47) * 15.33A = 33.11 watts wasted!
"16.63v
controller out
14.47v"

PWM or (17.00-14.51) * 13.1A = 32.6 watts wasted
"17.00v
controller out
14.51v"

PWM or 16.62-13.92 * 16.10a = 43.47 Watts going to heat up controller?
"16.62
controller out
13.92v"

The 'duty cycle' limits amps. Watts in = watts out, during PWM, one can not use measured Vin volts since they are an ave of Vbatt and Voc while amps is an ave or Ipanel (Isc) and Ioc or zero.

Voc goes down with low light but the entire range of zero to Voc is available until light is very low.

i think it is in float, that is were the 13.92 instead of 14.4x/5x
and the near 13v at battery come into play,
because float voltage and lower amps
won't sustain a higher voltage at the battery (because there are loads)

just like i have a higher than avg bulk setting
i raised the float setting, i set the float high with all loads off,
then checked it with loads running, so it was not dropping to low during solar float

my batteries spend almost no time at zero load, actually never since there is always inverter idle, even when all other loads are off

well ok..some days when it, is not hot, and nothing is running except for the fridge cycling, they get some float time, because solar exceeds idle drain parasitic loads