Solar install on a Trailer, newbie questions

MURPHY'S LAW

Natural voltage correction (referred to as intrinsic)

Unnatural voltage correction correction (referred to as fallible)

Need a clue? Really? It's called resistance biasing/error of the sensing system

Got money? Challenge my MEE credentials.

Temper Temper. None of those arguments are helping the OP

I.M. MOST H.O...

Improving and protecting the cabling terminations is something that has not been mentioned in this thread. My vote is to include the subject.

My point is vd between the panel and controller means the panel operates at a higher voltage so there is less current and it can enter into the area where current drops like a rock with increased voltage drop. Isc is greater than Imp which is much greater that I at voltages above Vmp. Heat reduces Vmp, therefore it is easier and easier to get the panel to operate above Vmp (region of rock slide current) when it is hot and there is vd. Maybe you do recommend 22awg!

Batt never gets to abs unless SUN does the taper cuz vd is based on panel current even in tiny doses and panel current does not taper, the controller sees a higher voltage than what is at the battery. Thus the reason you suggest a voltage sensor, without it the batt v is less than the controller v due to vd when current is flowing at whatever rate the panel makes it and not some reduced acceptance rate. With the sensor the panel operates at a higher voltage which means less current.

vd is based on current when it is flowing. I run my pump for 30 mins a hr, the pipe friction is based on when the pump is running not 1/2 the pump rate.

It is 25C here today and my panel is 60C where on the IV curve does the current crater at these conditions?

to be absurd let's say vd at some pt is 2v and the controller sees 14.6v and the battery is @ 12.6v. vd stays @ 2v since the current is in busts of full power, the width (time) of the pulse (current) changes. Batt acceptance has declined to nil but every time the controller is ON the full panel current for some fraction of a second blast at the battery with 2v of drop. With each pulse, 2v @ whatever A is made into heat in the wire.

mike-s wrote:

PWM limits the voltage, and indirectly the current. Not the instantaneous current, which you seem fixated on, but the actual charge current - how fast coulombs flow into the battery.

PWM limits current by making the pulses of power shorter and the non power time longer at some Hz. Over a time frame the current can be less than the panel but the pulses are full strength with full strength vd based on the full strength current.

red31 wrote:
panel current is either on or off, the on time tapers but not the current.

What's your point? As long as current is flowing, the battery is charging. If voltage drop prevented the battery from reaching its absorption voltage as you claimed, then no current would be flowing. But, of course, unless there's current, there's no voltage drop. And, as the battery approaches full charge, it draws less current.

PWM limits the voltage, and indirectly the current. Not the instantaneous current, which you seem fixated on, but the actual charge current - how fast coulombs flow into the battery. PWM won't taper off unless the battery is holding the desired voltage for some time after the PWM goes into the off state. The longer the battery holds at that voltage, the more fully charged it is, the lower the PWM duty cycle and the lower the current into the battery.

panel current is either on or off, the on time tapers but not the current. Get a scope to get the real values when on and not the average that meters report since it happens so fast.
That is how power is regulated either full power or no power.
vd is based on current when ON

acceptance is adjusted by changing the ON time. When there is no need for any current the controller is not connected to the panel or OFF, when there is a need the full power the panel makes is applied. This is all done at a very high Hz.

mike-s wrote:

And, why you're injecting charts applicable to an MPPT controller into a PWM discussion is a mystery.

The charts are standard IV - power curves. Would ya like to see more with temp and/or irradiace effects? How current goes up to the left of Vmp with heat and how Vmp moves to the left (lower) with heat.

they show if vd is high the panel will operate at higher than batt voltage and the current drops. I don't care for my panel to operate to the right of the Vmp which is lowered by heat. NOCT conditions and Vmp of a 12v panel is down to 16v even less when hotter and the IV curve shows that past Vmp the current drops.

red31 wrote:
current doesn't taper

Yes, it does. Just as a cell phone which will only charge at 1.5 A won't draw more than that from a 2.4 A charger, so too is the charge current here reduced as the battery approaches full. When looking at the IV curve for a panel, the current must be considered a maximum, not a fixed value.

And, why you're injecting charts applicable to an MPPT controller into a PWM discussion is a mystery.

current doesn't taper, anytime the controller is ON you get full power based on panel operating @ batt V + vd, anytime the controller is OFF ya get Voc and no power. Less sun = less current. If I turn my 12w/1A light on for 1 hr/day I do not claim its current is 1/24A, that is ave over some time frame, on is 1A, off is zero.

During bulk at or near max voltage and current, the voltage drop will have the panel operate at a higher voltage = less current. Isc>Imp>>>>Ioc

I don't care to be in the red area, warm here and Vmp is lowered with heat.



@ 50% duty cycle panel makes full power, vd based on 4A not 2.



I'm sure you don't suggest everyone use 22awg.

red31 wrote:
Controller to batt voltage drop limits batt charge voltage.

Current 'taper' during abs does not solve voltage drop, the panel is ether on or off, the taper comes from more off time and not reduced current from the panel.

Charge voltage is not limited below that required, since any reasonable combo of panel and wire will be able to draw the voltage at the battery up to its full absorption voltage. During bulk charging, voltage drop (both before and after a PWM controller) will result in a slight loss of efficiency, but it does not limit the ultimate charge voltage. As the battery nears a full state of charge, the current drops and so does the voltage drop.

Without remote voltage sensing, but with a significant voltage drop, the battery still gets charged, but the flat part of the battery voltage curve ("Stage 2" below) looks more like a ramp up to the final voltage.


After the controller goes into PWM regulation the voltage drop simply doesn't make any significant difference - it goes into regulation because there's energy in excess of that needed to hold the battery at the absorption voltage. There might be an early period of "99% on" PWM until the battery itself begins to hold at absorption voltage, but when PWM begins to taper the battery is being held at the required voltage.

curly5759
You can find various lengths of MC4 solar wire, say ya need 15' from panel to controller, you buy one 30' with male/female MC4 connectors, cut it in half and connect the MC4s to the panel and the cut end to the controller. You can also find 'tray cable' with ring terminals attached to one end in various lengths to connect the controller to the batt or make your own.

https://www.solarblvd.com/product-category/cables-wires/solar-panel-wiring/

https://www.renogy.com/renogy-solar-tray-cables/


voltage drop between panel and pwm controller causes the panel to operate at a different voltage and the higher the voltage the less current. Voltage higher than heat reduced Vmp and the current drop is steep.

Controller to batt voltage drop limits batt charge voltage.

Current 'taper' during abs does not solve voltage drop, the panel is ether on or off, the taper comes from more off time and not reduced current from the panel.

Less sun = less panel heat, less current and less voltage drop!

Moved from Technology Corner

Thanks for the replies and links. Never thought about running the wires down through the fridge vent.
This will not be my primary source of charging, just to keep the battery when we are not using the TT. We only use it a few times a year for a few days. I also want to be able to recharge the battery after a night of running the heater.
What/who is a good source of solar switches and wiring?