Pass through power?

TexasDan

Not sure I am not grasping the full relationship of the PV panels, charge controller, and battery bank relative to power use in daylight. Does your inverter receive what I will call "pass through power" from the PV panels and charge controller when the battery bank is fully charged or must the bank be pulled down to its (preset) recharge level before the charge controller will allow any PV power through to charge the batteries? Thanks.

inetdog

Re: Pass through power?

TexasDan wrote: »

Not sure I am not grasping the full relationship of the PV panels, charge controller, and battery bank relative to power use in daylight. Does your inverter receive what I will call "pass through power" from the PV panels and charge controller when the battery bank is fully charged or must the bank be pulled down to its (preset) recharge level before the charge controller will allow any PV power through to charge the batteries? Thanks.

The battery voltage will very quickly drop under load to the point that the CC will start delivering current, even though the battery is not being discharged very far. At that point ideally all of the load current will come from the CC.

BB.

Re: Pass through power?

Basically, the charge controller is "holding" the battery voltage between 13.6 (float) and 14.5 volts (absorb--charging). And it is regulating output (average) output current to do that.

As you start adding DC loads, it will pull the average voltage down and the charge controller will start to add more current to bring the bus voltage back up to the set point...

If you pull the voltage down below 13.6 volts, then the battery bank is no longer charging.

If you pull the voltage down below 12.7 volts, then the battery bank is being discharged.

More or less, very similar to how your car battery and alternator (/generator) system works. The battery is responsible for all current, and the alternator is there to help or even recharge the battery when the motor is running.

Even though it sounds like I am saying the alternator maintains the battery bus voltage--It is really the battery that maintains the voltage. Over the longer term, the alternator or charing source is responsible for the battery bank's state of charge. You can run your loads from a battery with a dead alternator (for awhile). However, most alternator/charge controllers will go "wonky" if you remove the battery and attempt to supply DC power directly (they need the battery bank to "buffer" the energy into a stable voltage).

-Bill

TexasDan

Re: Pass through power?

Thank you both. The auto analogy helped me quite a bit and I understand the need to pass all PV current through the CC and BB to standardize and regulate its output.

spoonman

Hi all,just browsing on this post and have a dumb question for what is probably a simple answer.
credit given to all the patient people who help out here on the forum.
I have been off grid the last 5 years on a modest 12 volt /240 inverter system and was asked by a friend recently,"what happens to the excess power from your panels when your batteries are full"?
I was'nt able to explain in a simple fashion how the system works in this scenario,even though Zi built it myself.
was hoping someone could write up a lay mans explanation that I might pass on to him and that might also be of use to beginners starting off.
Thanks in advance to all help given,Andy.

spoonman

Meaning,is the power used directly from the panel production thru the inverter/batteries to the load without draining down the batteries too far or do the batteries cycle thru again and begin the charging process if conditions allow. Thanks

jonr

Q1: it's dissipated as heat in the panel.   Q2: if your panels are producing more energy than you are using, the batteries won't run down.

spoonman

Thanks for that Jonr,easier for both he,and I to get our heads around!