[RE-wrenches] C-40 question; how PV controllers work

[Larry Crutcher, Starlight Solar Power Systems]

Quote: "Your charge controller controls the load and current, hence the name "controller"."

This is a common misunderstanding about how PV charge controllers work. The load, not the controller, determines the current flow. Most PWM charge controllers do not have a "charge rate limit", they simply control voltage. The C-Series controller in question uses PWM to stop current flow at a set point so that voltage is limited. Refer to the simple series circuit as shown below. 

PV POS------------CONTROLLER------------LOAD------------PV NEG

Remove the controller from this circuit and the same current flows based on load, up to the instantaneous PV capacity. Changing load equals changing current. Of course, without the controller voltage will climb limited only by the potential of the PV array. 

All PV solar charge controllers are voltage controllers. Some modern PWM controllers, like the Outback FM series, have programable current limiters but not the C-40. 

Larry Crutcher
Starlight Solar Power Systems


 
From: re-wrenches-bounces at lists.re-wrenches.org [mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Chris Mason
Sent: Thursday, October 25, 2012 5:50 AM
To: RE-wrenches
Subject: Re: [RE-wrenches] C-40 question
 
It does "take". Your charge controller controls the load and current, hence the name "controller". It is not a fixed resistance. If you program a charge rate limit, the controller will control the current flow to limit the charge rate, hence it is "taking" a certain current up to the limit of the source's ability to supply that current but not above, regardless of the size of the array