mppt vs pwm

Apparently, panels use to have blocking diodes installed, but not anymore?

jrnymn7 wrote:
Re; diodes, I thought that's what's inside the little black box?

Those are bypass diodes and serve no purpose for 12V panels in parallel. Not to be confused with blocking diodes which prevent a panel from draining the battery at night.

jrnymn7 wrote:
but in a pinch, say if one's controller crapped out, couldn't you just use a direct connection?

yes or to top charge or equalize, but ya gotta monitor.

if you want to do a trickle charge buy a 5w~15w panel expressly for that purpose

100w panels at 13v would do a very poor job of charging when you actually used the rv and needed to charge the batteries

why do you think panels are at a higher voltage and controllers are used ?

because that is what is needed to have an effective system

Hi jrnymn7,

All too often, voltage from a nominally 12 volt panel would drive the battery bank voltage up too high for float. As Mr. W said, blocking diodes would be needed.

jrnymn7 wrote:
Seems to me, if using 12v panels, if all you ever did was bulk charging, you wouldn't need a controller at all. And if you were to de-rate the 12v panels to max out at say 14.8v, you could abs charge without a controller, as well?

Re; diodes, I thought that's what's inside the little black box?

Re; overcharge, But then couldn't one simply de-rate the panels to a suitable float voltage?

jrnymn7 wrote:
Seems to me, if using 12v panels, if all you ever did was bulk charging, you wouldn't need a controller at all. And if you were to de-rate the 12v panels to max out at say 14.8v, you could abs charge without a controller, as well?

And yes, I do realize at times there would be insufficient voltage available for charging, but in a pinch, say if one's controller crapped out, couldn't you just use a direct connection?

at the very least you would need reverse blocking diodes

or at night the panels would become a load on the batteries using power
solar panels ARE solid state devices, they create voltage and current when exposed to light, but they also will use power if connect to batteries in the absence of light

there is also the issue of overcharge if the batteries are in storage and not being use
in any system above trickle charge a controller is needed

If you read some of the comments below the video Red31 posted, one viewer wonders about using a dc-dc buck converter for solar. Hmmm, that sounds eerily familiar.

I'm still not convinced a buck converter with both cv AND cc wouldn't work. Perhaps the only prohibitive factor could be cost?

Salvo wrote:
Your confusion stems from the fact that solar panels are not voltage sources but current sources. In bulk mode, the panel is directly connected to the battery. The panel voltage is equal to battery voltage. As battery voltage rises, so does the panel voltage. When the battery voltage reaches the absorption set point, pwm action begins.

When using a pwm charge controller, panel voltage is never at 17V. Panel voltage has two states, either Vbat or Voc (panel open circuit voltage).

^^This has described what has puzzled me about PWM charging when in bulk mode, thank you.

Seems to me, if using 12v panels, if all you ever did was bulk charging, you wouldn't need a controller at all. And if you were to de-rate the 12v panels to max out at say 14.8v, you could abs charge without a controller, as well?

And yes, I do realize at times there would be insufficient voltage available for charging, but in a pinch, say if one's controller crapped out, couldn't you just use a direct connection?