mppt vs pwm

[pianotuna]

Hi,

A nice little video comparing mppt vs pwm with the batteries in bulk mode.

mppt vs pwm

[Ductape]

After 12 pages, I just want to thank PT for posting a good example of how DC to DC conversion can deliver higher charge currents and wattage than simply connecting the panel to the battery. Lots of good discussion also regarding the language of science and engineering vs. marketing claims.

Almost as lively as the gas vs. diesel debates.

As for me, the upcoming install will definitely be MPPT. And my focus will be on harvesting in less than optimal conditions, not how it works under ideal conditions because we won't be parked in Arizona. Not necessarily an economic decision, but who can resist the tech toys? After all, none of us really got into RVing out of economic necessity. I hope.

[jrnymn7]

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

[CA_Traveler]

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.

[red31]

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.

[MrWizard]

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

[pianotuna]

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?

[jrnymn7]

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?

[MrWizard]

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

[jrnymn7]

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?

[ewarnerusa]

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.

[jrnymn7]

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?

[Salvo]

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).

MrWizard wrote:
you seem to be under the assumption that panel output is 14v instead of 17v ?
and doesn't get altered and processed to become 14+ charging volts
try measuring the panel voltage at the input of the controller

[NinerBikes]

So far, I've stayed small in my solar panel application, stayed 12V, and stayed PWM. Observing and learning from others more experienced than me has proved helpful.

All this stuff will change again for charging needs when LiFePo gets more cost effective and mainstream in RV battery applications. What will we debate to death and fanboi over then???

[JiminDenver]

BFL13 wrote:

MrWizard wrote:
Well I give in and will drop the debate
The proffered explanations, do not match the true definition of PWM
So mfg have borrowed and corrupted the terminology

Yes, salesmen vs engineers again. ISTR the usual sort of bulk converter also has some variety of PWM to hold its output voltage constant. It can get very frustrating tying to follow all this!

I know my head is swimming but wada thread. 🙂

[grizzzman]

MrWizard wrote:
you seem to be under the assumption that panel output is 14v instead of 17v ?
and doesn't get altered and processed to become 14+ charging volts
try measuring the panel voltage at the input of the controller

a shunt controller goes on off

a PWM controller "modulates" the voltage

i know you don't believe me , you think i'm wrong
test equipment will tell the truth either way

When battery is say around 12 volts in the morning a PWM controller will
go into bulk. Durring this phase the panels are just plain connected to the battery untel absorbsion voltage setpoint is met. At this point it goes into PWM. Remember solar panels are current devices. It is only after the battery resists the amps (as decided by the voltage setpoint)
That voltage will rise to the setpoint. The big consern with what you are stating is misinformation.

The poor "lurker" who is trying to get a handle on solar may choose to believe you.