mppt vs pwm

[pianotuna]

Hi,

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

mppt vs pwm

[brulaz]

vermilye wrote:

pianotuna wrote:
Hi jrnymn,

Since all the controllers I've seen just look at battery voltage they switch out of bulk faster than one might expect. Often I see the Blue Sky change from float to bulk when clouds pass by.

I wonder if this is true of the Bogart Industries SC2030 charge controller. According to their description, it communicates with a TM-2030 to "adjust charging current based on real time battery information". Could be sales hype, but since the 2030 actually keeps track of amp hours in & out, it might be more accurate than battery voltage. Anyone have any further info on this controller?

The roque also maintains and logs Ah and Wh info. But I'm quite sure it doesn't use that info to switch modes. It's just the set points versus the battery voltage. And it has a remote sensor wire for the battery voltage.

To me, PianoTuna's observation is simply that ongoing loads were such that battery voltage drops below the MPPT cutin setpoint when clouds appear. Beforehand and without the clouds, the panels/controller was able to maintain the battery voltage above the cutin (or at the float voltage).

Raising that cutin setpoint when boondocking might help if this is a concern.

[vermilye]

pianotuna wrote:
Hi jrnymn,

Since all the controllers I've seen just look at battery voltage they switch out of bulk faster than one might expect. Often I see the Blue Sky change from float to bulk when clouds pass by.

I wonder if this is true of the Bogart Industries SC2030 charge controller. According to their description, it communicates with a TM-2030 to "adjust charging current based on real time battery information". Could be sales hype, but since the 2030 actually keeps track of amp hours in & out, it might be more accurate than battery voltage. Anyone have any further info on this controller?

[brulaz]

BFL13 wrote:
The $102 Eco-Worthy MPPT 20a controller has an adjustable high set point to reach Vabs, an adjustable Float, and the voltage that triggers a return to MPPT is not adjustable but is 13.2v.
...

When the trailer is in storage or on 110V, I set the float back to 13.2V (the same float V as the Progressive Dynamics charger when on 110v). That seems to work fine with little water loss over long periods although I think my batts call for 13.1V

But when boondocking, I appreciate being able to set the float higher (13.6V) so MPPT kicks in earlier at a higher voltage. Have been told that the higher "float" voltage should not be a problem for the batteries as they'll be all night without any charging.

So far this has worked well. But I suppose it could set it even higher when boondocking and the Rogue kept in MPPT as much as possible.

[jrnymn7]

Brulaz,

Exactly, it's about Vbatt (surface charge, actually) vs. Vabs setpoint. The lower the C-rate (in amps), the lower the Vbatt required for charging, and the lower the voltage drop. So it should go without saying, the controller should remain in mppt well into the charge, if the array is of modest size in relation to the bank.

[jrnymn7]

CA Traveler wrote:
My series panel shading in storage clearly shows the effect of bypass diodes.

Perhaps I'll be able to more testing with summer sun and different kinds of shade.

Ah, yes, it was your OP that got me confused. I will address it in your thread.

[brulaz]

jrnymn7 wrote:


...
Or do folks see mppt drop out of mppt at a lower than expected SOC, and stay there?

And Brulaz brings up a good point. Perhaps some have their mppt's setpoint too low, and this is causing premature de-bulkulation?

Not sure how the MPPT would measure SOC. According to Rogue they just compare the battery voltage, which can vary with loads, SOC, to the setpoint (14.8V in my case). And move into Absorb mode when the setpoint is reached.

The manual also makes this point:

Rogue wrote:
Under some conditions (very low light and shading) the array’s power curve will be nearly flat and will have no discernable maximum power point to track. This can be especially evident when using series-wired modules.
During these periods, which are common in the morning and evening, and potentially during periods of array shading, the PV array produces little usable energy and the MPT-3048 may attempt a more efficient direct connection between the array and the batteries.

[CA_Traveler]

My series panel shading in storage clearly shows the effect of bypass diodes.

Perhaps I'll be able to more testing with summer sun and different kinds of shade.

[jrnymn7]

PT,

I'm wondering if when one sees an mppt drop out of mppt, seemingly early, if it's not just a matter of a (temporary) drop in panel voltage, which in turn would not be able to support the amperage that WAS going into the battery, thus amps would begin to taper? Seems to me, it would be like turning down the voltage on a PS, while still in bulk. Suddenly Vbatt would be at or above that of the supplied voltage, and switch the batteries into abs mode.

Or do folks see mppt drop out of mppt at a lower than expected SOC, and stay there?

And Brulaz brings up a good point. Perhaps some have their mppt's setpoint too low, and this is causing premature de-bulkulation?

[BFL13]

The $102 Eco-Worthy MPPT 20a controller has an adjustable high set point to reach Vabs, an adjustable Float, and the voltage that triggers a return to MPPT is not adjustable but is 13.2v.

It drops to Float right after reaching Vabs, so if you want to spend any time at that voltage you have to choose the Float voltage to be the same as Vabs. Then you must adjust the Float voltage down to your chosen value if you want to float at a "storage" level for maintaining the batts while not camping..

Since the Float only goes up to 14.4 and I choose 14.8 as Vabs, I get to 14.8 at some point during the day and then it drops to 14.4 till dark. Then voltage falls off to actual Vbatt by morning which is below 13.2, so MPPT kicks off again for the new day.

My 6v batteries really like that profile and get to baseline SG without needing an equalize session. My T-1275s want more time at 14.8 or higher, so this controller is not quite right for them. (The PWM Solar30 stays at the chosen Vabs -can be up to 15- till dark so that controller was better for the T-1275s as it turned out)

PWM and MPPT controllers have adjustable settings depending on models and price. As noted what happened between my 6s and T-1275s, you should compare your battery specs with the controller specs to get a good match before buying.

[jrnymn7]

Thanks, Mr. Wizard, that helps a lot.

[brulaz]

Thought most MPPT controllers allow you to set the voltage at which "bulk" (MPPT) stops and "absorb" starts.

And shouldn't there also be a low setpoint voltage for switching from float back into MPPT?

The higher you set these voltages the more time the unit will spend in MPPT (bulk) mode.

I've increased the upper limit on my Rogue MPPT controller to 14.8V and the lower to 13.6V (when boondocking). This seems to have increased the amount of time in MPPT by quite a bit.

And you can also control the amount of time spent in absorb, or eliminate it completely.

[MrWizard]

mena...!

that wasn't 17ampHrs for the day total
not 17amps charge rate

the remarkable part is he did it with 280w of solar
i've done it but i have 505w of solar

like he said, the LiFePo have a very slow voltage rise
which maintains the the voltage spread and gives the mppt something to work with

[mena661]

17A while it's raining? Wow!

[12thgenusa]

jrnymn7 wrote:
I'm a little curious as to why comparing mppt to pwm often results in being accused of having some "aversion" to watts... what's up with that??? No one is denying mppt takes wattage and turns it into amps at a given voltage. We're just trying to get past the marketing hype, and get to the real facts. If that offends some people, I suggest they take a step back, and ask themselves why they are so emotionally attached to their mppt controllers? I mean, seriously?

Sorry. Maybe I should have used a 😉 instead of a :). It was just a little reference to the fact that every time the MPPT/PWM discussion comes up it gets stated that watts don't really matter; It's amps into the battery that count.

[BFL13]

jrnymn7 wrote:
I'm a little curious as to why comparing mppt to pwm often results in being accused of having some "aversion" to watts... what's up with that??? No one is denying mppt takes wattage and turns it into amps at a given voltage. We're just trying to get past the marketing hype, and get to the real facts. If that offends some people, I suggest they take a step back, and ask themselves why they are so emotionally attached to their mppt controllers? I mean, seriously?

That might be my fault. I hate Watts. I only like amps and amp hours. They are honest. Watts are sneaky mixtures of variables that can be presented to prove anything. A salesman's friend! 🙂