I was able to run a couple tests with blue sky at same time of year and location as my test from two years ago (flat, tilted, tracking results one) that :A. compares PWM with MPPT, andB. compares MPPT at 14.0v with MPPT at 12.2v (battery) First test:0900 battery 13.3v-- 130w panel and PWM at 7.3a (same as two years ago at 0900) Scaling this to 230, should be 7.3 x 230/130 = 12.9aThe actual 230w MPPT was 13.1a and 176wSecond set with sun higher at 1000.Test one-- battery 14.0v130w panel rated Isc is 8.2a but the IV curve drops this at mid-13s on up, Got actual Isc as 8.21 but with the 14.0v battery got 7.8a, scaled up to 230 should be 13.8aMPPT was 13.59. 230w Panel rated Isc is 8.3a, 37Voc. Got 8.26/34.7Test two-- a few minutes later with loads running and battery voltage now down to 12.2 holding there.PWM 8.2a-- would be 14.5a at 230. 230 panel now at Isc 8.42 and 34.7Voc. Still at 189w with 12.2v and 15.48a.So as shown in the previous set of comparisons last month, the MPPT "performance" is all about battery voltage as to how many amps you get.Summarizing the above on the same 189w (of 230w) you can have 13.59a with 14.0v, or15.48a with 12.2v.At high noon MPPT should do better than here at 1000 but some clouds coming in, not sure will get a noon reading. Will edit that in if available.

Nice comparison. PWM is pulse width modulation. It "lops" the incoming voltage coming in to whatever it thinks the batteries need, then eventually just pulses a charge. MPPT (maximum point power tracking) will fiddle with the amps/volts to get the right voltage coming in. PWM is cheaper, but you lose a good chunk of energy due to the fact that what it can't use, it discards. For example, a 24 volt, 300 watt panel will essentially be a 12 volt, 150 watt panel, while with a MPPT controller, it can use the higher voltage and downconvert it.For a large area of solar panels, a PWM controller might be useful. For the limited real estate on most RVs, you want every single watt you can get, thus a good MPPT controller.

mlts22 wrote:Nice comparison. PWM is pulse width modulation. It "lops" the incoming voltage coming in to whatever it thinks the batteries need, then eventually just pulses a charge. MPPT (maximum point power tracking) will fiddle with the amps/volts to get the right voltage coming in. PWM is cheaper, but you lose a good chunk of energy due to the fact that what it can't use, it discards. For example, a 24 volt, 300 watt panel will essentially be a 12 volt, 150 watt panel, while with a MPPT controller, it can use the higher voltage and downconvert it.For a large area of solar panels, a PWM controller might be useful. For the limited real estate on most RVs, you want every single watt you can get, thus a good MPPT controller.thanks for the clarification.

The heart of a MPPT controller is a dc-dc converter with a variable voltage input that's controlled by a microprocessor of some sort. The controlled dc-dc converter forces the solar panels to operate at the optimum voltage-current combination for the current light conditions. It uses some sort of algorithm to find the optimum operating voltage for the panels, which changes as the light conditions change. The PWM controller doesn't have the capability to force the panels to operate at the optimum voltage-current combination.

The above comments are mis-reading the results shown.The MPPT "advantage" is all at the lower battery voltages. This means the RVer who is just using his solar to recharge his battery bank gets essentially no advantage. His bank will be in the 13s right away in the morning and go up from there.The MPPT advantage would go to those who run loads with their solar, where battery voltage remains in the 12s all day. This way, you get the advantage in higher amps from MPPT to run the loads.You can run loads after your batteries are full with either PWM or MPPT too, using "spare solar" but now the batts are full and floating.You could lower your solar float to 13.2v and get some (but only a little) MPPT advantage at that voltage instead of at 13.8 or whatever."Depends" whether that would be worth the bother most days.Other considerations may still prevail, where 24v panels cost less than 12s, or you want to use thinner wire, or you want more watts per square foot of panel with your limited RV roof space.But just going with 12s PWM vs 12s or 24s MPPT and what happens with the amps in each case for the same wattage, what you see in the OP is how it is. You do not "lose" anything with PWM when both get you the same amps!!!! Forget the watts.

Yet Another PWM vs MPPT Comparison Test | Good Sam Community

20 Replies

NinerBikes
Explorer
May 21, 2014
BFL13 wrote:
NinerBikes wrote:
BFL13 wrote:
greenrvgreen wrote:
IMO, a "real world test" must be done with a load on the batts equal or GREATER than the capability of the panels. AFAIK, I've never "recharged" my batteries, but I'm constantly in the process of trying to replace what I'm constantly taking.

+1 on the PWM with 12v panels. I was surprised by how efficient that combo is.

You will note in the OP that the 12.2 volt test was done with battery loaded. Had over 100a load compared with about 24a in from solar. You still have to wait until the 100a or whatever load takes the battery voltage back down to the level you want to measure MPPT performance at.

You can do "replacement" every day and get however close to full each day that gets you, depending on the weather etc. Every so often you must do a full 100% "overcharge" (equalization type of charge works for this) or your batts will get sulfated permanently losing some capacity.

Various techniques available for doing that, including by-passing the controller with a "split bank" method if still camping.

You CAN only do the bypassing and split banking if you have 12V panels that run at a Vsc of 17 to 17.5... the goal being to get the equalization voltage at the battery either up to 16.0V, or your Specific Gravity up to 1.280 or thereabouts, depending on what your baseline new battery SG was.

I see no reason you cannot by-pass the MPPT controller and use 24v panel direct. It can only do its Isc of say 8.3a. I have not tried it though. Perhaps the battery voltage would rise too high before the SG got up there?

The 12v panel voltage in the 17s is the Vmp, which means nothing to PWM, but is important for MPPT. 12v panel Voc can be important where you sometimes see ratings in the 22s instead of 21s for the same wattage, which leaves the Isc lower than usual. You want highest Isc per watt for your panel dollar with PWM.

And start off with 29 to 30V at the panel, into a 12V battery, no controller? Will it work? I don't even know. Seems excessive.
BFL13
Explorer II
May 21, 2014
NinerBikes wrote:
BFL13 wrote:
greenrvgreen wrote:
IMO, a "real world test" must be done with a load on the batts equal or GREATER than the capability of the panels. AFAIK, I've never "recharged" my batteries, but I'm constantly in the process of trying to replace what I'm constantly taking.

+1 on the PWM with 12v panels. I was surprised by how efficient that combo is.

You will note in the OP that the 12.2 volt test was done with battery loaded. Had over 100a load compared with about 24a in from solar. You still have to wait until the 100a or whatever load takes the battery voltage back down to the level you want to measure MPPT performance at.

You can do "replacement" every day and get however close to full each day that gets you, depending on the weather etc. Every so often you must do a full 100% "overcharge" (equalization type of charge works for this) or your batts will get sulfated permanently losing some capacity.

Various techniques available for doing that, including by-passing the controller with a "split bank" method if still camping.

You CAN only do the bypassing and split banking if you have 12V panels that run at a Vsc of 17 to 17.5... the goal being to get the equalization voltage at the battery either up to 16.0V, or your Specific Gravity up to 1.280 or thereabouts, depending on what your baseline new battery SG was.

I see no reason you cannot by-pass the MPPT controller and use 24v panel direct. It can only do its Isc of say 8.3a. I have not tried it though. Perhaps the battery voltage would rise too high before the SG got up there?

The 12v panel voltage in the 17s is the Vmp, which means nothing to PWM, but is important for MPPT. 12v panel Voc can be important where you sometimes see ratings in the 22s instead of 21s for the same wattage, which leaves the Isc lower than usual. You want highest Isc per watt for your panel dollar with PWM.
NinerBikes
Explorer
May 21, 2014
BFL13 wrote:
greenrvgreen wrote:
IMO, a "real world test" must be done with a load on the batts equal or GREATER than the capability of the panels. AFAIK, I've never "recharged" my batteries, but I'm constantly in the process of trying to replace what I'm constantly taking.

+1 on the PWM with 12v panels. I was surprised by how efficient that combo is.

You will note in the OP that the 12.2 volt test was done with battery loaded. Had over 100a load compared with about 24a in from solar. You still have to wait until the 100a or whatever load takes the battery voltage back down to the level you want to measure MPPT performance at.

You can do "replacement" every day and get however close to full each day that gets you, depending on the weather etc. Every so often you must do a full 100% "overcharge" (equalization type of charge works for this) or your batts will get sulfated permanently losing some capacity.

Various techniques available for doing that, including by-passing the controller with a "split bank" method if still camping.

You CAN only do the bypassing and split banking if you have 12V panels that run at a Vsc of 17 to 17.5... the goal being to get the equalization voltage at the battery either up to 16.0V, or your Specific Gravity up to 1.280 or thereabouts, depending on what your baseline new battery SG was.
12thgenusa
Explorer
May 21, 2014
BFL13 wrote:
How about if the idea is to run loads all day you get the batts charged up using the high set point at 14.8, then add the loads to knock that voltage back down below 13.2, then reset the high set point (not the float setting) to 13.2 so it doesn't go back up on you when the loads are not so much from time to time?

I believe setting the "high point" lower will make the controller kick out of MPPT even quicker.

I do run quite a bit of loads during the day and it does hold the voltage down which keeps the controller in MPPT for much of the day. Powering loads during the day is nice in that it's "cheaper" power. By that I mean that you don't have the losses of charging/discharging the batteries. The power goes directly to the loads.

It's a balancing act though. You don't want to demand too much such that your batteries don't get recharged. On the other hand, the more you use for "free" during the day, the less you have to put back in the batteries the next day.
BFL13
Explorer II
May 21, 2014
greenrvgreen wrote:
IMO, a "real world test" must be done with a load on the batts equal or GREATER than the capability of the panels. AFAIK, I've never "recharged" my batteries, but I'm constantly in the process of trying to replace what I'm constantly taking.

+1 on the PWM with 12v panels. I was surprised by how efficient that combo is.

You will note in the OP that the 12.2 volt test was done with battery loaded. Had over 100a load compared with about 24a in from solar. You still have to wait until the 100a or whatever load takes the battery voltage back down to the level you want to measure MPPT performance at.

You can do "replacement" every day and get however close to full each day that gets you, depending on the weather etc. Every so often you must do a full 100% "overcharge" (equalization type of charge works for this) or your batts will get sulfated permanently losing some capacity.

Various techniques available for doing that, including by-passing the controller with a "split bank" method if still camping.
greenrvgreen
Explorer
May 21, 2014
IMO, a "real world test" must be done with a load on the batts equal or GREATER than the capability of the panels. AFAIK, I've never "recharged" my batteries, but I'm constantly in the process of trying to replace what I'm constantly taking.

+1 on the PWM with 12v panels. I was surprised by how efficient that combo is.
BFL13
Explorer II
May 20, 2014
12thgenusa wrote:
BFL13 wrote:
You could lower your solar float to 13.2v and get some (but only a little) MPPT advantage at that voltage instead of at 13.8 or whatever.
"Depends" whether that would be worth the bother most days.

On most controllers, MPPT is only operating in bulk mode, not Absorb or Float. Rogue in fact calls bulk mode, MPPT mode. Changing float set point would have no effect.

I may be mixed up in what is possible here.

The Eco-Worthy MPPT controller is the same. It gets the batts up to the chosen set-point say 14.8, then drops out of MPPT and goes PWM to the chosen float set point. No time seems to be spent at "absorb" before going to float, although it says absorb for a second there if you don't blink! It may just be my set-up where the batts are near full by the time they hit 14.8.

What I was thinking was the scenario where you are running loads near max amps of the controller after getting the batts to 14.8 and it drops to float would kick it back into bulk so MPPT.

But the batt voltage has to drop below 13.2 before it will go back into bulk. The "loaded voltage" on the nearly full batts would have to be below 13.2 but that would not be your "float voltage"

How about if the idea is to run loads all day you get the batts charged up using the high set point at 14.8, then add the loads to knock that voltage back down below 13.2, then reset the high set point (not the float setting) to 13.2 so it doesn't go back up on you when the loads are not so much from time to time?

Then you have to reset that to 14.8 for next morning. Anyway you are right-- it doesn't work like I was thinking.
pianotuna
Nomad III
May 20, 2014
Hi BFL13,

Thanks for checking. I do seem to get better results for about the same wattage, but then I push my batteries hard.
12thgenusa
Explorer
May 20, 2014
BFL13 wrote:
You could lower your solar float to 13.2v and get some (but only a little) MPPT advantage at that voltage instead of at 13.8 or whatever.
"Depends" whether that would be worth the bother most days.

On most controllers, MPPT is only operating in bulk mode, not Absorb or Float. Rogue in fact calls bulk mode, MPPT mode. Changing float set point would have no effect.
JiminDenver
Explorer II
May 20, 2014
There is also the thought that a different MPPT controller may extract more out of the high voltage panel. Once I get the TS-mppt I'll see how they compare.