Heat 1, MPPT 0

[BFL13]

Previously we noted that heat is hard on MPPT due to the panel's loss of voltage with increasing heat. Doesn't bother PWM though, you still get Isc or more.

This Spring, I took some measurements posting the MPPT vs PWM values, and at high noon was getting about 15.5 amps vs 14.5 for PWM.

The thought then was when it warmed up for Summer the MPPT "advantage" would not be even that much. So here we are in some hot weather (for here) so a comparison was made.

I have been noticing lately that the expected amps just aren't coming in and wondered what was the matter. Checked everything, nothing found wrong, then measured temp under panel. Oops.

So here are the Spring/Today figures in blue sky no clouds all same set-up.

Ambient temp- 16C/24C
Under panel temp- 44C/48C
Voc-35.4/34.0
Isc- 8.7/8.4
Amps output 15.71/13.88 (both at 13v battery)
Panel watts (of 230w)- 205/181

So instead of getting 1 amp more than PWM, now I am getting 1 amp less than PWM for my 230w. It seems the only difference in conditions is the temperature. The under panel temp is not that much more compared with the big jump in ambient, but it is enough to hurt the MPPT.

BTW, panel voltage coefficient is - 0.330%/degree C. Rated Voc is 36.8v got 34, diff is 2.8. Temp diff is 48-25C = 23 and 23 x .33 is 7.6 and 7.6% of 36.8v (rated Voc) = 2.8v and that minus 36.8 is 34, which us what I got for Voc so that all works out.

Bottom line us that MPPT sucks unless you use it in the Arctic 🙂 I would do better with two 115w panels than with the single 230w. Fortunately, with the warm weather there is also no furnace to run, so the loss in solar doesn't matter, but I still get annoyed when I don't get those amps in whether I need them or not! Drat and phooey!

I can't even complain that this is a surprise, since I used to post about that before I got this set-up. I got it because the price of the 230 was better than two 115s. Now I am paying the other "price" in aggravation.

[JiminDenver]

Don

The trailer was damaged in a hail storm and while the insurance authorized repairs, the service center says it will be totaled. We may get it back cheap and it's really not bad, or we may be starting over. In that case there is a Passport we both like that the Expy can pull.

[pianotuna]

Hi,

Problems? I hope it is nothing serious.

The TS MPPT 60 is more efficient than the 45 because it has 3 circuits "stacked" vs the 45 which has only 2. It is a bit more money.

JiminDenver wrote:
I may still get a TS-MPPT-45 but until we know what is happening with the trailer,everything is on hold.

[JiminDenver]

mena661 wrote:

JiminDenver wrote:

I wanted to mention that there is a person on you tube by the name of icurnet that successfully uses two 150w 12v panels in series. He has a bunch of videos including time lapsed days where he exceeds 20a at times.

Is that using the EcoW?

Yes, with the Eco-w. I should have mentioned that too. lol

Until seeing the videos I assumed that two 12v panels in series would exceed the Voc limit. He uses them in a house daily.

[BFL13]

Mena, can't be. The Eco-W limit is 42Voc.

[mena661]

JiminDenver wrote:

I wanted to mention that there is a person on you tube by the name of icurnet that successfully uses two 150w 12v panels in series. He has a bunch of videos including time lapsed days where he exceeds 20a at times.

Is that using the EcoW?

[BFL13]

There is no evidence that there is anything wrong with the Eco-
W so no reason to change horses IMO.

Not sure what is remarkable about the 20a with two aimed 150s in series. In parallel they would get 150/130 x 8.2 = 9.46 x 2= 18.9, so 20 with MPPT is as expected IMO

[JiminDenver]

I may still get a TS-MPPT-45 but until we know what is happening with the trailer,everything is on hold.

It would be interesting to see a side by side comparison between the controllers. Right now I would consider the only advantage in a more expensive controller is more features. Should someone prove that there is something else to be gained, so be it. Otherwise the Eco-w's are functional and as long as they are used properly, dependable too.

BFL

I wanted to mention that there is a person on you tube by the name of icurnet that successfully uses two 150w 12v panels in series. He has a bunch of videos including time lapsed days where he exceeds 20a at times.

[BFL13]

12thgenusa wrote:
Refresh my memory. How are you obtaining the PWM amperage for comparison on the 24-volt panel.

I discovered with my various wattage 12v panels that they have Isc in proportion to the wattage (except some with extra high Voc which then have lower than usual Isc) So my 80w got 5a, the 130 got 8.2 and the 120 got 7.6.

So it works out that 230w worth of 12v panels would get 230/130 x 8.2= 14.5amps I was getting 15.5 with the 230 and MPPT so that was the comparison. Now I am getting a bit less than the 14.5 I would be getting if I had two 115w panels and PWM.

Only thing that has changed is the ambient temperature. The under-panel temp has not changed much with the rise in ambient.

The wattage as reported on the controller readout, matches the amps as seen on the Trimetric and the controller times the battery voltage. Now the wattage is consistently lower than before and so are the amps.

[12thgenusa]

Refresh my memory. How are you obtaining the PWM amperage for comparison on the 24-volt panel.

[BFL13]

I tried a couple things today- at 1030 and then at 1230.

Conditions today at noon the same so same readings. However, I did move the panel right up to the trailer and swapped out the long hot wire for a short cool set that had been in storage out of the sun

This did not change any of the readings, so the wire idea is eliminated. Also shows my regular panel-controller run with long but fat wire is not costing me anything in amps compared with the short run.

Earlier in the day it was cooler and I did get some numbers that show a little better, but not a lot.

Panel Isc was just over its rating so insolation good, sun high enough etc.
Ambient 22C back of panel 44C ( yesterday noon was with 24/48)
Panel wattage was a little higher at 184 vice 181

Got 14.03a at 13.1v, 14.53a at 12.7v, and 15.57a at 11.9v

So the under panel temp was 44C same as in the Spring with ambient then 16C so that leaves the difference in ambient temp as the prime (only?) suspect.

Panel voltage and amps were the same with same panel temp, but the wattage was lower with the higher ambient temp and amps thus lower for any same battery voltage.

So that all happens in the controller which is in a cool shaded spot in the cargo bay but is at ambient temp. Hmmmm. Now I suppose I should put a bag of ice against the controller !!!

EDIT: ok first the temp on the board the controller is mounted to is 23C , same as ambient. The controller was 31.5C --they do warm up when running; I can't say if that is a normal amount.

I put some things from the freezer against the controller with it first showing with the load added on 13.0v 12.4a 161w in Float, but then with the load running it changed to Bulk 13.0v 14.31a, 184w

After a time with the freezing bags against the controller, the controller was down to 25C but no change in watts at 184w. I couldn't keep it going long enough to get the controller down to whatever it might have been above ambient when ambient was 16C.

So I don't have any more ideas. I see the "controller snobbery" has come up a few times over the Eco-Worthy not being True Blue etc and the implication is that this whole thing could never happen to them with their expensive "proper" controllers.

To that I say, run your own tests and post the results and let's see!
Snobbery is not test data folks.

It would be worth knowing if some controllers are better than others for how many amps are lost in hot weather, ASSuming it is indeed there and not in the panel which was the first thought (maybe still correct but doesn't seem like it now)

[pianotuna]

Hi,

That is assuming a quality controller--and BFL's may not fit that description.

MrWizard wrote:

If the panels get so hot the voltage is low, the MPPT should be passing the amps straight thru

[mena661]

BFL13 wrote:
I haven't measured comparable voltage drops Spring/Now, but does wire resistance go up if the wire is hotter?

Yes.

https://answers.yahoo.com/question/index?qid=20071006180136AA7RBgV

[BFL13]

I could well be missing something here about what is really happening. Near as I can tell the only difference in the two situations was the temperature as described in the OP.

Battery SOC (near full) was taken out of play AFAIK by using loads at higher amps than the panel can ever do then seeing how much of the load the panel took (as seen on Trimetric) and also on the controller's own ammeter reading.

Panel is tilted up with a breeze behind it so no trapped heat, just the sun on the front, temp taken at back on the white part.

Panel wattage taken from controller's readout, which appears to use its ammeter amps x battery voltage. One thing I see is that the panel wattage stays about the same while you can vary the battery voltage with loads. As the batt voltage changes, that makes the amps change where the wattage is steady. In the Now test as seen in the OP, panel wattage was only 181-4ish when in better times it is closer to 200. (of 230)

It is a little cooler today in a sea breeze but with same good sunshine blue sky so I will get another set of numbers for comparison with yesterday's if panel temp is lower.

EDIT- another thought--the panel to controller wiring is strung out along the ground from the contraption to the trailer, so that wire is getting hotter in the sun too. I haven't measured comparable voltage drops Spring/Now, but does wire resistance go up if the wire is hotter?

[MrWizard]

By noon, the batteries have been charging at 16 amps for "4" hours, so after receiving 64 amp hours, there is going to be drop of in battery acceptance, even without heat causing a drop in panel voltage

I know I have a heat problem, I wish I had made my brackets taller

But I would not be do quick to say a 0.5 amp drop during heat is a loss from PWM to mppt (8.5>8. Or 16.5 > 16)

Did either of you check watts output with a "watt meter"
You can't directly compare amp hours only
The mppt will be boosting voltage, which means higher watts at less amps
If the PWM is doing 8.5a*x volts and the mppt is doing 8.0a * y volts, there may not be any loss at all, there may even be a gain
If the panels get so hot the voltage is low, the MPPT should be passing the amps straight thru