Test Method PWM vs MPPT ?

[BFL13]

I might get a chance to compare MPPT with my PWM on the set of two 100w panels. I get 12.6 (Isc) now with PWM so that is the "standard"

I was thinking of a quick connect set-up to swap controllers in place, and also to run the two 100s as 12v like now and as a 24v in series.

I gather MPPT does better on lower battery voltage. Does having a loaded voltage on the battery work for that same as if the SOC were lower? If so I could do two voltages, one low one higher on each test. Or?

Is it ok to swap controllers in place? I might have voltage drop that has no effect on the PWM but might bother the MPPT, no idea.

Any suggestions on how to do a quickie test (of course with no clouds that day, and do it mid-day, etc etc.)?

I have no idea how to test for the (bogus?) claim that MPPT will have a greater percentage gain in the shoulder hours. If there is an easy test for that I could do that I suppose (have Trimetric)

Not clear yet whether I will get the chance but hints of it. (borrowing the MPPT) Want to be ready ahead of time so can prepare a test set-up that is fair. (Otherwise, those MPPT guys will moan and whine 🙂 )

[Old___Slow]

Just finding a place to jump in~ carry on~

Well, I now have the two Controllars.

For those who see on EBay parts from HK direct to your home, it works.
12 days from order to del. I ordered the PWM Type 20 (20A 12V/24V)working voltage12v24v Rated charge current 20A Rated load current 20A @ $16.98 today to my door. No problem with Customs whatsoever.

Now, being back home, 150 miles from the RV with two Deep Cycle 12v Die Hards, no way for testing of the $49.95 MPPT and the $16.98 PWM that I now have in hand.

Me thinks from reading this thread, the small stuff will have to be bought from HK. China Post(Air Mail) Shipping on small orders of panels must be through the roof.

Reading this thread, from a novice point of view, makes me wonder if the highter priced Controllars are all, skies the limit for pricing?? Smoke and mirrors for free.

The new 20A PWM from HK direct, looks awesome but only about half the size and weight of the MPPT. Seems less guts in the PWM, how would I really know. Anxious to see how the (WORKING MODE) LCD acts. I will say the out side looks quality built.

O&S
Floyd

[Salvo]

I would use a double pull double throw switch to be able to switch the controllers in an instant. You would switch plus battery to either controller and switch plus panel power to either controller. The grounds can remain common. Not sure how your positive ground controller will affect this wiring configuration.

Sal

[BFL13]

No the other. Mine are Poly (or whatever not Mono is)

[HiTech]

CYC100W mono panels on This page?

Jim

[BFL13]

If Battery Acceptance becomes a factor for the higher voltage test in the 14s, I have a drill for that. I turn off solar, turn on some lights to lower the voltage, note the neg amps on the Trimetric, turn on solar, note the new amps showing and the diff is solar. As long as solar amount is the most solar can do, we're good or else I turn on more lights.

You do have to be quick though, since lights dim and then draw fewer amps. OTOH, an inverter has amps creep where it draws more amps as time goes by and batt v falls.

With the 458AH bank it will still take 20amps when batt v gets to 14.3 or so anyway, but not for long after, that is true. And we are talking somewhere over 12a here.

Sun panels are made by Chinayard. Have curves for 24v but not 12v. Expect are the same as most others though.

I don't have the model number if there is one, I am not at the trailer site till later in the week.

http://chinayard.com/solar%20product/solar%20module/solar%20modules.htm

the local dealer is out of stock waiting for a new shipment so he is taking a break if anyone is wondering where he got to. 🙂

[HiTech]

What model panel(s). Interested in looking up the curves and more detailed specs.

Jim

[hmknightnc]

BFL13 wrote:

Where it gets sticky is all this stuff about voltage levels. My morning voltage these days is usually 12.6ish and soon gets into the 13s. It has no value for me to know what the comparable amps would be at 12v. I would just like to know what diff it would make if I had MPPT instead of PWM in my "operating range" (say 12.6 to 14.6v)

If I can, I will try for a test of each kind (12 and 24) around 13 and another around 14.3ish.

Well that's a good test for your real world conditions under these I suspect that battery acceptance rate will start to have a major influence in the results

I will bet you a cold one that you see little to no difference between the two since the battery will become the limiting factor. And any difference you do see will certainly not be worth the cost in the difference in the controllers

[BFL13]

My 100w panel specs are Voc 21, Isc 6.4 Vmp 17.5, Imp 5.71 ("with a 5% tolerance" among panels with that same 100w rating)

I get lower Voc usually, but have seen higher, it seems due to temperature variation, which does not bother the Isc, the way that all works. I get about 6.4 and 6.2 for Isc going from one panel to the other.

I don't know if the 6.2 one is lower all round or just its Isc. I am happy with that 6.3 average since it matches what I get with my Sharp panel

[JiminDenver]

My mistake BFL, you will be in series so the differences in VOC wont have the same effect as if I were trying to parallel two high voltage panels with different VOC.

[HiTech]

The amps of the lower one at its operating voltage limits the current the two can deliver in series.

Raw Voc is reasonable to use if the panels are of similar technology, but really it is only for combining to determine if the controller can handle the panels in the configuration you want IMO. If you have two panels, one with Vmpp at 73% of Voc and one at 83%, straight Voc is not too useful in that case for figuring the potential watts you will generate. Vmpp of the system as a whole is what will be used by a perfect MPPT controller.

In this case you might well end up with a Vmpp of the system at about 74% of the overall series Voc because pulling the low percentage panel to any higher voltage would crush the amps and watts the system could put into the controller. If the volts distributed unevenly across the two panels, then all bets are off and you'd have to measure the actual Vmpp to have any idea where it would land.

In parallel it would almost certainly be somewhere around 74% of Voc (assuming the two Voc's are equal) for the same reason - pushing a single panel much past its Vmpp is likely to crush the total watts of the whole system. Thus panels with matched Vmpp at likely operating conditions (NOCT being a decent starting point) matters much more than matched Voc's in my opinion.

Voc is easy to measure though, so if you can find the Vmpp for each panel from charts or by measuring it, then you can likely use the actual current Voc times that percentage of Voc to get Vmpp pretty closely for different measured Voc's on each panel.

Jim

[BFL13]

I really only care about what amps I get. I'm Rving and somebody says if only you swapped this controller for that one you would get more amps. How many more? How much will that cost extra?

So I would try the other one out first instead of buying it on spec. How would you try it out? Stick it in there instead of the one you have now. Should be so simple.

Yes, the test MPPT controller would have to be able to handle my two panels in either 12v or 24v. "If I fry it I own it" being likely.

[JiminDenver]

I think the difference in MPPT that matters is the VOC and not the amps. I can't run my panels together on the Eco-worthy even if it could handle the amps because they act so differently VOC wise in different light.

Whatever MPPT controller you get, make sure it can handle the combined voltage.Mine is limited to 42v. Your panels in series would be to high for it at max.

[HiTech]

In series it will likely pick a voltage that is little to low for one panel and ever so slightly too high for the other, which will put out maximum watts for the system overall at that point, unless the panels are badly mismatched for Amps at mpp or volts at mpp, which it sounds like they are not.

What is not clear to me in series is what the factors are when pulling the combined voltage of series panel down that determine the voltage of each individual panel. I think if I put a piece of foil in between the MC3 connections and pressed them together, it would five me a simple voltage tap between them to be able to determine the voltage of each.

Jim

[BFL13]

It's not for sure I will get to run this test, but at least I'll be ready thanks to you guys providing these tips.

I will have to note what the MPPT controller does in the way of being PWM at times so I test it when it is doing MPPT.

I already have the results for PWM side of the test I suppose, but I will run both anyway if I have to change any wiring from the way it is now that might throw off the numbers wrt voltage drops somehow.

All I will do for the 12v test is leave my array as is and swap controllers in place and see what the amps are now. Ought to be easy.

I will then redo my two panels into series so it is a 24v 200w "panel" and see if the MPPT amps are any different from what they were on the 12v test.

Where it gets sticky is all this stuff about voltage levels. My morning voltage these days is usually 12.6ish and soon gets into the 13s. It has no value for me to know what the comparable amps would be at 12v. I would just like to know what diff it would make if I had MPPT instead of PWM in my "operating range" (say 12.6 to 14.6v)

If I can, I will try for a test of each kind (12 and 24) around 13 and another around 14.3ish.

The two panels are not quite the same in real life when I take Voc and Isc and Sun says there is a small tolerance in their specs, so if that screws up the MPPT --too bad! 🙂

I often get say 20.3 Voc (temp effect AFAIK down from 21.x) but 6.4 Isc on one and 6.2 on the other, and it comes out at 6.3 av using both together at 12.6a. that compares well with my 130w Sharp panel at 8.2 Isc. 100/130 x 8.2 = 6.31

In series to do the 24v test, it will come out however the lower panel does I suppose, can't be helped. The amps I get will tell the tale.

[HiTech]

Ok makes sense. BFL tends to pick his panels to optimize PWM, going for max Isc per watt. Mine also happen to have high Isc/watt though I did not pick them specifically for that attribute.

Jim