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pianotuna

Regina, SK, Canada

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Posted: 01/27/21 09:10am Link  |  Quote  |  Print  |  Notify Moderator

Stircrazy,

We are not recommending against MPPT. There was a budget constraint, so the extra cost of MPPT did not "fit" the frame.

Back when panels were $5 per watt, MPPT was a no brainer. Now they make sense only if the owner has run out of roof real estate and maxed out the panel numbers.

Good PWM controllers are also 3 stage chargers, and some have voltage sensors on the battery bank.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

BFL13

Victoria, BC

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Posted: 01/27/21 09:25am Link  |  Quote  |  Print  |  Notify Moderator

In Float the MPPT controller keeps the voltage to the battery at the Float set-point, but the issue is the controller wrt the panel voltage.

The panel voltage that you can measure is actually a sort of average between on and off farther down (higher voltage) the IV curve knee than Vp and it varies with the load changes during Float.

If you don't want to call that on/off "PWM" give it another name, but some or all MPPT controller booklets call it PWM.


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pianotuna

Regina, SK, Canada

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Posted: 01/27/21 09:34am Link  |  Quote  |  Print  |  Notify Moderator

Here is a video from Morningstar about the tristar line.

https://youtu.be/eze03B-UNpo

pianotuna

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Posted: 01/27/21 09:36am Link  |  Quote  |  Print  |  Notify Moderator

Here is an upcoming webinare about LI batteries:

https://register.gotowebinar.com/register/5062950191830473998

pianotuna

Regina, SK, Canada

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Posted: 01/27/21 09:39am Link  |  Quote  |  Print  |  Notify Moderator

Here are several past webinares that have been recorded:

https://www.morningstarcorp.com/recorded-webinars/

FWC

The Wilderness

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Posted: 01/27/21 09:45am Link  |  Quote  |  Print  |  Notify Moderator

The MPPT is operating as it always does - as a buck (or in some cases a boost) converter, regardless of the charging phase. The difference between this and PWM is that current in != current out. With PWM I_in = I_out, always.

This is often not a big deal, but if you have loads running while in float, it can be. You want to support the loads off of the solar as much as possible. If you can't convert the extra panels volts to current then you are throwing away power that then has to be put back into the batteries by the solar panels. So in short, MPPT is working even in float.

On technical note, a buck converter has a large inductor in it, so while you are PWM'ing a transistor on the input side, as long as the inductor isn't saturated you won't see the voltage move as the field collapse in the inductor is holding the voltage up. This is different from PWM where you will see the voltage oscillate up and down based on the state of the transistor.

BFL13 wrote:

In Float the MPPT controller keeps the voltage to the battery at the Float set-point, but the issue is the controller wrt the panel voltage.

The panel voltage that you can measure is actually a sort of average between on and off farther down (higher voltage) the IV curve knee than Vp and it varies with the load changes during Float.

If you don't want to call that on/off "PWM" give it another name, but some or all MPPT controller booklets call it PWM.


* This post was edited 01/27/21 09:58am by FWC *

time2roll

Southern California

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Posted: 01/27/21 10:11am Link  |  Quote  |  Print  |  Notify Moderator

StirCrazy wrote:

I tdhink people need to learn more about MPPT chargers before they recomend against them..... yes they benifit more during bulk charging, no they do not switch to PWM mode, they are a three stage MPPT charger so basicly a DC_DC charger that converts DC to AC then back to DC at the most efficent combination ov voltage vs current.


"Re: MPPT vs PWM controllers?

MPPT - you only gain it's wattage conversion efficency while it is in BULK mode, once the controller eases off when switching to Absorb, all the ones I know of, revert to PWM mode for absorb and float.
Mike that is the very point that I find is hardest to get across to everyone.And its the very reason you dont get 50% and above gains from them as most people claim.On another similar site a well know poster talked about |the mysteries of MPPTversus PWM" He never ever mentions that fact only give figures to show theory gains.
You are also correct with "all the ones I know of, revert to PWM mode for absorb and floatOt of dozens I regularly test have never found one not to be like that."

https://forum.solar-electric.com/discussion/13231/mppt-vs-pwm-controllers #25


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BFL13

Victoria, BC

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Posted: 01/27/21 10:38am Link  |  Quote  |  Print  |  Notify Moderator

With either MPPT or PWM controllers in Float (both being PWM in Float defining PWM that way) you see the same thing when a load comes on.

The solar controller shows how many amps are "available" and the Trimetric monitor shows how many amps are to the battery. When a load comes on that needs some of the amps the battery was getting, the amps to the battery drops. If the load needs more than that, beyond what the solar has "available", then the Trimetric shows amps now coming from the battery to make up the difference.

That is the same with any charger of course; the loads come first and the battery gets whatever is left over, if any.

On PWM "wasting" power, you have to compare with the power lost due to panel heating, wire loss, and controller loss, because MPPT controllers do their amps to the battery by power out/battery voltage not like PWM controllers that just deliver amps. I have done some "field tests" where amps to the battery stayed the same when swapping an MPPT with a PWM.

Usually, you get a few more amps to the battery with MPPT "depending" on the whole situation, but not as many as often advertised by MPPT vendors who pick the best situations for their claims.

So it is fair to tell the OP here that he should stick with his PWM and if it does the job, as seems likely, there is no point in changing to MPPT.

1L243

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Posted: 01/27/21 11:18am Link  |  Quote  |  Print  |  Notify Moderator

Thanks for all the great information. I will install the system as it is now except for going to 8ga wire from the panel junction to the Charge Controller at the batteries. According to the low voltage calculator this helps to lower voltage drop over 30 feet to 5.76%. Speaking of the low voltage calculator. I put in the parameters of the 500 watt kit as it came from the manufacture and it still came in at 4.5% voltage drop which is above the 3% recommended goal. Makes me wonder about the accuracy of the calculator. The kit comes with a 15 foot run to the Charger Controller and 10ga wire.

As far as MPPT vs PWM the PWM came with the kit and just did not want to throw it away. The difference in price between the was only $100. In the future I will probably go MPPT just because you seem to have more options.

Thanks again


2017 Coleman 300tq by Dutchman Toy Hauler. 34.5 feet long and under 10k Gross. 500 watt Solar 2000 watt Inverter, 1999 Ford F250 2WD 7.3 4R100 DP Tuner, S&B Cold Air Intake, Gauges, 6.0 Trans Cooler, Air Bags.


BFL13

Victoria, BC

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Posted: 01/27/21 11:34am Link  |  Quote  |  Print  |  Notify Moderator

You added a 25% "gain" by going to five panels from four with PWM, and four panels was likely enough for your summers, so you are already ahead.

Your scenario was no solar in the woods in winter, so no point trying for best "low light" performance.

How do those 27s look for SG with your new hydrometer? [emoticon]

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