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gcrank1
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# Posted: 10 Apr 2021 10:40pm
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Ive read a LOT online but would like real-world experience comments if my thought on this is correct:
An mppt scc will always perform 'at least as well' as a pwm.
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Steve_S
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# Posted: 11 Apr 2021 04:48am
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MPPT will equal or do better than PWM.
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ICC
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# Posted: 11 Apr 2021 09:11am - Edited by: ICC
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The only thing PWM does better than MPPT is a cheaper price, but at the cost of less performance.
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rpe
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# Posted: 11 Apr 2021 09:14am
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We inherited a 220W panel my son wants to use to charge the 12V car battery at his sugar shack. Voltage output of the panel is up over 24V. I'll follow this thread in the hopes of learning what charge controller gadget he needs for that rig.
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spoofer
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# Posted: 11 Apr 2021 09:25am - Edited by: spoofer
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He needs a mppt charge controller that can handle, say 250 watts. It prevents the battery from overcharging etc. A deep cycle marine style battery is a better "cheap" choice.
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ICC
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# Posted: 11 Apr 2021 10:18am - Edited by: ICC
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Maybe a (hopefully) simple explanation of how the PWM and MPPT chargers differ will make it easier to understand why MPPT offers better performance?
First, the charge current going into a battery must be at a voltage higher than the battery's at rest voltage, but not too much higher or the electrolyte will be overheated and evaporate.
Using the same (pretend) PV panel and battery for purposes of illustration: 24 volt panel output at 10 amps with a 12 volt battery. The battery will need 14 volts coming into it for charging. (actually more like 14.4, but this is a simplified example).
It also helps to know that Volts x Amps = Watts and that Watts are the amount of energy.
The PWM charger takes 14 of the incoming volts and uses them at 10 amps to charge the battery. 10 amps x 14 volts = 140 watts going into battery. The unused volts and their amps are wasted as heat. 100 watts wasted.
The MPPT charger first looks at the battery voltage; 12, and decides it needs to output 14 volts to charge. The MPPT charger then converts the 24 volts to 14 volts. (24 volts x 10 amps = 240 watts) So the 240 watts of energy is changed to 14 volts.... (Watts/ Volts = Amps)....(240 watts divided by 14 = 17.14 amps). So the Volts are reduced and the Amps increase. Yes, there are internal conversion losses but for now we will ignore that. The MPPT charger outputs 17 Amps instead of 10, a big gain of energy going into the battery.
FYI, an MPPT charger is not 100% efficient. The efficiency rate also varies with the difference between the voltage from the PV panels and the voltage output to batteries. To complicate things as the voltage difference increases the efficiency rate falls. So a PV array that supplies 120 volts to an MPPT charger used on a 12 volt battery bank will be a little less efficient thatn an array wired to supply 50 volts to the MPPT charger. BUT! there are times when the higher voltage is better, is needed, to reduce losses in the long wires when an PV array is distant from the controller. Such is the life of a PV system designer.
Other variables also have to be considered.
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ICC
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# Posted: 11 Apr 2021 10:28am - Edited by: ICC
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If you have an MPPT controller you can connect PV paanels in series and harvest power when the solar is insufficient to make enough power from a single panel that is "correctly" voltage matched to the system.
For example when using a PWM controller it is best, with a 12 volt battery, to use what are called 12 volt panels, which are panels that have a Vmp of something like 17 to 18 volts. When the sun is obscured these may not produce a high enough voltage to actually charge a 12 volt battery through a PWM controller. This is exacerbated when the panel temperature increases as voltage falls as panels heat up. An MPPT controller will allow two of those panels to be placed in series. The voltage will likely be high enough even with heavy clouds.
We have actually made power by moonlight just to see if it could be done. We waited until we had a full moon and it was after 11 PM at night. We reconfigured the wiring of some panels to place many more in series. We got almost 1 amp by moonlight. Of course, when the sun would come up the overvoltage would have shut the controller down. But it was fun.
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paulz
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# Posted: 11 Apr 2021 10:37am - Edited by: paulz
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Thanks ICC, good explanation. I already knew the answer to the first question. 
I'm still using my old PWM (Harbor Freight 150w setup) to keep the batteries for several vehicles in my shop topped up, on a cord with alligator clips I can move from one to another, and I don't bother to unhook the panels when moving. Seems to work well for that, where ultimate o output isn't really important.
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ICC
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# Posted: 11 Apr 2021 11:38am
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I would not go to the expense of an MPPT controller for anything like that. I am thinking of everything else, everything that is a little larger. IMO, if you have more than one small battery MPPT is best. Or if the battery is used for something as simple as a single night light, then MPPT is not needed.
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gcrank1
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# Posted: 11 Apr 2021 02:45pm
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It kinda looks like about 200w of array might be the tipping point but you gotta have at least 24v input to the cc, and more is better?(within the input limits of the cc)
I see an Epever 20a mppt Tracer model on Amazon that looks 'attractive' for the features included and price.
Rpe, what are the specs on the panel, they should be listed on a mfg plate on the back.
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ICC
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# Posted: 11 Apr 2021 03:34pm - Edited by: ICC
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Quoting: gcrank1 .....but you gotta have at least 24v input to the cc, and more is better?
re input voltage: If the battery is 12-volt lead-acid type it needs about 14.2 to 14.4 to do a charge as quickly as possible and without damaging the battery..
So any volts higher than that much is going to be wasted with a PWM controller. Looking at it that way I see an MPPT still being a winner over the PWM. Not as big a winner if the incoming panel voltage was higher, but still a winner.
More is better only because then if the solar drops the incoming because of clouds or time of day, then the MPPT can still convert to something that still can charge. The only thing MPPT cannot do is increase the incoming voltage. That could be designed for but is pretty much not needed.
And then one must factor in their own economics. I don't like buying the cheapest of anything unless I know I only need or want it to work a short time. I do like a good deal, but the quality I percieve is important to me. I guess that is why I do not shop at Harbor Freight. I still use a few corded Makita and Porter-Cable tools which are 35+ years old. The Outback MPPT charge controller I bought in 2002 is still working, though it is working for someone else now.
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Brettny
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# Posted: 11 Apr 2021 06:52pm
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The only thing I'm going to use PWM on is my outhouse light.
Today I'm at our property and I didnt see the sun once, infact is drizzled most of the day. With my 230w 32v pannels i was seeing 13.1v @ 5a at one point. At that point the pannels where inputing 29v to the CC. With PWM anything over 14v (or so) would be wasted.
I have a 40a EPever BN series, the one that looks like a big heat sink. You can input 150v and output 12v. You gain alot of flexibility with a MPPT CC. At one point I even had my pannels in series.
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gcrank1
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# Posted: 11 Apr 2021 09:50pm - Edited by: gcrank1
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My 10w(?) Coleman and 15w SunForce panels get the SF 7a cheapy that came in the SF 'kit', Im pretty sure it is just a simple switching control, not even pwm. The panels each put out about 17-18v in bright sun. Just for a trial I put each onto my depleted old LA 18ah jump pack when at 50ish % dod at mid-day WITHOUT the cc, in a few hours prime sun it charged up. I figured with the very low amps it wouldnt cook it, they are really just battery 'maintainers' not chargers anyway.
Guess I should say, For Info Only, Dont Try This
But for my 3 banks of 2 x 102w in series arrays (for nominal 24v into the mppt cc) it sure seems sticking with mppt will maximize my limited available sun. Ive been mixing the arrays up depending upon how much battery bank I have so as to keep in the est. C.1 - C.15 charge rate for LA AGM.
I agree that for Rpe's son the car battery is a poor choice, waayyy low amp-hours available. But, he has it....and for limited use of some LED lights it can work. When it dies (not 'if' but when) get at least a marine deep cycle 100ish ah, typically a Group 27. Note that only 50% of those listed amp-hours are net usable each cycle or you murder the battery. There are better batteries for solar storage, the marine grp27 is the basement model and price.
Fwiw, iirc, a 'car' battery with something like 850CCA only has like 65ah/32ah net and nowhere near the number of cycles of even the cheap marine battery.
An old style RV 50w incandescent light bulb would use that 32ah's up by calc in about 8 hrs., ime more like 5 hr's, You definitely want LED bulbs!
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gcrank1
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# Posted: 17 Aug 2022 09:29am - Edited by: gcrank1
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Did you cut&paste that from the Diysolarpower forum or are you the one that posted that statement there?
It 'sounds' like a marketing line from somewhere...
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ICC
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# Posted: 17 Aug 2022 01:36pm
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I don't understand what the users point was to dven post that. PWM vs MPPT is a topic that has been flogged to death
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gcrank1
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# Posted: 17 Aug 2022 02:42pm
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I was expecting a spam link
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NorthRick
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# Posted: 17 Aug 2022 04:43pm
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Quoting: gcrank1 I was expecting a spam link
Not a very good spammer. Forgot to include the link. 
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Peewee86
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# Posted: 17 Aug 2022 08:45pm
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I’m surprised that PWM controllers still exist in today’s marketplace. I guess for the most inexpensive systems maybe they make sense. Years ago the cost difference between PWM and MPPT was bigger than it is today. I think the Victron MPPT charge controllers are the gold standard. I have been using them for the last five years and my experience has given me no reason to consider anything else.
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gcrank1
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# Posted: 4 Sep 2022 03:04pm
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Its gotta be the price.
Over at diysolarforum.com Ive seen a number of times cheap 'mppt' scc that have been 'looked into' and they are pwm; ie, cant trust the ad copy and label. In fact, if it is cheap it likely is Not mppt anymore than cheap inverters that say Pure Sine Wave are.
It is really looking like some 'Pacific Rim' marketers will say anything buyers want to hear just to make the sale.
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harry89
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# Posted: 5 Sep 2022 06:21pm
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PWM controllers are relatively simple controllers and they are good for switching loads that have relatively low voltage or current. The problem with them is that the Pulse Width Modulation (PWM) control scheme can only be applied where there is a direct relationship between the control signal and the load current. Many PWM schemes require a pure resistive load (i.e. a load for which the load current is linearly proportional to the load voltage)  – if you load has a significant non-linear component to the load current/load voltage relationship then a PWM controller will struggle to make accurate current control adjustments.  MPPT controllers are more complex than PWM - they typically feature at least a charge pump or a high performance switched-capacitor power supply. (Some have both!) Most of these can be used with a wide range of loads and input voltage conditions. These days, with solar panel cost as cheap as it is, there aren't many situations where a PWM controller can justify its use over MPPT.
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ketchgould
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# Posted: 23 Sep 2022 01:21pm
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I am trying to decide between buying a MPPT charge controller on its own ($30) and then buying a pure sine wave inverter on its own (1000 watt for $100) or an all in one controller that will also connect to grid or generator, MPPT charge controller and pure sine wave inverter (3000 watt, 80amp for $339).
Any thoughts?
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Nobadays
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# Posted: 23 Sep 2022 03:19pm - Edited by: Nobadays
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Just looking at the prices you quote, you either know someone who knows someone.... or you are looking at really cheap Chinese equipment.
Be aware it is not uncommon for this cheap solar equipment to be mislabeled, as in MPPT when tested is really a PWM charge controller. The same is true with inverters, labeled PSW when in fact they are MSW. An all in one 3000/80 for $339? Again looks a little suspect.
Hop over to diysolarforum.com for some great diy information. There are even "blueprints" for different sized systems. Do a little searching around there and you will find reviews on a lot of different hardware and batteries.
Edit..l meant to add, do you want to go to your cabin to enjoy the place/area, or to tinker with a solar system that is always on the fritz? Buy once, cry once.
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gcrank1
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# Posted: 23 Sep 2022 03:50pm
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Sounds Too cheap to be true or really good!
You cant cheap out on the control units for solar and have a quality system to be improving on over time. And I say this not as a snob but as a practical diy guy who tends to go on the 'less expensive' side of things perhaps more than I should. And I tinker a lot.....
I can tell you how I made my basic 12vdc systems (small to larger), or my combo 12vdc/120vac, or my straight 120vac. And I can tell you that if I was starting over today (it got wrecked or stolen) Id go with 24v.
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ketchgould
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# Posted: 23 Sep 2022 04:09pm
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The prices I found were on Amazon, thanks for the tips on reliability.
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gcrank1
Member
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# Posted: 23 Sep 2022 09:11pm
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Ive been looking at 'better than bottom tier' equipment lately. The old caveat of,"The joy of low cost disappears with the agony of poor performance" (or somesuch thing) rings too true too often.
Or, "cheap is cheap for a reason".....
One big mistake made is to start buying bits and pieces for a perceived 'system' and finding out the b&p's dont play well together or are completely wrong.
It is a system, and fitting proper stuff together when all is from various vendors is not to be entered into lightly. Thing is, there are really no 'regs' that require all these components to be compatible. You buy and assemble at your own risk unless you get a package from a supplier that also offers customer support.
Buyer beware
And
Research is your friend
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ICC
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# Posted: 23 Sep 2022 10:05pm
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I usually do not like "things" that are combined "things". I usually prefer components. My stereo system of yesteryear was assembled of individual amp, speakers, etc.
Likewise, my solar systems have separate charge controllers and inverters. And of the same brand as often those items can communicate with each other and can have a shared control/display unit. The exception to the separate components that make my solar systems has been a combined inverter-charger. Some of those make a great deal of sense when combined. Maybe I am old fashioned that way. My home system actually has more than one charge controller as I have arrays that face different directions. That works well for me.
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ICC
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# Posted: 23 Sep 2022 10:21pm
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Oh, my experiences with all sorts of electrical and mechanical devices has led me to generally stick with items from established brand names with a track record of service and quality.
The cabin solar system is the same Outback hardware that I installed in 2009, except the batteries and newer, better lightning protection that was added later. An updated monitor unit that brought wi-fi to the system was introduced a few years ago.
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Brettny
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# Posted: 24 Sep 2022 05:41pm
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Quoting: ICC usually do not like "things" that are combined "things". I usually prefer components. My stereo system of yesteryear was assembled of individual amp, speakers, etc.
Me either. There was a member here who has an all in one unit and was having trouble with it due to the massive standby draw.
When looking for an inverter always find the spec on the stand by loss. Cheap inverters have a high draw so it has to be off more or you need a bigger battery.
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gcrank1
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# Posted: 24 Sep 2022 08:43pm - Edited by: gcrank1
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Im a proponent of using a size inverter fairly matched to the load; ie, a 'big' inverter to run a couple LED lights and a USB charger is likely to have more elec loss running the inverter than the devices.
We run LED lights, USB ports, fans and an old tv c/w an integral vhs player easily off a 300W psw inverter which has very low power loss. If I had some bigger load stuff (I needed to run off the bats) that was basically occasional use I have a bigger capacity inverter for those that Id switch on to run them. As is, I run the 2000W inv/gen for those things.
By segregating my loads it really improved my setup requirements and efficiency.
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Steve_S
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# Posted: 25 Sep 2022 09:14am
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Pro-Tips
Low Frequency Inverter/Chargers with good torodial transformer coils are more efficient, this also applies to AIO's (All in ones). Now several Mid grade products from MPP Solar & Growatt and others are making LF Units, some with built-in Split Phase 240VAC to accommodate more people. Previously you had to Parallel & link AIO's.
If you go Higher End to Tier-1 product, then you can get very efficient systems, for example, my Samlex EVO 4024 is 94% Efficient (8W standby, non eco mode) whereas my older "Value Grade" YIYEN APC 3Kw LF Inverter/Charger was only 88%. Victron's LF AIO's & straight Inverter/Chargers are also around 95% Efficient and sip power on Standby.
Many people do not realize the differences & capabilities between HF (High Frequency) versus LF (Low Frequency) and the trade-offs. They see the price of LF being higher (Big Torodial Coils are NOT Cheap) vs HF's which use banks of MosFET's (Cheap as snot).
Samlex EVO-4024 Inverter/ Charger :
https://samlexamerica.com/products/ProductDetail.aspx?pid=575
Yiyen APC-3024 Low-Frequency Pure Sine Inverter/Charger : (They are an OEM for others as well)
https://www.yiyen.com/product/apc-series-pure-sine-wave-inverter-charger/
The Victron Pheonix Inverters that come in 250 to 1200W are extremely efficient and quite affordable to boot with a lot of goodies built in.
https://www.currentconnected.com/product/ve-phoenix/
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