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Solar Charge Controller: MPPT Best?
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Vanagon Nut
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PostPosted: Sun Oct 07, 2012 4:55 pm    Post subject: Solar Charge Controller: MPPT Best? Reply with quote

Hi all.

I will be installing a solar set up at some point. Assuming it's a fixed position Mono crystal 100 Watt panel on a Westfalia used for travel.......

Is an MPPT charge controller truly better than a PWM type for harvesting power when the panel is partially covered or when conditions are overcast?

If so, overall, is an MPPT controller worth the extra $ ?

Not that this figures in, per se, but I would have 100 AH battery with a TruckFridge as the main draw. (this may change if I actually pass my Amateur Radio test. Wink )

I would forgo features like LED, meter, for a lesser priced good quality MPPT basic controller. I can't see needing one rated beyond 10 Amp output but I will consider future needs. That said, this Morningstar MPPT is pricey:

http://www.solar-electric.com/mosumpsochco.html

maybe this would do?

http://www.solar-electric.com/12vo10ampmpc.html

I could always install a voltmeter later.

Thanks for any insights!

Neil.
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PostPosted: Sun Oct 07, 2012 5:25 pm    Post subject: Reply with quote

There is a model of MPPT controller on the market, sold under many names and packages, that is in no way MPPT and is really just junk.
I bought one and threw it out.
If its less than $100, it's NOT MPPT.

I am running just a regular PWM controller and very happy with it. I have 225ah of capacity and it keeps them full easily. Make sure you use proper wire and MP4 connectors, as they ROCK!
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Vanagon Nut
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PostPosted: Sun Oct 07, 2012 6:01 pm    Post subject: Reply with quote

Phishman068 wrote:
There is a model of MPPT controller on the market, sold under many names and packages, that is in no way MPPT and is really just junk.
I bought one and threw it out.
If its less than $100, it's NOT MPPT.

I am running just a regular PWM controller and very happy with it. I have 225ah of capacity and it keeps them full easily. Make sure you use proper wire and MP4 connectors, as they ROCK!


Thanks for the tips.

Yes. Had read here of a product that starts with a "Y", IIRC, that is edit: purported to be junky.

Ironically, the 10 Amp product I link to (pdf of manual for it: http://www.solarconverters.com/pdf_manual/i-8023%20pt%2012-24-10.pdf ) is made in Canada:

http://www.solarconverters.com/contact.htm

Not suggesting that by virtue of being made in Canada, that the product is good, just that it's something somewhat tangible and the website appears to be written by the owner.
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PostPosted: Sun Oct 07, 2012 6:37 pm    Post subject: solar Reply with quote

Blue Bay Bus No. Arizona wind and solar is a great co. got all my gear there. When I went over to order my gear they said for the higher cost of that controller was not necessary for our use. The extra power they get you was not cost efficient. So I just went with a morningstar 10 amp solar controller my 140 watt panel puts out 7 amps and they work great together. That saved me over $100. Very Happy
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PostPosted: Sun Oct 07, 2012 6:43 pm    Post subject: Reply with quote

I agree, I just have a regular PWM controller with my KD-135 panel.

Remember though, that with a PWM controller your panel voltage can't be too much higher than the battery voltage. That means you're limited to a <= 140W panel, as the higher power panels (and some lower) are over 22V.
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Vanagon Nut
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PostPosted: Sun Oct 07, 2012 7:40 pm    Post subject: Reply with quote

Oh, ok. Thanks.

This isn't the only consideration, but IIRC, with a partially blocked panel (camping near trees, poor sun) an MPPT controller will harvest power better than an PWM. Installing panel so its moveable not too hard, but I usually travel solo so would prefer a fixed mounted panel.

PMW is certainly less $. Comparing 10 Amp rated controllers, this:

http://www.solar-electric.com/ss-10l.html

costs less, has a 5 year warrantee, and IIRC, a PWM puts less stress on batteries when charging due to "tapering" off as battery charge rises. That said, I have no idea if an MPPT controller does this as well.


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PostPosted: Sun Oct 07, 2012 8:32 pm    Post subject: Reply with quote

Vanagon Nut wrote:
IIRC, with a partially blocked panel (camping near trees, poor sun) an MPPT controller will harvest power better than an PWM.


Sorry, but fist time I hear this.
My understanding of solar panels in the 5-100W range:
- typically made of 36 cells connected in series, each providing about 0.55V and X amps, X being different depending on the size of the cell (all cells the same size in a panel)
- The amount of amps is strongly influenced by the amount of sun. The voltage is too, but much less. More sun: more amps, and a tiny bit more volts.
- All cells in series MUST provide the same amount of amps. If a single cell is fully shaded, the total output of the panel is zero, regardless of the controller type. See this. There are technical ways to avoid this, but my current understanding is that most panels don't implement them (see bypass diodes in the same site). Given this, I don't understand why some people mount their panels under the roof rack bars, but I'm getting off-topic.

MPPT in a nutshell:
Assuming a 20V, 5A nominal panel (100W).
- a PWM charger will "trim" the excess voltage and keep the amps the same, i.e. you'll typically charge your battery at 14V, therefore the output of the PWM charger is 14V, 5A (70W - 70% efficiency).
- an MPPT charger has electronics to convert volts into amps. A good one will be around 90% efficiency. Therefore, you'll still be charging around 14V, but closer to 6.5 amps.

Panels are designed around 20V, so when the sun is partially blocked, the little voltage drop doesn't bring the whole system below 14V, preventing any charging to happen. It is assumed to be better to have losses in strong sun that no charging at all in weak sun.

Bottom line: the MPPT gain (typically 20%) is max in strong sun (high panel voltage) or when the battery is discharged (low voltage), and can be negative (due to the amps converter circuitry) in marginal sun conditions (although I've seen MPPT designs that have an PWM mode to prevent this).

Vanagon Nut wrote:
a PWM puts less stress on batteries when charging due to "tapering" off as battery charge rises. That said, I have no idea if an MPPT controller does this as well.

They must do so, otherwise they'd destroy batteries in very short order - boiling the electrolyte.

Caveat: I've never installed/operated a single solar panel in my life. I just unpacked my first one yesterday, and I'm planning on building an MPPT controller based on this design to control it.

Regarding your original question about MPPT or PWM, what I read here a few month ago was basically "since MPPT gives you at most 20% more, chose the less expensive between a panel 20% larger and an MPPT charger". I'm going the MPPT charger, partly because I'm having fun doing it, but also because I want the panel to fit in the loggage rack, strongly limiting the panel size.

Whew, that was a long one.

Good luck,

Jean-Marc
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PostPosted: Sun Oct 07, 2012 9:05 pm    Post subject: Reply with quote

I use the following 150V 10A MPPT controller. With remote panel for under $100 mailed to US.

http://www.yoosmart.com/epsolar-mppt-tracer1215rn-...-mt-5.html

I choose the high voltage because I have some grid tie panels too for extended stays.
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PostPosted: Sun Oct 07, 2012 9:12 pm    Post subject: Reply with quote

PWM here, works great
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PostPosted: Sun Oct 07, 2012 9:29 pm    Post subject: Reply with quote

jmranger wrote:
Vanagon Nut wrote:
IIRC, with a partially blocked panel (camping near trees, poor sun) an MPPT controller will harvest power better than an PWM.


My understanding of solar panels in the 5-100W range:

- typically made of 36 cells connected in series, ....

- All cells in series MUST provide the same amount of amps. If a single cell is fully shaded, the total output of the panel is zero, regardless of the controller type. See this.



Ah, ok. I think I get it. Like in a string of lights, in series, if one bulb burned out, all lights are off.

.....

jmranger wrote:
- an MPPT charger has electronics to convert volts into amps. A good one will be around 90% efficiency. Therefore, you'll still be charging around 14V, but closer to 6.5 amps.

Panels are designed around 20V, so when the sun is partially blocked, the little voltage drop doesn't bring the whole system below 14V, preventing any charging to happen. It is assumed to be better to have losses in strong sun that no charging at all in weak sun.


Right. Thanks. Yes. I basically understood all that. Smile A typical panel is "over built" (my term) to account for ambient temperature differences, etc. As per circuit design of an MPPT, if I'm not mistaken, it actually converts DC input to AC, then back to DC for loads.

This is the page (pdf) I read that led me to my faulty thinking:

http://www.schams-solar.de/download/DESCRIPTION/comparison-mppt-pwm.pdf

From that pdf:

....... (c) So, we tested with black umbrella to create the clouds, to cover 1/3 area of glass panel to see how it moves,
or we discharge battery into 12v for easy acceptance of charging. On PM 13.00, environment was stable and we got following data:"


Thinking again, since the image shows two panels, maybe they're connected in parallel, only one was shaded, the other still put out power? Anyhow......

jmranger wrote:


Vanagon Nut wrote:
a PWM puts less stress on batteries ......

They must do so, otherwise they'd destroy batteries in very short order - boiling the electrolyte.

Regarding your original question about MPPT or PWM, what I read here a few month ago was basically "since MPPT gives you at most 20% more, chose the less expensive between a panel 20% larger and an MPPT charger". I'm going the MPPT charger, partly because I'm having fun doing it, but also because I want the panel to fit in the loggage rack, strongly limiting the panel size.


Jean-Marc



Thanks Jean-Marc.

The more I think about all this, the more I realize that if I went with an MPPT, I would be wise to use an MPPT with a higher amperage rated output. Which of course raises the cost!

That's a point I considered too; panel size or added panels to compensate if using a PWM (assuming that aspect was critical to me. As with others, the % efficiency gain is likely not critical)

Neil.
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PostPosted: Sun Oct 07, 2012 9:45 pm    Post subject: Reply with quote

I have the Morningstar Sunsaver MPPT with no complaints other than price. That said Vanagon systems typically are small enough that the benefits of MPPT are marginal.

-Rob

FWIW one of my fav world traveling Vanagons "Nacho" uses MPPT: http://www.drivenachodrive.com/about-nacho/solar-electricity-for-nacho-vanagon/
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PostPosted: Sun Oct 07, 2012 9:52 pm    Post subject: Reply with quote

Vanagon Nut wrote:


The more I think about all this, the more I realize that if I went with an MPPT, I would be wise to use an MPPT with a higher amperage rated output. Which of course raises the cost!

Neil.


I was under the impression higher voltage panels are usually cheaper than 12V, since most panels above 100W are usually about 20V and up. And yes if you go with MPPT you need to use higher voltage panels to reap the benefits.

-Rob
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PostPosted: Sun Oct 07, 2012 10:44 pm    Post subject: Reply with quote

MPPT is most beneficial when battery voltage is low, and ambient temperatures are low, since cooler PV panels produce higher voltages.

If you have no more roof space for more panels then MPPT will allow a little more harvest, but in most cases more wattage can be installed for less money than the cost of a MPPT controller over a PWM.

Some MPPT controllers, like my BlueSky sb2512i, can only handle 12 volt nominally rated panels. I also have the accompanying battery monitor and that has shown 25% higher output amperages than input, but the batteries were down at 12.0 volts, the sun was bright, and it was a cool day. Most of the time I only see about 5 to 8% more out than in, due to the MPPT Dc to dc conversion that keeps lower battery voltage from artificially limiting wattage.
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PostPosted: Mon Oct 08, 2012 5:35 am    Post subject: Reply with quote

Vanagon Nut wrote:
This is the page (pdf) I read that led me to my faulty thinking:

http://www.schams-solar.de/download/DESCRIPTION/comparison-mppt-pwm.pdf

From that pdf:

....... (c) So, we tested with black umbrella to create the clouds, to cover 1/3 area of glass panel to see how it moves,
or we discharge battery into 12v for easy acceptance of charging. On PM 13.00, environment was stable and we got following data:"


Thinking again, since the image shows two panels, maybe they're connected in parallel, only one was shaded, the other still put out power? Anyhow......

I can't get their data to make sense. Look at the voltage columns in their "final data" table, page two. The purpose of the charge controller is to provide a constant voltage to the battery (the exact voltage depends on the battery state).
- on the "clear sky" scenario, I don't understand why both controllers would be charging at voltages so different
- on the "shaded" scenario, both voltages are plain unrealistic - you normally never charges a battery outside the 12.8-14.5V range
If the voltages don't make sense, wattage and gain won't either. There's something I don't understand (or that they don't), but I don't know what.

Vanagon Nut wrote:
That's a point I considered too; panel size or added panels to compensate if using a PWM (assuming that aspect was critical to me. As with others, the % efficiency gain is likely not critical)

Combining panel is another tricky scenario, unless you use identical panels. Connected in parallel, they must have the same output voltage. In series, the same output current. Whatever extra one panel provides over the other is just lost. With panels significantly different, connecting the low wattage one may result in a lower power output overall.
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PostPosted: Mon Oct 08, 2012 6:10 am    Post subject: Reply with quote

nocreditnodebt wrote:
MPPT is most beneficial when battery voltage is low, and ambient temperatures are low, since cooler PV panels produce higher voltages.

True dat!

Quote:
If you have no more roof space for more panels then MPPT will allow a little more harvest, but in most cases more wattage can be installed for less money than the cost of a MPPT controller over a PWM.

Er, something of an apples vs. pomegranates comparison. MPPT makes any panel more productive regardless of the wattage (above comment on low battery and ambient temp noted). However, for really small panels (e.g., 5-10 watts), there's so little to work with, and the output's so low, that no controller is needed. However, once the wattage is several tens of watts up to a couple of hundred watts, MPPT is a must.

Quote:
Some MPPT controllers, like my BlueSky sb2512i, can only handle 12 volt nominally rated panels.

Well, yeah, but my BS controller (SB6024) with handle the 68 V VOC on my 190 watt Sanyo HIT Double panel. Different limits for different controllers.

Quote:
I also have the accompanying battery monitor and that has shown 25% higher output amperages than input, but the batteries were down at 12.0 volts, the sun was bright, and it was a cool day. Most of the time I only see about 5 to 8% more out than in, due to the MPPT Dc to dc conversion that keeps lower battery voltage from artificially limiting wattage.

It's not the DC/DC conversion that's limiting charging, but the controller sensing the battery state of charge. That is, any good MPPT controller will do the same thing.

MPPT basically is all about forcing the panel to operate at its electrical sweet spot while ensuring the battery bank sees the voltage it wants (higher voltage for a low state of charge, lower voltage for trickle charging a "full" bank). The DC/DC conversion isolates the panel's higher voltages from the battery bank's demands.

On shading cells... it all depends on how the panel is wired internally. Mixes of parallel and series wiring can let a panel function at varying degrees of shading. This is a consideration (how much shading will I accept for how much does the panel output and/or cost) the consumer must make.

Finally, a warning about Blue Sky. My first SB6024 failed after about three months in service - a current sensing component failed, killing the controller. Blue Sky needed some arm twisting to acknowledge the problem. They sent a replacement (our schedule was so tight I had to have it overnighted to us) but it was a)clearly used and b) full of fine red dirt/dust. When asked why we didn't get a new unit instead of one that was clearly used and full of dirt, I got "well, we said we'd replace a defective unit, but we never said you'd get a new unit." By that time the old controller was shipped back; BS took two weeks to find it, even though Delivery Confirmation/Signature Required showed when, where, and how the returned unit had been delivered. The story was "somebody put it on the wrong shelf." Bottom line: if the SB6024 goes Tango Uniform again, it won't be a Blue Sky replacement - ever. YMMV.
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PostPosted: Mon Oct 08, 2012 6:52 am    Post subject: Reply with quote

I would put the price difference, MPPT versus PWM, in a bigger , or a more efficient panel.

Proper MPPT controllers start at 10A and cost $150 to $200.
For that money you can get Kyocera 140W panels (160€ in europe)
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PostPosted: Mon Oct 08, 2012 9:54 am    Post subject: Reply with quote

alain riaud wrote:
Proper MPPT controllers start at 10A and cost $150 to $200.

Not quite, me thinks.

The better Chinese stuff, like I posted above, seem to work fine.

The Morning Star MPPT controller can be had around $250 last I looked, if you insist. The main advantage, for me, is (only) the mod bus which most people live well with out (now if I could finally get the protocol docs for my Chinese MPPT controller I would be golden....)
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PostPosted: Mon Oct 08, 2012 10:30 am    Post subject: Reply with quote

jmranger wrote:
Vanagon Nut wrote:
This is the page (pdf) I read that led me to my faulty thinking:

http://www.schams-solar.de/download/DESCRIPTION/comparison-mppt-pwm.pdf

I can't get their data to make sense. Look at the voltage columns in their "final data" table, page two. The purpose of the charge controller is to provide a constant voltage to the battery (the exact voltage depends on the battery state).
- on the "clear sky" scenario, I don't understand why both controllers would be charging at voltages so different
- on the "shaded" scenario, both voltages are plain unrealistic - you normally never charges a battery outside the 12.8-14.5V range
If the voltages don't make sense, wattage and gain won't either. There's something I don't understand (or that they don't), but I don't know what.

Vanagon Nut wrote:
That's a point I considered too; panel size or added panels to compensate if using a PWM ....

Combining panel is another tricky scenario, unless you use identical panels. Connected in parallel, they must have the same output voltage. In series, the same output current.


ya I quoted from that pdf to shed some light ( ha ha) on my thinking. FWIW, was not suggesting that study was accurate.

I found what appears to be a good price on this Solar Converters Inc 12/24V 10 Amp MPPT: http://www.solarconverters.com/sp12_10.htm here:

http://www.solarseller.com/solar_converters_mppt_charge_controllers_maximum_power_point_tracking.htm

this is obviously a "no frills" unit, but may be suitable.

Interesting to get input here folks. Much appreciated.

Neil.
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PostPosted: Mon Oct 08, 2012 10:31 am    Post subject: Reply with quote

Talking with the guy who sold me our panel and MPPT controller (on our boat, BTW, not on a Westy), the cost of panels is dropping appreciably. Let's hear it for economy of scale and a maturing market.

The cost of MMPT controllers is somewhat of a shaky number. That is, there are inexpensive controllers available but, as if often true, you get what you pay for. A good MPPT controller will probably cost at least the equivalent of a very good meal for two at some place much better than Ruby Tuesday.

That being said, the 10A floor is ...ah... open to reconsideration. Smile
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PostPosted: Mon Oct 08, 2012 11:13 am    Post subject: Reply with quote

RBEmerson wrote:
......

The cost of MMPT controllers is somewhat of a shaky number. That is, there are inexpensive controllers available but, as if often true, you get what you pay for. A good MPPT controller will probably cost at least the equivalent of a very good meal for two at some place much better than Ruby Tuesday.

That being said, the 10A floor is ...ah... open to reconsideration. Smile


Ok, so max. 10A rating on MPPT output is overkill?

Though my grey matter may not yield this, I'm studying up for my "Basic" Ham license, hoping to get 80+% (the latter allows HF use). I anticipate installing some kind of Ham rig, so that + my TF and lower battery voltage due to night use, might add up to more than a 5 Amp load (when transmitting.... with fridge door left open.... Wink ) With this 95W panel, http://www.solar-electric.com/etso95wa12vo.html it seems the max. Amps is 5.13 Amps, but then even with an MPPT, I doubt that number would happen. i.e. maybe a 5A rated MPPT or PWM would suffice.

In terms of quality, it seems to me that some charge controller makers are "ma & pa" type set ups. Maybe some actually make their products in-house which might allow for better QC? i.e. from Solar Controllers Inc. FAQ"

"Is lightning a problem?
Lightning is always a problem. After about 20 years of designing power electronics, I have seen small signal MOS or Microprocessor related devices get fried by nearby strikes. The cause is usually the parasitic SCR structure inherent in the MOS process gets triggered by the EMP burst- and you buy a new one.
The industry has made tremendous jumps in improving these technologies, but I still shy away from them.
Solar Converter Inc. Charge Controllers are all analog / transistor based. These units have been tested to and passed ANSI 62.41 6KV- simulated direct lightning strike. The test itself utilizes a very large capacitor and is charged to 6 KV (6000 volts), then it is placed on the terminals of the unit. This is both across the PV input and both PV input to earth ground. Personally speaking, without massive precautions, I have yet to see or hear of a MOS or Micro device pass this test at the 500 V level rather lone 6 KV (6000V). Forget about strikes in the area affecting this equipment - it will take something a lot heftier and a lot closer to take out this equipment."



Neil.
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1981 Westy air cooled to 15º ABA swap: http://tinyurl.com/y9n4xob8

50º ABA Swap in to '88 Westy: http://tinyurl.com/yap5hpwt

Vanagon VAG GAS engine swap Google Group:
https://tinyurl.com/2f24rmh

VE7TBN
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