Magic extra amps from Solar Panels

Submitted: Friday, Aug 08, 2008 at 11:29

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Boobook2

If you are considering a solar set up then you should consider MPPT controllers. I just recieved and tested my new solar panels and Outback solar controller. I was very sceptical but these solar regulator controllers and regulators are brilliant. MPPT stands for Maximum Power Point Tracking.

I have my set up running. The 2 x 85W panels are currently producing about 6 Amps into the controller and unbelievably the controller is charging the battery at about 8A. On a good day I should get about 13A out of the Controller ( and about 10A from the solar panel).

It does this by maintaining constant power verses constant current like most PWM units do.

The controller wasnt cheap, I got it from the US and it was about $500 delivered. Given that I have 170W of panels, I would otherwise lose 40W with a normal controller so it is about break even. They are 95% plus efficient as opposed to 70% for normal controllers.

There are cheaper ones like the Morningstar MPPT for about $280 from ebay in the US. The one I got has an output which can be used when the battery is full which I will use to triger the charging of my vehicle aux battery but only after the trailer's one is full.

These things are about 3 times the price in Australia so they are not worth considering but with the AUD like it is right now they are definitly worth considering as an alternative to additional panels.

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Reply By: Robin Miller - Friday, Aug 08, 2008 at 13:39

Friday, Aug 08, 2008 at 13:39

Hi Boobook2

They are good stuff alright , but until recently have been to expensive for what they do.

Essentially and to keep it simple if a solar panel puts out 18v max and your charge a 12v battery , then the 18-12 or 6volt difference is effectively wasted as heat.

These devices put an optinmum load on the panel ,do a proper conversion over whatever voltage the panel is currently putting out and effecively transfer up to 30% more energy into the battery.

Robin Miller

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Reply By: Member - Redbakk (WA) - Friday, Aug 08, 2008 at 13:53

Friday, Aug 08, 2008 at 13:53

Boobook2....tell us more about your set up...ie van or camper trailer...panels mounted flat ( on roof or placed out on the ground) or angled and/or move with sun (automated) etc....how many batteries and what size etc etc..this aditional info helps us access your purchace as quite often it is the stuff you don't tell us that makes a difference..." I wish you told us that"

AnswerID: 319774

Follow Up By: Boobook2 - Saturday, Aug 09, 2008 at 08:33

Saturday, Aug 09, 2008 at 08:33

Redbakk,

I am just instaling it now. But the plan is for 2 AGM's in the trailer and one as the Aux in the 4wd. I have 2 x 85W and will get them made up into a folding panel to sit at about the right angle facing the sun. They are portable on the basis that I want them in the sun, and the camper in the shade if possible which is not possible if I fix them to the trailer.

One point that might be confusing is that the Maximum Power Point Tracking is not solar tracking ( where the panel follows the sun). MPPT electronicaly tracks the maximum power output of the panels voltage and current, then converts that to the charging voltage and current. This is different to a normal PWM system that only converts the Voltage ( and current is the same which is why they are only 70% efficient at best). Ie you get about 55watts out of an 85watt panel.

Think of a transformer. You put 240V and say 1Amp in, and get say 12V and 20Amps out. Both are 240Watts.
With the MPPT you put 17v and 5A in from the panel and get 12V and 7.5A out. ( both 85 Watts). This works by going from DC - AC - DC inside the unit.

Thre is a good description here
http://www.solar-electric.com/charge_controls/mppt.htm

At the end of the day it basically means you get 30% more value out of yout solar panels that would otherwise be wasted.

The upside is that the one I got also will allow me to charge the batteries in the trailer first, then charge the Aux in the 4wd (with the addition of a timer circuit). That is optimal for me when I want to leave the trailer and go for day drives which will charge the aux from the alternator anyway.

I hope that makes sense.

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Reply By: wheeleybin - Saturday, Aug 09, 2008 at 17:36

Saturday, Aug 09, 2008 at 17:36

The MPPT Reg is brilliant but the 30% is not what you will get when summer comes as when the temperature rises and the panel efficiency decreases due to the heat the gap from panel output to battery input narrows.

In colder climates you will get a higher % return than in hotter climates but the winter is when you need to maximise your return from the panel.

The hard part now is the US Dollar is gaining ground against the AUD.

Blue Sky is a good MPPT Product with patented technology.
Richard

AnswerID: 319988

Reply By: Mainey (wa) - Sunday, Aug 10, 2008 at 05:51

Sunday, Aug 10, 2008 at 05:51

Information from the nominated website above:

“OK, so now we have this neat 120 watt solar panel, it's rated at 120 watts at a particular voltage and current.
The Kyocera KC-120 is rated at 7.1 amps @ 16.9 volts.
7.1 amps x 16.9 volts = 120 watts.
So what happens when you hook up this 120 watt panel to your battery?
Unfortunately, what happens is not 120 watts.
Your panel puts out 7.1 amps.
Your battery is setting @ 12 volts under charge

7.1 amps x 12 volts = 85 Watts.

You lost 35 watts - but you paid for 120. That 35 watts is not going anywhere, it just is not being produced because there is a poor match between the panel and the battery.

*With a very low battery, say 10.5 volts, it's even worse*
you could be losing as much as 35% (10.5 volts x 7.1 amps = 75 watts. You lost 45 watts.
Here is where the optimization or maximum power point tracking comes in.
**Assume** your battery is low, at around 11.5 volts...”

Unfortunately you have to ‘believe’ in their **assumption** that the Aux battery is only 11.5 Volts for their mathematical equation to be correct, as it's definitely not correct with a charging battery !!

An Auxiliary battery when powered by a decent Solar system will never get down to 12 Volts, let alone down to 11.5 Volts.
I have never seen my AGM battery system below 12 Volts, my fridge cuts out at 11.6 Volts, it's never, ever been disconnected !

Yes, if somehow the Solar panel Voltage is reduced, this can also be caused by an elcheapo Solar Regulator, their numbers will add up, just too many "if's" "maybe's" and hopelessly incorrect "assumptions" for me to accept the perceived benefits.

The reason *quality* Solar systems are so successful is because the Aux battery is not run down during the day, as the Solar system powers the appliances direct during the day, the Aux battery only powering the appliances at night.

I’m not suggesting they don’t work at all, just the reason used to explain how they work is not appropriate, considering the well known Solar charging facts available.

Mainey . . .

AnswerID: 320060

Follow Up By: Boobook2 - Sunday, Aug 10, 2008 at 09:24

Sunday, Aug 10, 2008 at 09:24

Mainey

I am not sure of your point.

You said "The reason *quality* Solar systems are so successful is because the Aux battery is not run down during the day, as the Solar system powers the appliances direct during the day, the Aux battery only powering the appliances at night. "

Whether a battery runs down or not is dependant on several factors, but 90% based on the amount Solar Power you have purchased, and the load you have. The quality of the system for different PWM systems is marginal maybe a few percent. PWM's preserve current, not voltage. ( they regulate Voltage)

Using a typical poly solar panel ( BP or Sharp) solar cell at it maximum power point ( ie 17.3V) charging a battery using PWM technology has a maximum *theoretical* effiency of :-

69% at 12V
75% at 13V and
79% at 13.8V

In practice the figures would be more like 66%, 72% and 77% ( say a 3% loss in the system)

A MPPT charger preserves Power and has a loss of 2 - 5%

So in all cases it is say 95% efficient.

So for a 120W panel you would lose the following power
PWM
41W lost at 12V
34W lost at 13V
29W at 13.8V

MPPT
6W lost at any voltage.

That was my original point with my 170W of panels I get an extra 40 - 50W depending on the state of the battery. That's why all large solar installations use it.

PWM systems are fine for small systems but with the price you can get them overseas now anyone getting over about 80W should consider the newer techonlgy because you can get it for free based on the reduced power losses.

I am not saying get it or a particular brand, I am just saying that people should consider MPPT based systems and that it does work as described on many web sites.

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Follow Up By: Mainey (wa) - Sunday, Aug 10, 2008 at 11:04

Sunday, Aug 10, 2008 at 11:04

Sorry, I thought my point was reasonably clear as I have stated->
“Unfortunately you have to ‘believe’ in their **assumption** that the Aux battery is only 11.5 Volts for their mathematical equation to be correct, as it's definitely not correct with a charging battery”

Can I then ask you please explain, in small words so I do understand, your statement (which I have copied below) how charging a 13.8 Volt battery with a 120 watt ‘BP or Sharp’ Solar panel with very realistic capabilities of 17.3 Volts and 6.9 Amps output, (for example only) has a theoretical * efficiency* of only a miserable 79% when the battery @ 13.8 Volts is FULLY charged ?

“ Using a typical poly solar panel ( BP or Sharp) solar cell at it maximum power point ( ie 17.3V) charging a battery using PWM technology has a maximum *theoretical* efficiency of
69% at 12V
75% at 13V and
79% at 13.8V ”

When I charge my AGM’s with my Solar system which has a very realistic capability of 200 + Watts, my AGM’s are ‘maintained’ @ 13.8 Volts by a $200, three stage Steca Solar regulator.
When not running any Auxiliary items like the fridge etc, as low as only half (½) Amp will be going to the battery, but the Solar system may be producing as high as 12 Amps, this is because the Steca Solar regulator works regulating the charge to the battery.Image Could Not Be FoundIt can readily be seen in picture above the battery is just getting a "trickle" charge because it's FULLY charged and only being "maintained" by the Solar regulator.

Image Could Not Be Found
Another picture from my “Members Profile” as photographic proof of the way my Solar system does work effectively maintaining the AGM's in peak condition.
This is showing 12 Amps is available at the Solar system but only 5 Amps is going to the AGM's giving them a small "boost" occasionally by the Steca tree stage Solar regulator keeps them 'regular' and clean.
(no need for Merve and his wheat bran here)

Mainey . . .

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Follow Up By: Boobook2 - Sunday, Aug 10, 2008 at 14:04

Sunday, Aug 10, 2008 at 14:04

Mainey said "Can I then ask you please explain, in small words so I do understand, your statement (which I have copied below) how charging a 13.8 Volt battery with a 120 watt ‘BP or Sharp’ Solar panel with very realistic capabilities of 17.3 Volts and 6.9 Amps output, (for example only) has a theoretical * efficiency* of only a miserable 79% when the battery @ 13.8 Volts is FULLY charged ?"

Mainey taking your example of 200W of solar Panel producing 12 amps.

A 200W solar panel runs at say 17.5V. Therefore produces about 11.5 Amps. ( 17.5V x 11.5A = 200W). Hopefully we are on the same page so far.

But your charger's output is say 13.8V at 11.5Amps or a total of only 153W available for charging or use by the load / accessories. ( 13.8V x 11.5A = 153W)

The other 47W is lost as heat inside your regulator.

Taking the same voltages and panel with a MPPT regulator then:-

The 200W Panel will still produce 17.5V and 11.5A but when the MPPT charger reduces the output voltage to 13.8V then the current available is not 11.5Amps, it is 14.5Amps because it maintains constant POWER ( ie 200W). Therefore an additional 26% of current capacity from the same solar panels under these conditions.

Alternatively you could have used only 160W of solar Panels to produce that same 11.5A of charging or load current.

40W less of Solar Panels is about $350 less for the same charge / load capacity with a MPPT charger over the PWM one you have.( plus the cost of the charger / regulator which is my original point)

The upside is that it is more efficient in low light or low battery conditions, the time you need as much current as possible.

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Follow Up By: Nomadic Navara - Tuesday, Aug 12, 2008 at 00:56

Tuesday, Aug 12, 2008 at 00:56

Boobook

There are two different things to consider here.

Firstly we can set up different experiments to see what difference you can get between the rated output of a panel and a so called operating power delivered by the panel. The more extreme you make the experiments the higher the losses you can achieve. But are these losses what you expect in the real world operating conditions?

In the real world your house battery does not drop to below 12 V often. It is mostly above 12 V. I have kept an eye on the charge and discharge cycles of the battery in my van. The battery is seldom below 12.5 V. In the morning by the time the sun is well up the charge voltage is above 14 V. There is much less power loss without a MPPT controller than is claimed in the Wind & Sun link given elsewhere in this thread. Battery charging is a dynamic process so the mathematics of working out the average power gain is beyond explaining in this thread.

So what is the real life gains in using an MPPT controller. There was a thread in the Caravaners forum a year or two back. I can not locate it to find the links provided therein. However the figures given in those references were no where as high as implied in the link in this thread. Remember the 35% example given is a maximum achievable result for a condition that is not often observed in real life battery operation. As the terminal voltage of the battery rises then the efficiency gain will rapidly drop off and the majority of the charging regime will take place at a lower percentage gain, particularly near the end of the boost phase and through the bulk phases as the regulator commences the constant voltage regulation. If you can achieve an average of 15% gain then you are doing well - that was the message in those references.

Do not get me wrong here - I am not speaking against MPPT controllers. In large systems they are desirable. What I am saying is do not use the peak gain figure of 35% as your design gain - use 15% at the most.

PeterD

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Follow Up By: Boobook2 - Tuesday, Aug 12, 2008 at 07:23

Tuesday, Aug 12, 2008 at 07:23

Peter, I would guess than in the long run real world your post is about right.

All I know is that In the few tests I have done so far I am seeing an increase iof 22 - 32% in amps. I am sure it can be less in the real world as I have only been testing it for about a week. Most of my testing is with a now full battery and sunny but cold days.

The purpose of posting this was to make potential buyers aware of the newer MPPT regulators given they are outrageously priced in Australia.

I would be interested to see the results of others who have them. I hope I don't go over the top by saying that some people who have never used or seen a product often have theories and opinions on this forum without any experience in the technology or products.

I am not selling these things, I just did some research and as I originally said, was surprised to see the measured results matched the theory and claimed efficiencies. I hope others can benefit from these discussions as there is not a lot on Australian forums, probably due to the outrageous prices here.

Thre are lots of forums in the US reporting high effiencies. I will monitor it over time.

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Reply By: Mike Harding - Sunday, Aug 10, 2008 at 15:26

Sunday, Aug 10, 2008 at 15:26

I'm a bit confused by this whole thread: a solar panel is capable of producing X watts under any given conditions. The amount of energy transferred to the battery is directly proportional to the efficiency of the electronics between the two.

If you use a linear regulator (you would be stupid but you might) then you'll waste a fair bit of panel output as heat. If you use a switch mode power supply to convert the panel output to a battery charging voltage then your losses will be decided by the efficiency of the switch mode design, typically 80%.

I fail to see how anyone can get more energy out of the panel except by improving the losses I mention above.

Mike Harding

AnswerID: 320127

Follow Up By: Boobook2 - Sunday, Aug 10, 2008 at 16:32

Sunday, Aug 10, 2008 at 16:32

Mike,
I know it is counter intuative at first. You don't get extra energy. you get extra amps because the output voltage is lower than the input voltage and the Power is constant.

The best way to think of it is a mains powered battery charger. You can get ones that are 40A or more out even though they only draw less than 10A in from the mains. That is because transformers keep constant power ( watts) and current = power / voltage. In fact these things use transformers.

See the link above, wikipedia or google MPPT solar. You will also see the Maximum Power Point specified on most good solar panel specs.

This is a good link on how it works but it does get a bit technical.
http://www.normenerji.com.tr/resimler/anasayfa/mppt.pdf

The reason that I originally posted this is that it is new and expensive technology in Australia but well adapoted overseas. All large solar instalations use this, even here. It is about 97% efficient on power.

The theory is good but I had to see it to really believe it as per my original post. After I bought one and set it up I checked and got 6A from the panels into the charger and 8A out charging the battery at the same time. I measured it with 2 ammeters and swapped them over to make sure one wasn't wrong.

Once you get your head around the fact that the power ( ie Volts x Amps) is constant like a transformer it makes sense, and subject to price IMHO you would never get a normal PWM Solar reg for over about 80 to 100W of panels ( provided you buy a regulator on ebay or elsewhere in the US for about 1/3 of the price they are here which is about $500 to $1500). The Morningstar MPPT one is from about $220 Aud which means it pays for it's self on any solar set up over about 65-80W.

I hope the links describe it better than I obviously am.

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Follow Up By: Boobook2 - Sunday, Aug 10, 2008 at 16:44

Sunday, Aug 10, 2008 at 16:44

Mike I am trying to get my head around explaining this and not sure I answered your question.

Try this.

Take any solar panel where you can get access to the stats.

www.energymatters.com.au has a good website for this.

Take for example this panel. Sharp 12V 80W Multi.

http://www.energymatters.com.au/sharp-solar-panel-80watt-12volt-multicrystalline-p-5.html?cPath=148_235

Here are a few specs.

Power = 80W
Max Power current = 4.67A
Max Power Voltage = 17.1
( 4.67x17.1 = 79.9Watts)

Here is the catch. It is 80W AT 17.1VOLTS, not 12 or 13.8Volts

Now to get it to 13.8v you use a solar regulator. If you had a perfect one then it would be 13.8V out at 4.67A.

Multiply 13.8V x 4.67A and you get 64.5 watts of power out.

That is because a linear or PWM is constant current.

The PWWM converts DC- AC- DC so it can use a AC transofrmer to maintain constant Watts ( like the 240v battery charger above)

Does that help?

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Follow Up By: Robin Miller - Monday, Aug 11, 2008 at 08:37

Monday, Aug 11, 2008 at 08:37

I don't agree guys

You do get extra energy , because normaly the solar panel runs into a mismatched load.

The idea of MMPT is to provide a correct load , sort of like tuning an aerial for best Vswr.

A good MMPt actually measures the output power and using feedback adjusts the load for max power.

Robin Miller

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Follow Up By: Mike Harding - Monday, Aug 11, 2008 at 11:05

Monday, Aug 11, 2008 at 11:05

>You do get extra energy , because normaly the solar panel runs
>into a mismatched load.

Yeah, true but I'm not convinced you get that much more - apparently the technique has been around for about 20 years. It would probably work best with panels in poor sunlight.

Bit technical but interesting analysis

Mike Harding

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Follow Up By: Robin Miller - Monday, Aug 11, 2008 at 11:57

Monday, Aug 11, 2008 at 11:57

Hi MIke

That note was worth reading. Its an interesting subject.

On a panel I have specked a bit (Sharp 24v 167w ) there are good spec curves and the panel puts out 27% more power at its max of 32v out than when connected to a 24v battery load.

The difference gets better with lower volts battery , so they work best when you need them , however they also do little with well maintained batteries.

I guess you wouldn't bother for the 6% the article got , so its benefits are situation dependant.

All good stuff.

Robin Miller

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Follow Up By: Boobook2 - Monday, Aug 11, 2008 at 13:08

Monday, Aug 11, 2008 at 13:08

Mike I think that article might be quite old ( in electronics terms). As I understand it, it is comparing direct conection to MPPT controllers based on Buck or Boost DC - DC conversion. Buck and boost are both pretty simple forms of PWM that can increase or decrease voltage but not current.

It looks like there are 2 components to the MPPT controlers, one is the Multipoint tracking, and then there is the DC - DC conversion using either Pump circuits, Boost circuits or as is used in the recent ones DC-AC-DC conversion. It looks like this is where the amps and efficiency are generated.

I like it cause I saw 2 Amps more charge current out of it than into it on a fairly sunny but cold Melbourne day. That's gotta be a good thing when every amp counts.
It convinced me.

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Reply By: Russ n Sue - Monday, Aug 11, 2008 at 15:00

Monday, Aug 11, 2008 at 15:00

I had a long diatribe about how these things don't work and where the errors in the logic are.....and then I remembered the war that broke out when I dared to suggest that electronic rust prevention systems don't work.

So I'm not going to present a case except to say this...

The theory is that these devices "match" the panel to the battery more efficiently. It doesn't matter which way you look at it, at some stage in this process the matched part of the load has to bump into the unmatched part. Then losses occur. Also, the internal resistance of a battery does not stay the same as the battery charges. What do they do about that?

Now, if panel manufacturers designed a panel with a knee-point at around 13.8 Volts, that would be a whole different matter...hmmmm.

AnswerID: 320253

Follow Up By: Boobook2 - Monday, Aug 11, 2008 at 19:10

Monday, Aug 11, 2008 at 19:10

Russ I am not sure about Rust prevention, that subject is surely debateable because the results are minimal and occuring over may years with many variables.

I just know that I have now tested several contidions and this works.

I think your description of "matching" isn't correct.

This works with exactly the same theory and electical principles as an inverter.

a 12V inverter takes a low voltage ( 12V) at very high current converts it to AC then to a high voltage at a low current BUT CONSTANT WATTS ( less losses)

What I am describing takes a Low current ( say 5A) and high voltage( 18) and converts it to a higher current ( say 7A) and lower voltage( 13.8)

It adapts to different voltages in the same way as any other switch morde charger ( which all good high current ones are )

Perhaps you could explain to me what I observed is wrong and why all major Solar installations use this technology.

Also you could explain why P = VI doesn't work?

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Follow Up By: Russ n Sue - Tuesday, Aug 12, 2008 at 09:57

Tuesday, Aug 12, 2008 at 09:57

Hi BooBook2

P = V x I
V = I x R

Therefore P = I x I x R (I squared R)

So, if your Watts (P) don't change and the resistance of the battery (R) you are charging is fixed by the state of charge of the battery itself and only changes slowly over time, then the current can't change either. Now if you are saying that the resistance of the battery is somehow changing (reducing) by the square of the current when using this charger, then I'll believe your theory.

If you treat the circuit as three separate entities, the source, the regulator and the load, then the electrical "matching" is equally important between the panel and the regulator as it it is between the regulator and the load. Somewhere there is going to be a mismatch. In this case you have a panel with an open circuit voltage of 17 Volts connecting to a battery that wants to be 13.8 Volts. Like I said, if solar panels were designed for maximum output at around 13.8 to 14.1 Volts, then there wouldn't be a problem.

Cheers

Russ.

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Follow Up By: Boobook2 - Tuesday, Aug 12, 2008 at 10:14

Tuesday, Aug 12, 2008 at 10:14

P=I squared R is right for a pure resistive resistive load. Ie the power lost in the resistive part of the Battery. But we are considering the current through a resistance and the cells.

Forget MPPT for a moment, and consider a normal battery charger. If your statement is correct then no chargers will be able to charge at diferent curents.

You can chose to not believe it. No problem. I am sorry I brought up the whole subject to be honest. I am defnding something I dont really care about that much. I just hope others get the chance to try these things.

Also solar panels are that voltage for a reason, so they work under low light conditions. A 13.8V maximum power point solar panel would only produce 13.8v at max sunlight. Ie it woul dbe less than 12v most of the time.

Despite all the theories of people who haven't tried them or understand them, I can assure you they do work, I have tried it, measured it and it is very basic electrical theory. Same theory as a 12v - 240v inverter. ( Where to those magical extra 228V come from?

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Follow Up By: Russ n Sue - Tuesday, Aug 12, 2008 at 17:13

Tuesday, Aug 12, 2008 at 17:13

Hi Boobook2,

I'm afraid you've got me there. Since we are talking DC, not AC at the battery, I carelessly assumed that the battery must be a resistive load. Now if it were in an AC circuit, then I guess it might be a reactive load by being either inductive or capacitive.

Now I'm going to have to hit the books to see if there is any other kind of load that I haven't heard of, and what part of a battery is resistive and what part is...err...ummm well...not resistive I guess. Or maybe I need to find out what is purely resistive and what is impurely resistive?

Seriously, have you taken into account what the effect of inserting your meter into the circuit to measure the current will be? Have you compared the current into the battery with a different regulator in place of the one you are testing? Have you tried connecting the solar panel/s directly to the battery and measured the current?

If this technology were as good as you say, it would have been adopted across the industry by now.

Cheers,

Russ.

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Follow Up By: Boobook2 - Tuesday, Aug 12, 2008 at 17:41

Tuesday, Aug 12, 2008 at 17:41

Russ

I used 2 ammeters and swapped them over. I am very sure it is right. I have seen 6.8A charging out of the unit at about 13.9v during a period of 3 hours of good sunlight out of a 85w panel now. For those who say it doesn't work with all their theories I would love to see the explaination given the panels short circuit current of the panel is 5.05A.

As you say, if it was this good then it would be used everywhere.

That comment kind of goes to my original point. The fact is that it is used everywhere for large installations where the payback is more obvious, and overseas where the products are more reasonably priced.

At $500 to $1500 for small units as the are priced in Australia it is just too hard to justify and they are not well known in the recreational market. Overseas where they are $250 to $500 for the same units they are well understood.

I am afraid that even though I started this thread I give up.

I obviously can not explain it right or convince people several in this forum. I really suggest people call a reputable solar supplier that supplies both PWM and MPPT and especially comercial equipment where it accounts for the majority of installations to get their experience.

To close it off with my original point. If you don't believe it then fine. For those who are considering new panels or regulators check them out. As an owner I can assure you that the technology does work as described, measurable and testable in minutes.

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Follow Up By: Mike Harding - Tuesday, Aug 12, 2008 at 18:01

Tuesday, Aug 12, 2008 at 18:01

>Despite all the theories of people who haven't tried them or
>understand them, I can assure you they do work

I agree, they will… sometimes, I just don’t think they’ll work very well and certainly not $500 well. Having said that, with the poor sunlight in winter Vic they’ll probably be at their best.

>I have tried it, measured it and it is very basic electrical theory.

Basic-ish :) – they rely upon impedance matching (resistance in this case) to gain extra power transfer but keep in mind this does not, by definition, result in extra efficiency and the loss of power transfer for a mismatch is not that big.

http://en.wikipedia.org/wiki/Maximum_power_theorem

>Same theory as a 12v - 240v inverter.

No, quite different.

>Where to those magical extra 228V come from?

A transformer. An “inverter” (a misnomer if ever there was one!) is simply a switch mode power supply.

In large solar installations when they are a tiny percentage of the cost it would certainly be worth using this technique but for a camping situation where they represent, what?, 20% of the cost…? I have my doubts. When the price comes down to $20 more than a standard switch mode solar converter (and it should – 8 bit micros are cheap) then go for it. Otherwise I’m with Jim (below – despite the fact that he is mad :)

Mike Harding

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Reply By: Best Off Road - Tuesday, Aug 12, 2008 at 08:13

Tuesday, Aug 12, 2008 at 08:13

I've been following this thread carefully and do not have the technical knowledge to match those posting.

However after reading all the feedback, I am of the opinion that $500 spent on an additional panel (say 50-60 watts) would give more benefit than an MPPT unit.

Am I mad?

Jim.

AnswerID: 320370

Follow Up By: Mike Harding - Tuesday, Aug 12, 2008 at 09:10

Tuesday, Aug 12, 2008 at 09:10

I suspect you're correct Jim.

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Follow Up By: Best Off Road - Tuesday, Aug 12, 2008 at 09:24

Tuesday, Aug 12, 2008 at 09:24

So you reckon I'm mad Mike LOL

FollowupID: 587164

Follow Up By: Russ n Sue - Tuesday, Aug 12, 2008 at 09:38

Tuesday, Aug 12, 2008 at 09:38

Dollar for dollar, Watt for Watt, there wouldn't be a lot in it. You can always charge a battery with a solar panel and no regualtor if you are desperate, but you can't charge a battery with a regulator and no solar panel. I'd buy another panel in preference to trying to ring another Amp or two (allegedly) out of some sort of whizbangery.

In essence, it all comes down to headroom. If you calculate your expected load, calculate or approximate your hours of full Sun you can expect (or how long you can go without Sun), calculate how much storage capacity you need so that you aren't constantly having a depth of dischgarge of your batteries that is damaging them, then you can buy the appropriately rated panels to meet the load demand and have a bit of headroom.

My load is such that I never discharge my batteries more than 20% and they are always fully charged by Midday (given reasonable Sun conditions.) Once this is achieved my solar regulator clamps the current going into the batteries and supplies current directly to the load. It wouldn't matter if I could produce 10 Amps or 20 Amps by some sort of skullduggery, the only current required is that drawn by the load.

So, with the cost of panels and the cost of gaining another Amp or two by using one of these whizbang regulators is taken into account, go for the panel and give yourself some headroom.

Cheers

Russ

FollowupID: 587165