MPPT Controller Question...

Phil,

Did you mean to say that your 2 panels are connected in series? They should be in parallel, NOT in series. The unloaded voltage (ie the feed to the controller, when disconnected from the controller) should be about 22 -24 volts, NOT double that, which it will be if your panels are in series. If in fact they are in series, both your controllers may be (at least) seriously upset and at worst, dead, which could account for what you are experiencing.

Please tell us they are not in series!

John

Phil,

My apologies - thought I was talking to the original poster!

Cheers

John

I am the OP ;)

Not in series.

Elaborate on a double plug on the load, the battery needs to be connected to the battery terminals and the load to the load terminals?

Sorry, I had to go for a no show. The storm hit alright, lots of thunder and rain but thankfully no wind. Tail end is a bit breezy. I can see it has just started to leave the other side of Wagga.

Everything is connected correctly. The panel is on the left, solar. The battery is in the middle. The load is on the right. The load is simply one of those 20 amp double plugs...I will take a photo and post it tomorrow.

The battery is new. It is about 6 or 7 months old. Until about 4 weeks ago, it was on a smart charger. I then went to Greens Lake on total solar. The window on the battery changed to white in a few hours and red in less than 48 hours. It was then that I connected the panel direct and it fixed the issue. I thought the controller might be faulty, so tried the 20amp one but got the same result. I then started recording everything and found that both controllers are doing exactly the same.

That is why I ask is it normal.

Sorry, believe it or not, I have to go again

What is the voltage on the input to the charger from from the solar panel?

I read 19.7 volts.

This morning the battery volts were 12.2 at 7:10am.

I turned the panel round to face the morning sun, turned the Engel up to 4 and plugged the laptop in to charge. At 7:36am the thermo of the Engel kicked in and the laptop says "plugged in not charging". The battery volts read 13.1

So in 26 minutes of morning sun with no regulator, the panels produced enough to get the Engel back to freeze, recharge the laptop and have enough left over to put .9volts into the battery.

At Greens Lake, I did pretty much the same thing but with the controller in line and the battery went into the red.

If your getting 19.7V into the controller, its a 12V controller and all is connected properly and your not getting amps into the battery then I would say your assumption the controller is faulty sounds pretty good.

Yes, it is 12 / 24 volt auto switching controller. The other one is just 12 volt 20amp.

I cannot post a photo. I need to get an image host first.

I am interested in the below post. I just Googled. It looks like the panels are 14 cell each giving a combined total of 28. If the below is correct, I just don't have enough cells to drive an MPPT.

The first thing I'd be doing is getting rid of those aligator clips.

Its just a point of unreliability.

You need some sort of secure permenent connection to the battery...either proper battery clamps or nuts and bolts with eye terminals on the connecting cables.

cheers

Yes, I know.

It is a very basic set up. The alligator clips are actually proper battery type, they just happen to come with the panel. I am hoping to get a small camper or pop top maybe next year. Then I will up grade the whole system. But for now it is shoe string budget and basic is best.

Do you know anything about what V8 Trooper is saying? I cannot find anything about it. I have Google blisters on my fingers and cannot find anything about it. If it is correct, it is so far the only answer that would explain why two different controllers give exactly the same measurements and results. Sure they both could be faulty but I think it would be unlikely for them to have the same measurements.

Voltage should not be an issue your 19V should be fine, mppt work by increasing or decrease the load on the panel to work out what current it can draw from the panel to get the most watts transferred to the battery.

ie Simplistic explanation, if you think of it as a graph with current drawn as a rising line and voltage as a decreasing line at some point they will cross and that is the maximum power point.

The maximum power transfer might occur at say 16V and 5A, if you connect the panel straight to the battery and it might want to draw 10 amps, the panel voltage would drop dramatically, ie panel output power at maximum power could be 17.8V@6.7A = 120W approx, if we short circuit the panel we may get 7.64V at .1 volts = less than 1 watt. The more load on the panel the less power after you reach a certain point, ie the maximum power point.

The mppt controller will keep increasing the current to the battery (keeping voltage within regulation limits) till the maximum power point is reached, if sun shine decreases then it will decrease the charge current to place the panel in the sweet spot again.

Having a higher voltage panel can become beneficial in that the mppt can use the headroom above the required battery voltage to generate extra current for charging the battery, for example take 19V@5A and convert this to 14.4V@ if the mppt can handle it in that If the battery wants more amps than the

Sorry pressed wrong key, should have just been convert this to 14.4V@6.6A. Ignore the rest, being able to edit would be nice.

Thanks again for the replies.

I still can't get my head around number of cells. If V8 is correct, I will just leave it and run without a reg. But since no one, including panel manufactures and solar experts make mention of it, I am starting to think number of cells is a bit of a garden path.

Anyway. You have made me think. What if I did connect the panels in series. 60 watts @ 24v.. That would give 60 watts with open circuit of 40 volts. I have seen plenty of MPPT sellers and manufactures say they recommend using a 24 volt panel (40 volt). In fact I am pretty sure the 20 amp reg I have recommends a 24v panel.

Maybe, both my regs would prefer a 24 volt panel system. Which in turn would explain why they both give the same results.

I am about to get hit by another thunder storm. So have to go. Yes, Wagga is getting hit again. Not as bad as yesterday but windy this time. I need something better than a tarp. I will be back when this storm passes.

I would be surprised if you don't have 36 cells panels, I also don't believe V8 was suggesting you don't use a regulator just that a mppt might not be worth using on a low voltage panel.

You should always use some type of regulator to prevent over charging of the battery.

That is interesting. In all my research I have not seen this mentioned before.

I am not sure exactly what to look for. If I see it correctly, each panel has 28 cells. 7 down and 4 across. Would that mean it's a 56 cell panel ?

This is it
http://www.gsl.com.au/mppt12.html

Kelpie,

From what I read so far in the thread you have 2 x 60 watt panels in parallel, giving you 120 watts.

If you place them in series you will still have 120 watts but the solar voltage will be doubled and the output current will be halved.

If you have a regulator that says it will accept 24V panels to charge a 12V battery it WILL NOT boil the battery unless it is faulty.

Advantages of seriesed panels:
- fewer cable losses between panels and regulator
- greater likelihood of the solar input to regulator remaining over the threshold MPPT tracking voltage (part of the regulator design), meaning greater likelihood of the MPPT working properly in marginal solar conditions.

Main disadvantage of seriesed panels is that if one of the two gets partially shaded the output from the pair drops drastically. So you will have to keep them BOTH fully in the sun to see the benefit.

Advantages of parallelled panels
- if one panel is affected by shade it doesn't affect other panels

Disadvantages
- Greater cable losses between panels and regulator. You should have reasonably heavy cable if it a long run, eg 10m
- depending on the MPPT threshold voltage of your regulator, in marginal conditions the voltage may drop below that value and stop the regulator from tracking, with a subsequent loss in efficiency.

So by all means hook up your panels in series and see how you go. Your panels' open circuit voltage will about 43 to 44V and when connected to the regulator to a half discharged battery the solar input voltage to the regulator should be about 34 to 36 volts.

If you haven't already got one, an inexpensive multimeter would be a good investment.

Cheers

Frank

Bugger! Hit the wrong button!

"If you place them in series you will still have 120 watts but the solar voltage will be doubled and the output current will be halved. "

Not quite. The open circuit voltage of the pair will be twice the open circuit voltage of one panel (assuming they are twins) and the output current (Isc and Imp) will be as for a single panel.

Still 120 watts total power.

Cheers

Kelpie,

"But they all insist a 24v panel will boil and kill a 12v battery even if an MPPT is used."

Mate, that is just the biggest load of bull!!

A 24V panel connected directly to a 12V battery will definitely stuff the battery. But through a regulator designed to accept 24V panels and a 12V battery, no way!

Also, mentioning the MPPT threshold voltage got me thinking ...

I wonder if you have a mismatch between your solar panels and your regulator. Some regulators may have a MPPT threshold voltage that is above your panels' maximum power voltage (Vmp). Threshold tracking voltage or minimum tracking voltage may be listed in the specs for your regulator. If it is higher, then putting your panels in series should improve things, as the Vmp from the pair would be double that of a parallel arrangement.

Cheers

Thanks Frank,

Yes, I will be getting a new multi meter tomorrow. The reason I was relying on the watt meter is because my multi meter got broken by a car driving over it.

I have found a solar forum also saying it can be done.

So pretty much, as long as you have full sun with no shade on either panel, the benefits out weigh the disadvantages.

What about cloud ?

I think you will tell me I am wrong, but here goes. Rounding the numbers just to make it easy. Say the series panels make 40volts at 120 watts amps would be 3. If clouds come over and volts drop to say half that, 20, would I be getting 6 amps? watts / volts = amps.

Thanks again Frank,

Seems you posted while I was typing :)

Yeah, a load of bull. Maybe they just say that in the hope I will buy a new bigger panel.

I will give it a go. I got the 20 reg out and it also says 12/24v. So tomorrow I will get a new multi meter to confirm whether or not the watt meter is faulty. With a proper working meter on hand to measure everything, I will series connect the panels and see what happens.

Kelpie,

There are some crap MPPT regulators out there. Some are not proper MPPT at all.

So providing you don't have one of those, and instead have a good, functioning one you will get the best from your panels in all conditions until the panel voltage drops below the regulator's minimum tracking voltage.

Panels work on light intensity, mostly visible light. So it can be cloudy but still enough light to generate useable output. What happens in cloudy conditions is that it's not the voltage that drops, it's the ability to produce power. Power is the product of volts times amps.

Simplistically the MPPT reg will adjust the load it applies to the panels to keep the product of volts time amps at a maximum. Some, particularly the more sophisticated ones, are better at it than others.

In monocrystalline panels the Vmp (maximum power voltage) is typically about 3/4 the open circuit voltage (Voc), but that's an approximation - it can vary with brand and prevailing conditions.

The simplest budget systems assume that rule. They test the Voc and then load the panels to hold the voltage at about 3/4 of the Voc. The power produced is then fed to a circuit that changes it from 40 volts at 3 amps (using your figures) to, say, 12 volts at 10 amps at the battery.

What happens then is further complicated by the multi-stage charging algorithm usually built into these regulators, but let's just stick to the solar part for the moment.

When a cloud comes the regulator would adjust the load on the panels so that the volts stayed at 40. Because of the reduced light, fewer amps can be produced, say 1.5. So power produced is 1.5 amps times 40 volts, = 60 watts. That is then converted to, say 12V and 5 amps at the battery.

There are more sophisticated methods in more advanced controllers, where the controller tries a series of voltage/current combinations until it finds one that gives the maximum product. There are a number of ways of doing this, no need to discuss them here, but the advantage of those is that they get the absolute best out of the panels in the prevailing conditions.

You won't always get the stated wattage out of your panels. The stated wattage is at a standard set of conditions which don't happen much in real life. Cell temperature in particular affects the output of panels, and being dark in colour they do get hot in the sun. After all losses and factors are accounted for, you will be doing ok to get, on average, about 70% of your stated 120 watts as useable output. So your sunny 40 volts and 3 amps could be 40 volts and 2.1 amps and your cloudy 1.5 amps could be only 1.05. But on a good day - cold clear bright sunshine on a mountain top :-) - you could get 100% and maybe more.

Cheers

Thanks again Frank for taking the time.

This is the 20amp reg I have - http://www.waohe.com/html_products/Solar-Charge-Controller-51.html

I haven't found my 10amp one on line. But I will try the 10 first.

Even if my watt meter is faulty and showing lower values, trying 24 volt sounds like a good idea. On a really good day I can get 5amps. But if a cloud comes over I am lucky to read 1.5 amps. (Oh, it is a mono panel.) According to my watt meter.

I understand the figures are all just best guess. But they are sounding pretty good to me.

No wonder the shops say it cannot be done. Five minutes, a couple of screws and a bit of wire and you have your panels in series and doubled or maybe trebled your charging ability. Or you could pay maybe $700 or $1,000 to upgrade and get the same result.

"The simplest budget systems assume that rule. They test the Voc and then load the panels to hold the voltage at about 3/4 of the Voc."

Actually, there are some even simpler ones which I think are an absolute cheat and not MPPT at all because they don't track anything, they just make assumptions.

They assume a 12V panel. They don't test for Voc. They assume a Vmp of about 17.5 volts (or whatever) and hold the panel at that voltage. What happens after that in terms of charging parameters is somewhat doubtful.

God knows what this one does, but anine dollar MPPT 20A regulator?

I don't think so.

Kelpie

Our follow-ups crossed in the ether and it's a bit embarassing because the $9 item I rubbished I found independently, before you posted your wahoe link.

Mate, I think you have a dud. I think it was a dud when it left the factory. And I think they knew it was a dud when they sold it to you. I think you need to find a decent unit and unfortunately that is going to cost a bit more than $9 on eBay.

I don't know what your budget is. A good non-MPPT is way better than a crappy rip-off and need not be too expensive - sub $100. Members of my club have had good results with Powertech brand, both non MPPT (=PWM) and MPPT. Available from Jaycar and, probably cheaper, eBay.

Cheers

$9 ?

I got ripped off. I bought it maybe 2 or 3 years ago and paid, I think $20. I used it on a 20 watt system for about 18 months and never had a problem. I have it connected now to this system and have no idea what it is doing because I have removed the watt meter. But It is holding 2 lights and the battery window is green.

One of the shops today tried to sell me a basic non-MPPT Powertech at $50.

There is a Jaycar in Wagga. The budget is "save ya money to get a van". I was going to get a new multi meter, but I will take your advice and get a Powertech controller instead.

Kelpie,

I have one of these sitting in my garage. I don't need it any more.

You can have it for the cost of postage.

But before I send it I want to test it. So if you can hang on a bit I'll let you know if it's a goer.

Cheers

Well, I was not expecting that. Thank you very much.

I am on a caravan park until the 20th. I will ask them tomorrow if I can use their post address. Otherwise, my next house sit starts on the 23rd near Nowra and I will be there until the end of Feb.

OK Kelpie.

Send me an email to frankp79 at hotmail dot com

This is an invitation only email address so any emails that I haven't asked for are dumped.

I don't know if I can do before the the 23rd, but I'll try.

Cheers

pink bubble gum it's done

QuoteKelpie D posted:
That is interesting. In all my research I have not seen this mentioned before.

I am not sure exactly what to look for. If I see it correctly, each panel has 28 cells. 7 down and 4 across. Would that mean it's a 56 cell panel }

Hi
There is your problem, they are cheap grid panels
They are not suitable for battery charging in parallel
The load voltage will be too low
If you are confident that the MPPT reg is suitable for a series connection of the panels[can accomodate at least up to 40V],that will solve your problem

PeterQ

Hi Kelpie
In addition,I doubt that anything is wrong with either Reg ,or your meter
But the PWM reg will not be suitable for the panels in series

Fit that MPPT reg as close to the battery as is practical.
note: the panels combined output will still be 120W,but the current into the reg will only be around 4Amax
The output into the load ,in good conditions should be around 8A

PeterQ

Kelpie,

Before you go ahead with my offer, I think you should check out oldtrack's suggestion.

Cheers

Thanks oldtrack123,

Actually what I don't know to look for is whether a cell is the square thing with corners at 45 degrees or if they are half that. My panels have a row of half squares across the bottom.

The panels are working just nicely.

I got a new multi meter today. It confirmed that the watt meter is in fact faulty. The watt meter told me the battery was 13.4 volts and the multimeter said 12.4. I tend to go with the multi meter because the window is white. The watt meter was saying 3.66 amps at 14.5 volts was going into the battery and at the same time I was reading 5.5 volts on the multimeter.

So, back to Jaycar. I got a cheapy PWM controller. It has been connected now for about 2 hours. Battery volts are 13.2 with nothing connected. I have not bothered to see what the watt meter would say.

So in short, In turns out it was a faulty watt meter giving me wrong figures. That made the math say I was doing OK, when in fact I was going down hill at a great rate of knots.

Thanks Frank,

I just replied to your email. I will reply to your first email shortly, have to take the kelpie for a walk first.

I would like to take your offer. I understand the 24 volt issue you mention in your email. It was also very good of you to go out of your way to get it tested. Good of Jaycar to help out too. The postage you stated will not do though, you would have spent more than $8 on petrol and time. I think a six pack is about $16 these days, so lets make it $24.

Thank you, mate. More than generous and gladly accepted.

Cheers!

Kelpie cannot post pics at the moment, buut he has emailed a couple to me.

Here's the label on the back of one of his panels


I did a bit of googling and found two versions of he GPM-2F-120W panels, one 28 cells, the other 36:

and


It's a bit confusing having the same model number for quite different panels, but I guess that's the Chinese way.

That aside, we can be assured that he has 28 cell panels. The Voc is 17.5V, Vmp is 14V.

I believe these will work in series into an MPPT regulator.

Will they work in in parallel into a PWM regulator?

Cheers

HI
That confirms thet are not battery charging panels .AS per my suspicion
12v Battery charging panels have an OC of around 21V
& MPP around 17V
The only way they will do the job of fully charging a battery is series connected with A MPPT reg that can take 40V .


PeterQ

Hi Frank
They will not fully charge the batterry as a parallell set
They may, if the battery is not too flat to start with
[low open circuit voltage'] but can put in a small charge & supply a connected load
I think that is what Keplie is seeing NOW but the voltage @Pmax is too low
It ned to be nearer 16<17V
Many regulators have problems starting up if the battery is TOO flat
Require a certain battery voltage to start operating.


PeterQ

Hi PeterQ,

I presume that with a PWM solar controller (or even without one), in parallel they would charge a battery to close on 14.0V. Not a full charge, as you say, but a charge nonetheless. Would that be correct?

Cheers

Thanks Peter. Follow-ups crossed in the ether. You beat me by a whisker :-)

Cheers

Peter,

Based on your Follow-up 23 above...

If Kelpie had a different PWM reg like the one I'm offering him, if he had the fridge on the load output and the fridge was running, would he get anything into the battery?

I'm thinking now that though the panel might run the fridge, the fridge load may pull the volts down too much.

The specs for the reg say the PV to battery differential is 0.8V and the PV to load differential is 0.4V.

Manual below if you're interested.

Cheers

Thanks Frank and Peter,

Before I purchased the panels, I did do some research. I recall findind a set of figures that matched very closely to more expensive brand panels. The second chart posted by Frank looks like it.

To be honest, I have not taken any further notice of the specs until now. It now seems that I got the one shown on the first chart above.

Just out of interest, I might give the series a go just to see what happens. I have more or less given up on both the MPPT regs I have. What is the worst thing that can happen if the series connection causes probs? I assume it will just burn out the reg? If that is the case I will try it.

Kelpie,

You said earlier in this thread that the documentation for at least one of your MPPT controllers said it was 12/24 volt. Did it say what the max Voc or PV voltage allowed is? For 24V panels it should be around 42V or more.

If there is any doubt, then there is a risk of damage.

Being cheap regulators they may not have much protection. If you're prepared to accept the risk of damage to them this is what I'd do:

Wait until you have a lengthy period of consistent sun, then
- hook up your panels in series; do not connect them to a controller yet
- place your watt meter in the output between the controller and the battery and connect to the battery.
- observe the wattmeter and write down what it says
- connect the solar. Check for leaking smoke :-)
- observe the wattmeter and write down what it says

Do that for both MPPT regulators

Tell us what the results are.

Cheers

Thanks Frank

It is not really very sunny today. I might follow your suggestion some other day.

The panel is now in series. I connected the 20amp $9 job. No smoke yet.

The Good...It is working. Battery volts have gone from 12.99 to 13.6 in about 15 minutes. All three lights are on on the controller for the first time. The watt meter is in line on the solar side. The multi meter confirms the watt meter readings - they are the same.

The Odd...I read 31 volts open direct at the panel terminals. Connected to the controller I read 13.1. The multi meter confirms 13.1 volts at the panel terminals when connected.

Confirming amps with the multi meter is a hassle with ando plugs, but the watt meter said 6 amps at 13.1 volts.

It has been about 30 minutes now. All still looks good. The 3rd controller light is now going off and on, indicating the battery has gone to float. Battery volts at the terminals is now 13.7. The watt meter says amps have dropped to 1.8.

BTW. All these measures are with no load. I have the Engle running off the Allrounder in the car whilst I am doing this.

Minor up date to the above.

It is not in float.

Just had some full sun. Amps jumped to 4.5 and the third light is on and steady. It looks like it is in bulk.

Still no smoke and looking good.

Kelpie D posted:

The Odd..

[1].I read 31 volts open direct at the panel terminals.

[2] Connected to the controller I read 13.1. The multi meter confirms 13.1 volts at the panel terminals when connected.

[3]Confirming amps with the multi meter is a hassle with ando plugs, but the watt meter said 6 amps at 13.1 volts.

It has been about 30 minutes now. All still looks good. The 3rd controller light is now going off and on, indicating the battery has gone to float. Battery volts at the terminals is now 13.7. The watt meter says amps have dropped to 1.8.

BTW. All these measures are with no load. I have the Engle running off the Allrounder in the car whilst I am doing this.


Hi
Perhaps you will not read it BUT,
[1] With those panels in series , with a MPPT controller, that is near enough to what one could expect
[2] I assume that reading is with the battery connected? & at the reg's battery terminals
You would be reading BATTERY voltage

[3] that is only 78W , but will be dependent on sunlight
The Max you could expect facing the panels direct into BRIGHT sun with a low soc battery would be around 18A


PeterQ