MPPT vs Alternator Question

[BlueStringPudding]

The last few days of lovely bright sunshine have lured me to check my battery monitor to see how the solar panels are doing.

 

I've noticed that the MPPT controller never charges at a voltage over 13-point-something volts even though the batteries aren't near full so it shouldn't be on float - whereas my alternator charges at 14-point-something volts until it drops into float charge.

 

Today I noticed a flashing light on the MPPT I'd not seen before and when I looked it up in the manual it was on equalisation charge, which it only does once a month. And low and behold, the voltage it's charging at is 14.22v.

 

I thought equalisation charge voltage should be higher than that - and shouldn't regular day-to-day charging be at the 14+ volts level?

 

The batteries are new so it's not a battery problem. The MPPT controller has never charged at a very high voltage so I'm curious as to what might be causing it or if I need to amend anything. It's a Mornigstar SunSaver MPPT controller and as far as I can tell, the settings are correct for my 12v battery set up.

 

[WotEver]

Hey BSP. Is the configuration correct as per Page 16 of this pdf?

 

Tony

[FidoDido]

maybe its set to Gel Batteries setting rather than bog standard Flooded? Gels don't like anything above 14.2 IIRC.

[nicknorman]

OK it may be a configuration issue but just bear in mind that the ideal charging voltage of 14.4v or whatever, can only be achieved by the solar controller if there is enough incoming solar power to get the voltage up there. If the batteries are fairly low, they will take a lot of charging current and the solar won't be able to get the voltage up to the ideal value until the batteries are getting fuller and thus taking less current. Therefore what you are seeing may be quite normal, it depends on how much solar you have, how big the batteries are, and what their state of charge is.

 

You say the voltage is now up to 14.2, but could that in part be due to having the batteries at a higher state of charge and stronger Spring sunshine?

[WotEver]

Yes, it's quite possible that the SOC is so low that it's limiting the controller's output (BSP did say "nowhere near full") but I thought it worth confirming the configuration first.

 

Tony

[BlueStringPudding]

You say the voltage is now up to 14.2, but could that in part be due to having the batteries at a higher state of charge and stronger Spring sunshine?

 

No - the MPPT is in equalisation mode. I can tell that from the led indicator, that's why the voltage is higher. But still not all that high.

maybe its set to Gel Batteries setting rather than bog standard Flooded? Gels don't like anything above 14.2 IIRC.

 

It used to be on sealed batteries setting for my old batteries, so never went in to equalisation mode. Those batteries were kaput by the end so I always assumed the low charge voltage was due to the batteries.

 

I now have new flooded batteries and set the configuration for that. (I will check it again just in case, though) - the controller wouldn't go into equalisation mode if it wasn't set for flooded batteries.

 

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Just checked the settings - switches are 1:OFF, 2:OFF, 3:ON, 4:OFF which I'm pretty sure is correct for 12v 4 x 110Ah flooded batteries. And jumper removed. But by all means correct me if I'm wrong. Thanks.

 

Edited March 10, 2015 by BlueStringPudding

[nicknorman]

How are you measuring the voltage? Presuming it's from the solar controller display, maybe you should try putting a multimeter on the actual batteries to see if the voltage displayed is correct.

Edited March 10, 2015 by nicknorman

[BlueStringPudding]

OK it may be a configuration issue but just bear in mind that the ideal charging voltage of 14.4v or whatever, can only be achieved by the solar controller if there is enough incoming solar power to get the voltage up there. If the batteries are fairly low, they will take a lot of charging current and the solar won't be able to get the voltage up to the ideal value until the batteries are getting fuller and thus taking less current. Therefore what you are seeing may be quite normal, it depends on how much solar you have, how big the batteries are, and what their state of charge is.

 

 

Possibly. There's 400w of solar, half pointing directly at the sun. And with the sun as high as it gets this time of year, and before the controller went into equalisation mode, the solar was putting 7.1A going in to the batteries at 13-point-something volts.

How are you measuring the voltage? Presuming it's from the solar controller display, maybe you should try putting a multimeter on the actual batteries to see if the voltage displayed is correct.

 

Just from the battery monitor - which is the same thing I measure the alternator voltage from. So should be comparable.

Edited March 10, 2015 by BlueStringPudding

[nicknorman]

Just from the battery monitor - which is the same thing I measure the alternator voltage from. So should be comparable.

Fair enough.

[FidoDido]

my Tracer MMPT shows 0.2V less than my Mastervolt MICC control panel.. I trust the £500 control panel more than the £20 MPPT thing!! Also the SOC % on the Tracer is a complete work of fiction.. Perhaps try measuring the real voltage at the batteries with a decent multimeter, and check the reading. Might be you are getting a decent voltage?

 

For comparison, my Tracer charges at up to 14.8V (equalisation charge), then drops back to 13.6V. It only really gets above 14V when the batts are pretty near 100% full.

have you connected the feed from the panel before the shunt for your battery monitor? If not, this might explain the difference?

[nicknorman]

Possibly. There's 400w of solar, half pointing directly at the sun. And with the sun as high as it gets this time of year, and before the controller went into equalisation mode, the solar was putting 7.1A going in to the batteries at 13-point-something volts.

So around 100W from the panels. Does seem a little on the low side for 400W panels in mid-march. You could try disconnecting all but 1 of the batteries, and see if the voltage rises significantly (with the sun shining). If it does, it means there wasn't enough oomph from the solar to get the voltage up. If it doesn't, it means the solar is regulating at the wrong voltage, I'll have a look-see if I can find the manual for that controller on line to check the config

[BlueStringPudding]

So around 100W from the panels. Does seem a little on the low side for 400W panels in mid-march. You could try disconnecting all but 1 of the batteries, and see if the voltage rises significantly (with the sun shining). If it does, it means there wasn't enough oomph from the solar to get the voltage up. If it doesn't, it means the solar is regulating at the wrong voltage, I'll have a look-see if I can find the manual for that controller on line to check the config

 

WotEver posted a link to the manual further up this thread

have you connected the feed from the panel before the shunt for your battery monitor? If not, this might explain the difference?

 

If the battery monitor was incorrectly wired in a way that would affect the reading, shouldn't it show the same discrepancy when displaying what the alternator is putting into the batteries? At the moment I'm comparing like for like - the reading for the alternator on my battery monitor and the reading for my solar panels on the same battery monitor.

[nicknorman]

OK so looking at the spec in the manual (page 45), it says for flooded:

 

Absorption voltage: 14.4

Float voltage: 13.7

Time until float: 3 hrs

 

From this one might deduce that it will only be in absorption mode for the first 3 hours after it starts working in the morning, then it will go to float. Which is crap! Maybe you need a better solar controller?

 

Edit: not entirely sure the above is correct, the clock only starts ticking once the voltage is up at 14.4. Anyway, there seem to be LEDs to tell you what is going on, variable flash rate according to bulk, absorption or float. Can you determine what the flash rate is when it's not doing what you think it should be doing? Obviously if it is in float mode, the voltage will only be 13.7 but we need to determine if that is the case before trying to think how to keep it in Absorption for longer.

Edited March 10, 2015 by nicknorman

[FidoDido]

I wasn't saying the battery monitor was wired wrong.. I was asking if the Solar panel input was across the Shunt (only required by your battery monitor if it reads amps), or just on the batteries themselves. Might be a difference between the two.

 

[Boredrider]

OK so looking at the spec in the manual (page 45), it says for flooded:

 

Absorption voltage: 14.4

Float voltage: 13.7

Time until float: 3 hrs

 

From this one might deduce that it will only be in absorption mode for the first 3 hours after it starts working in the morning, then it will go to float. Which is crap! Maybe you need a better solar controller?

 

Edit: not entirely sure the above is correct, the clock only starts ticking once the voltage is up at 14.4. Anyway, there seem to be LEDs to tell you what is going on, variable flash rate according to bulk, absorption or float. Can you determine what the flash rate is when it's not doing what you think it should be doing?

 

My interpretation of the manual is that first thing in the morning it will start in bulk mode (given that the sun is shining) and continue until battery voltage reaches 14.4V, then it will continue for 3 hrs at 14.4 before switching into float at 13.7.

 

Page 40 talks about some free software and a lead, with which you can tweak the settings, but by the looks of it 15.0 volts is the absolute max, so whilst you may be able to improve your daily charge settings, you won't be able to equalise at 15.5V. Unless someone on here with greater experience of this controller knows different..............

[BlueStringPudding]

Thanks Boredrider and NickNorman. So it charges on a timer rather than responding to the batteries? Seems like a bit of a waste of sunlight.

 

So maybe it is the controller that's the problem. It's possible I've just not seen the first three hours of the morning charge yet. Although I'd like more than three hours before it goes into float if the batteries can take it

 

I do (probably) have an alternative Mppt controller I could swap it for. It's a Tracer. I'm not sure it's in full working order and was trying to avoid having to wire it in in case it's not working. But it's a potential back up if the MorningStar isn't doing what it should.

Edited March 10, 2015 by BlueStringPudding

[BlueStringPudding]

I wasn't saying the battery monitor was wired wrong.. I was asking if the Solar panel input was across the Shunt (only required by your battery monitor if it reads amps), or just on the batteries themselves. Might be a difference between the two.

 

Oh I see. That I don't know off the top of my head. I'll have to follow some wires to find out.

[Loafer]

First of all, that is just not big enough to be a 'proper' MPPT controller. However, that's not relevant here.

 

My meagre 300W of solar was giving me 18.5A today at 14.8V on a bunch of Trojans. I saw 22A one day last week.

 

There's deffo summat wrong with yours.

 

Try disconnecting all your panels on a nice day, then reconnect one at a time, checking for a current increase each time. It may be that one or two of them aren't connected. I had that once, where an MC4 plug had pushed the female part into it's own housing and failed to make a connection.

 

Are your panels in series or parallel?

 

Edited for syntax.

I should add that mine had only just reached 14.8V. Shortly afterwards, the current started to tail off to keep the 14.8V, otherwise they'd have run away.

Edited March 10, 2015 by Loafer

[Boredrider]

I wouldn't be in a rush to change controllers just yet. It only uses the timer when it is in absorption mode. This comes after the bulk phase, which is where it should start on a sunny day, in bulk mode it should take everything the panels can give and send to the batteries. As the batteries charge, current will reduce, and voltage will rise, until voltage reaches 14.4V and the controller switches to absorption. It will stay in absorption for 3 hours, regulating the voltage to 14.4, and then when the three hours is up, it will switch into float, where voltage is regulated to 13.7.

 

All the above assumes that the sun continues to shine, the panels aren't shaded, and the batteries are not being asked to run any 12V loads. So I guess it could be a few days before you are able to confirm that the controller is working as it should!!

 

From what you have said about voltages in the OP and post #8 I doubt that you are getting out of bulk charge mode. The equalisation mode is a bit of a red herring at the moment.

[Loafer]

Ended up around 3A.

 

ETA Sorry, that should have been tagged on to the end of post #19.

Edited March 10, 2015 by Loafer

[BlueStringPudding]

First of all, that is just not big enough to be a 'proper' MPPT controller.

 

 

I don't understand what you're getting at? "Big enough" and "Proper"? Do you mean in terms of max Amps or max Voltage, or something else?

 

The Tracer I have can take more amps than the MorningStar, assuming it's working. Not that I would imagine that would make any difference with my solar set up.

 

My old solar panel was putting 47v into the controller, and with my old batteries and new batteries I've never seen the battery monitor show the controller is charging the batteries at anything higher than 13 point something volts. Now with the old panel gone and 4 new panels, same thing.

Edited March 10, 2015 by BlueStringPudding

[BlueStringPudding]

 

 

From what you have said about voltages in the OP and post #8 I doubt that you are getting out of bulk charge mode. The equalisation mode is a bit of a red herring at the moment.

 

Again, quite possible. I'll keep an eye on it when it's good and sunny and try to time the flashes on the led!

[by'eck]

The last few days of lovely bright sunshine have lured me to check my battery monitor to see how the solar panels are doing.

 

I've noticed that the MPPT controller never charges at a voltage over 13-point-something volts even though the batteries aren't near full so it shouldn't be on float - whereas my alternator charges at 14-point-something volts until it drops into float charge.

 

Today I noticed a flashing light on the MPPT I'd not seen before and when I looked it up in the manual it was on equalisation charge, which it only does once a month. And low and behold, the voltage it's charging at is 14.22v.

 

I thought equalisation charge voltage should be higher than that - and shouldn't regular day-to-day charging be at the 14+ volts level?

 

The batteries are new so it's not a battery problem. The MPPT controller has never charged at a very high voltage so I'm curious as to what might be causing it or if I need to amend anything. It's a Mornigstar SunSaver MPPT controller and as far as I can tell, the settings are correct for my 12v battery set up.

 

 

The mppt controller is a multi-stage charge device which will automatically drop to a lower float voltage when it thinks batteries are fully charged or nearly so.

 

An standard alternator relies only on it's internal regulator, limiting charge voltage to14+ volts as batteries approach full charge, and then remaining at this single regulated voltage.

 

It's likely the equalisation mode on the mppt controller isn't at a true equalisation voltage, but just a half way house by invoking absorb mode.

[BlueStringPudding]

 

 

It's likely the equalisation mode on the mppt controller isn't at a true equalisation voltage, but just a half way house by invoking absorb mode.

 

Thanks for your reply. What does "invoking absorb mode" mean?

[Loafer]

 

I don't understand what you're getting at? "Big enough" and "Proper"? Do you mean in terms of max Amps or max Voltage, or something else?

 

The Tracer I have can take more amps than the MorningStar, assuming it's working. Not that I would imagine that would make any difference with my solar set up.

 

My old solar panel was putting 47v into the controller, and with my old batteries and new batteries I've never seen the battery monitor show the controller is charging the batteries at anything higher than 13 point something volts. Now with the old panel gone and 4 new panels, same thing.

 

A true MPPT controller has much more to it than could be fit inside that little one, I believe. There's a lot on utube about 'false' MPPT controllers and the ones that work well are quite large compared to that one.

 

There are CERTAINLY some 'improper' ones, i.e. 'PWM' controllers that say 'MPPT' on them, about the same size. It's not relevant to the OP's problem, and should perform better than he's saying even if they're 'false' MPPT.

 

Go to utube, and search 'MPPT' and you may be surprised. I certainly was. I have one of them now in a box, having bought a 'proper' one. Which actually works.

 

There are many of them tested and video'd on there, how those manufacturers get away with it I just don't know.

 

Morningstar wasn't one of them, but all the fake ones were about that size.

 

There are ways to tell without test equipment:

 

Once your batteries are at absorb voltage, the controller should reduce it's output. A 'PWM' controller will just pulse the voltage from the panels on and off, the work cycle dependent upon the battery SOC.

 

An MPPT controller raises the panel voltage until the current falls to keep the absorb voltage steady. There is no pulsing.

 

Also, and MPPT controller will show you two voltages: the panel voltage, and the battery voltage. A PWM controller is always at battery voltage, even at the panels. It is nothing more than a scheduled switch, on, off, on, off when full.

 

Solar panels are CURRENT sources, and have a max current they can deliver. If they are delivering their max CURRENT at BATTERY voltage, that is a lot less POWER available than delivering that max CURRENT at the PEAK CURRENT VOLTAGE, usually about 17V in a 12V system.

 

Plus you can series up your panels with a true MPPT controller, up to about 150V, so you don't get heat losses in your cabling.

 

It's all there on google. And utube.

 

My old solar panel was putting 47v into the controller, and with my old batteries and new batteries I've never seen the battery monitor show the controller is charging the batteries at anything higher than 13 point something volts. Now with the old panel gone and 4 new panels, same thing.

 

You won't see panel voltage on your battery monitor. You'll see battery voltage. A true MPPT controller shows you both. If you have a tracer MPPT, the little instruction manual explains the power gain by keeping the panel voltage higher than the battery voltage using a DC-DC converter. Which isn't a small item!