mppt controller

[pessimist]

Having read the previous threads on these solar controllers I still have a couple of questions.

How do I tell a good from a bad one? Is it just price or is there something I should look for in the spec? Prices seem to vary wildly for what seem to be similar items.

The question of wiring in series or parallel still seems moot. I'll probably be adding a couple of extra 80w panels to my existing 80. The new panels would only be deployed on the mooring/at anchor so I'm tempted to leave the existing controller (cheapo, non mppt) in situ and add a new controller. Any problems with this?

As ever, thanks for any advice.

Cheers,

Colin

 

[pessimist]

Found this http://www.ebay.co.uk/itm/Tracer2215RN-MPPT-20A-150V-Solar-Charge-Controller-Regulator-12V-24V-UK-/281166935530?pt=UK_Gadgets&hash=item4176daf5ea

Any good?

 

[[3889]]

I was looking at upgrading from PWM to MPPT and was pointed at this video which I found informative:

I also noticed that whilst all sub £20 "MPPT" controllers on eBay were almost certainly only PWM, some of the dearer models were also marketed by other sellers as PWM at far lower prices so the whole thing is a bit of a gamble. Checking a reputable seller's offerings is one way to get some reassurance.

In the end I decided to stay with PWM as there is a better return for £ by spending the extra on larger panels, provided you have the deck space, of course.

 

[joha]

I have Victron blue energy fitted was about £80 quiddish 70/15 MPPT and I think Victron are a reputable company. I have only one 80watt panel and if memory serves I think its good for upto 200watts you may need to go the next size up and that one is a bit more £

J

 

[TradewindSailor]

I have a Blue Sky MPPT controller which I am very happy with but they are a little expensive.

I have also replaced similar units for other cruisers. A few observations:

The marine environment is very aggressive to electronic circuitry :
A friend had a similar Blue Sky controller. They are marine ruggedised, meaning that the circuit boards are coated with a coating to protect it from condensation and salt deposits. BUT the coating doesn't cover everything as heat must be dissipated too. My friends unit was shorted out by a few drops of salt water, possibly from wet clothing or a leaky hatch; even though the unit seemed to be well protected ...... result was a blown unit.
I replaced it with a much cheaper domestic unit. It's boards are also came protected against moisture, although the casing, sockets, and switches caused some concern. I sprayed the circuits and switches with Corrosion Block which should protect against water ingress and mounted the unit in a very protected location. So far so good.
The smaller units are often fully encapsulated, even those for intended for domestic units; so this problem may not be relevant to you.

 

[nigelmercier]

I also noticed that whilst all sub £20 "MPPT" controllers on eBay were almost certainly only PWM ...

MPPT controllers are PWM. The converse is not necessarily true.

 

[William_H]

MPPT controllers are PWM. The converse is not necessarily true.

Ay? Pulse width modulation controller switches the connection + panel to +ve battery on and off at a ratio of on to off to produce the desired charge as related to chrage state of the battery. In fact the battery smooths out the ons and off to give a resultant voltage which is used to feed back to the pulse width gnerator. So gives 14volts as an average.

MPPT is vastly different. MPPT is a switch mode power converter converting the 20 volts of the panel to 14volts or more likely a voltage depending on the stae of charging required. In this conversion it is able to provide more current at 14v than the panel provides at 20volts. It is not as simple as that however.
If you put a short circuit on a panel it produces no power in the load the power being wasted inj the internal ressitance of the panel. High current no volts.
If you get 20 volts out of the panel but don't suck current then again you have no power.
If you put a variable resistor on the output of the panel you can get max power out into the resistor as heat. This is something like near max current at about 18 volts. This point of max power that can be sucked out (at best volts and amps) is the Max power pointy and varies with amount of sun light. The MPPT controller uses the panel aoutput at a voltage and current that best gets all the power out then converts this power to what the battery needs.
So in a way MPPT does suck power from the panel in pulses of varying width well actually from a capcitor which is constantly filled by continuous current form the panel but that is where the similarity ends

Now by contrast if you connect a panel directly to a battery the voltage that you suck power out of the panel will be about 14v the other 6v the panel generates in bright sun is wasted while the current will be near max. However if the sun is less than optimum your voltage of the panel amy fall until there is not enough to charge the battery ( 14v) so you get nothing. Hence panle makers put enough cells in to give more than 14v for most sun levles at the waste of power at full sunlight.
A PWM contoller at best can only give as much power as a directly connected panel probably less with losses in the switch transistor (.7 volt) and can only cut charge back from max to stop boiling the battery.

 

[nigelmercier]

Pulse width modulation controller switches the connection ... on and off at a ratio of on to off ... MPPT is vastly different. MPPT is a switch mode power converter ...

So how do you think a SMPS works then?

"... the pass transistor of a switching-mode supply continually switches between low-dissipation, full-on and full-off states..."
http://en.wikipedia.org/wiki/Switched-mode_power_supply

 

[[3889]]

MPPT controllers are PWM. The converse is not necessarily true.

Oh well, at least I'm not alone in my ignorance.

https://www.google.co.uk/search?q=mppt+vs+pwm+charge+controller&rlz=1C1CHMO_enGB524GB524&oq=mppt+v+pwm&aqs=chrome.2.69i57j0l5.6823j0j7&sourceid=chrome&espv=210&es_sm=93&ie=UTF-8

 

[nigelmercier]

Oh well, at least I'm not alone in my ignorance...

What I was trying to explain is that you should not discount an MPPT controller because it mentions PWM.

 

[sailinglegend420]

Found this http://www.ebay.co.uk/itm/Tracer221...81166935530?pt=UK_Gadgets&hash=item4176daf5ea

Any good?

All good (expensive) controllers or regulators will have a programmable feature to perfectly match YOUR battery needs, not just a "Sealed, Gel and Flooded battery option" - that's too simple. You need to accurately match the battery's charging voltages, but more importantly adjust the "Time at absorption" to match the size of your bank, otherwise they can switch to float much too early. At a much lower float voltage there may not be enough hours of sun left in the day to fully charge the batteries.

 

[Tony Cross]

MPPT controllers are PWM. The converse is not necessarily true.

True. An MPPT controller can be thought of as having two halves; the PWM half is what actually controls the battery charging, the MPPT half maximises the input voltage to the PWM part.

 

[GHA]

Make you own

Or at least see how to..

https://www.youtube.com/playlist?list=PLjzGSu1yGFjWv4KeN-7TSYeQIcicM9Ghl

 

[pessimist]

Thanks everybody. I understand now.................a bit

 

[nigelmercier]

True. An MPPT controller can be thought of as having two halves; the PWM half is what actually controls the battery charging, the MPPT half maximises the input voltage to the PWM part.

Exactly.

 

[danielefua]

A probably dummy question: if I have two equal panels, 100W for 12V batteries nominal, and want to fit an MPPT controller, what should be the rating of the latter? And how should I connect the two panels?

Daniel

 

[Tony Cross]

A probably dummy question: if I have two equal panels, 100W for 12V batteries nominal, and want to fit an MPPT controller, what should be the rating of the latter? And how should I connect the two panels?

Daniel

There are two values you need to know:

1. The output current to your battery. This is the maximum charging current that the controller can deliver. Ideally it wants to be at least 10% of your battery Ah capacity.

2. The open circuit voltage of your panels (printed on the panels usually). This must not exceed the maximum input voltage that the controller can handle. If you wire the panels in series it's the sum of the two max voltages you need to use.

 

[danielefua]

There are two values you need to know:

1. The output current to your battery. This is the maximum charging current that the controller can deliver. Ideally it wants to be at least 10% of your battery Ah capacity.

2. The open circuit voltage of your panels (printed on the panels usually). This must not exceed the maximum input voltage that the controller can handle. If you wire the panels in series it's the sum of the two max voltages you need to use.

These are the specs of each panel:
Max Power: 100W
Max Power Voltage: 17.8V
Max Power Current: 5.62A
Open Circuit Voltage: 21.6V
Short Circuit Current: 5.97A
Maximum System Voltage: 600V (what is this????)
Series Fuse Rating: 10A
Cell Efficiency: 19.9%
Number of Cells in series: 32
Max Power tolerance:+/- 5%

The panels are two, obviously not illuminated in the exact same way, and my battery bank is at 12V.

I would appreciate very straightforward replies to my following questions:
1) can I connect the two panels in parallel as they are or do I need to fit decoupling diodes (no mention of embedded diodes in the panel specs) or, else, I need a regulator with two inputs or, even worse, two different regulators?
1bis) if I need diodes or other complications, could I just connect the panels in series and let the MPPT regulator take care of optimizing the charging of 12V batteries?
2) what is the rating of the regulator I should fit?

Thank you in advance.

Daniel

 

[noelex]

1.Yes parallel is fine and arguably the best way. There is no need for any extra diodes

2. You need a controller which is OK with an input voltage of about 25v (this will be virtually all regulators). The maximum current is a bit under 12A with a MPPT regulator slightly less for a non MPPT regulator, but 10A is too small which means it will probably have to be a 15A model.

 

[William_H]

These are the specs of each panel:
Max Power: 100W
Max Power Voltage: 17.8V
Max Power Current: 5.62A
Open Circuit Voltage: 21.6V
Short Circuit Current: 5.97A
Maximum System Voltage: 600V (what is this????)
Series Fuse Rating: 10A
Cell Efficiency: 19.9%
Number of Cells in series: 32
Max Power tolerance:+/- 5%

The panels are two, obviously not illuminated in the exact same way, and my battery bank is at 12V.

I would appreciate very straightforward replies to my following questions:
1) can I connect the two panels in parallel as they are or do I need to fit decoupling diodes (no mention of embedded diodes in the panel specs) or, else, I need a regulator with two inputs or, even worse, two different regulators?
1bis) if I need diodes or other complications, could I just connect the panels in series and let the MPPT regulator take care of optimizing the charging of 12V batteries?
2) what is the rating of the regulator I should fit?

Thank you in advance.

Daniel

These are the specs of each panel:
Max Power: 100W
Max Power Voltage: 17.8V
Max Power Current: 5.62A
Open Circuit Voltage: 21.6V
Short Circuit Current: 5.97A
Maximum System Voltage: 600V (what is this????)
Series Fuse Rating: 10A
Cell Efficiency: 19.9%
Number of Cells in series: 32
Max Power tolerance:+/- 5%

The panels are two, obviously not illuminated in the exact same way, and my battery bank is at 12V.

I would appreciate very straightforward replies to my following questions:
1) can I connect the two panels in parallel as they are or do I need to fit decoupling diodes (no mention of embedded diodes in the panel specs) or, else, I need a regulator with two inputs or, even worse, two different regulators?
1bis) if I need diodes or other complications, could I just connect the panels in series and let the MPPT regulator take care of optimizing the charging of 12V batteries?
2) what is the rating of the regulator I should fit?

Thank you in advance.

Daniel

Max system voltage. I think this relates to the max number of panels you can have in series. So often in a domestic PV system the 8 or more panels are in series giving a max voltage around the 320 volts. This can mean that some parts of a panel can be 320v difference to other parts which in my case are mounted on an iron roof. So there is a max insulation capablility for the electrics of the panel. so 600v not a concern.

An MPPT controller starts with a switching transistor which switches the input from the panels at high frequency to feed a transformer. Some MPPT controllers can take a high voltage in but not necessarily a high current. So as an extreme my home PV system with MPPT controller /inverter takes 320v DC in at 5 amps. because all apnels are in series. if the panels were in parallel it would have to take 40v at 40 amps. It can not handle the current becuase the input transsitor/s can not take the high current but can handle the high voltage.
So with your boat MPPT controller it will have a max panel current and max panel voltage. You may be obliged to wire panels in series to keep the power but reduce the current.
Being a "transformer" the input voltage and current ( max power ) do not have to relate to the output voltage and current
So check the ratings of the controller it may be necessary to wire panels in series. good luck olewill