solar panel newbie still confused

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dunkelly

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Ok so i am a numpty but having read all the stuff in the forum i still cant find an answer basic enough for my needs . I dont really understand battery charging physics and so i have gone initially for a very simple 20 watt panel with a cheap pwm charge controller to cut my teeth on . All i really want to know is at what voltage should i disconnect at the high end and the same at the low end . i dont intend to ' load' the solar panel as such just using it to top up the battery on anchorage . the batteries are sealed lead acid .
 
The controller usually has settings fixed in it. But if it hasnt I suggest something around 13.7 v which is where the maintenance voltage of your alternator usually is. There is no need to set a minimum - do you really want the solar panel to switch off when the voltage in the battery gets low?
 
i think i meant when the solar panel voltage was low but im not really sure what i do mean , hence the very confused . i thought they were capable of discharging batteries when the sun went down and needed to be stopped or does that happen automatically
 
dunkelly said:
i think i meant when the solar panel voltage was low but im not really sure what i do mean , hence the very confused . i thought they were capable of discharging batteries when the sun went down and needed to be stopped or does that happen automatically
Click to expand...

f you have a controller, the most you need to do is set the charging voltages, if that with only 20w. What make/model of controller ? What settings does it have ?
 
dunkelly said:
Ok so i am a numpty but having read all the stuff in the forum i still cant find an answer basic enough for my needs . I dont really understand battery charging physics and so i have gone initially for a very simple 20 watt panel with a cheap pwm charge controller to cut my teeth on . All i really want to know is at what voltage should i disconnect at the high end and the same at the low end . i dont intend to ' load' the solar panel as such just using it to top up the battery on anchorage . the batteries are sealed lead acid .
Click to expand...

Tell us what controller you have !

Does it have "load" terminals in addition to the battery and solar panel connections? If so are you confusing the settings for the "load" disconnect and reconnect voltages with settings for the actual battery charging parameters
The fact that you are talking about "the low end" suggest you may be

If the above is the case you can ignore the load terminals and the disconnect and reconnect settings for them.
 
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thankyou i think that is exactly what is confusing me . its just one of the cheap blue ones on e bay ( its on the boat unfortunately) , until i get to grips with what i am doing i thought i would experiment with that before going bigger and better . so is it that i can just leave it as it was factory set and the internal electronics or diodes or whatever look after the battery charging ?
 
LadyInBed said:
With just a 20w panel some might not bother with a controller at all
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In my experience a controller is almost always a good idea even with a small panel. I had an ancient 5W panel connected to my start battery without a controller for a while until I noticed it had got over 16V. That was in the middle of winter. Not good for the battery.
 
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LadyInBed said:
With just a 20w panel some might not bother with a controller at all, with a controller it's fit and forget as the controller will block any possible overnight discharge.
Click to expand...

A frequently quoted rule of thumb is to fit a controller if the ratio of watts to Ah capacity exceeds 1 watt per 10Ah and to fit a controller to all panels over 10 watts
 
Elbows said:
In my experience a controller is almost always a good idea even with a small panel. I had an ancient 5W panel connected to my start battery without a controller for a while until I noticed it had got over 16V. That was in the middle of winter. Not good for the battery.
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Yes. I suggest that SOME might not use a controller as the OP said "i dont intend to ' load' the solar panel as such just using it to top up the battery on anchorage". Inferring occasional use.
 
LadyInBed said:
With just a 20w panel some might not bother with a controller at all, with a controller it's fit and forget as the controller will block any possible overnight discharge.
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Solar controllers should not be thought of as "fit and forget". Any halfway decent controller will be configurable and the charging voltages should be set to suit your battery type and, to a lesser degree, your type of usage.

The controller is not there to stop "overnight discharge", that should be taken care of by the panels, any decent panel will be fitted with blocking diodes.
 
PaulRainbow said:
Solar controllers should not be thought of as "fit and forget". Any halfway decent controller will be configurable and the charging voltages should be set to suit your battery type and, to a lesser degree, your type of usage.

The controller is not there to stop "overnight discharge", that should be taken care of by the panels, any decent panel will be fitted with blocking diodes.
Click to expand...

Victron say "Blocking diodes prevent current flowing from the battery to the module when no electricity is being generated. It is recommended to use
blocking diodes when a charging regulator is not used"

That implies that when a charging regulator is used blocking diodes are not necessary.
 
PaulRainbow said:
Solar controllers should not be thought of as "fit and forget". Any halfway decent controller will be configurable and the charging voltages should be set to suit your battery type and, to a lesser degree, your type of usage.
Click to expand...
Talk about nit picking! OK after configuration . . .

There controller is not there to stop "overnight discharge", that should be taken care of by the panels, any decent panel will be fitted with blocking diodes.
Click to expand...
Obviously not the purpose of the controller, but with NO blocking diodes are you suggesting that the controller doesn't stop "overnight discharge"?
 
LadyInBed said:
Talk about nit picking! OK after configuration . . .
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Not nit picking at all. You said controllers are fit and forget, that's not correct. They need to be configured and they may need to have that configuration changed, as recent threads on here prove.


Obviously not the purpose of the controller, but with NO blocking diodes are you suggesting that the controller doesn't stop "overnight discharge"?
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I'm not suggesting anything, i'm stating facts.
 
I've fitted solar to all my boats. The first was a Leisure 17 with a 10w panel, small battery and no controller. This kept the battery adequately charged all summer on our swinging mooring without any additional intervention. It seemed like magic at the time.
The others I've fitted slightly bigger panels and cheap non configurable controllers. They've all been great with no issues or failures, mind you I've no fridges or radar.
Keep it simple and you'll not go far wrong.
 
PaulRainbow said:
I'm not suggesting anything, i'm stating facts.
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So it's a fact that the controller doesn't stop "overnight discharge"! ​I wonder what D1 does.

Circuit-Diagram-of-the-solar-power-supply.png
 
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Almost every solar controller has a system to prevent overnight discharge. Rather than a blocking diode, it is often a relay. This means most users should not be concerned about overnight discharge and fitting a blocking diode will be counterproductive, reducing the overall output.

There are some exceptions, but they are rare and the controller handbook will warn that a blocking diode is required, although many panels have very low self discharge so even in these cases the output can be overall slightly greater without fitting the additional diode (although the differnce is small). Without a controller fitting a blocking diode is sensible although once again with many panels the small loss during the day produced by the blocking diode can be similar or even greater than the reduced self discharge.

A blocking diode will reduce a 12v panel output by a little over 2% in daylight hours when not regulating and if using an MPPT controller. If usning a non MPPT contoller (sometimes called PWM), or no controller at all, the loss induced by the blocking diode is much more variable, but on average a similar 2% loss will be typical on average.


Very few panels are fitted with a blocking diode as standard. A blocking diode would reduce the STC output and consumers would likely purchase the otherwise identical panel with a slightly higher wattage measurement.The diodes you see in panel junction boxes are nearly always bypass diodes which have an entirely different function and will not prevent discharge at night.
 
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noelex said:
Almost every solar controller has a system to prevent overnight discharge. .......................

Very few panels are fitted with a blocking diode as standard. '...............................................The diodes you see in panel junction boxes are nearly always bypass diodes which have an entirely different function and will not prevent discharge at night.
Click to expand...

After a good deal of reading, before breaking for an early lunch, they are the conclusions I was coming to, although I think probably it is the electronic circuitry itself that prevents overnight discharge rather than a relay.

Small solar panels , designed for direct connection without a controller, usually have blocking diodes. My present one does, as do all the panels in the same range (5W to 50W). Its predecessor also had a blocking diode.
 
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