Should I use a charge controller?

[Otter]

We have two 120watt panels, when I fitted them I included a charge controller on each because we leave the boat for a couple of weeks at a time. They're connected to a 440ah bank of ordinary leisure batteries. I've subsequently read that they can reduce the charging rate by about 30%. The issue is that in summer hols we are full time liveaboards so need the panels - can I test to see if the panels already have blocking diodes? I checked the literature they came with but the A6 scrap of paper was written in Chinglish and I couldn't make out if they do. If they do already have a blocking diode then I want to be able to bypass the controllers in the summer and have them connected in the winter - what would you suggest?

Thanks!

 

[sailorman]

why not use a windgen controller with a dump resistor

 

[VicS]

We have two 120watt panels, when I fitted them I included a charge controller on each because we leave the boat for a couple of weeks at a time. They're connected to a 440ah bank of ordinary leisure batteries. I've subsequently read that they can reduce the charging rate by about 30%. The issue is that in summer hols we are full time liveaboards so need the panels - can I test to see if the panels already have blocking diodes? I checked the literature they came with but the A6 scrap of paper was written in Chinglish and I couldn't make out if they do. If they do already have a blocking diode then I want to be able to bypass the controllers in the summer and have them connected in the winter - what would you suggest?
Thanks!

Establish if they have blocking diodes and remove them if they do ( but be aware that some panels may also have bypass diodes ) This will involve opening and resealing the connection block.

Use a decent MPPT controller. This will regulate the charging when you are away and maximise it when needed. It should give more bangs for your buck than running uncontrolled

why not use a windgen controller with a dump resistor

'cos a dump resistor is not needed with solar panels like it is with certain wind generators. Their output can be controlled with electronic gizzmos, even enhanced by MPPT gizzmos.

 

[Otter]

Establish if they have blocking diodes and remove them if they do ( but be aware that some panels may also have bypass diodes ) This will involve opening and resealing the connection block.

Use a decent MPPT controller. This will regulate the charging when you are away and maximise it when needed. It should give more bangs for your buck than running uncontrolled

Thanks for the reply, what would a blocking diode look like? I assume a bypass diode is to avoid the problems of shading? I'd sort of come up with a half baked plan of putting a blanket over the panels and with everything off seeing if the battery voltage goes down? - Would that show if there wasn't a blocking diode?

 

[tawhiri]

Yes cover the pannel with some cardboard and see if any leakage current flows from the battery back to the pannel with a current meter.
I would use a permentantly connected PWM controller. it may not give 100% to the batteries but it is cheap, and a good one will not loose too much current.
I did as you mentioned previously and connected the batteries directly to a 50W panel and forgot to reconnect the controller when I left. The result was a 16.4 Volt battery that you could cook an egg on.

 

[sailorman]

Thanks for the reply, what would a blocking diode look like? I assume a bypass diode is to avoid the problems of shading? I'd sort of come up with a half baked plan of putting a blanket over the panels and with everything off seeing if the battery voltage goes down? - Would that show if there wasn't a blocking diode?

details & photo`s here
http://en.wikipedia.org/wiki/Diode

 

[Otter]

details & photo`s here
http://en.wikipedia.org/wiki/Diode

I love how those mean something to you!

Tawhiri - thanks for that, I know how to use a voltage meter but do them all have current meters and how do I use one :redface:

 

[Hadenough]

We have almost the same set up, 240w of panels(3x80) but all through one controller with a remote meter. I'm no expert but from my experience I think you will need to keep the controller. Even today I am getting 21v feeding 4A to the batteries. I know that in bright sun I get 9 / 10A and more from the panels. FWIW I think that even with a slight loss though the controller (although I think it is negligible) you will manage the summer with the output of the panels as they are. We turned the charger off three weeks ago and have been maintaining no less than 12.7v at the batteries. That's in Suffolk on board 24/7 with fridge, Eber and usual 12v lights.

 

[VicS]

I love how those mean something to you!

Tawhiri - thanks for that, I know how to use a voltage meter but do them all have current meters and how do I use one :redface:

Using the voltmeter in the way you suggest to monitor the battery volts would take an age and half and then be inconclusive because you'd not know by how much the volts would have fallen without the panel connected.

Diagrams below show how to measure volts with a voltmeter and amps with an ammeter.

However for a good explanation see the Boat Electrical Notes on Tony Brooks' TB training website. With little electrical knowhow you will find the site very useful.
http://www.tb-training.co.uk/

 

[noelex]

With that much solar you will need a controller.
A good PWM controller looses very little over direct connection, except when the batteries are being overcharged and then you want the output from the panel reduced.
A good MPPT controller will actually do a little better than direct connection.