Solar panel charge controller recommendation?

[Trundlebug]

It's just a switch, which has to be able to take the maximum current. Beyond that, no matching involved, so a 10A controller will be fine for your 150W panel, which will be flat out at about 8A (power is given at panel voltage of 19 - 20V). A 20A one won't cost much more, though, and will cope with more panels if you ever fit them.

Aha! I was working with the current at 12v for the controller rating, so I've just learned something important there, thank you.
My panel is this one http://www.titan-energy.co.uk/150w-semi-flexible-mono-solar-panel-122-p.asp
which has an optimum working voltage of 29v so at max power it's going to be chucking out around 5.7A according to the info supplied.
So as you say I actually only need a 10A controller not a 15A, that should save me some money. I'll have another look and see what alternatives are now presented.

Many thanks. I'm glad I posted this!

 

[JumbleDuck]

Aha! I was working with the current at 12v for the controller rating, so I've just learned something important there, thank you.
My panel is this one http://www.titan-energy.co.uk/150w-semi-flexible-mono-solar-panel-122-p.asp
which has an optimum working voltage of 29v so at max power it's going to be chucking out around 5.7A according to the info supplied.
So as you say I actually only need a 10A controller not a 15A, that should save me some money. I'll have another look and see what alternatives are now presented.

I'm intrigued that it's chucking out ~30V ... panels for 12V systems normally do about 20V open circuit. Sounds as if it may be intended for 24V systems. If I were you I'd ask the suppliers what controller(s) they'd recommend. I suspect you'll need a proper MPPT controller.

 

[homer]

Thanks for your replies so far.

It seems paying about the £50 mark is about what most have done to get a controller of reasonable quality.

Has anyone tried one of the cheapy eBay specials like these?
http://www.ebay.co.uk/itm/New-30-20...195574?pt=UK_Gadgets&var=&hash=item19f053a376
or
http://www.ebay.co.uk/itm/MPPT-15A-...91066556309?pt=UK_Gadgets&hash=item43c4eb2f95

I have tried both of these. The second (grey one) was rated at 15 amps and worked ok when I had 170Watts of panels. I added another 100 Watts and, although I never saw more than 12 Amps going through it, it blew after a few weeks. I now have one of the first sort (the black one) rated at 30 Amps. Been working for 2 months ok but it does get very hot. I checked with the supplier who said that this is normal but I am was not very happy and added some cooling fins (cut from old beer can) which help. I can only assume that it is wasting energy though and so have now bought a somewhat more sophisticated version as a spare (not fitted yet).

 

[Trundlebug]

I'm intrigued that it's chucking out ~30V ... panels for 12V systems normally do about 20V open circuit. Sounds as if it may be intended for 24V systems. If I were you I'd ask the suppliers what controller(s) they'd recommend. I suspect you'll need a proper MPPT controller.

I looked on their website for the controllers they sell and they only do a 10A one.
On that subject, since my previous post I have looked again and the 10A controllers state that the 10A is at the battery voltage, not the panel voltage.
10A controllers don't seem to be rated as high as 150w
Are you sure about what you said earlier? Examples:-
http://www.bimblesolar.com/10amppt for max 130w panel
http://www.amazon.co.uk/efficiency-controller-regulator-voltage-battery/dp/B007ZLZFHA same again
http://genasun.com/all-products/sol...or-lead/gv-10-pb-10a-solar-charge-controller/ max 140w

Based on this I'm sticking to 15A or 20A controllers.

 

[noelex]

Controllers are rated for the maximium current which is always output. The input may be at a higher voltage and lower current, but that does not help. You still have to have a current capacity greater than the max that will go into the batteries for max efficiency. (They usually self protect if try and go over this)

 

[JumbleDuck]

I looked on their website for the controllers they sell and they only do a 10A one.
On that subject, since my previous post I have looked again and the 10A controllers state that the 10A is at the battery voltage, not the panel voltage.
10A controllers don't seem to be rated as high as 150w
Are you sure about what you said earlier?

You don't get any more amps out of the basic (switching or PWM) controllers than you put in, so while the controller has to be able to handle the current to the battery, because that is what it has to switch, that current is physically limited to what the panel can produce.

So my 100W of panels can produce 5A at 20V and my regulator must therefore be able to handle 5A, so I have a 10A one.

I don't think MPPT controllers can increase the current: they just adjust their switching so the panel works at the combination of V and A which gives maximum power out. That gives you a smallish increase in A, but your 150W panel will still be running at about 30V and you'll therefore not get much more than 5A out of it, through the controller and into the battery.

At least that's my understanding. Correction welcome.

 

[Trundlebug]

You don't get any more amps out of the basic (switching or PWM) controllers than you put in, so while the controller has to be able to handle the current to the battery, because that is what it has to switch, that current is physically limited to what the panel can produce.

So my 100W of panels can produce 5A at 20V and my regulator must therefore be able to handle 5A, so I have a 10A one.

I don't think MPPT controllers can increase the current: they just adjust their switching so the panel works at the combination of V and A which gives maximum power out. That gives you a smallish increase in A, but your 150W panel will still be running at about 30V and you'll therefore not get much more than 5A out of it, through the controller and into the battery.

At least that's my understanding. Correction welcome.

No that doesn't sound right Jumble.
The controller doesn't just put its unregulated voltage straight through to the batteries at e.g 29v and 5A.
It regulates the voltage to 14.4 or whatever, and surely in so doing there is a commensurate increase in current so the power is the same (minus conversion losses).

On the input side of the controller there will be 29v and 5A. That's 145W.
On the output side there should be 145/14.4 = around 10A.

 

[noelex]

but your 150W panel will still be running at about 30V and you'll therefore not get much more than 5A out of it, through the controller and into the battery.

The panel is kept at Vmp, but this higher voltage is converted into more current at the battery voltage. This is how MPPT controllers work.

In practice 150w will give a peak output of over 10A with a MPPT controller as Trundlebug said above.

 

[JumbleDuck]

No that doesn't sound right Jumble.
The controller doesn't just put its unregulated voltage straight through to the batteries at e.g 29v and 5A.
It regulates the voltage to 14.4 or whatever, and surely in so doing there is a commensurate increase in current so the power is the same (minus conversion losses).

Regulation ain't the same thing as DC-DC conversion. My regulator takes in 16 - 20V and uses pulse width modulation at 25Hz to produce a suitable effective output voltage. It's only switching off and on very quickly, though, and there is no way to get a high current out than in from that system.

The panel is kept at Vmp, but this higher voltage is converted into more current at the battery voltage. This is how MPPT controllers work.

In practice 150w will give a peak output of over 10A with a MPPT controller as Trundlebug said above.

Thanks. It does look as if the better controllers are effectively switched mode power supplies, in which case yes, you can get about the same power out as in. I'm not convinced that the cheaper MPPT (or claimed MPPT) devices are more than slightly cleverer PWM devices.

 

[noelex]

I'm not convinced that the cheaper MPPT (or claimed MPPT) devices are more than slightly cleverer PWM devices.

Yes I agree, in fact in many cases they are worse.
Correct MPPT is quite complex and it requires a good quality controller. Don't buy a cheap MPPT controller in most cases you are better off with simpler non MPPT (sometimes called PWM) model.

 

[JumbleDuck]

Yes I agree, in fact in many cases they are worse.
Correct MPPT is quite complex and it requires a good quality controller. Don't buy a cheap MPPT controller in most cases you are better off with simpler non MPPT (sometimes called PWM) model.

Phew! I wasn't completely wrong, then.