Solar Charge Controller

Hi,

If choosing MPPT go for the highest voltage the controller can accept. Get the line losses down to 1%. Use a quality controller.

I have seen 17 amps @13.8 volts when the temperature outside was 39 c (100 f) from 256 watts of panels.

The unisolar panels do 3.88 amps each. I have four for a total of 15.52 amps.

So, at least in my case, MPPT works well for me at high temperatures.

wbwood wrote:
Do you lose any power coming in with longer cables? Is there a loss between 10', 20' 40'?

Depends on the wire size and the amps of your source. And then there is MPPT vs PWM where wire size is not as critical. I believe someone already mentioned this.

Do you lose any power coming in with longer cables? Is there a loss between 10', 20' 40'?

MEXICOWANDERER wrote:
wbwood,

What are your objectives?

Just recharging two group 27 batteries (without having to use our onboard generator). We have a couple fantastic fans, water pump, carbon monoxide detector, fridge panel, maybe a couple hrs of tv (12volt), and lights are LED already (minimal use on those). No inverter.

steveh27 wrote:
I seem to have a problem with my 120 watt portable:

http://www.amazon.com/Infomon-Monocrystallline-Portable-Folding-Solar/dp/B005WMD8VY/ref=cm_cr-mr-title

I've had it 2 years & only used it a few times. I was getting up to the 6 amps it puts out, but now I'm only getting up to 3 amps.

It has this cheap controller:
http://www.ebay.com/itm/Solar-Charge-Controller-Overloading-Short-circuit-Reverse-Discharging-Protection-/300916227986?tfrom=301218792237&tpos=top&ttype=coupon&talgo=undefined

This year I did install a quick disconnect plug to the battery through the box for easy plug in. That 1 foot short wire is 18 ga.

The 2 wires I used before came with the panel are 18 gauge. 1 is 15 foot long with clamps for the hookup. The other is a 25' extension with the quick disconnect plugs. I just put together a 10 gauge wire 22' foot long with the quick disconnects. All 3 wire hookups give me only up to 3 amps, even the clamps direct to the battery. Yesterday I checked the panels Open Current Voltage & it was over 20 volts even through the 25' extension. It's rated at 21.8 I could not get my multimeter to work checking the Short Circuit Current amps. (I'm a novice with it). It's rated at 7.3. I did clean the panel, no change.

Today I hope to check the SCC amps with the multimeter, and cover one of the panel sides to see if either is not connected properly. Any other ideas?

You should get all 7.3a at the battery with panel aimed at high sun. First get the Isc with the meter with panel not connected to battery. Then connect to battery. If you get less than whatever Isc is at the time (it varies with amount of insolation) at the battery, find your wiring problem. (18 gauge is very skinny---I used #8 with my 130w panel.

Your 20.x voltage is ok. The panel gets hot and loses voltage so 20.3 w would be typical for a panel rated 21.9 eg. Luckily amps go up with heat so PWM does not lose any amps. (unlike MPPT in heat)

I seem to have a problem with my 120 watt portable:

http://www.amazon.com/Infomon-Monocrystallline-Portable-Folding-Solar/dp/B005WMD8VY/ref=cm_cr-mr-title

I've had it 2 years & only used it a few times. I was getting up to the 6 amps it puts out, but now I'm only getting up to 3 amps.

It has this cheap controller:
http://www.ebay.com/itm/Solar-Charge-Controller-Overloading-Short-circuit-Reverse-Discharging-Protection-/300916227986?tfrom=301218792237&tpos=top&ttype=coupon&talgo=undefined

This year I did install a quick disconnect plug to the battery through the box for easy plug in. That 1 foot short wire is 18 ga.

The 2 wires I used before came with the panel are 18 gauge. 1 is 15 foot long with clamps for the hookup. The other is a 25' extension with the quick disconnect plugs. I just put together a 10 gauge wire 22' foot long with the quick disconnects. All 3 wire hookups give me only up to 3 amps, even the clamps direct to the battery. Yesterday I checked the panels Open Current Voltage & it was over 20 volts even through the 25' extension. It's rated at 21.8 I could not get my multimeter to work checking the Short Circuit Current amps. (I'm a novice with it). It's rated at 7.3. I did clean the panel, no change.

Today I hope to check the SCC amps with the multimeter, and cover one of the panel sides to see if either is not connected properly. Any other ideas?

Doesn't have to be "hot climate" to lose amps with MPPT due to panel temperature over PWM in same situation.

Here, east side of Vancouver Island, by the sea, cool breezes, with 230w tilted up (no heat trap underneath) and MPPT, ambient at 16C, I was getting 15.5a to battery, panel temp was 44C. (measured with IR looking up at white part under a tilted up panel)

At ambient 25C nice summer day for here, panel temp now 51C and amps are 13.5 instead of 15.5. (PWM would be 14.5) So we have gone from being 1 amp more than PWM in the Spring to being 1 amp below PWM in Summer.

Some solar info dug up by Googling, says you lose about 10% with MPPT when panel temp is 50C, so my 13.5 vs 15.5 comes out in ballpark where 2/15.5 = 13%

Hate to think what the results would be in a "hot climate" in the summer :)

BTW, the panel specs are for panel temp of 25C standard test conditions. How can they get the panel temp that low? Ambient would be near freezing to get panel temp 25C it seems.

Vixen21 wrote:
Maybe I am Crazy But......
Are you sure you don't have that backwards? and that the wire size is much more important with PWM controllers than with the MPPT because of the higher voltages with the larger panels that use MPPT?

pianotuna wrote:
Hi,

One example is wire size. He doesn't understand that, for a PWM controller, any wire that is capable of legally carrying the maximum current from the panels is adequate.

It does, however, matter a LOT if an MPPT controller is to be used, because in that case voltage drop is important to avoid.

Vixen21 wrote:

pianotuna wrote:
Hi,

Because it is mostly a rant.

Vixen21 wrote:
Why not just read Handy Bob's Blog, it taught me a lot.

What information does he rant about that is wrong or incorrect?

Actually wire size matters more with MPPT.

With PWM your already throwing away power since the panel voltage is substantially above the battery voltage and output current is fixed (current out = current in). As long as the wire voltage drop with a PWM controller keeps you above about 14V or soit doesn't matter. (Assuming the controller is at the battery, which is where it should be for PWM or MPPT). typically with a 12V panel nominal output voltage is in the 18-20V range so you can have 4-6V of drop across the cable before you see much current change.

with a MPPT controller power out=power in, so any voltage drop between the panel and controller is a power drop to the controller and a reduction in output current.

I did experiments last winter and did a writeup. Short summary, even 100 ft of #10 wire didn't reduce the current from 160W of solar using a PWM controller. Using the 160W of solar (two 80W in parallel) with MPPT controller with the same 100ft resulted in a noticeable power loss comared to a 10ft cable. Still was higher current than PWM. Connecting the panels in series and MPPT resulted in a noticeble increase in current due to lower power loss in the cable. Power loss is related to the output current squared (I^2R) so two series panels cuts the current by 1/2 and the power loss by a factor of 4.

That said, solar panel output current drops with temperature, reducing the benefit of MPPT controllers in hot climate. I have MPPT to get the last bit of current to the batteries, but really on a cost benefit basis, for 100-200W panels IMHO a good PWM controller is more economical and more than adequate, and for the price difference you can almost buy an extra 80-100W panel now. So the potential 10-15% current gain with MPPT really is pretty spendy on a $/Amp basis.

wbwood,

What are your objectives?

Maybe I am Crazy But......
Are you sure you don't have that backwards? and that the wire size is much more important with PWM controllers than with the MPPT because of the higher voltages with the larger panels that use MPPT?

pianotuna wrote:
Hi,

One example is wire size. He doesn't understand that, for a PWM controller, any wire that is capable of legally carrying the maximum current from the panels is adequate.

It does, however, matter a LOT if an MPPT controller is to be used, because in that case voltage drop is important to avoid.

Vixen21 wrote:

pianotuna wrote:
Hi,

Because it is mostly a rant.

Vixen21 wrote:
Why not just read Handy Bob's Blog, it taught me a lot.

What information does he rant about that is wrong or incorrect?