iv/power curve

PT, an additional amp is roughly confirmed by Salvo's results where he got 8.5 instead of 8.

Hi BFL13,

While I do indeed have equalize--the 15.4 volts was during normal operation when the temperature hit -34 C.

Those 19 "extra" watts less overhead amount to about an additional amp going into the battery bank.

If we get "quirky" with the math the extra 12 watts sorta kinda makes the panel "worth" 0.74 cents per watt more or $8.88. In the bad old days a watt cost 5.50 so the panel became "worth" an extra $66.00. Since I have four panels at that "old" price, the savings were $264.00 which more than paid for the difference in price of MPPT vs PWM.

BFL13 wrote:
(PT forgot to mention his controller has an Equalize setting )

BFL, 'ya gotta stop hating on the MPPT thing, your Eco-W is right now thinking of how to steal watts.:B

The battery does not get all the watts. The watts at the battery is the amps it is getting and battery voltage.

So with my 130w panel doing its max 8.2amps with battery voltage rising through say 13.5v, watts at the battery just then is
8.2 x 13.5 = 111w so the MPPT guys all snicker and say I am "losing"
130-111 = 19w that they would be busy making more amps with.

You can't make many amps out of 19w but can cost you an extra $200 for a controller that will squeeze them out.

The PWM case is that voltage drop on the wires just adds to that 19w loss but you still get the 8.2 amps so you don't care. The MPPT guys go nuts because losing any watts at all hurts them in the amps.

Also the voltage drop on the wiring and the efficiency of the MPPT controller itself means a slight loss in watts between panel and battery, so even there battery watts are less than panel watts.

I didn't answer the math question if the panel is getting more light so is at max amps but has some voltage drop on the wires is that as many amps as with less light but no voltage drop.

Waiting your test results.

Don't hate me for a watts question!!

small panel, Vmp 17v. Batt @ 14v. Direct connect. Sunny, high noon.

No voltage drop. The panel is operating @ less than 100%, the battery gets all the watts.

3v drop (3/17 = 17+%), the panel is operating @ 100%, the battery gets the same watts as above?

I have the Eco-W set at 14.8 and I hope it does not get cold enough that it goes to 15 :) We are entitled to some sort of summer!

(PT forgot to mention his controller has an Equalize setting )

That darn Eco-W better get me some amps though. If it doesn't do any better than PWM I will be annoyed. Must have faith....we'll know soon enough. One month to go :)

BFL13 wrote:
The Imp has no meaning with PWM, Imp is an MPPT thing. You care about Isc. Isc is what you get at the battery minus a titch for wiring etc. If the panel is getting enough light, you will get rated Isc, such as the 8.2 amps of my 130w panel.

You only get that many amps when the sun is higher mid-day when you can point the panel all day. if the panel is just left pointing south, you will only see that full Isc briefly at noon.

Now as battery voltage rises, you go right on the IV curve and Isc tapers a little. Say to 8.0 from 8.2 by 14v. Still lots. But also by the time the batts are up to 14.7 they are nearly full, so now you also get amps tapering from the battery acceptance rate falling.

So before you get to the dreaded 15v cliff, you are all done anyway--batts near full and amps have tapered right down from that.

I can only get the battery voltage to 15 anyway by disconnecting the controller and going panel-direct because the controller is set to limit the voltage in the 14s.

Your 230w/ Eco-W will get you to 15v.

Hi,

I get to 15.4 volts with my blue sky 3024di MPPT. My panel input is a nominal 33 volts.

I believe it is more important to have a temperature compensated controller, with a probe on the battery, whether you have a portable or fixed installation. Any controller that offers that feature is going to do a pretty good job of charging. If there are adjustable set points that's icing on the cake.

The Imp has no meaning with PWM, Imp is an MPPT thing. You care about Isc. Isc is what you get at the battery minus a titch for wiring etc. If the panel is getting enough light, you will get rated Isc, such as the 8.2 amps of my 130w panel.

You only get that many amps when the sun is higher mid-day when you can point the panel all day. if the panel is just left pointing south, you will only see that full Isc briefly at noon.

Now as battery voltage rises, you go right on the IV curve and Isc tapers a little. Say to 8.0 from 8.2 by 14v. Still lots. But also by the time the batts are up to 14.7 they are nearly full, so now you also get amps tapering from the battery acceptance rate falling.

So before you get to the dreaded 15v cliff, you are all done anyway--batts near full and amps have tapered right down from that.

I can only get the battery voltage to 15 anyway by disconnecting the controller and going panel-direct because the controller is set to limit the voltage in the 14s.