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cliffy49

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Posted: 06/30/21 03:01pm Link  |  Quote  |  Print  |  Notify Moderator

All right, I need some more help from the experts. I am looking at purchasing 2 residential panels with the following spec.;
Watts (STC) 285 W
Max Power Voltage (VMPP) 32.2 V
Max Power Current (IMPP) 8.84 A
Open Circuit Voltage (VOC) 39.2 V
Short Circuit Current (ISC) 9.61 A
Max System Voltage 1000 VDC

Am I correct in assuming that a mppt charge controller that will accepts 100 volts and 20 amps would work with these panels.

I am currently trying to get a better understanding of charge controllers so your help is greatly appreciated.


cliffy49
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BFL13

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Posted: 06/30/21 03:32pm Link  |  Quote  |  Print  |  Notify Moderator

Two 285s in series will add their voltages so the controller does need about 80v for the total Voc so yes, 100Voc input would be right.

A 20 amper will just run what one of those 285s can do, so at least a 40 amper would be needed. I would choose a 40 instead of going to a 60 because the panels will get hot in the sun and be about 10% down in watts from that heating, so that keeps you under what a 40 can do. Also if mounted flat they will not get full sun, so that keeps the watts down too.

Tracer makes a decent 40 amp MPPT that would do at a good price. Lots of other choices with various features and prices.

MPPT uses output watts / battery voltage for amps out (which go to loads first and any left over go to the battery)

2 x 285 = 570w less 10% for heat = 513w minus say 2% wiring loss panels to controller, so now 503w input to the controller. controller efficiency maybe 96% so output watts = 483w so picking three battery voltages:

483/12 = 40.25 amps
483/13 = 37 amps
483/14= 34.5 amps

As you see, you get more amps to the battery when the battery is low. However you get more watts into the controller at mid-day high sun. but by then the battery is higher in voltage, so you likely never see the set--up doing all it could do. for that you would need to aim the panels at the sun at high noon and have the battery voltage down low.

Solar gets the job done though, so expect to be pleased you got it.

* This post was edited 06/30/21 03:44pm by BFL13 *


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Almot

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Posted: 06/30/21 06:52pm Link  |  Quote  |  Print  |  Notify Moderator

For 2*285W you need at least 40A MPPT.

Renogy Rover 40 should be able to do the job, though I would use slightly smaller panels with this one, 2*260W. This controller will try to equalize the battery every 2 months and I "think" this feature can't be disabled. Some people wouldn't want this to be done automatically in their absence. An economic alternative is Renogy MPPT Rover 30 with Bluetooth, it allows to disable equalization feature, but you would have to use panels no bigger than 400W total, i.e. 2*200W.

Victron MPPT 150/45 will handle 2*285W and will allow you to change the charging profile, including equalization.

Maybe people will suggest something cheaper than Victron 150/45 and not much worse, but 45A MPPT is a lot of a controller, this is gonna cost ya.

* This post was edited 06/30/21 07:05pm by Almot *

pianotuna

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Posted: 06/30/21 11:51pm Link  |  Quote  |  Print  |  Notify Moderator

cliffy49 wrote:



Am I correct in assuming that a mppt charge controller that will accepts 100 volts and 20 amps would work with these panels.

I am currently trying to get a better understanding of charge controllers so your help is greatly appreciated.


It depends on the controller. Mine, when purchased in 2005 was top of the line. It only accepts 50 volts input.

There are *always* trade offs. The higher the input voltage the thinner the wire can be--BUT the MPPT efficiency may be lower.

One famous make says it will accept 100 amps. And so it will--but only if the battery bank is 48 volts.

In my opinion I would NOT do two 285 watt panels in series.


Regards, Don
My ride is a 28 foot Class C, 256 watts solar, soon to have SiO2 batteries, 3000 watt Magnum hybrid inverter, Sola Basic Autoformer, Microair Easy Start.

BFL13

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Posted: 07/01/21 11:47am Link  |  Quote  |  Print  |  Notify Moderator

PT, why not have two 285s in series?

cliffy49

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Posted: 07/01/21 12:28pm Link  |  Quote  |  Print  |  Notify Moderator

BFL13 wrote:

PT, why not have two 285s in series?


I have the samew question.

Almot

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Posted: 07/01/21 05:34pm Link  |  Quote  |  Print  |  Notify Moderator

It will be hard to find 45A MPPT that doesn't accept 100V, but you should always check, of course.

Efficiency will decrease (by 5-10% maybe?) when the voltage increases to 80-90V, but you get the convenience of pulling a thin wire and the ease of wiring in series, just plug one pigtail into another. Running 2*285W instead of 2*220W will dwarf these losses.

pianotuna

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Posted: 07/01/21 07:31pm Link  |  Quote  |  Print  |  Notify Moderator

cliffy49 wrote:

BFL13 wrote:

PT, why not have two 285s in series?


I have the samew question.


Because of shading. Because the voltage on the panels is already high enough that it won't lead to wire looses. Because the MPPT may function with better efficiency at a lower voltage. Because there will be lower heat loss within the controller.

That makes it a "walk" in baseball.

Almot

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Posted: 07/02/21 04:05pm Link  |  Quote  |  Print  |  Notify Moderator

Shading is a killer for most panels when wired in series. I observed a significant drop with 2*245W when one of them was only partially shaded. Don't remember now, but the percentage of drop was much higher than percentage of shaded area.

Wiring 2*285 in parallel would require #8 cable if distance is 25ft or longer. With cable #10 at 25ft he'll have to put up with voltage drop 3.1% - a little higher than the recommended 3%.

cliffy49

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Posted: 07/04/21 10:59am Link  |  Quote  |  Print  |  Notify Moderator

Okay another question for the experts. Since most of the controllers I have looked at will not accept any wire larger than 8 gauge, would it be okay to use on of these adapters?

[image]




This would be for running wire from the controller to the battery.

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