Ok, I have done research and read what I could find. I am pretty sure the installation I have down, but I just want to make sure I am barking up the right tree on certain aspects of the build.I recently removed a solar system from my home I just sold to re-install on my new home. Since the newer home is going to be smaller I thought about keeping two of the panels to install on the 5er. They are Sharp ND-208U1F.What I am trying to understand is what size/type controller to go with. I guess I should preface I am trying to keep the cost down. I figured since I already have the panels I would try solar on my RV. I don't necessarily "boondock", but when we take the TH out it is usually where there is no shore power. So I would like to not use the generator to charge my batteries.If my two panels produce 416 watts then Ohm's law says that is 35 amps with a 12 volt system. Correct? Therefore I need to go with a 40+ amp controller? What options of controller do I have? I see, Morning Star, Blue Sky, Outback etc. Is the price difference between the MPPT and the PWM worth it for my application? There seems to be a slew of controllers out there, but what is quality and what is junk?My head is swimming with all that I have been reading and I guess all I need is just some real life experience opinions.

Those are nominal "24 volt" panels. You will need a 40Amp MPPT controller to take the 24 volt input to 12 volts output to your battery.Be prepared for a lot of opinions as to "best".Doug

MPPT controller will be needed or else translate the battery in the RV to 24 volts. I'd go MPPT and 125% of the input wattage for sizing the controller (i.e. able to do 500 watts of input). It should be an excellent system when all is said and done.I'd choose a controller that has battery voltage sense wires, and a temperature compensation probe on the battery.I'd research til I found the best price for a true MPPT controller that met my needs.

30 amp Morningstar should serve you well. Kill it with a 45 if you must.http://www.morningstarcorp.com/products/tristar-mppt/

smkettner wrote:30 amp Morningstar should serve you well. Kill it with a 45 if you must.http://www.morningstarcorp.com/products/tristar-mppt/There is no must about it. This is why I posted the thread. I am looking for advice.I assumed if my amperage the panels were producing is over 35 amps then a 30 amp controller would not work.How is it you suggest a 30 amp? Also, the controller is good for 400 watts, but my system is 416. Am I am missing something here?

36v panels you need an mppt controller to use for charging 12v batterieseven with mppt you will never see more than 29.5a sustained output, most likely lessa 30amp mppt controller will do the job, just make sure it is a real mppt and not one of the $30 fakes

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30 Replies

time2roll
Nomad
Sep 08, 2015
Calkidd wrote:
I remembered I had another question regarding a controller. I have read not to purchased hard mounted controllers. That is ones that mount in your cabinet with a built in screen. Is this true?
This does not make sense. Some have a display, some an optional display, some have a remote display, some have full network communications and controls. All are good if they meet your requirements.

Personally I think the display is overrated unless that will be your primary way to monitor battery voltage. No harm in having a display if it is included.
Crabbypatty
Explorer
Sep 08, 2015
I mounted the Morningstar TS 45 controller to the wall closest to the battery inside my outside storage bay. It sits next to the Xantrax 2000watt Pro Sine Wave inverter. Runs cool as a cucumber and with the exception of the LED's you don't even know that its on. Based on my mission. Rv use. The person in the Altestore.com said its a waste of money for the MPPT vs the PWM controller. Certainly the MPPT is the best but at $140 PWM vs $450 MPPT and I m only going to use it maybe 30 nights a year. Out of which I dry camp half of that.

Look up the place I bought from as they give technical assistance. throughout the process. I called the guy like 10 times to make sure all was good. He never was selling me anything otherwise he would have sold me the MPPT and the wire. Shipping on the weight of the wire is ridiculous.

Ill shoot some pics today and post them later.
Calkidd
Explorer
Sep 08, 2015
I remembered I had another question regarding a controller. I have read not to purchased hard mounted controllers. That is ones that mount in your cabinet with a built in screen. Is this true?
BFL13
Explorer II
Sep 08, 2015
Salvo wrote:
As far as fringing, noon isn't as critical as tracking the sun. However, for max power (fringing or not), nothing beats noon. The sun goes through the least amount of atmosphere and the rays are strongest.

Agree! :) Don't forget "high noon" is about when the sun is bearing True South, which is a variable depending on your time zone and longitude. Where we camp in Summer Time, high noon is at 1312.

(Technically, high noon is not quite the same time as when the sun passes through South, because the Earth is moving and rotating too, but never mind that :) )
Salvo
Explorer
Sep 08, 2015
As far as fringing, noon isn't as critical as tracking the sun. However, for max power (fringing or not), nothing beats noon. The sun goes through the least amount of atmosphere and the rays are strongest.
BFL13
Explorer II
Sep 08, 2015
Salvo, ok I read all that but I am not convinced. Still pretty sure I got the effect earlier and later than at high noon with the panel facing South. One guy said maybe not as much as at noon. No way to know at the time (say 3pm) if you would have got more at noon. Interesting.

You can sometimes get more than the 1.25 allowance like they said, but how long "depends". I remember seeing the higher amps for more than five minutes straight, but this would not be enough to overheat the controller (at least not mine at the time!)

All this means is that you should build your set-up so the controller is not right up against its limits for current or especially, for Voc input, because it will overheat with high current or just instantly fry if it gets hit with over its rated Voc input from say, cold panels.
Salvo
Explorer
Sep 08, 2015
Here's a good discussion on cloud edge effect.
BFL13
Explorer II
Sep 08, 2015
Salvo wrote:
You're overrating this effect. It's a bonus if you got a solar tracker. The panel needs to be perpendicular to the sun to take advantage of this effect.

A lot of people confuse the lens effect with a cooler, cloud-covered panel. When the sun appears the cooler panel will output more current (for a short time) in mppt mode.

pianotuna wrote:
The folks who are promoting 30 amp controllers are not taking into account cloud 'lensing' effects. Some controllers don't mind this--others it will let out the magic blue smoke.

I think (not sure now) the sun is brighter then from all angles, so I would like to know more about why Salvo says it has to be right on the panel (assume he means close to that)

I have seen "edge of cloud effect" many times, which I take to be the same as "lensing" I am pretty sure (been a while) I got it with my panel fixed facing South at other times than at high noon, but I can't say how far off in angle to the side.

It is seen as a higher than normal Isc on the panel due to above normal insolation. (The sun is much brighter during this time) and this also makes for extra input wattage to an MPPT controller.

Since those times, I have been using my panel on a twirler mostly aimed near the sun, so I am going by memory on that off- angle lensing.

In any case, the extra amps you get in and whether the controller can handle them is the issue. It heats up internally with more amps and the internal heat can damage the controller if it lasts long enough.

That is why the US NEC says to make your controller 1.25 times the array Isc amps to allow for when the panel does more than its rating at times. (Unless the controller has a built- in "clipper" to prevent the amps going above and overheating it)
pianotuna
Nomad III
Sep 07, 2015
Salvo, Thanks for the clarification on lensing.
Salvo
Explorer
Sep 07, 2015
You're overrating this effect. It's a bonus if you got a solar tracker. The panel needs to be perpendicular to the sun to take advantage of this effect.

A lot of people confuse the lens effect with a cooler, cloud-covered panel. When the sun appears the cooler panel will output more current (for a short time) in mppt mode.

pianotuna wrote:
The folks who are promoting 30 amp controllers are not taking into account cloud 'lensing' effects. Some controllers don't mind this--others it will let out the magic blue smoke.

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