PWM vs MPPTon a 400 watt system.

pterrydactyl

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I purchased a Rich Solar kit at 200 watts. I plan to expand to 400 watt soon. The kit came with a 30A PWM controller. Others have advised a MPPT. Of I go MPPT how large should I go? 40A or 60A or..? I do plan to have a dc to dc charger (40A) installed in truck. I will use 200A of battery. Does this affect the selection of either controller? 400 watt is big as it’ll get on this 28’ 2003 travel trailer..on my fifth wheel I’ll go lots bigger but for now let’s stick to what I’ve informed.
 

williamsk913

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What you have could work for panels in parallel. If you want to wire your panels in series, I would go with a 30a mppt, just make sure your voltages are within the specs. This is just slightly over panelled but should work.
 

pterrydactyl

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What you have could work for panels in parallel. If you want to wire your panels in series, I would go with a 30a mppt, just make sure your voltages are within the specs. This is just slightly over panelled but should work.
Will the 30A MPPT be adequate when I expand to 400 watt or will I need to purchase another controll/charger?
 

MisterSandals

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Will the 30A MPPT be adequate when I expand to 400 watt or will I need to purchase another controll/charger?
Assuming your trailer has a 12V system...
400W / 12.8V = 31.25A charging ... max with 400W of solar.

If your panels are laying flat on a roof, you'll likely get less that 400W so you will be close to maxing out a 30A SCC but it should handle it (though will run hot at max amps).
 

ewestland

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What about the wire size? I put in a 300-watt system with #10 wire, which I believe is rated for 30 amps. I want to add one more 100-watt panel.
  1. Do I need to go up a wire size, say to 8 AWG?
  2. I already have a 30-amp Renology inline fuse, that should protect the wire if it gets above 30-amps, right?
  3. My panels are flat on my RV roof. I am going to use an EPEVER MPPT solar charge controller. 30 or 40 amp?
Thanks
 

rmaddy

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What about the wire size? I put in a 300-watt system with #10 wire, which I believe is rated for 30 amps. I want to add one more 100-watt panel.
  1. Do I need to go up a wire size, say to 8 AWG?
  2. I already have a 30-amp Renology inline fuse, that should protect the wire if it gets above 30-amps, right?
  3. My panels are flat on my RV roof. I am going to use an EPEVER MPPT solar charge controller. 30 or 40 amp?

The wire size depends on the current. It sounds like you will have 4 100W panels. How will they be arranged? 4S? 4P? 2S2P?

What are the full specs of the panels?

In 4S and 2S2P 10AWG should definitely be plenty unless the wires from the panels to the charge controller in really long. In 4P you need a combiner box and each panel needs a fuse. With 4P the wire from the combiner box to the charge controller may work with 10AWG but 8AWG might be needed depending on the specs of the panels.

400W on 12V will work with a 30A charge controller. The wire from the charge controller to the battery needs to handle 30A. 10AWG should be fine, along with a 40A fuse on that wire between the controller and the battery.
 

ewestland

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Thanks for the helpful and quick reply.

The Renogy kit came with 3-way Y branch connectors, I was going to swap them out with these Solar Y Branch Connectors. That would be 4P, correct?

These are the panels, Renogy RNG-100D-SS. I have three currently and have a 4th one coming.

Would this be the wiring diagram for a 2S2P? From what you are telling me, should I go this way?

Thanks again!
 

rmaddy

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Those Solar Y branch connectors would give you 4P. Given the specs on the panels 10AWG should be fine even at 4P as long as the wires from the panels to the charge controller is under 15 feet.

The diagram you linked is correct for 2S2P. The only purpose of the breaker would be to act as a PV disconnect. Make sure it can handle the 50V the panels could put out on a really cold day.

Personally I think 2S2P would be much better than 4P unless you have a lot of shading issues on the RV roof (which is quite possible).
 

12VoltInstalls

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  1. Do I need to go up a wire size, say to 8 AWG?
For your needs 10ga is fine. You can gain a slight bit of efficiency with 8ga but it both isn’t needed and you probably won’t have a measurable gain anyway
  1. I already have a 30-amp Renology inline fuse, that should protect the wire if it gets above 30-amps, right?
A 30A fuse would be at the battery between pwm and battery
  1. My panels are flat on my RV roof. I am going to use an EPEVER MPPT solar charge controller. 30 or 40 amp?
You say you’ll never go above 400W. If so 30A controller is fine. If you ever add 200W you’ll be buying a new SCC for 40A.
Depending on region flat will work ok. If at a northern latitude I’ve had reasonably good results with vertical panels- no snow or ice accumulation. If your roof mount was adjustable you’ll get quite a bit more harvest using them with a more optimal sun angle.
 

grizzzman

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Deciding on a MPPT or a PWM solar controller really has everything to do with panel voltage, size and use,. Cost is another consideration.
As an example if you are a fair weather camper, like to boondock and shading is an issue then a parallel with a PWM (the money saved could be used to buy another panel that would easily trump using a MPPT in terms of power)
 

chrisski

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The PWM controllers tend to limit you so that each panel added on needs to be in parallel. That just limits voltage loss and could drive your ssystem to have wires too thick. I wanted to go 6P, but I also wanted wanted 10 AWG or thicker wires and a 3% voltage loss. For rooftop 100 watt panels on my RV, that did not work out, so I went 3S2P to meet the 3% loss with 10 AWG. I could not do that with a PWM.

So, any panels added onto a 12 volt system need to be in parallel. If your PWM is capable, you could put the panels in a 2S configuration.

I have the same panels you listed and IME, the panels output slightly more than 6 amps tops, so you should be able to put four of them in parallel and stay under the 30 amp limit For 12 volts. For a 24 volt system, that would be 2S4P.
 

12VoltInstalls

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If your PWM is capable, you could put the panels in a 2S configuration.
I’ve done that. 24V nominal panel input 12V batteries. Some PWMs support charging like this, some do not.
It gave some low-light benefit (which was my goal) but in good sun 1/2 the watts weren’t harvestable on pwm
 
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chrisski

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I’ve done that. With 12V batteries. Some PWMs support this, some do not.
It gave some low-light benefit (which was my goal) but in good sun 1/2 the watts weren’t harvestable on pwm
Did you exceed the voltage rating of the PWM When you put this in 2S?

The PWMs I looked at have a 12 volt PV input limit of up to 21 volts, perhaps up to 24 volts. Hard to find PV panels to put in series to stay under that limit. Perhaps voltage limits don’t matter for PWMs or there’s a better brand of PWM I did not look at.

ON my MPPT, last year I never noticed the low light level advantages of panels in series until this year when I hooked up a 24 volt system on my MPPT. I did see that the 2S voltage if not in series, would not of reached the SCC limits to start charging. Oddly enough, the prior year running 12 volts in the same type of weather, the panels still produced.
 

12VoltInstalls

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The PWMs I looked at have a 12 volt PV input limit of up to 21 volts, perhaps up to 24 volts.
I used the P30L for my experiment. It is auto-recognize for 12V/24V battery systems. Nevertheless, I contacted windyNation to confirm this was fine. They emailed ’yes’ almost immediately.

Hard to find PV panels to put in series to stay under that limit. Perhaps voltage limits don’t matter for PWMs or there’s a better brand of PWM I did not look at
This is why I feel comfortable saying for many products that similar appearance and listing text does not necessarily mean, “just another rebranded clone.”
While the P30L appearance is that of a slew of other PWM controllers, it seems to have much more flexibility and functionality than for example a recognized-brand but unnamed clone I have here that misses many of the features and menu possibilities of the P30L.
I don’t know if they have proprietary software or just wrote the PO to a better spec or it’s actually different inside because they spec’d the thing just so but… it is a great product on the cheap controller shelf.

VOC does matter for PWMs except when it’s designed for it.

Yes, I’ve done a lot of weird little experiments along the way LOL
 

brb58

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I used the P30L for my experiment. It is auto-recognize for 12V/24V battery systems. Nevertheless, I contacted windyNation to confirm this was fine. They emailed ’yes’ almost immediately.
You might put them in series if you are running a 24V battery but you are going to lose half of your charge current if you do it with a 12V system.
 

brb58

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These days, MPPT solar controllers are so inexpensive, there really is no reason to go PWM. You get some people that seem to think that you need to be over a certain size system to get the benefits of MPPT. The reality is there is no system too small to use MPPT. Some have this "rule of thumb". It's the same wrong "rule of thumb" used by a lot of people that don't know how to use math..
 

12VoltInstalls

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you are going to lose half of your charge current if you do it with a 12V system
It gave some low-light benefit (which was my goal) but in good sun 1/2 the watts weren’t harvestable on pwm
Ya, so, well. I said that.
You get some people that seem to think that you need to be over a certain size system to get the benefits of MPPT. The reality is there is no system too small to use MPPT. Some have this "rule of thumb". It's the same wrong "rule of thumb" used by a lot of people that don't know how to use math..
Are you having a rough day? Geeesh
It’s Christmas!

Anyway, I know how to do math.

In practice, the reality is that on one hand the minimal voltage over battery voltage of one or two panel systems sorta isn’t quite as effective as it is when giving mppt 100V, and on the other hand for 100- or 200W of panel on pwm does a really good job charging batteries. In fact, I recall Will did a video a few years back where the pwm units surprised him how much they were putting out.

Anyways- while my thumbs have nothing to do with it- 100 or 200, maybe 300W systems are just not as remarkably improved as 3S, 4S, 6S x several strings is. Further, i support the idea of facing panels two 90* separated compass directions. Parallel connection for two 100W panels. So 2S2P @400W total is the first higher-voltage rung. Not a stupid persons rule of thumb, an actual planned outcome.

I survived for several years on a pwm just fine. True- “there is no system too small” to use mppt. Nevertheless, pwm can work well for many 0.2kW systems.
 

saggys

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I went from a Trace C12 PWM to a Morningstar Sunsaver MPPT 15A with two 80 watt panels in parallel and the difference is negligible. The only benefit I see is to wire the panels in series and charge a 12 volt system.
 

brb58

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Anyway, I know how to do math.

Anyways- while my thumbs have nothing to do with it- 100 or 200, maybe 300W systems are just not as remarkably improved as 3S, 4S, 6S x several strings is. Further, i support the idea of facing panels two 90* separated compass directions. Parallel connection for two 100W panels. So 2S2P @400W total is the first higher-voltage rung. Not a stupid persons rule of thumb, an actual planned outcome.
So a 300W system consisting of 3 100W 20V panels isn't worth doing MPPT for? You basically have to have 3 of those panels on PWM to get the same output of 2 of those with an MPPT.

If a 100W panel is 20Vmpp and 5A Impp, you will get 5A out with a PWM and 7.14A with an MPPT @ 14V charge. You don't think a 42% improvement is worth it? If you have 3 100W panels, that is 15A vs 21A.

As far as series vs parallel, assuming you have similar voltage drop between the panels and the controller by sizing the wires appropriately, you will get the exact same output. really the only reason you do series is to be able to use smaller wire and get a little more early morning late evening output.
 
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