Solar Charge controller, how many amps?

navillus

New Member
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Feb 11, 2021
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I want to install 600 watts of solar on my van. After performing a basic calculation of 600/12 = 50, it seems that I would need at a minimum a 50 amp charge controller. I am a little confused as I am looking at starter kits from Grape solar and Rich solar 3 X 200-watt panels with only 40 amp solar charge controllers; are they figuring the panels will not put out a true 100 watts?

I appreciate any advice on this.
Thanks
 

snoobler

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Welcome to the forum.

600/12V is a depleted battery
600/14.4 is a battery taking maximum current = 41.7A

Thus the max charging current is somewhere in between.

The SCC also likely has a maximum of around 520W @ 12V @ 40A.

In short, you are leaving about 80W on the table in perfect conditions.

1613066824307.png



Blue is what you'd get with a 520W array.

Green + Blue is what you'd get with a 600W array on a 40A controller. The red is what you'd miss out on due to the 40A current rating.

In reality, you need perfect conditions to get 600W, perfect panel tilt, sun position, clear sky, 25°C, 1000W/m^2 on the panels, so the red area will not be a frequent concern. Flat on a van roof = you'll never get 600W.

Additionally, if these are PWM controllers, their inefficiencies ensure you'll never get 600W, and never get near 40A.

Short answer: 40A is probably fine for your situation.
 

navillus

New Member
Joined
Feb 11, 2021
Messages
55
Welcome to the forum.

600/12V is a depleted battery
600/14.4 is a battery taking maximum current = 41.7A

Thus the max charging current is somewhere in between.

The SCC also likely has a maximum of around 520W @ 12V @ 40A.

In short, you are leaving about 80W on the table in perfect conditions.

View attachment 36839



Blue is what you'd get with a 520W array.

Green + Blue is what you'd get with a 600W array on a 40A controller. The red is what you'd miss out on due to the 40A current rating.

In reality, you need perfect conditions to get 600W, perfect panel tilt, sun position, clear sky, 25°C, 1000W/m^2 on the panels, so the red area will not be a frequent concern.

Additionally, if these are PWM controllers, their inefficiencies ensure you'll never get 600W, and never get near 40A.
Thank you very much for the response. If I choose a 40 amp controller, will there be any damage to the controller if the panels perform close to their peak?
 

snoobler

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Highly unlikely. Most SCC can be "over paneled", but it is dependent on the SCC. Some can be crazy over paneled, but others are less tolerant.

My Victron 250/100 can only use 5900W @ 48V, but because it can accept PV input of about 150Vmp and 70A, it means it can safely handle about 10,000W of PV.
 

Steve_S

Offgrid Cabineer, N.E. Ontario, Canada
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No panel ever puts out 100% of its design label due to many factors, that is LAB Only. Sun Angles, Cloud, dust and such DO affect performance. But then Colder temps also increase performance. Also realize that a Van Roof is never going to be optimally positioned.

You do not mention what size of battery system. More often than not, folks trip right here. If you are building a 12V/100AH battery system and it is lead, then you can only really use 50% or 50AH, if it is LFP (LiFePO4) then you can safely and comfortably use 80% or 80A. A 100AH LFP will take 50A Charge but the lead will balk a bit and will need to be tweaked.

Factors to Consider
- Size of Battery System and Type of Battery. More Battery = More Charging Capacity needed.
- Then to size an SCC that is capable of delivering sufficient power (Volts & Amps ~ Amps being key) to recharge used power within a "Low Sun Hour Day".
- Then to install enough Solar Panel to enable the SCC to do the charging in the required time frame.
- Supplemental Charging can be done with a decent Inverter/Charger or a separate AC->DC Charger. Alternators can be used BUT there is many tricks & issues to deal with and that varies depending on the battery chemistry being used. Lead/AGM is easier than LFP but that also has tradeoffs to account for.

Solar Controllers can be a tad tricky. One of the best Stand-Alone "Value" Solar Controllers are EP-Epever's with some models capable of outputing 100A Charge if there is sufficient solar panel. Premium SCC's like Midnite Classics can do Hyper-VOC for Cold/Hot Temp correction and can accommodate about 20% Over Panelling without risk. MANY SCC's will NOT TOLERATE Overpanelling, even 10V can release the magic smoke. But that's "some" of the difference between a $400 SCC & a $1000 SCC.


EPEVER: https://www.epsolarpv.com/product/44.html
Midnite Solar Classics: http://www.midnitesolar.com/pages/pages.php?article_ID=14

FYI: Grape Solar is a good "Retail" plug'n play sort of gear and premium-priced for what it is, mostly due to the extra "Plug & Play" stuff. It is retail big box stuff, so you pay extra for that. Avoid Renogy at ALL costs, just search for complaints (web wide) and you will be overwhelmed.

If you can provide more detailed information, your plans for charging Solar/External/Alternator etc then you will get better responses and direction.
 

snoobler

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Almost no panel ever puts out 100% of its design label due to many factors, that is LAB Only. Sun Angles, Cloud, dust and such DO affect performance. But then Colder temps also increase performance. Also realize that a Van Roof is never going to be optimally positioned.

Fixed. :)

If my Victron hardware is to be believed, I routinely see > 100% at peak solar. Of course, I'm in AZ at 6800ft (15% less atmosphere), and it's 20°F cooler than Phoenix but with the same sunshine you would expect in a desert.

My conditions are often more favorable than the lab; >1000W/m^2 solar radiation, lower temperature.
 

navillus

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Feb 11, 2021
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Very new and getting information from Renogy stating I need a fuse between solar array and solar charge controller. If I have 3 panels 210 watts, wired in series. 9.3 amps a panel. Do I need a fuse between my panels and solar charge controller (40amp)? My panels have a Max Over-current protection rating 20? Is this the same as "Max series fuse rating?"
 

Bud Martin

Photon Sorcerer
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Aug 27, 2020
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2,368
Very new and getting information from Renogy stating I need a fuse between solar array and solar charge controller. If I have 3 panels 210 watts, wired in series. 9.3 amps a panel. Do I need a fuse between my panels and solar charge controller (40amp)? My panels have a Max Over-current protection rating 20? Is this the same as "Max series fuse rating?"
What does the sticker on the back of the panel say about the fuse?
It sounds like it recommends 20A fuse. You can use DIN mounted fuse holder that can be used as disconnect so you can disconnect the panel first before disconnecting the batteries from the SCC.
 

chrisski

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Aug 14, 2020
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What I take max series fuse rating to be is you need to fuse each leg of a parallel series when you add each leg's amperage up and it exceeds the max series fuse rating. I see this come to three or more sets of parallel panels. Two sets of parallel panels does not need to be fused.

So, no you do not need a fuse for one set.

Having a way to shut that one set of panels off is nice for things like maintenance or shutting down the system for storage.
 

navillus

New Member
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Feb 11, 2021
Messages
55
What I take max series fuse rating to be is you need to fuse each leg of a parallel series when you add each leg's amperage up and it exceeds the max series fuse rating. I see this come to three or more sets of parallel panels. Two sets of parallel panels does not need to be fused.

So, no you do not need a fuse for one set.

Having a way to shut that one set of panels off is nice for things like maintenance or shutting down the system for storage.
 
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