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What is a Solar Charge Controller?
The Charge Controller takes the power made by the solar panels and
Also, we have interactive solar wiring diagrams that are
Finally, for this blog post you’re reading right now, we have a calculator that will help you choose a charge controller. I HIGHLY recommend reading this post to truly learn how to use the calculator, but if the calculator is all you’re looking for, you can download that HERE.
How does the Charge Controller Work?
Solar panels typically put out a voltage that is too high for batteries to use. If you have your solar panels wired in series
MPPT vs PWM CHARGE CONTROLLERS
There are two main types of charge controllers. They are MPPT and PWM. This blog post is a crash course in solar design and getting into the specifics of the differences is out of the scope of this blog post. Here’s what you need to know regarding MPPT vs PWM charge controllers MPPT is the newer, more efficient technology. From here on out, any time I talk about charge controllers, I will only be talking about MPPT charge controllers as I want to guide you to build a high-end, expandable solar setup.
HOW TO MATCH SOLAR PANELS TO A CHARGE CONTROLLER
One of my favorite series of charge controllers is the Victron BlueSolar MPPT Charge Controller. If you’ll notice, there are MANY different sizes of charge controllers:
- Victron SmartSolar MPPT 75 | 10
- Victron SmartSolar MPPT 75 | 15
- Victron SmartSolar MPPT 100 | 15
- Victron SmartSolar MPPT 100 | 20
- Victron SmartSolar MPPT 100 | 30
- Victron SmartSolar MPPT 100 | 50
- Victron SmartSolar MPPT 150 | 35
- Victron SmartSolar MPPT 150 | 45
- Victron SmartSolar MPPT 150 | 60
- Victron SmartSolar MPPT 150 | 70
- Victron SmartSolar MPPT 150 | 85
- Victron SmartSolar MPPT 150 | 100
- Victron SmartSolar MPPT 250 | 85
- Victron SmartSolar MPPT 250 | 100
WHAT DO THOSE NUMBERS MEAN?!?
*MATH ALERT*
Let’s say, for example, you have 4 x
EACH 100w solar panel has an Open-Circuit Voltage (Voc) of 21.6 volts. and an Optimum Operating Current of 6.72 Amps. Those are the only two numbers we are concerned about for now. I generally recommend just wiring all of your solar panels in series for simplicity and efficiency sake. Which means: Those 4 x 100 watt solar panels get wired together like this:
Since they are wired in series, the voltages get ADDED together for a total of 86.4 volts. (Open-Circuit Voltage (Voc) of 21.6 x 4 panels) The amps on the “upstream” side of the 100w solar panels
So, the 86.4 volts is under the safe threshold of the 100 max volts of the Victron SmartSolar MPPT 100 | 30 solar controller.
100 is the first number. What about the 2nd number, 30?
The 30 in the Victron SmartSolar MPPT 100 | 30 is the MAX resulting amps AFTER the solar controller has worked
- We have 4×100 watts of solar panels totaling 400 watts of solar.
- Assume batteries are 12.6v
- Amps = Watts / Volts
This means, that at 400 watts and 12.6v we can expect up to 31.74 amps coming out of the solar controller.
400 watts / 12.6 volts (Battery) = 31.74 amps coming out of the charge controller.
Now, we are talking about that Victron SmartSolar MPPT 100 | 30, we have to compare that 2nd number, 30.
31.74 amps is a bit over the 30 amp threshold. BUT…
Solar panels rarely put out their full wattage. AND…
In the Victron SmartSolar MPPT 100 | 30 manual, they say their controller is good for solar arrays up to 440 watts:
AND… If you happen to go ‘over’ on your Amperage, it’s not that big of a deal in terms of damage. It’ll just be lost power that the controller won’t convert.
So, basically, the Victron SmartSolar MPPT 100 | 30 is pretty perfect for those 4 x 100 solar panels.
But what if you like playing it safe? What if you want some wiggle room? Great! Size up to the Victron SmartSolar MPPT 100 | 50. Sure, it’s a little more money, but if it’s worth your
Now, Why would you want wiggle room or safety margin? Let’s talk about temperature
Solar Controller vs Temperature
DID YOU KNOW… As temperatures drop, solar panels actually put out MORE power.
Totally honest though, the math gets messy, SO I made a calculator that you can input all of the values for your setup so YOU can see how temperature affects your solar panel setup AS WELL AS will give you a recommendation on what solar controller you need taking solar panel temperature into account.
Access that calculator (and it’s instructions) for free, here
Now that you’ve gone through the Charge Controller Wizard, you’ve gotten a very helpful piece of information:
Based on the inputs, you now have a recommended charge controller size that takes temperature into account.
Sure, it says “Solar Controller 100 | 40” which is formatted like the Victron charge controllers, but you can, ultimately use any charge controller brand you like. The premise is mostly the same.
Now… a Victron SmartSolar MPPT 100|40 doesn’t exist. All you have to do, is simply round up to the next nearest available size, which would be the Victron SmartSolar MPPT 100|50.
*This calculator will give you some wiggle room and a buffer for the panels you have input. If you feel you want to round down a size, ALWAYS listen to the minimum specs that the manufacturer has made.*
Confused? Don’t want to do math?
No problem. I’ve got you…
Here is a list of solar panel combinations with my recommended Victron solar controller size. I’ve picked these combinations assuming you’ll never be somewhere with a daytime high of colder than -10 degrees Fahrenheit.
- 100 Watt Solar Panel Options:
- 100 watts: Victron SmartSolar MPPT 75 | 10
- 200 watts: Victron SmartSolar MPPT 100 | 20
- 300 watts: Victron SmartSolar MPPT 100 | 30
- 400 watts: Victron SmartSolar MPPT 100 | 50
- 175 Watt Solar Panel Options:
- 175 watts: Victron SmartSolar MPPT 100 | 20
- 350 watts: Victron SmartSolar MPPT 100 | 50
- 525 watts: Victron SmartSolar MPPT 100 | 50
- 700 watts: Victron SmartSolar MPPT 150 | 70
- 875 watts: Victron SmartSolar MPPT 150 | 100
Now that you know what kind of charge controller is compatible with your solar panels, it’s time to learn how to choose an inverter for your DIY Camper setup. Check that out here:
https://www.explorist.life/how-to-choose-an-inverter-for-your-diy-camper/
Everything that you are learning here is put to use in our FREE Interactive Solar Wiring Diagrams. If you haven’t yet, check them out as they are a complete solution for a camper van electrical system. Check them out here: https://www.explorist.life/solarwiringdiagrams/
Remember, this is just one part of a full camper van electrical educational series. To see all of the individual guides, click here: https://www.explorist.life/diy-campervan-solar
Finally, If you found this guide helpful, It’d truly mean the world to us if you’d share it with somebody who can use it, pin it to pinterest for later reference, or share it to a facebook group when somebody has a question about this subject. Click the bubble in the lower right corner to subscribe to be notified of future updates and as always, leave any questions you’ve got in the comments below.
Hi. Wonderful website with a lot of incredible information.
I have 2 6V golf cart batteries in my trailer and want to upgrade to solar power. All solar controlers show 12V and 24V. What solar controler would you recomend for 6V batteries?
Thank you,
Chris
You will likely be wiring your two 6v batteries in series effectively making them 1 12v battery. From there the same rules as any other 12v battery apply.
Good info but, your charge controller wizard won’t work on my iMax and what about wiring panels in parallel to avoid shading issues? So not sure why you recommend series.
I just checked on a mac and it’s working fine for me. It’s on google drive so make sure you aren’t trying to open it in microsoft excel or something.
Regarding series vs parallel for your panels: I recommend series over parallel because the increased voltage allows for smaller and fewer wires which makes installation easier as well as (and maybe more importantly) the increased voltage allows the MPPT solar controller to fully do it’s job and have plenty of voltage to make the most amount of amps possible at any given time.
You should design your system so you have no shading and if you have a bad panel, it should be replaced.
Ya lost me, Nate. Your first diagram w/ 4 solar panels (and the preceding paragraph) talks about 6.72 A, but immediately below that image and subsequently, you talk about 5.29 A.
Is that an oversight or my ignorance?
Oops! Good catch. That was an error on my end as I switched example panels halfway through writing this. It SHOULD be fixed now.
I may want to upgrade the system I am designing at a future date with more panels. If I buy a more powerful charge controller than I need today will I lose any efficiency and if so how much? For example lets say that I need a Victron 150/45 but buy a 150/60. Any other downsides to buying more powerful charge controller than I need today?
Very little (if any) efficiency will be lost. I’d highly recommend buying for your plan of future expansion like you’re talking about.
Hey – thanks for all the great info! I have a query regarding the Aims Power 30A Charge Controller listed in your shop. Right under the heading it states ” make sure this fits by entering your model number.” What do you mean? Thanks again!
That is just information that is auto-pulled from the Amazon listing. Just ignore it until I get around to deleting that part. 🙂
hello thanks for the info mate xan you link me to the calculator that works how much power im using and what solar panels and batteries i would need please
Of course! Here it is: https://www.explorist.life/what-size-of-solar-system-is-needed-to-power-a-camper/
Hi There,
I am setting up a 300 watt system – (3) 100 Watt panels but I was going to set them up in parallel. Can you tell me what the benefit would be to hook them up in series? I am looking at a 30 amp charge controller, will that be big enough?
Hey Jim! Here is a blog post that talks about series vs parallel: https://www.explorist.life/solar-panels-series-vs-parallel/
For that setup, you’d be looking for the Victron SmartSolar MPPT 150 | 35
Hey Nate,
Very informative thanks.
I have two panels of 160 each for total of 320 watts. The optimum voltage of 22.8 volts and 8.6 amps. So In series I get 45.6 volts and a measly 7.01 amps. Shouldn’t I wire them in parallel to increase the amps? I have two 6v agm’s in series and a blue sea MPPT 100/50 charge controller for future upgrade.
Ok I reread the article and I think I found my mistake. Wiring panels in series gives me 8.6 A according to the info on the panel but if I do the watt conversion I get 320 watts divided by 12.6 which is 25.4 Amps. I just forgot this step because I thought in series I would only get the 8.6 amps listed on one panel since we aren’t adding the amps. I guess the charge Controller does something to bump up the amps! I really don’t understand this part but I’ll go with it if you say it’s correct.
Ok if I run the Blue Sea Circuit Wizard I should use the original 8.6 amps of the batteries in series because the wire is before the charge controller and I get 10 gauge which seems correct.
Also, the ampacity of a 10 gauge wire is 30A if I am reading correctly so isn’t using a 30 amp breaker on a 10 gauge wire the Same as not even having a breaker?
Hey Nate,
I’m trying to decide if there is an advatage to 2x300w panels 18v, 16.66a. Would it produce much more power than your above example? And what size controller would i need. Im so confused. Cheers 🙂
I’m not sure what you’re asking in the first question, but on the page explorist.life/solarwiringdiagrams I have a full setup featuring 2 x 300 watt panels that may help you out.
Nate, I read your blogs and learned a lot. I have a question regarding connecting more than 10 or maybe 20 panels. I saw many houses have a lot of panels on their roof. If they are in serious, the voltage would be over 250 or more, while the max voltage in the controllers is 250…if the panels are in parallel, the Amps can be easily go over 30amps….what kinds of wires can take 30amps?? I think most mc4 are 8 or 10amps.
In something like that, lets pretend you wanted to have 25 panels… (This is incredibly generalized and theoretical, btw…) You’d wire 5 panels in series. You’d do that 5 times so you’d have 5 sets of 5 panels wired in series. Those 5 series strings would then get wired in parallel and wired to the charge controller. MC4 connectors would be used up until the point at where everything gets wired in parallel. From then on would be lugs, crimps, screw terminals, or whatever other method the particular install calls for.
Hi Nate, thank you so much for your reply. I just checked out your wiring pages and it has answered all my questions!!! You rock!!
Hi Nate,
I have 3 x 50Watts rigid panels wired in parallel into a cheap old 10A mppt controler , and 1 x 150Watts semiflexible into a PWM 10A controller. Of course the system works but leaves a lot to be desired. It gives me 12 to 14 Amps at noon. If I put them in series it seems the Victron 100/30 could handle them. What sort of benefit am I looking at, and does it matter the sequence of the panels in series?
In the mean time, I read your other article Parallel vs in series and I understand I should have the 3x50W panels in parallel and the output in series with the 150W panel to the 100/30 Victron. This looks reasonable to me. But again, what sort of benefit or increase are we expecting over todays all parallel situation? Does it really matter that the 3x50W are rigid and the 150W semiflexible?
Yeah, same as in the other reply: “I would keep the like panels together and not integrate the non-like panel. So… 3 x 50 watt panels into an MPPT and the 150W panel into a separate charge controller. Mixing panel sizes on one charge controller is truly not ideal.”
I would keep the like panels together and not integrate the non-like panel. So… 3 x 50 watt panels into an MPPT and the 150W panel into a separate charge controller. Mixing panel sizes on one charge controller is truly not ideal.
Thank Nate for advice. However, I do not see any mixing of non-like panels. I would like to think that 3 x 50W panels in parallel will behave as one 150W. Then this one in series with another 150W. See my point?
Oh, okay; I see… but still… IMO; that’s an incredibly messy way to do things. Your junction box is going to be a rats nest of wires as you’ll have to fuse each of your parallel strings PLUS a master disconnect for those 3 panels then run that in series with yet ANOTHER master disconnect for the whole array. It’s just a messy way to design an array.
I still stand by my statement that the 3×50 panels should go into one MPPT and the 150 panel should go into a 2nd charge controller.
Hi Nate, thanks for all your hard work.
I am installing 2 x 355w panels on my bus. When I do the calculations like listed on your series vs. parallel post, I get 8.9 Amps at 97.8 Volts pre-charge controller, and 56.3 Amps at 12.6 Volts into the battery.
However, when I plug the numbers into your charge controller wizard, it is saying I’ll only receive 10.95 Amps at 12.6 Volts into the battery. I’ve tried changing out the temperature coefficients with other numbers on the spec sheet(in case I’m just inputting the wrong number) but the Amps don’t fluctuate by more than 1 or 2. Any idea what I could be getting wrong?
That is strange. You should be somewhere in the 60amp ballpark at 12v. Maybe take a screenshot of your inputs and share it here: https://www.facebook.com/groups/DIYCampervanCrew/
Dear Nate,
Should I always go for the highest voltage panels when it comes to using MPPT controllers? i have to choose between 180w 18v mono panel (36cell) and 200W 23V poly panel (48 cells). I understood that higher voltage panels tolerate low irradiance issue better so that the panels keep on working on cloudy days thanks to its initial higher voltage whereas 18v panels would stop charging. The mono and poly panel cost difference is less than 10 USD. .
Not necessarily. Wiring multiple panels in series will yield the same result. The only time I suggest making sure to buy a higher voltage panel is when somebody wants to run only one-single panel. Typically; mono panels produce more power per square inch than their poly counterparts. So, when roof space is at a premium; mono is the way to go.