Wiring size mistake?

[Sugarkryptonite]

Hi guys

I am in the process of building out my Sprinter van. I started out with the intention of using 400W of solar (2x 200w panels, optimum operating voltage of 19.2v and short circuit current 11.05A each). I ran 10 AWG solar panel wire from the roof of my van through a roof gland and to the back of the van where my electrical system is. I would say the total length of wire is something like 15ft.

I then received another 200w panel, making my system 600w total. Looking up the DC current wire charts, it seems like my wire is now too small.

My 3 panels are wired in parallel with a 12v LiFePo4 battery bank.

1) Should I just wire my panels in series instead of parallel so I don't have to change the wire going into the roof and walls of my van (a bigger headache)?

2) If I do that, how do I wire the MC4 connectors? Does that mean I just get rid of my branch connectors and go positive from one panel to negative of the next, and so on?

3) I screwed up the sizing on my charge controller and will have to get a much larger one it seems. My current one is MPPT rated at 30A, but has a 12v/380W and 70v PV voltage limit.

I'm still a bit of a newb at this, but does that mean with an open circuit voltage of 69v (23v x3 in series = 69v), I need a controller with at least a PV voltage limit of 70v, and a 12v limit of at least 600w?

 

[Rocketman]

The amps number that matters when running isn’t the short circuit current- it is the Imp - my guess is it is in the high 9’s. Three panels in parallel would be right near the 30amps the #10awg wire can handle.

So you could leave the wire - but if you can replace it easy enough I would go with#8 - because in a van you will want all the power you can get. But because the panels are flat - you will seldom see full rated watts - (only at noon in June) - so it will also be fine to leave it as #10 awg.

With putting three panels in parallel you need to fuse each string- there are MC4 fuses to do that.

The MC4 branches should be rated for 30amps - I would contact the manufacturer just to verify.

What brand of SCC?
We are in December near the Winter solstice- unless you are in Australia you will have very low sun angles on flat panels, the sun is going through at lot of atmosphere- you will not get anywhere near rated power.

On my MotorHome I have one array that is 600w going into a Victron mppt 100/30 - so it is over paneled. We are halfway down the Baja peninsula, this week that array’s max watts was 315w (it is almost flat). During the summer in Utah it would spend time maxed out (clipped) at about 410 to 425watts. If I tilted them, then it would be several hours it was maxed out. I over paneled because I needed more power when conditions were not ideal - when conditions are ideal I fill my battery every day.

So with only a 30a controller in the summer you will be clipped- you have to decide if it is worth it right now to get a bigger mppt SCC or if that is something you want to leave for later.

 

[Sugarkryptonite]

The amps number that matters when running isn’t the short circuit current- it is the Imp - my guess is it is in the high 9’s. Three panels in parallel would be right near the 30amps the #10awg wire can handle.

So you could leave the wire - but if you can replace it easy enough I would go with#8 - because in a van you will want all the power you can get. But because the panels are flat - you will seldom see full rated watts - (only at noon in June) - so it will also be fine to leave it as #10 awg.

With putting three panels in parallel you need to fuse each string- there are MC4 fuses to do that.

The MC4 branches should be rated for 30amps - I would contact the manufacturer just to verify.

What brand of SCC?
We are in December near the Winter solstice- unless you are in Australia you will have very low sun angles on flat panels, the sun is going through at lot of atmosphere- you will not get anywhere near rated power.

On my MotorHome I have one array that is 600w going into a Victron mppt 100/30 - so it is over paneled. We are halfway down the Baja peninsula, this week that array’s max watts was 315w (it is almost flat). During the summer in Utah it would spend time maxed out (clipped) at about 410 to 425watts. If I tilted them, then it would be several hours it was maxed out. I over paneled because I needed more power when conditions were not ideal - when conditions are ideal I fill my battery every day.

So with only a 30a controller in the summer you will be clipped- you have to decide if it is worth it right now to get a bigger mppt SCC or if that is something you want to leave for later.

Thanks for your response. The Imp of each panel is 10.42A.

1) But is the amp rating of an MPPT charge controller the amount of current it can take in? Or put out to charge the batteries? I have seen other people with 600W of solar and their max was like 460-480W at best, which at 13.5v of lithium is around 35A. I want to make my setup sufficient for the time of year where it is making the most amount of power, I don't want to lose out on any even if it's lower the rest of the year.

2) What happens if a solar array puts out more power than an SCC is rated for? Does it just burn up, or it just won't output as much power as the array is putting out?

I had bought this charge controller:

Amazon.ca

As you can see it says "12V/390W max input", whereas I now have 600w total... ?

 

[Rocketman]

I would not use that SCC for three panels. Because it says that’s over the limits. High quality SCC’s you can overpanel- can’t with that one.

When you replace it - look closely at Victron mppt’s. They are high quality great units, but they are more expensive.

Also, do you have a shunt based battery monitor- like a Victron Smartshunt or BMV712 - if not you really need one so you know how full or empty the batteries are.

Good Luck

 

[ShaneC]

Thanks for your response. The Imp of each panel is 10.42A.

1) But is the amp rating of an MPPT charge controller the amount of current it can take in? Or put out to charge the batteries? I have seen other people with 600W of solar and their max was like 460-480W at best, which at 13.5v of lithium is around 35A. I want to make my setup sufficient for the time of year where it is making the most amount of power, I don't want to lose out on any even if it's lower the rest of the year.

Amp rating is for the charge side. A 30A MPPT means it can charge a 24V battery at 680W for example. You need to check what the input limits are though, the most important is the max VoC, you've already found that is going to limit you connecting these in series as that would be 69V, far too close to the 70V limit. If you want to connect in series you should look at a 100V MPPT.

2) What happens if a solar array puts out more power than an SCC is rated for? Does it just burn up, or it just won't output as much power as the array is putting out?

I had bought this charge controller:

Amazon.ca

As you can see it says "12V/390W max input", whereas I now have 600w total... ?

So long as you don't exceed the max input VoC (taking into account cold weather conditions that increase the voltage from the panels) then the MPPT should only draw what current it can from the panels. Excess current shouldn't negatively affect it, your charge speed will just be maxed at that 390W.

 

[Sugarkryptonite]

Amp rating is for the charge side. A 30A MPPT means it can charge a 24V battery at 680W for example. You need to check what the input limits are though, the most important is the max VoC, you've already found that is going to limit you connecting these in series as that would be 69V, far too close to the 70V limit. If you want to connect in series you should look at a 100V MPPT.

So long as you don't exceed the max input VoC (taking into account cold weather conditions that increase the voltage from the panels) then the MPPT should only draw what current it can from the panels. Excess current shouldn't negatively affect it, your charge speed will just be maxed at that 390W.

Thank you.

In the description of the SCC it says “12V/390W and 24V/780W PV max input power (PV array limited power input function)”

Does that mean this SCC also has another limit for its input, or is that just written wrong and is meant 390w / 12v = 32.5A ~ 30A output?

 

[Sugarkryptonite]

I would not use that SCC for three panels. Because it says that’s over the limits. High quality SCC’s you can overpanel- can’t with that one.

When you replace it - look closely at Victron mppt’s. They are high quality great units, but they are more expensive.

Also, do you have a shunt based battery monitor- like a Victron Smartshunt or BMV712 - if not you really need one so you know how full or empty the batteries are.

Good Luck

Rocketman I looked up the spec sheet for some Victron SCC's, and it says (for example the 100/30), Nominal PV power, 12v = 440w, Max PV open circuit voltage = 100v, AND Max PV short circuit current = 35A.



I am now confused. I see people saying that you can overpanel as much as you want as long as you don't exceed the Max PV open circuit voltage listed in the datasheets, and the rest will just be lost as the SCC will only produce as much as listed, but this is contradictory to their spec sheet which lists a max input current. So that means that there is a very small range of overpaneling that you can actually do?...

Say for example as you mentioned you are safe with your 600w of panels, but if someone hooked up 800w of panels in parallel they would potentially exceed the 35A Max PV short circuit current rating, thus making their overpanel not safe?

 

[timselectric]

Yes, you have to be careful with Victron.
It operates differently than most.
I'm not a Victron expert. But as I understand it. When it does its sweep, it shorts the circuit. So short circuit current can damage it if the rating is exceeded.
Most other SCC's don't do this.

 

[Q-Dog]

Rocketman I looked up the spec sheet for some Victron SCC's, and it says (for example the 100/30), Nominal PV power, 12v = 440w, Max PV open circuit voltage = 100v, AND Max PV short circuit current = 35A.

View attachment 184115

I am now confused. I see people saying that you can overpanel as much as you want as long as you don't exceed the Max PV open circuit voltage listed in the datasheets, and the rest will just be lost as the SCC will only produce as much as listed, but this is contradictory to their spec sheet which lists a max input current. So that means that there is a very small range of overpaneling that you can actually do?...

Say for example as you mentioned you are safe with your 600w of panels, but if someone hooked up 800w of panels in parallel they would potentially exceed the 35A Max PV short circuit current rating, thus making their overpanel not safe?

It depends on the controller. Not all Victron controllers have the same limitations.

 

[740GLE]

Over panel as long as you stay under VOC and ISC.

So VOC 100v & ISC 35A that’s 3500w of Pv of over paneling, that will clip at say 420w at 12v, lol

Perfect for those gray overcast days!!!

 

[ShaneC]

If I were you I would just see how you get on with your current mppt wired in parallel. Yes it will clip at 390w but you might be surprised at how little that matters with a 600w array laid flat in winter

 

[Sugarkryptonite]

If I were you I would just see how you get on with your current mppt wired in parallel. Yes it will clip at 390w but you might be surprised at how little that matters with a 600w array laid flat in winter

Thanks. Is it safe to run it like this, though? Doesn't it mean that the controller can only handle 390W and could get damaged above that? Similar to how Victron rates their controllers with a short circuit current maximum?

 

[Rocketman]

Contact the manufacturer and ask…

 

[ShaneC]

Thanks. Is it safe to run it like this, though? Doesn't it mean that the controller can only handle 390W and could get damaged above that? Similar to how Victron rates their controllers with a short circuit current maximum?

I tried to find the datasheet for your mppt model but failed. That's the problem with random amazon products sadly. Most mppts will only pull the current they need so can be safely over panelled. If in doubt just disconnect the third panel once the input starts to get near to being clipped. Alternatively get something like the Tracer 6415AN. 150V max VoC so you can wire in series with plenty of headroom, 60A charging so it won't clip your 600W input.

If you're still planning things out then I'd also consider going to a 24V setup. You'd only need a 30A mppt to charge at 600W. If you've already bought a 12v inverter then don't worry about it.

 

[Sugarkryptonite]

I tried to find the datasheet for your mppt model but failed. That's the problem with random amazon products sadly. Most mppts will only pull the current they need so can be safely over panelled. If in doubt just disconnect the third panel once the input starts to get near to being clipped. Alternatively get something like the Tracer 6415AN. 150V max VoC so you can wire in series with plenty of headroom, 60A charging so it won't clip your 600W input.

If you're still planning things out then I'd also consider going to a 24V setup. You'd only need a 30A mppt to charge at 600W. If you've already bought a 12v inverter then don't worry about it.

Datasheet is here. Model. TD2307.

https://static1.squarespace.com/static/52cc27e7e4b065ff5fdf1937/t/5fae301869c60d415b147302/1605251098881/MPPT+solar+charger+user%27s+manual.pdf

Pretty much the same info that is listed on the Amazon ad.

 

[ShaneC]

Hrm OK, usually input current limit would be given in amps. I'd be wary of putting more than 2 panels on that mppt then it that is a hard limit. Sounds like you'll need another charge controller if you want to use all 3 panels.

 

[Sugarkryptonite]

Hrm OK, usually input current limit would be given in amps. I'd be wary of putting more than 2 panels on that mppt then it that is a hard limit. Sounds like you'll need another charge controller if you want to use all 3 panels.

Thanks for the reply. In your experience it's more common to see max short circuit current as a hard limit? All of the datasheets I've seen like Epever, Renogy, etc, are all listed in watts depending on voltage. Only one I saw like that was Victron. Too confusing.

 

[ShaneC]

Thanks for the reply. In your experience it's more common to see max short circuit current as a hard limit? All of the datasheets I've seen like Epever, Renogy, etc, are all listed in watts depending on voltage. Only one I saw like that was Victron. Too confusing.

Impossible to know if over panelling would cause issues, it depends on the SCC. Victron can't take much excess current but others don't care. The risk is the controller burning up in the van which isn't worth it to me. Just connect two panels for now unless you want to get that epever one I mentioned which would handle all three panels in series.

The other option is to change to a 24v system but I don't know what other components you have already bought.

 

[Rocketman]

The Victron 100/30 can take lots of excess current for its size. It can handle 35amps of INPUT current- it can only output 30amps.

So with three of the OP’s panels that is 33amps of short circuit potential- the 100/30 can handle 35amps…

I agree the OP needs a different charge controller to maximize his system (or an additional one). If he wants Victron- I would look at the 150/35 or 150/45 or 100/50 - The 150/45 or 100/50 will capture all the watts no clipping… the 150/35 could still have some clipping- but remember his panels are flat- he won’t lose a lot.

 

[Sugarkryptonite]

Hi guys

So I sprung for the purchase of a Victron 100/50 MPPT. I have gotten no charging out of it so far as it has been pretty cloudy. Even then, my old Chinese MPPT would have charged even a little bit.

Reading through the Victron manual it states that charging will not commence unless the PV voltage is 5v higher than the battery voltage! That means my panels need to put out over 18v for my lithium batteries to charge? Seems a bit ridiculous. My panels only have an open circuit voltage of and 23v maximum. Looks like I have no choice but to rewire my panels in series instead of parallel for it to work?