A few questions about MPPT

[Napalm]

I have 4x 2w 5v 500ma panels soldered to a microusb and schottky diode. It charges my 3800mah power bank over a cloudy day. That was my first real solar project not counting charging AA batteries with those lawn lights from the dollar store and an incandescent bulb.

Whats your solar setup?

I don't have a major setup... it's 2x 180watt in series. (72cell each, 36volt each. So in series it's 72v or 73v. The amps are less so it's around 4.89amps per panel. Due it it being in series , the amps stay the same. The volts double)

Some people connect 2 panels in parallels , which will then be 36v x 9.78 amps (4.89a x 2) = 352w
mine is 2 panels in series, which gives 72v(36x2) x 4.89amps = 352w

Most wires that are 2-3mm thick copper can handle volts upto 110v or even 220v. (like check your normal extention leads wires on inside. they are fairly thin). The amps on other end. If your pushing 5amps it can be a thin wire. Where'as pushing 10amps over wire , that needs a thicker lead.

Efficiency on 72v is also much better... due to mppt and how it acts on volts to produce watts. If a normal 12v panel was used which produces around 18v or upto 20v. The mppt gets more efficient if it has higher volts (at least 3-4v above the 12v or whatever your battery capacity is) . That is why mppt is better than those PWM chargers. So if you buy a solar panel that is 24v which pushes real volts of 33v to 36v. MPPT is very good.
Pushing it upto over 60volts makes both panels super efficient .

i'm running 2x 105ah Deep cycle battery's. (both in parallel). This is kinda my downfall. As my inverter is 12v 600watt Pure Sine wave. I can't push my battery setup to 24v.

Cause i could connect my battery's in 24v (just a cable change) then i would get much more bang for my buck. Then i need a 24v Pure sine wave inverter.

 

[Napalm]

I have 4x 2w 5v 500ma panels soldered to a microusb and schottky diode. It charges my 3800mah power bank over a cloudy day. That was my first real solar project not counting charging AA batteries with those lawn lights from the dollar store and an incandescent bulb.

Whats your solar setup?

Yeah. so yours is basically an 8w doing around 2000ma +- , i'm guessing it can charge 10,000mah if you had a good power bank and fairly good amount of sun. If it's full sun... mayeb 15,000mah

2,000mah , minus 20% loss (there is always loss) x 6 to 8 hours of sun. That can do 12000mah easily.

I think the 10watt or 12watt Solar panel also with USB, just gets more efficient, some can also pump 2,1amp or 2.4amp (2100ma or 2400mah)
Then definitely a 20,000mah battery is needed and a high quality charge cable. As not all charger cables are meant for 2.1amp and 2.4amp or 3amp. <check the net for a nice 5v 3amp usb charger cable.. to make sure it will pump full power of the smaller Solar panel>

 

[Goombah111]

2,000ma , minus 20% loss (there is always loss) x 6 to 8 hours of sun. That can do 12000mah easily.

You would think but it takes all day to charge the 3800. I think its actually 400ma cause I know theyre 5v 2w. Ill have to check cause maybe it's not outputting the advertised levels or there is more loss than expected.

Maybe it is the cable, would not be surprised.

 

[Goombah111]

i'm running 2x 105ah Deep cycle battery's. (both in parallel). This is kinda my downfall. As my inverter is 12v 600watt Pure Sine wave. I can't push my battery setup to 24v.

Cause i could connect my battery's in 24v (just a cable change) then i would get much more bang for my buck. Then i need a 24v Pure sine wave inverter.

I just got a 500w continuous 24v pure sine wave inverter (supposedly pure, might have to get myself an oscilloscope) for the new system I plan to run because the controller supports more watts that way. How much did you spend on your batteries ?

 

[Napalm]

I just got a 500w continuous 24v pure sine wave inverter (supposedly pure, might have to get myself an oscilloscope) for the new system I plan to run because the controller supports more watts that way. How much did you spend on your batteries ?

I already had the battery's luckily. As i had a backup power UPS running on my tv setup. Incase of loadsheddings. So the grid would charge battery's and it trips over within 0.1seconds to backup battery if power goes out.

We had it.. at some days where it's loadsheddings twice a day for 2.5hours to 3hours each time. <not enough power on grid.. or one of the power generators at power stations kicked the bucket..>

 

[Napalm]

You would think but it takes all day to charge the 3800. I think its actually 400ma cause I know theyre 5v 2w. Ill have to check cause maybe it's not outputting the advertised levels or there is more loss than expected.

Maybe it is the cable, would not be surprised.

Could be that the mini solar setup not good quality panels or not getting enough sun to do anything.

 

[Goombah111]

Could be that the mini solar setup not good quality panels or not getting enough sun to do anything.

Definitely gonna check on that soon. Got my 240w panel today, just as big as expected. My homemade one is dwarfed by this beast. This should help me learn more about solar systems. The old panel was just too small to bother upgrading the rest of my equipment. Hows it look?





Turns out its a 30v 8a SunTech which is apparently(?) better than Trina.

 

[Napalm]

Definitely gonna check on that soon. Got my 240w panel today, just as big as expected. My homemade one is dwarfed by this beast. This should help me learn more about solar systems. The old panel was just too small to bother upgrading the rest of my equipment. Hows it look?

View attachment 50564



Turns out its a 30v 8a SunTech which is apparently(?) better than Trina.

View attachment 50565

Nice big panel... Just remember.. you can only hook upto 2 panels of these together in parallel. as this panel pushes 7.92amp. If you add in para it adds amps. So having 2 of them will have volts @ 30v but amps @ almost 16amps. (if you have 2 of them both ++ and -- connected) to stay on 30v or so. So the Max fuse is 20amps. You cannot add a 3rd panel in para. (If you do add a 3rd. best to run in series, they will add up to 60v but then amps will stay @7.95amps)


That one is pretty heavy... mine weigh slightly less. I got 2 of these one's. 36v nominal.. but open volt of 45v per panel.

 

[MisterSandals]

If you do add a 3rd. best to run in series, they will add up to 60v

37.2 x 3 = 111.6v

 

[Napalm]

37.2 x 3 = 111.6v

if your MPPT can handle 150v . It's no problem in series.

The fuse rating is problem... as 20A is the fuse rate over all panels in parallel. Can only have 2 like that. then you have to switch to series yes. (volts go up.. amps stay low)

 

[Sirtate]

So... before you go and buy a 20A mppt.. First check 2 things.

1. What battery setup you got (is it 12V setup?) Cause doesn't matter what solar panels you buy.... if your battery's are 12v it will charge at 13.8volts @ 20amps maximum... which gives you 276Watt (and most mppt's won't do full 20amps solid for 3-4 hours. It might go down to 18amps or less depending on the weather. So if your solar panels are higher than say 350watt to 400watt solar. your going to be "bottlenecking" yourself if your MPPT is only 20amp. If you have say 2x 180watts or 2x 200watt panels or say 1x 350watt or 1x 400watt panel. You will be losing anything above 276watts. Unless your battery setup is in 24v.. Then your good for upto 520watt solar array.

2.Check your inverter. The inverter can run 12v or some run only 24volt. There are a few that has a dipswitch to change from 12v to 24. Most of the time they are bought to be running at only 12v or only 24v. So if your Inverter is 12v only.. your limited to said 276watt as above at maximum.

Rather buy the 30amp MPPT or 40amp (they cost slightly more) but can charge upto 30amps so then your good for 400watt solar panels and 40amp on over 500Watt solar panels even on a 12V or Parallel linked 12v battery's (Say if you link 2 or 3x 12V battery's together. All the + together. All the - together)
View attachment 50083

if i understand you correctly;

If I have 500w worth of panels wired in series into my 25A-MPPT controller (assuming input voltage isn't exceeded), my controller won't blow up?

Is it similar to me plugging my 15w phone charger into an outlet at home, and then replacing it with a 1500w hairdryer?
IE; the potential for 1500w is there (1800w actually on a 15a circuit) but the phone charger only pulls what it wants at the moment

in my example, the charge controller would pull 350w from the panels, when available, and ignore the rest?

I am trying hard to find a panel that won't exceed the wattage of my 25a controller... i have a 165w panel installed already, and i am finding 300-400w panels (which would physically fit) all over the place for a fraction of 160w panels...
it would be great to get my full 25a of charging earlier/later in the day with just $150 worth of panels

 

[Napalm]

if i understand you correctly;

If I have 500w worth of panels wired in series into my 25A-MPPT controller (assuming input voltage isn't exceeded), my controller won't blow up?

Is it similar to me plugging my 15w phone charger into an outlet at home, and then replacing it with a 1500w hairdryer?
IE; the potential for 1500w is there (1800w actually on a 15a circuit) but the phone charger only pulls what it wants at the moment

in my example, the charge controller would pull 350w from the panels, when available, and ignore the rest?

I am trying hard to find a panel that won't exceed the wattage of my 25a controller... i have a 165w panel installed already, and i am finding 300-400w panels (which would physically fit) all over the place for a fraction of 160w panels...
it would be great to get my full 25a of charging earlier/later in the day with just $150 worth of panels

Heya. You can always have more Power on Solar panel. vs what your controller can do. Just remember Solar panels and sun conditions is not always optimal... so maximum watts won't be charged to MPPT unless you get that 5-6hours of full sun. The more panels, the more sun it grabs and maybe you can get more potential for 7 or 8hours of the day to store that power.

The panel limit.. is on your MPPT amps limit.. and also your Solar panel Circuit cuttoff or short. Got to do with wire thickness too.

Linking Solar panels in series pumps the volts and thinner cables is fine due to the Amps being steady on the combo'd panels.
More amps means... thicker wire needed.

As sketch shows, If you parallel Panels, The Volts stay same but amps double up. Pushing 16Amps to your 25A MPPT.
If you add a 3rd panel it will be 24amps (which is running your MPPT to 99% when there is full sun) <-- some thick wire would be needed for full length to MPPT and also your MPPT won't last long.

In Series the Volts go up..(double or triple if you add a 3rd. but the amps stay on 8Amp. Most wire can run 110v to 220v easily. You can push 36v or 54v all day long.. maybe even a 4th with 72v. They will still only push 8amp. Your MPPT on other hand can then utilize the nice amount of volts pushing 72v and give you higher amps going to your battery banks. --> But take into account if it's a 12v battery setup or 24v battery setup. There is limitations *so keep them in mind when buying panels, you can go slightly higher.. but don't go less*.
Example. 12v battery bank with 25amps. 12v x 25amps = 300w. but normally the Boost or float is around 13.7v So say... 342w.
If you setup is 24v that makes things better... as then the 25Amp charger can charge @ 24v x 25amps = 600w or 27.4v x25 @ 685watt.


Para vs Series





Where the fuse cutoff happens on Parallel (is strangely called Maximum series fuse. It strangely doesn't mean the panels are in series) It's the amount of Panels you link together to fuse the panels amps together. You can check that on the back of your panel. Says maximum series fuse. If that amount if 20AMP(which is fine with your 25AMP mppt. It's under that amount. If won't hurt your MPPT). If you panel only uses say 5.2amps. if you link 3, it will then push 15.6amps standard. <but you must eyeball the maximum output at full sun. the short circuit output. Cause your panel will short itself if it gets to say 5.6amps. That amount will show on your panel too>

If all 3 your panels say maximum series fuse is 20amps. And each one standard uses 5.2amps with a short circuit amp of 5.6. Then 3 panels is perfect in parallel and nothing will burn or fuse). Problem comes in, when you want to add a 4th one. Then it goes over 20amps and it will put too much strain amp wise on your MPPT.

 

[Goombah111]

If I have 500w worth of panels wired in series into my 25A-MPPT controller (assuming input voltage isn't exceeded), my controller won't blow up?

Probably not. Whats your controller? It should have a designated maximum watt input.

The 20a Epever I just got apparently handles a little over 30a input according to it's "Max PV Array Power" 780w/24v but will only output 20a, if that.



Thats what it seems like anyway, not gonna test it.

 

[Napalm]

Probably not. Whats your controller? It should have a designated maximum watt input.

The 20a Epever I just got apparently handles a little over 30a input according to it's "Max PV Array Power" 780w/24v but will only output 20a, if that.

View attachment 50702

Thats what it seems like anyway, not gonna test it.

Which EPever / EPSolar do you have? If it says it's a 20amp.. that is the rated max charge either at 13.7 or 14.4 at boost. Won't go higher than that. Even if you tripple or quad the array. <that max Array PV is propably a calculation they made, based on Amps per best on the market Solar panel. Maybe 2x 380watt solar panels at 9.50 A. / Short circuit current (Isc): 9.82 A.

24x20amps is 548watts. (battery charges at 13.7v float x amps is watts to battery)

If you battery solution is 24v setup (it will never charge more than the 13.7volt and maybe boost to 14.4 for 1hour). It will also never charge higher than 20amps if your Charge controller is 20A controller.

I would bank on 548watts as the max. But your array can be around 600 to 700watts (maybe 2x 300w panels or 2x 350watt or 2x 380watt).
What will be going to battery bank is only 548watts.

 

[Napalm]

To illustrate. 20amp charger on Battery's (24v or higher)

So even on Semi cloudy days.. or mild sunshine.. because panels are higher rated.. it can still store the good amount (Full capacity that your charger can handle. It basically milks the sun more.. so that the MPPT stays as efficient as possible.


So always better to have more Panel size power vs the MPPT. As the panels don't always give full power, the more power you got or the more area they cover. The better. Means the MPPT controls the flow, and even if sun is not so good. Due to panel being overspec, it still provides the 90% or 100% flow to the bucket (the battery)

 

[Sirtate]

To illustrate. 20amp charger on Battery's (24v or higher)

So even on Semi cloudy days.. or mild sunshine.. because panels are higher rated.. it can still store the good amount (Full capacity that your charger can handle. It basically milks the sun more.. so that the MPPT stays as efficient as possible.
View attachment 50708

So always better to have more Panel size power vs the MPPT. As the panels don't always give full power, the more power you got or the more area they cover. The better. Means the MPPT controls the flow, and even if sun is not so good. Due to panel being overspec, it still provides the 90% or 100% flow to the bucket (the battery)

Which EPever / EPSolar do you have? If it says it's a 20amp.. that is the rated max charge either at 13.7 or 14.4 at boost. Won't go higher than that. Even if you tripple or quad the array. <that max Array PV is propably a calculation they made, based on Amps per best on the market Solar panel. Maybe 2x 380watt solar panels at 9.50 A. / Short circuit current (Isc): 9.82 A.

24x20amps is 548watts. (battery charges at 13.7v float x amps is watts to battery)

If you battery solution is 24v setup (it will never charge more than the 13.7volt and maybe boost to 14.4 for 1hour). It will also never charge higher than 20amps if your Charge controller is 20A controller.

I would bank on 548watts as the max. But your array can be around 600 to 700watts (maybe 2x 300w panels or 2x 350watt or 2x 380watt).
What will be going to battery bank is only 548watts.

I found the manual for the controller....
Page 15 talks about 'Protection'
To Wit:
"The Solar Charge Controller will limit input power to 300W or 600W depending on model. A PV array with higher maximum power than the MPPT's rated power will be limited to the rated power of the device."

so, that worry is looked after... (I figure that an extra 100-200W will allow 25amps worth of charging on cloudy days, or during shoulder periods)

Next question;

What is the limiting factor for Series Fuses?

the current panel has a 15a Series fuse, with a 8.82amp max current...

does that mean im limited to another panel with 6amps if i wire in series? (15a-9a=6)
what about Parallel?

 

[Forbisher]

I found the manual for the controller....
Page 15 talks about 'Protection'
To Wit:
"The Solar Charge Controller will limit input power to 300W or 600W depending on model. A PV array with higher maximum power than the MPPT's rated power will be limited to the rated power of the device."

so, that worry is looked after... (I figure that an extra 100-200W will allow 25amps worth of charging on cloudy days, or during shoulder periods)

Next question;

What is the limiting factor for Series Fuses?

the current panel has a 15a Series fuse, with a 8.82amp max current...

does that mean im limited to another panel with 6amps if i wire in series? (15a-9a=6)
what about Parallel?

Panels in Series do not need fuses.
2S2P does not need fuses.
2S3P would need fuses.
You tagged on to another thread so not really sure what you are asking.

You don't say what brand or model of SCC you have.

 

[Sirtate]

Panels in Series do not need fuses.
2S2P does not need fuses.
2S3P would need fuses.
You tagged on to another thread so not really sure what you are asking.

You don't say what brand or model of SCC you have.

whoops!
that was a bit of a misfire...
but thanks for the response!

 

[Sirtate]

Heya. You can always have more Power on Solar panel. vs what your controller can do. Just remember Solar panels and sun conditions is not always optimal... so maximum watts won't be charged to MPPT unless you get that 5-6hours of full sun. The more panels, the more sun it grabs and maybe you can get more potential for 7 or 8hours of the day to store that power.

The panel limit.. is on your MPPT amps limit.. and also your Solar panel Circuit cuttoff or short. Got to do with wire thickness too.

Linking Solar panels in series pumps the volts and thinner cables is fine due to the Amps being steady on the combo'd panels.
More amps means... thicker wire needed.

As sketch shows, If you parallel Panels, The Volts stay same but amps double up. Pushing 16Amps to your 25A MPPT.
If you add a 3rd panel it will be 24amps (which is running your MPPT to 99% when there is full sun) <-- some thick wire would be needed for full length to MPPT and also your MPPT won't last long.

In Series the Volts go up..(double or triple if you add a 3rd. but the amps stay on 8Amp. Most wire can run 110v to 220v easily. You can push 36v or 54v all day long.. maybe even a 4th with 72v. They will still only push 8amp. Your MPPT on other hand can then utilize the nice amount of volts pushing 72v and give you higher amps going to your battery banks. --> But take into account if it's a 12v battery setup or 24v battery setup. There is limitations *so keep them in mind when buying panels, you can go slightly higher.. but don't go less*.
Example. 12v battery bank with 25amps. 12v x 25amps = 300w. but normally the Boost or float is around 13.7v So say... 342w.
If you setup is 24v that makes things better... as then the 25Amp charger can charge @ 24v x 25amps = 600w or 27.4v x25 @ 685watt.


Para vs Series
View attachment 50688




Where the fuse cutoff happens on Parallel (is strangely called Maximum series fuse. It strangely doesn't mean the panels are in series) It's the amount of Panels you link together to fuse the panels amps together. You can check that on the back of your panel. Says maximum series fuse. If that amount if 20AMP(which is fine with your 25AMP mppt. It's under that amount. If won't hurt your MPPT). If you panel only uses say 5.2amps. if you link 3, it will then push 15.6amps standard. <but you must eyeball the maximum output at full sun. the short circuit output. Cause your panel will short itself if it gets to say 5.6amps. That amount will show on your panel too>

If all 3 your panels say maximum series fuse is 20amps. And each one standard uses 5.2amps with a short circuit amp of 5.6. Then 3 panels is perfect in parallel and nothing will burn or fuse). Problem comes in, when you want to add a 4th one. Then it goes over 20amps and it will put too much strain amp wise on your MPPT.

ok, so lets imagine I have an existing panel that gives ~19v and ~9a in full sun with a 15a Series Fuse...I have found inexpensive 400w panels that push 40v and 10amps... these will physically fit on the roof of my camper...

My Furrion 25A MPPT can accept 70v...

My math says; 19v+40v in series will give me 59v... and a total of 9.75amps...(165w+410w)/59v=9.75a
is this correct?

I'm leaning this way because i'm not keen on rewiring the leads from the roof to the SCC, all of the wiring can be done on the roof...

If one of those panels is shaded, is that an issue? (other than a drop in performance, of course)
Some people have said that a series panel in shade brings the whole array down...

 

[Forbisher]

ok, so lets imagine I have an existing panel that gives ~19v and ~9a in full sun with a 15a Series Fuse...I have found inexpensive 400w panels that push 40v and 10amps... these will physically fit on the roof of my camper...

My Furrion 25A MPPT can accept 70v...

My math says; 19v+40v in series will give me 59v... and a total of 9.75amps...(165w+410w)/59v=9.75a
is this correct?

I'm leaning this way because i'm not keen on rewiring the leads from the roof to the SCC, all of the wiring can be done on the roof...

If one of those panels is shaded, is that an issue? (other than a drop in performance, of course)
Some people have said that a series panel in shade brings the whole array down...

You are confused.
How many watts is the 19Vmp x 9A panel? 19 x 9 is 171 watts.
Why do you keep mentioning 15A fuse as it is irrelevant.

19V is Vmp not Voc which is what you use to calculate max volts input.
Is 40V on the 400 watt panel Vmp or Voc?
What are the specs on both of your panels?
Voc
Vmp
Amps
Seriously?? $234 for a 25A SCC??
Furrion 25A MPPT specs

Wall Mount MPPT Solar Charge Controller

Furrion's 25-Amp and 50-Amp solar controller with MPPT technology optimizes your solar panel output to provide the maximum amperage to your RV batteries.

furrion.com