Help sizing charge controller

[cmutwiwa]

Ok, the controllers in the first link accept up to 130 V for the 20-40 A sizes, and 150 V for the 50 and 60 A size.

The controllers in the 2nd link accept up to 105 V when used in a 24 V system. (specs here).

To use your panels in a 24 V system, you *must* put them in series, a single panel won't produce enough voltage.

With three panels, you are looking at 38.6 * 3 = 115.8 Voc, at 25 deg C. I think it stays warm enough there that the 130 V limit would be OK if you go with the 30 or 40 A controller. The 150 V limit of the 50A and 60 A controllers is definitely ok.

The 105 V limit of the 2nd link disqualifies it from consideration.

Thank alot sensij for the helpful info.
I will try the controller in the first link.

[sensij]

True, the only online place I can & I do shop reliably is eBay, and most of the items are always from China, there are the American controllers I see most of you recommend but they dont ship to Kenya and the few that does the shipping price is way beyond my budget. The only option I have is to try...see links below, your advice is most welcome...

https://www.ebay.com/itm/MPPT-Solar-Charge-Controller-DC12V-24V-36V-48V-Auto-Battery-Charger-Regulator-CE/142046896220?hash=item2112a7a05c:m:mQYZFJjMf2C9d4-eRcUqEuA

https://www.ebay.com/itm/30A-40A-50A-60A-MPPT-12V-24V-36V-48V-DC-System-Solar-Charge-Controller-Regulator/371878936500?hash=item5695b63fb4:m:m8y0CDcrtlNtAQ0Z2xcIlKA

Ok, the controllers in the first link accept up to 130 V for the 20-40 A sizes, and 150 V for the 50 and 60 A size.

The controllers in the 2nd link accept up to 105 V when used in a 24 V system. (specs here).

To use your panels in a 24 V system, you *must* put them in series, a single panel won't produce enough voltage.

With three panels, you are looking at 38.6 * 3 = 115.8 Voc, at 25 deg C. I think it stays warm enough there that the 130 V limit would be OK if you go with the 30 or 40 A controller. The 150 V limit of the 50A and 60 A controllers is definitely ok.

The 105 V limit of the 2nd link disqualifies it from consideration.

[cmutwiwa]

Hold the bus there my friend. What the heck do you think the wiring cost is going to be with 12 volts distribution? You will need to own stock with Freeport-MacMoRan. 12 volts is fine for RV's because the distances are so short. The other downside is 12 volt gizmos are expensive and usually very low quality.

My company does a lot of lighting, and I mean a lot of lighting. The only advantage, and it is a stretch, low voltage fixtures can be smaller but comes with a premium price. Bottom line is low voltage cost more to install, but offers no operational savings. So look at the big picture. Do not let the trees blind you preventing you from seeing the forest.

Yes I've thought of the same too Sunking, I've already made up my mind to go with a 24V system. Thank you so much for your sincere advice on this forum.

[cmutwiwa]

You're going to have to post links to what you are looking at for more specific help. I'm not sure what vendors will reliably deliver to Kenya, or what the pricing will be, so it would probably be better for you to share what you are seeing in the budget you have in mind. The links will cause your post to be "unapproved" and go to moderation before it shows up, but the moderators will see it isn't spam and approve it.

True, the only online place I can & I do shop reliably is eBay, and most of the items are always from China, there are the American controllers I see most of you recommend but they dont ship to Kenya and the few that does the shipping price is way beyond my budget. The only option I have is to try...see links below, your advice is most welcome...

https://www.ebay.com/itm/MPPT-Solar-Charge-Controller-DC12V-24V-36V-48V-Auto-Battery-Charger-Regulator-CE/142046896220?hash=item2112a7a05c:m:mQYZFJjMf2C9d4-eRcUqEuA

https://www.ebay.com/itm/30A-40A-50A-60A-MPPT-12V-24V-36V-48V-DC-System-Solar-Charge-Controller-Regulator/371878936500?hash=item5695b63fb4:m:m8y0CDcrtlNtAQ0Z2xcIlKA

[sensij]

The only rating I see on controllers listed online is output, how do I tell if the controller I need will handle 150 V max input?

You're going to have to post links to what you are looking at for more specific help. I'm not sure what vendors will reliably deliver to Kenya, or what the pricing will be, so it would probably be better for you to share what you are seeing in the budget you have in mind. The links will cause your post to be "unapproved" and go to moderation before it shows up, but the moderators will see it isn't spam and approve it.

[Sunking]

The only rating I see on controllers listed online is output, how do I tell if the controller I need will handle 150 V max input?

Spec sheet.

[Sunking]

Thanks Sensij, yes right now all loads are 12V, however this has been a limitation, I need to power a PC mostly during the day, so changing the lighting to accommodate the 24V system is an expense am willing to incur. I've read on other post here that its not a good idea to connect the panels in parallel since this will increase the current hence more cost in wiring and high power loss, so I think it will be better off doing it in series like you say.

Hold the bus there my friend. What the heck do you think the wiring cost is going to be with 12 volts distribution? You will need to own stock with Freeport-MacMoRan. 12 volts is fine for RV's because the distances are so short. The other downside is 12 volt gizmos are expensive and usually very low quality.

My company does a lot of lighting, and I mean a lot of lighting. The only advantage, and it is a stretch, low voltage fixtures can be smaller but comes with a premium price. Bottom line is low voltage cost more to install, but offers no operational savings. So look at the big picture. Do not let the trees blind you preventing you from seeing the forest.

[cmutwiwa]

Assuming the controller you select has 150 V max input, put all three panels in series.

.

The only rating I see on controllers listed online is output, how do I tell if the controller I need will handle 150 V max input?

[cmutwiwa]

Correct, you can not power 12 V loads directly from a 24 V battery. If your loads are *all* 12 V, and the only reason you are considering an inverter is because of the 24 V battery, you would be better off just sticking with a 12 V system.

Thanks Sensij, yes right now all loads are 12V, however this has been a limitation, I need to power a PC mostly during the day, so changing the lighting to accommodate the 24V system is an expense am willing to incur. I've read on other post here that its not a good idea to connect the panels in parallel since this will increase the current hence more cost in wiring and high power loss, so I think it will be better off doing it in series like you say.

[littleharbor]

Max Voc. for a 12 volt system with the cc shown is 80 volts, only 105 for 24 volt system. Although the controller apparently can tolerate a max voltage of 190 volts.
Tried posting stats from their pages but it turns into some other text when submitted.

[sensij]

Thank you again Sunking, I really dont think I will use that much wattage, considering its mostly for lighting, TV & Radio.
I was looking at the MPPT controllers on eBay and came across one with this setup diagram, and I was wondering can the DC output on the controller power 12v light bulbs when the system is a 24v? may be that question doesnt make sense or it answers itself but I really need to be sure whether I will need to power the bulbs off the inverter output so I can acquire AC bulbs.

Correct, you can not power 12 V loads directly from a 24 V battery. If your loads are *all* 12 V, and the only reason you are considering an inverter is because of the 24 V battery, you would be better off just sticking with a 12 V system.

[sensij]

Also...should I wire the panels in series or in parallel?

Assuming the controller you select has 150 V max input, put all three panels in series.

I would also suggest that before you going spending lots of money on the big battery and charge controller it sounds like you are considering, take some time instead to figure out how much power and energy you really need. There is no reason to oversize that part of the system if your loads don't require it, regardless of how much PV power you have.

[cmutwiwa]

Also...should I wire the panels in series or in parallel?

[cmutwiwa]

This is where AGM can be used because they can tolerate higher charge and discharge rates of C/4 to C/2 so that same 400 AH battery could power a 2400 to 4800 watt Inverter. But doing so is really going to mess with daily Watt Hours and Peukert Law. Think about that for a minute. A 24 volt 400 AH battery can only supply you with roughly 2400 watt hours per day. If you had say a 3000 watt load, Peukert Law would limit you to about 1800 watt hours or 40 minutes run time out of a 24 hour day.

So be realistic and do not over size your Inverter and do not take it to the limit.

Thank you again Sunking, I really dont think I will use that much wattage, considering its mostly for lighting, TV & Radio.
I was looking at the MPPT controllers on eBay and came across one with this setup diagram, and I was wondering can the DC output on the controller power 12v light bulbs when the system is a 24v? may be that question doesnt make sense or it answers itself but I really need to be sure whether I will need to power the bulbs off the inverter output so I can acquire AC bulbs.

[Sunking]

Thanks Sunking, I think that answers my question, now I know its smart to go 24v considering my panels wattage and that I need atleast 400Ah battery bank and a 60Amp MPPT controller...
One last question, whats the maximum size of inverter can I use in my setup, I know this will depend mostly on my load, but whats the limit for my setup?

You are welcome.

Ideally you normally do not want your Inverter to be any larger than your panel wattage using FLA batteries. That does not mean the Inverter should be as large as panel wattage. You only size the Inverter for maximum connected load that will be on at the same time. Once you figure that out and say the calculation is 800 watts, divide that by .85 and you come up with roughly 1000 watts. The reason for doing this is two fold.

1. Inverters are most efficient when running near maximum power.
2. If you recall I said batteries have minimum and maximum charge and discharge rates. For FLA batteries this limit is roughly C/8 for a true deep cycle, and some can discharge at C/6 where C = the AH capacity. So if you have say a 400 AH battery max discharge current would be 400/6 = 67 amps and at 24 volts x 67 amps = 1600 watts max inverter size so you would shop for 1500 watts or less. If everything was designed within limits, your panel wattage would also be roughly 1500 watts.

This is where AGM can be used because they can tolerate higher charge and discharge rates of C/4 to C/2 so that same 400 AH battery could power a 2400 to 4800 watt Inverter. But doing so is really going to mess with daily Watt Hours and Peukert Law. Think about that for a minute. A 24 volt 400 AH battery can only supply you with roughly 2400 watt hours per day. If you had say a 3000 watt load, Peukert Law would limit you to about 1800 watt hours or 40 minutes run time out of a 24 hour day.

So be realistic and do not over size your Inverter and do not take it to the limit.