First Solar System - Questions about Charge Controller Amps?

[OffGridMikey]

I have a 200W PV with a 30 amp PWM charge controller. Currently I'm only planning DC lighting and other DC loads for a small 150ft hunting cabin which has limited use about 2-4 days every 2 months. If all the planned loads are turned on simultaneously the current draw is 15-18 amps @ 12vDC but I'm already thinking of future electrical additions. So here are my questions?

1) Does this 30 amps apply to just charging or both charging and supplying the load side?

If I ever need AC I may add a DC-AC inverter to the setup but I know these can draw a lot of 12V DC current leading to question 2...
2) Could I have a separate switched and/or fused circuit running off the battery bank directly to the inverter if the amp draw is > 30 amps?

Here is a link to my 30amp Charge Controller. Since I'm an ME and not an EE the diagram below confuses me a bit about if the 30 amp applies to current in from the PV as well as Battery current out or if current out is just passed through and it's my job to fuse it on the other side.

System-diagram.jpg

Thanks in advance for any help!



Thanks in advance,

[OffGridMikey]

Talked to the supplier

Ok,

I talked with the supplier and the technician mentioned that it would support more than 30amps on the load side but I'm still not 100% because I've got no idea on how well the internal circuitry would handle more than 30 amps.

If I had a 600 watt 12DC-120AC inverter calculations show actual DC current draw would be 55.6amps if I had around a 5 amp load on the AC side. Not that I would but want to make sure If I added a 600 watt inverter I wouldn't risk burning up the charge controller.

So building off question 2 above would I just need a better/bigger charge controller or is it OK to create a second circuit directly off the battery for the inverter and fuse / breaker the load to make sure it's ok?

Again and help for this 'knuckle dragger' would be great...

[Sunking]

Ok first off a 200 watt panel operating through a PWM controller at most can only supply about 10 to 11 amps of current to either the battery, load, or split between both load and battery. A 30 amp PWM controller just means it can handle up to 30 amps from the panels. The panel supply the current. All the controller does is either connect the panels to the batteries or disconnects the panels to the batteries and nothing more.

I see your controller has a load terminal. In short it is useless and only made for very small loads. More than likely only about 5 to 10 amps max if even that much. All it is there ifor is a fused terminal with a Low Voltage Diconeect relay in the even the battery voltage drops below a specified point. You do not use the Load Terminal to connect the batteries or an inverter. For the most part are never used.

Back to the controller output. It is connected directly to the batteries. The only current flowing through the controller is that from the panels and nothing else. How much current and when depends on what is going on.

Assuming the batteries are fully charged and no load devices are turned on demanding power, no current is flowing even if it is noon with bright sun light. Batteries are like a glass filled with water, when full you cannot put in any more water so the controller turns off and sits there.

If the batteries are discharged, and the sun is out, the controller turns on and connects the panels to the batteries. How much current actually flows depends on ho wmuch panel wattage you have, how much sunlight there is, and what state of charge the battery is in. If th ebatteries are in a low state the controller turns on full an dgives th ebatteries all the current the panels can generate at the time. A 200 watt panel at solar noon on a very bright day around 10 amps at best or around 120 watts from a 200 watt panel. Interesting huh only 120 watts from a 200 watt panel huh?

If say it is solar noon on a bright day, the batteries are in a discharged state and say you have a load demanding 20 amps, the panels can only supply 10 amps through the controller and the rest is comming from the batteries and being discharged at a 10 amp rate.

Replace that 30 amp PWM controller with MPPT and your panels can now deliver up to 17 amps. Interesting huh? Who would ever think you can get 200 watts from a 200 watt panel? Never going to happen with a PWM controller. With PWM it takes 300 watts of panels to make the same power with a 200 watt panel with MPPT. Bet you wished you had known that before you bought anything. It would have saved you money and get you more power.

[OffGridMikey]

Your Reply

I see your controller has a load terminal. In short it is useless and only made for very small loads. More than likely only about 5 to 10 amps max if even that much. All it is there ifor is a fused terminal with a Low Voltage Diconeect relay in the even the battery voltage drops below a specified point. You do not use the Load Terminal to connect the batteries or an inverter. For the most part are never used.

Below is the wiring drawing that I sketched out. Nothing is actually wired yet but if I understand what you say the load terminal is nothing more than a LVD relay between the battery and the actual load side. Should I change my wiring to tap off of a bus bar above my battery disconnect switch?
Solar Cabin - Current.jpg

Bet you wished you had known that before you bought anything. It would have saved you money and get you more power.

That PWM is only $30 from the supplier so I don't feel as if I'm out much and I could use it for another small application outside of the cabin. I'll take your advice and get the MPPT controller and I'm still in the process of selecting my batteries so it's not as if I've bought the whole farm. This cabin is only used 2-4 days in a row every 2 months or so and I've purchased all low power DC LED lighting and power efficient DC accessories. Figuring each day I just need a charge controller that can top off the battery from the night before, now I just need to select the right AH deep cycle battery. Based on my application do you have any recommendation on brand of MPPT and or source for batteries?

Also being away for over 1-2 months with any loads disconnected how will this affect battery life. I'm considering led-acid filled ones because cost, I'm comfortable maintaining them and they would be in a plastic case outside the small cabin. When I say small I mean like 15' x 10' with no more than 15-20 amps of maximum draw if everything was on at one time. Sure I'd like to have a DC-AC converter to run a decent laptop off the power supply so I want to make sure I have some room to expand. Solar makes sense because the power company wants 5K to run polls and a line out to the property and with power on the property it would change the tax base about another 1K / year. If I invest 1-2K in a solar system and spend 200-400 dollars on batteries every 3 years I feel I come out ahead. Even adding more 100W panels is about $170/panel for the same brand is why I didn't hesitate to get a kit to play around with.

[Sunking]

Below is the wiring drawing that I sketched out. Nothing is actually wired yet but if I understand what you say the load terminal is nothing more than a LVD relay between the battery and the actual load side. Should I change my wiring to tap off of a bus bar above my battery disconnect switch?

Your assessment is correct the load terminal is nothing more than a relay and a small fuse to power small loads.

Battery loads get connected directly from the battery term post of battery buss bar through a over current protection device

That PWM is only $30 from the supplier so I don't feel as if I'm out much and I could use it for another small application outside of the cabin. I'll take your advice and get the MPPT controller and I'm still in the process of selecting my batteries so it's not as if I've bought the whole farm. This cabin is only used 2-4 days in a row every 2 months or so and I've purchased all low power DC LED lighting and power efficient DC accessories. Figuring each day I just need a charge controller that can top off the battery from the night before, now I just need to select the right AH deep cycle battery. Based on my application do you have any recommendation on brand of MPPT and or source for batteries?

If you go with a MPPT controller wire the two panels in series vs parallel right now as shown in your diagram.

As for battery size depends on what you do with the controllers of leaving it PWM or go with MPPT. Assuming you go with a Flooded Lead Acid battery which is the best choice limits the size vs charge current. FLA should have no less than a C/12 charge current or no greater than C/8. So if you keep the PWM controller with 200 watt panels then the smallest 12 volt battery is 8 x 10 amps = 80 AH, or the largest is 12 x 10 amps = 120 AH.

Change to a MPPT and the charge current jumps up to about 16 amps so you can support a larger battery of 128 to 192 AH.

If it were me I would choose 120 AH as it will work with either a PWM or MPPT. Depends on what you want out of it. As women will say bigger is better.

For a MPPT controller with 200 watt panels a excellent choice is Morning Star Sunsave MPPT 15 amp controller. Only down side with 15 amps it is maxed out at 200 watts with a 12 volt battery, and 400 watts with 24 volt battery.

For batteries in the 80 to 200 AH range there is quite a few options. Depends on what kind of quality and how high a cycle life you want out of them. At 12 volt 120 AH capacity you are looking for BCI Group 27 or 31 something like a Trojan 27THM or Concorde PVX-1180T. What you want to look for is the 20 hour capacity.

Also being away for over 1-2 months with any loads disconnected how will this affect battery life. I'm considering led-acid filled ones because cost, I'm comfortable maintaining them and they would be in a plastic case outside the small cabin.

No problem just turn off all loads and disable any automatic Equalize feature if the charge controller has an EQ setting. The batteries will just sit there being float charged each day. Just make sure the water levels are good if you use flooded, and no worries if AGM. Once batteries are fully charged they hardly draw any power, thus no gassing to worry. Gassing is not going to be a problem in a 10 x 15 cabin with such a small battery. No more danger than you blowing yourself up with a good long fart after drinking bear. Might smell bad, but no danger of blowing up. Well unless you hold a lit match up to your butt when you fart or directly above batteries while they are bubbling. Trust me it can be done. Did it one time and one time only in college as a dare. I won twice. I won the cash bet I would not do it, and I won again because I did not have to shave my butt or family jewels for a month.

[SunEagle]

Your assessment is correct the load terminal is nothing more than a relay and a small fuse to power small loads.

Battery loads get connected directly from the battery term post of battery buss bar through a over current protection device








If you go with a MPPT controller wire the two panels in series vs parallel right now as shown in your diagram.

As for battery size depends on what you do with the controllers of leaving it PWM or go with MPPT. Assuming you go with a Flooded Lead Acid battery which is the best choice limits the size vs charge current. FLA should have no less than a C/12 charge current or no greater than C/8. So if you keep the PWM controller with 200 watt panels then the smallest 12 volt battery is 8 x 10 amps = 80 AH, or the largest is 12 x 10 amps = 120 AH.

Change to a MPPT and the charge current jumps up to about 16 amps so you can support a larger battery of 128 to 192 AH.

If it were me I would choose 120 AH as it will work with either a PWM or MPPT. Depends on what you want out of it. As women will say bigger is better.

For a MPPT controller with 200 watt panels a excellent choice is Morning Star Sunsave MPPT 15 amp controller. Only down side with 15 amps it is maxed out at 200 watts with a 12 volt battery, and 400 watts with 24 volt battery.

For batteries in the 80 to 200 AH range there is quite a few options. Depends on what kind of quality and how high a cycle life you want out of them. At 12 volt 120 AH capacity you are looking for BCI Group 27 or 31 something like a Trojan 27THM or Concorde PVX-1180T. What you want to look for is the 20 hour capacity.

No problem just turn off all loads and disable any automatic Equalize feature if the charge controller has an EQ setting. The batteries will just sit there being float charged each day. Just make sure the water levels are good if you use flooded, and no worries if AGM. Once batteries are fully charged they hardly draw any power, thus no gassing to worry. Gassing is not going to be a problem in a 10 x 15 cabin with such a small battery. No more danger than you blowing yourself up with a good long fart after drinking bear. Might smell bad, but no danger of blowing up. Well unless you hold a lit match up to your butt when you fart or directly above batteries while they are bubbling. Trust me it can be done. Did it one time and one time only in college as a dare. I won twice. I won the cash bet I would not do it, and I won again because I did not have to shave my butt or family jewels for a month.

Wow. That brought a picture in my head that will never go away. I appreciate your candor and graphic description. NOT.

[OffGridMikey]

Series / Parallel & Batteries

If you go with a MPPT controller wire the two panels in series vs parallel right now as shown in your diagram.

As for battery size depends on what you do with the controllers of leaving it PWM or go with MPPT. Assuming you go with a Flooded Lead Acid battery which is the best choice limits the size vs charge current. FLA should have no less than a C/12 charge current or no greater than C/8. So if you keep the PWM controller with 200 watt panels then the smallest 12 volt battery is 8 x 10 amps = 80 AH, or the largest is 12 x 10 amps = 120 AH.

Change to a MPPT and the charge current jumps up to about 16 amps so you can support a larger battery of 128 to 192 AH.

If it were me I would choose 120 AH as it will work with either a PWM or MPPT. Depends on what you want out of it. As women will say bigger is better.

For a MPPT controller with 200 watt panels a excellent choice is Morning Star Sunsaver MPPT 15 amp controller. Only down side with 15 amps it is maxed out at 200 watts with a 12 volt battery, and 400 watts with 24 volt battery.

Going with MPPT. So wiring the two 100W panels in series will give me 100W @ 24V correct? Then the MPPT handles the voltage and power change down to 12V? Either way I should have room to add 2 more 100W panels (for a total of 4) if I go with the 15 amp MPPT.

Now onto the battery, my original plan was to grab 2 of these Marathon Batteries (92AH) which were listed under deep cycle / electrical applications. Costco had some 110AH deep cycle batteries right at $120 but I'm skeptical on those.

My planned battery setup was two in parallel as my drawing showed i would have had 184AH @ 12V going with the Marathons. To your point about charge rates through the PWM, it would not support this configuration unless I used a single battery correct?

Concerning gases my buddy is absolutely the worst so I may just install a 12v propane igniter at the end of the spare bunk he sleeps in... Good thing I already have proper ventilation in the old cabin...

[Sunking]

Going with MPPT. So wiring the two 100W panels in series will give me 100W @ 24V correct? Then the MPPT handles the voltage and power change down to 12V? Either way I should have room to add 2 more 100W panels (for a total of 4) if I go with the 15 amp MPPT.

With a 15 amp MPPT charge controller operating @ 12 volt battery the maximum input is 200 watts period. If you elect someday to go to 24 volt battery then you can go up to 400 watts panel power.

Now onto the battery, my original plan was to grab 2 of these Marathon Batteries (92AH) which were listed under deep cycle / electrical applications. Costco had some 110AH deep cycle batteries right at $120 but I'm skeptical on those.

My planned battery setup was two in parallel as my drawing showed i would have had 184AH @ 12V going with the Marathons. To your point about charge rates through the PWM, it would not support this configuration unless I used a single battery correct?

Avoid parallel batteries, more trouble than it is worth. If you want 200 AH @ 12 volts then you buy two 200 AH 6 volt batteries and wire them in series for 12 volts. Sams, Walmart, Costco (actually they do not make them Interstate Battery makes them) all make Golf Cart 6 volt batteries and they will be around 200 AH. Personally I would spend the extra cash for Trojan T-105 or T-105 RE as they will last quite a bit longer than the Interstate Flavor. .

[OffGridMikey]

Ok Got It

Got it on the panels & battery configuration with that MPPT controller.

200W should be fine because in my application I'm not looking for the panels to do more than charge the battery bank during the daytime. FLA @ 12V 180AH I'd be right there at the 15 amp minimum charging rate c/12.

Since it's a hunting cabin daytime amp draw might be ~4amps with two guys charging phones/iPads. Night time amp draw could be as high as 11-16 amps from like 7pm - 12 pm with all lights on and a 3 amp DC TV. The longest we are out there in a row is 4-5 days max and typically a 2.5 day trip is standard. I held off on the batteries to make sure I got something that could handle 2.5 days with little sun etc.. when I'm not out there the batteries will float charge with no loads on them.

Is there a method you prefer to size batteries and take into account actual usage? Since I'm not doing my home where loads would be more consistent and the actual use is sporadic I want to make sure I'm looking at the right size/type of batteries.

[Sunking]

For this I would recommend for each watt of solar panel 1 AH of battery capacity at 12 volts. A bit of overkill but worry free. It will allow you and your buds to stay up drinking beer and telling lies (hunting and fishing stories) until you pass out. A decent pair of golf cart batteries will cost around $300. Golf cart means 6 volt 200 AH @ $150 each or less.

[OffGridMikey]

Perfect Thanks

For this I would recommend for each watt of solar panel 1 AH of battery capacity at 12 volts. A bit of overkill but worry free. It will allow you and your buds to stay up drinking beer and telling lies (hunting and fishing stories) until you pass out. A decent pair of golf cart batteries will cost around $300. Golf cart means 6 volt 200 AH @ $150 each or less.

Thanks for the help man, I'll do just that.

[Sunking]

You are welcome partner. One caveat; assuming MPPT controller. Georgia Solar Insolation is decent assuming you are not in deep woods with shade issues. Does Georgia have trees?

If memory serves me correctly when I play golf there I am always in the trees. Augusta National was a Son of a BIIIIITCH the one time I got to play it.

[OffGridMikey]

Yea Right

You are welcome partner. One caveat; assuming MPPT controller. Georgia Solar Insolation is decent assuming you are not in deep woods with shade issues. Does Georgia have trees?

If memory serves me correctly when I play golf there I am always in the trees. Augusta National was a Son of a BIIIIITCH the one time I got to play it.

Dude if you played Augusta National then you are one lucky fellow...

No real shade issues at the cabin other than clear area is sunrise to 2pm and from there I'll probably have to move 20ft to catch the afternoon sun. Land was some old paper company land. We've re-planted most of it, have about 8 food plots on 330 acres and the camp site has 3 cabins. We've been rustic for 10 years with just a camp fire and covered BBQ area but I'm bringing power now.

BTW I picked up the 2x T-105's for $119 from Batteries+ since they had them in stock. With the core charge and taxes it ran me about $280 so I'm pretty happy with that. Probably do the install weekend after next.

[Naptown]

There is a course near me where they have recreated the most famous holes in golf. The turn at Agusta national (including the leaderboard)
The one in the lake at Sawgrass and others.
I've heard it is a tough course to play.

[Sunking]

There is a course near me where they have recreated the most famous holes in golf. The turn at Agusta national (including the leaderboard)
The one in the lake at Sawgrass and others.
I've heard it is a tough course to play.

Bet that course is called Tour 18? It is a Chain course. We have two of them in TX.