adding new panels

[ula]

Hello This is my first post. I have put together a small off grid 12 v system. It consist of 4 100w panels and a 40 amp mppt charge controller. I have 4 batteries in parallel. I would like more power and thought adding 2 more 100w panels would do it. It seems that I would also have to upgrade my charge controller but cant really afford to do that at the moment. My one thought was to put the 2 new panels on my old pwm charge controller and connect that to the batteries.... kinda like 2 separate mini systems going to the same batteries.....probably not possible but wondering if there are any ideas out there that can get me around having to spend the money on upgrading my charge controller.....

[Mike90250]

Virtual Tracking Array :
aim some panels east, some south, some west. The ones with the best sun produce the most amps, so you get lower peak amps, but more consistent amps through the day

[SunEagle]

It would be nice to know the rating of your batteries and panels along with the make and model of your 40amp MPPT CC.

I am not saying you don't need more panels but knowing what your existing system is comprised of may help us understand how you can grow it or improve it.

[Logan5]

If you want more power upgrade your voltage, 24 volts is good, 48 volts is even better. As long as you are stuck inside the 12 volt box you will want for more power no mater how much money you spend.

[ula]

I have 4 6v Duracell sligc125 batteries 235ah at 20 hour rate. the cc is renogy 40amp mppt tracer and the panels are 100w windy nation panels.

[SunEagle]

OK. You currently have a 12v 470Ah battery system, 400 watts of panel and a 40A MPPT CC.

The 400 watts will get you about 33 amp of charging (400w / 12v = 33.3a) using that CC. Which is around a C/14 for the batteries (470 / 33 = 14.2). That is a little low and not enough to properly charge them.

You should charge between C/12 and C/8 where C = Ah of the battery system. So you need between 40 and 59 amps which requires about 500 to 720 watts of panels and a 45 to 60 amp MPPT charge controller for a single system.

[ula]

Thanks Suneagle. so basically I have too much battery for my current system. Would it be more cost effective to upgrade to a 24v system? Would I need to get a new inverter? I'm just trying to figure out the least expensive way to get my batteries charging all the way. Thanks for your time!

[SunEagle]

Thanks Suneagle. so basically I have too much battery for my current system. Would it be more cost effective to upgrade to a 24v system? Would I need to get a new inverter? I'm just trying to figure out the least expensive way to get my batteries charging all the way. Thanks for your time!

Well going to 24 volt battery system might help you in one place but you still may need more panel wattage. With that same 400 watts charging 24 volt battery you get about (400w / 24v = 16.6A)

But your battery system is now a 24v 235Ah, so 235Ah / 16.6A = 14.1. You still have too little amount of charging. You now need between 20 to 30 charging amps which is about 500 - 700 watts of panels. At least you don't have to upgrade to a bigger charge controller from that 40A tracer.

Oh. And you will need a new 24volt inverter.

[Logan5]

If you are concerned with the batteries SOC, get them on an AC powered smart charger right away.

[ula]

ok so if I do 24v system with 2 more 100w panels and a Solinba 1200w Pure Sine Wave Off Grid Power Inverter DC24v to AC110v 60Hz , I should be good? I guess it would not be acceptable to get a 24 to 12v converter for my current inverter? And we also have our lights running off the cc load at 12v. How would I deal with that?

[SunEagle]

ok so if I do 24v system with 2 more 100w panels and a Solinba 1200w Pure Sine Wave Off Grid Power Inverter DC24v to AC110v 60Hz , I should be good? I guess it would not be acceptable to get a 24 to 12v converter for my current inverter? And we also have our lights running off the cc load at 12v. How would I deal with that?

There may be other ways to safely (and have less losses) converting 24v to 12v for existing loads.

What you do not want to do is just tap your battery system directly to generate 12volt. That would cause an unbalanced load on the 24volt system.

[Logan5]

You would use a step down converter. they are inexpensive and a straight forward install. I have installed 24 to 12 units in RV, s to maintain the original 12v gear. A lil more complicated but well worth it.

[cabindave]

ULA, what model renogy charge controller do you have? You should check the manual. Most of the 40 amp MPPTs were rebranded Tracers. If it is the model I am thinking of, it will automatically switch to 24 volt if attached to a 24v battery bank (check the manual though), then you connect the panels second. You shouldn't have to upgrade the charge controller. It should handle up to 800 watts with a 24 volt bank.

You are correct that you cannot run a converter before an inverter. Even if you could it would be cheaper and more efficient to buy a new inverter. The lighting can easily be handled by a converter provided it is not over a certain wattage. I use the Pyle brand 700 watt 24-12 converter. Works well.