3x Solar panels - 2x Charge controllers - 1x battery

[Dodge]

Sounds like a plan. I built a small portable system with an 80watt panel and a 65Ah battery. The panel is a little small to keep the battery happy but it is portable and has worked for me when I need a little power while I fly my RC stuff.

Sold on that idea! Thats brilliant!

Just emailed the club seeing if they might be interested in it as a permanent fixture at the local field =]

[Sunking]

Ahh! Now that makes sense, I use lipo/li-ion batteries for my RC stuff, and they all need balancing as they charge!

I may keep 2 batteries in for the 240w panels, and one in for the 75w system. And use the smaller for things like lights etc and the bigger for powering the bigger things,

OK so you are a RC Toy Man like myself. I fly 3D planes. So you have some understanding of Amp Hours and C-Rates. Unlike LiPo batteries where RC guys talk about 20C, 30C Discharge rates, and 1C up to 5C charge rates, Pb batteries cannot do that. Instead C-Rates are expressed at opposite much slower rates like C/8, C/10, C/20. Pb batteries require at least a C/12 charge, and cannot be charge real fast and generally speaking no faster than C/8. There are some exceptions, like golf cart batteries that can be charged faster up to C/4. The upper limit has more to do with gassing and boiling over. Not good.

Fortunately solar lends itself well to Solar application because if you use recommended practices charge rate falls C/12 to C/8. The ideal charge rate is C/10. Ok where this is leading is if you have a 200 AH battery, ideally you want to charge it at 20 amps, Well if that is a 12 volt battery using a MPPT Controller requires 250 watts of solar panels give or take 50 watts. So as you can see panel wattage and battery are matched to work with each other. If you have a 240 watt panel your battery AH capacity is limited to the C/8 C/12 boundary.

MPPT CHARGE CURRENT = PANEL WATTAGE / BATTERY VOLTAGE.

240 watts / 12 volts = 20 amps.

So at C/8 the smallest battery you can use is 8 Hours x 20 amps = 160 AH.
At C/12, the largest is 12 hours x 20 amps = 240 AH.
Ideal size is 10 Hours x 20 Amp = 200 AH

So a pair of 225 AH 6-volt golf cart batteries is a good match for a 240 watt panel.

Now your turn. What size for the 75 watt panel?

[littleharbor]

If you need 420+ Ah of capacity then using 6 volt 220 Ah. golf cart batteries would only be 2 strings, which is more manageable. Better yet would be a pair of L-16 batteries.

[SunEagle]

Ahh! Now that makes sense, I use lipo/li-ion batteries for my RC stuff, and they all need balancing as they charge!

I may keep 2 batteries in for the 240w panels, and one in for the 75w system. And use the smaller for things like lights etc and the bigger for powering the bigger things,

Sounds like a plan. I built a small portable system with an 80watt panel and a 65Ah battery. The panel is a little small to keep the battery happy but it is portable and has worked for me when I need a little power while I fly my RC stuff.

[Dodge]

Wiring batteries in parallel increases the chance of unequal charging and discharging due to different resistant paths in the circuit. What that does is make some of the batteries work harder and die quicker so soon all of your batteries die an early death.

Ahh! Now that makes sense, I use lipo/li-ion batteries for my RC stuff, and they all need balancing as they charge!

I may keep 2 batteries in for the 240w panels, and one in for the 75w system. And use the smaller for things like lights etc and the bigger for powering the bigger things,

[Dodge]

With a 420Ah battery system you need approximately 42amps of charging. That requires an MPPT type charger rated 45amps and about 500 watts of panels (12v x 42A = 504w).

So you will need to more than double that 240 watts you currently have as well as get a true quality MPPT type charger rated at least 45amps.

Your other choice would be disconnect 2 of those 105Ah batteries and only have a 210Ah 12volt system. That will match up to your CC and panel wattage. It will also get you out of the danger of having more than 2 batteries wired in parallel.

Ah ok, so whoever had it last just over compensated on the batteries

Cheers for the information,

[SunEagle]

How come it becomes a can of worms?

Sorry for all the questions, and i appreciate the answers, im not too shabby on electronics in some regards, but this is all quite new to me,

Wiring batteries in parallel increases the chance of unequal charging and discharging due to different resistant paths in the circuit. What that does is make some of the batteries work harder and die quicker so soon all of your batteries die an early death.

[SunEagle]

Sounds good! I think I will just get rid of the 75w setup for now. Saves messing about!

They are wired to make a 12v 420ah system. which solar panels would be ideal for this?
I dont spend every day in the van, so it might not get used for a day or two,

With a 420Ah battery system you need approximately 42amps of charging. That requires an MPPT type charger rated 45amps and about 500 watts of panels (12v x 42A = 504w).

So you will need to more than double that 240 watts you currently have as well as get a true quality MPPT type charger rated at least 45amps.

Your other choice would be disconnect 2 of those 105Ah batteries and only have a 210Ah 12volt system. That will match up to your CC and panel wattage. It will also get you out of the danger of having more than 2 batteries wired in parallel.

[Dodge]

My bad. I thought I read T-105 which is a 6 volt, 225 Ah battery, Your 105 Ah batteries are 12 volt aren't they? If so, and all four are paralleled 420 Ah. Four 12 volt batteries in a parallel configuration is another can of worms that could be done better with 6 volt batteries.

How come it becomes a can of worms?

Sorry for all the questions, and i appreciate the answers, im not too shabby on electronics in some regards, but this is all quite new to me,

[Dodge]

Sounds good! I think I will just get rid of the 75w setup for now. Saves messing about!

They are wired to make a 12v 420ah system. which solar panels would be ideal for this?
I dont spend every day in the van, so it might not get used for a day or two,

[littleharbor]

You can use two charge controllers on a single battery bank. Each controller should be connected directly to the battery though. What model charge controllers are you using? I'm assuming you are set up as a 12 volt system from your description. That being said you are way under paneled for that size battery @ 450 amp hours you would want no less than 25 amps and preferably 40 45 amps to properly charge that size bank. You have less than 15 amps.

My bad. I thought I read T-105 which is a 6 volt, 225 Ah battery, Your 105 Ah batteries are 12 volt aren't they? If so, and all four are paralleled 420 Ah. Four 12 volt batteries in a parallel configuration is another can of worms that could be done better with 6 volt batteries.

[SunEagle]

I also doubt that the 10A CC is really an MPPT type. I would not trust a product just because it may be labeled something when it really is not. Especially if it costs very little. That is a basic bate ans switch action to get people to purchase a product.

I would also not use the 75w panel on the same battery system even with a quality MPPT CC. There is always a chance of the two CC's fighting each other to charge the same battery with different charging amps.

I would use that 75w for a small portable system that can be dragged around to places that have not power. Just make sure you size the battery so it's Ah rating is no more than 10 x the Imp rating of that 75w panel.

Also please clarify what your battery system is rated. I know you have 4 x 105Ah but are they 6v wired to make a 12v 210Ah system or 12v wired to make a 12v 420Ah system. If it is the second then you do not have enough panel wattage or a big enough charge controller to keep them happy.

[littleharbor]

What is the max Voc. for your controllers?

[Dodge]

You can use two charge controllers on a single battery bank. Each controller should be connected directly to the battery though. What model charge controllers are you using? I'm assuming you are set up as a 12 volt system from your description. That being said you are way under paneled for that size battery @ 450 amp hours you would want no less than 25 amps and preferably 40 45 amps to properly charge that size bank. You have less than 15 amps.

Ah ok,
They are MPPT, but not sure on the brand, I will have to check,

Cheers for the info, might get rid of the 120's and get something bigger on,

[littleharbor]

You can use two charge controllers on a single battery bank. Each controller should be connected directly to the battery though. What model charge controllers are you using? I'm assuming you are set up as a 12 volt system from your description. That being said you are way under paneled for that size battery @ 450 amp hours you would want no less than 25 amps and preferably 40 45 amps to properly charge that size bank. You have less than 15 amps.