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

[Mike90250]

SLI's can take rapid discharge (cranking the engine over) and rapid recharge (80A alternator spinning up) BUT they cannot withstand deep cycles more than 10% depth, or they start to degrade quickly.

[J.P.M.]

Sunking - you say SLI's can do 1C?
Would that be the type you recommended as the best compromise for solar over expensive agms and high internal resistance deep cyclers?
The range of charge c/8 to c/12 : is that for deep cyclers only or SLI's too?
And when I get my capacity figure by multiplying that denominator (ie. 8 in c/8) by my sustained panel output amps,
what rating will that refer to in regards identifying the correct battery - C20, C100 or what?
Thanks

It seems that SunKing is either incommunicado as of late or no longer among us.

[Soundhound]

Sunking - you say SLI's can do 1C?
Would that be the type you recommended as the best compromise for solar over expensive agms and high internal resistance deep cyclers?
The range of charge c/8 to c/12 : is that for deep cyclers only or SLI's too?
And when I get my capacity figure by multiplying that denominator (ie. 8 in c/8) by my sustained panel output amps,
what rating will that refer to in regards identifying the correct battery - C20, C100 or what?
Thanks

[SunEagle]

OK last one I promise haha

How would it work to install a switch that chance from one set of 2x batts to, another set of 2x batts,
So that the solar would charge set 1, then once fully charged, switch it over so they would then charge set 2 (And would also switch the load)
Just another idea that popped up...

Seems like a lot of complexity (and cost) to charge 2 sets of batteries and run your loads. Remember you will have limited sunlight so while the first set of batteries can get charged your second set will probably not see enough to get back up to 100% SOC.

You may want to research something like little harbor has listed. I do not have any experience with those CC's but they may have the "brain power" to charge each set of batteries one at a time.

From what I remember of your earlier posts If you try to charge all of the batteries at the same time you will need more panel wattage.

[littleharbor]

You can buy controllers that will charge two banks of batteries. Morningstar Sunsaver Duo.jpg

[Dodge]

OK last one I promise haha

How would it work to install a switch that chance from one set of 2x batts to, another set of 2x batts,
So that the solar would charge set 1, then once fully charged, switch it over so they would then charge set 2 (And would also switch the load)
Just another idea that popped up...

[Dodge]

Remember that a balanced system should produce between 1/8th and 1/12th the Ah battery rating for charging. Adding more batteries may work for a short time but then you increase the chance of killing off all of the batteries due to limited or slow charging from too little amps.

That is one of the problems we hear from a lot of people. Their system works just find for a few months and then their batteries can no longer hold the original charge because the plates have been sulfated due to lack of charging amps. Try to keep in mind the long term plan to extend your batteries to their full life instead of a short term plan that will cost you a lot more money.

Ah Ok, thanks again,
Ill leave the system as it is for now, nice seeing full charge on the batteries anyway =]

[SunEagle]

So since removing the other panel, charge controller and 2x batteries, ive noticed my charge controller is now flashing green (meaning batteries are at max charge,
Would it be worth lobbing another battery on or should I keep it as the 2?

Remember that a balanced system should produce between 1/8th and 1/12th the Ah battery rating for charging. Adding more batteries may work for a short time but then you increase the chance of killing off all of the batteries due to limited or slow charging from too little amps.

That is one of the problems we hear from a lot of people. Their system works just find for a few months and then their batteries can no longer hold the original charge because the plates have been sulfated due to lack of charging amps. Try to keep in mind the long term plan to extend your batteries to their full life instead of a short term plan that will cost you a lot more money.

[Dodge]

So since removing the other panel, charge controller and 2x batteries, ive noticed my charge controller is now flashing green (meaning batteries are at max charge,
Would it be worth lobbing another battery on or should I keep it as the 2?

[SunEagle]

I've always been a massive fan of Solar, and the fact you can get electric from the Sun, and not some big company.
So I really appreciate the time you have all taken to reply to my very noobish questions, and have helped me understand how these systems are calculated =D

Glad we could help.

I have had been involved with solar since the mids 70's. I am glad it has finally made some headway as one possible energy sources. But I have also been in the electrical power industry for over 40 years and know that RE is just not enough to keep the lights on 24/7. We still need nuclear or fossil fuel powered generation. But I do enjoy solar technology.

[Sunking]

75watt panel / 12v = 6.25
@ C/10 = 10 hours at 6.25 amps = 62.5
So an example from a quick search on Google is the Bosch L5.

And just to clarify, 10C 1300mah Lipo, in theory could be charged at 13 amps
However with a 60ah Pb, at C/10, can only be charged at 6 amps?

Yes Sir anywhere from 5 to 8 amps. How fast is determined by you Sun Hours. Like I said earlier generic charge rates are C/8 to C/12. However there are exceptions. A SLI battery made to crank engines can charge discharge at 1C, hybrids like a golf cart battery C/4 to C/5, and AGM's as fast as C/2. Having said that charging fast does not mean it is the best practice for any battery. Same true for LiPo's, charging fast generates heat, and that is not good for batteries.

FWIW LiPo batteries we use are heavily abused. Discharge rates are taken to extreme levels of 6 watts per AH/cell. If you did that to a Pb battery would be a disaster and a melt down. Not even EV batteries are called to discharge at 20 to 30C. Take that 12 volt 60 AH battery and apply a 6 watt/AH/Cell discharge to it and you are talking hitting that battery with 6 watts x 60 AH x 6 cells = 2160 watts. That is enough to melt the lead plates inside.

[Sunking]

I've always been a massive fan of Solar, and the fact you can get electric from the Sun, and not some big company.
So I really appreciate the time you have all taken to reply to my very noobish questions, and have helped me understand how these systems are calculated =D

Just one little problem. Anything you take off grid is going to cost you 5 to 10 times more then that big ole company the rest of your life. Instead of your money going to the electric company, a lot more of it is going to the battery company. So be careful what you ask for because you just might get what you want.

[Dodge]

I've always been a massive fan of Solar, and the fact you can get electric from the Sun, and not some big company.
So I really appreciate the time you have all taken to reply to my very noobish questions, and have helped me understand how these systems are calculated =D

[Dodge]

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?

75watt panel / 12v = 6.25
@ C/10 = 10 hours at 6.25 amps = 62.5
So an example from a quick search on Google is the Bosch L5.

And just to clarify, 10C 1300mah Lipo, in theory could be charged at 13 amps
However with a 60ah Pb, at C/10, can only be charged at 6 amps?

[Dodge]

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.

Honestly, I havent even worked out what I need yet,
My new laptop is arriving today and that will be the main thing, however will be working out requirements for each component during the rebuild. Which has now turned into a bigger headache than if i just left it haha