My Amp doubt

[marcos]

Well there is one thing I am not sure about.

I have a 24V 115W solar panel and a 5A charge controller that says its suitable for both 12V and 24V panels up to 150W.
I use 12V battery.
Here is how i think: the controller converts the voltage to 12V (ok, 15 or something, really) and charges the battery with that. I understand that converting the voltage to 12V the current should then be something close to 10Amp in order to give the totat output of 115W.
Now, the charge controller says it manages currents up to 5Amp, so does it mean that by using 12V battery I'm losing like half of the energy?
In other words: does it charge a 12V battery at 5Amp or 10Amp?

My question: Would it be more efficient in this my case to use 2x12V batteries in paraller giving a 24V total?
And if so, can I then connect my 12V loads to one of the two and alternating between the two, say I use today the first one and tomorrow the other?

I have also a theoretical question about lithium batteries. I know they are expensive, but anyway I'd like to know: Can they be conected to solar panel the way Pb batteries are?

[marcos]

correction

My question: Would it be more efficient in this my case to use 2x12V batteries in paraller giving a 24V total?

sorry, the batteries should be connected in series, of course

[RifRaf]

a 5a charger cannot charge at more than 5a, you need a bigger charger for that, so yes at 12V charging you will not use all the energy the panel could produce, unless the charger is pretty inefficient . if your charger is able to charge a 24v battery at 5a then you will utilise more output from your panel and connecting the batteries together in series would then work,though then your 115w panel would be getting too small to charge at the full 5a

[marcos]

thanks

[Sunking]

There are two types of charge controller Linear (shunt or PWM) and MPPT.

Linear controllers input current = output current. So if you have a 115 watt panel made for 24 volt battery systems, the output voltage should be 36 volts and an output current of 3.2 amps. So at the input of the controller you have 36 volts x 3.2 amps = 115 watts, and at the output roughly 12 volts at full charge current of 3.2 amps = 38 watts.

If the panel is 115 watts for 12 volt system, the input to the CC is 18 volts 6.38 amps (115 watts) and output is 12 volts @ 6.38 amps 76 watts.

With a MPPT controller the input current does not = output current as they are true DC to DC converters. With 36 volts and 3.2 amps input (115 watts) the output at full charge is 13 volts @ 8.4 amps = 109 watts.

What a deal huh?

[john p]

no one in his right mind or his left mind for that matter is going to go out and spend hundreds of dollars on a MPPT charger for one 24v 115 w panel.. and is it it a panel suitable for 24 v battery charging ?? he says its 24v ?? that aint gunna charge a 24v battery if it really does put out 24v even if he buys a box of MPPT charge controllers..

but admit a 5 a charge controller of any type for a 115 w panel if its charging 12v battery is useless. it least it shows they take more abuse than MPPT ones do....

using half a 24v system(2 x 12v ) batts in series to power something that runs on 12v is a perfect recipie for battery failure ..
the calculation done with MPPT controller is assuming it has no losses.. . yet to see that,and have seen many many of them.

[Sunking]

John you need to calm down and read what I am saying. If you have a Linear charger using a panel made for 24 volt battery systems, and using it on a 12 volt battery, you are throwing away 70% of your power. That was the point of the math exercise to demonstrate the huge losses using linear CC. Current in = Current out.

24 volt solar panels operate at 36 volts, and 12 volt panels operate at 18 volts.

[Sunking]

the calculation done with MPPT controller is assuming it has no losses.. .

115 watts input/ 109 watts output is not loss less, it is 95% efficient which is about average for MPPT controllers. The better ones are 98% efficient. Best you will ever get out of a linear CC is 70%

[john p]

sunking I think you missed the 2 main points
he says the panel is 24v I asked .. is that its real output?? if it is it wont charge 2x 12v batts in series..FACT,,,,, if it really puts out 36v then of course it coiuld be used to charge 2 x 12v batts in series
its way too expensive to use a MPPT charger on just one 115 panel.

im not calm today.. my experiment im doing for another forum is going very badly,, wasted now almost 2 work days . and $2000 worth of batteries just bought by supplies..

but my 2 points are valid on any day..

[Sunking]

John read his post. 12 volt battery as in singular battery at 12 volts. Then he ask a theory question of 2 12 volt batteries in parallel to get 24 volts. Did you catch that 2 in parallel for 24 volts.

I am assuming when he says a 24 volt panel, he means a 24 volt panel for 24 volt battery systems which is actually 36 Vmp.

Now with that said if his panel Vmp is 24 volts, he can charge a 24 volt battery with a MPPT controller, but not with a Linear controller. That is a fact.

[Mike90250]

I'll bet "marcos" the OP, has a spinning head trying to follow you two

[RifRaf]

i agree, the OP was asking about a very simple setup, sure the charger will have a fair percent of loss but why confuse the issue, what most people call a 24v panel is capable of 36v into the correct charger, and therefore the 2 batteries in series would be ok, if you read the post the charger was capable of 12 or 24v charging. the mistake about the batteries being connected in parallel was corrected in the second post minutes later!

[john p]

ok you all win in future i will assume like you have everyone that says a panel is 24 v I now know they mean 36v....
as for anything about the 2 batteries in parallel . i did read and amazingly understood it was a mistake..

[Sunking]

I'll bet "marcos" the OP, has a spinning head trying to follow you two

Mike you are right. All I was really trying to point out is using a 24 volt panel with a Linear CC, on a 12 volt battery is a huge waste.

[john p]

This is what I think is the problem. And I think its the problem that occurs many times where a person asks a question,especially if its a very small system. ie one x100w solar panel, one cheap charge controler one battery ,and he wants to power either a few lights or is just trying to find a use for what he has.
example.. he asks about upgrading one component.. then the first thing that should be asked id "how much money are you willing to spend" ?

Its silly offering and giving all the advantages of some super dooper expensive part if he only says he wants to spend a few dollars.
I could give many examples of replies on forums where the person asking one simple question never gets an answer to his question but gets an explanation of everything else under the sun and hundreds of maths figures to explain it all.So the person asking the question goes away still not knowing anything about what he asked about..

Mabe we should all read more carefully what the person is asking, note the size of his system ,then give an answer that is economically achievable. and try to find out what percentage of loss in the system he is willing to sacrifice to keep costs down.
And try to put yourself in their shoes many dont understand the maths or even understand any electrical theory.

If a person is looking to buy a new refrigerator they just looking usually at its energy rating and if its big enough for their needs.. they not wanting the salesman to give pages of information on how the compressor works and all its design paramaters