# solar charging regulators

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#### Thunderchild

##### New Member
I bought a couple of panels on ebay that are 20 watts and listed as 12 volts but they are actually 17.5, now I'm aware that i will need more than 12 volts to charge lead-acid batteries but surely 17.5 is a lot. do charging controllers work with switch mode cicuitry ? so that the voltage can be dropped and the amperage increaased a little ? or am I best just using a proper smps to do it ?

#### ericgibbs

##### Well-Known Member
I bought a couple of panels on ebay that are 20 watts and listed as 12 volts but they are actually 17.5, now I'm aware that i will need more than 12 volts to charge lead-acid batteries but surely 17.5 is a lot. do charging controllers work with switch mode cicuitry ? so that the voltage can be dropped and the amperage increaased a little ? or am I best just using a proper smps to do it ?
hi TC,
Was that the off load voltage.?
Solar panels have a highish output resistance, about 5R or so.

So at 1amp you may only get ~12.5v

You may require a reverse blocking diode if the panel is connected to a battery.

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#### Thunderchild

##### New Member
well its 21+ volts no load and on the back says 17.5 volts, if I count up the cells and calculate them all in series @ 0.5 V each (36 cells X 0.5 V) its 18 volts so thats about right

#### ericgibbs

##### Well-Known Member
well its 21+ volts no load and on the back says 17.5 volts, if I count up the cells and calculate them all in series @ 0.5 V each (36 cells X 0.5 V) its 18 volts so thats about right
You can charge SLA 12V batteries at 13.8V or 14V for cyclic use.

Have you an ebay link to panels.?

#### HarveyH42

##### Banned
A charge controller is a good investment, unless you get free batteries. A 5 amp controller cost around $20, an new 10 AH battery is around$40...

#### ericgibbs

##### Well-Known Member
Brand New 20 Watt Solar Panel on eBay, also, Solar Panels, Gadgets, Consumer Electronics (end time 14-Mar-09 15:23:40 GMT)

on the back of the panel it says 17.5 volts and 1.15 amp well I got up to 1.25 amps shor circuit and 21.5 volts open circuit
hi,
As Harvey says a charge controller is required.

Code:
Electrical Specs:
Max Power: 20WP
Open Circuit Voltage (V): 21.88 + 2
Short Circuit Current (A): 2.49 + 0.4
Max. Power voltage (V): 17.64 + 2
Max. Power Current (A): 1.135

#### nickelflippr

##### Member
Take a look at how the RV industry handles charging lead acid battery's. For instance, the Progressive Dynamics Converter/Charger. Using a 14V-14.1 is a little low for flooded lead acid type, and is usually the setpoint for gel and maybe some AGM type of batteries. Also its good if a charge controller has an equalizer cycle, if the battery's are flooded lead acid type, either manual or automatic.

Going with a lower end solar charge controller, like the Morningstar Sunsaver/Sunkeeper, are usually just an analog pwm device. The upper end controllers out there use MPPT, and are of the programmable type.

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#### Thunderchild

##### New Member
ok so do these controllers just dissipate the 17.5-12.5ish volts or convert it reducing voltage and oncreasing amps ?

#### nickelflippr

##### Member
ok so do these controllers just dissipate the 17.5-12.5ish volts or convert it reducing voltage and oncreasing amps ?
The impression I get is that you would lose some efficiency with a straight PWM controller (depending on temperature, overcast conditions, etc.). What kind of voodo electronics goes on, that makes MPPT better, haven't a clue. The MPPT thing probably just not worth the effort or expense for a small solar array?

#### Thunderchild

##### New Member
what is MPPT ?

I'm guessing that I do not need straight 17.5 volts to charge a 12 volt battery and so there being a good 25 % over voltage a decent switch mode controller will conver the 4-5 volts extra into extra current making it a bit more efficient. ok so I can't connect the battery straight to a smps as it still needs to be "charge controlled" what sort of charge controlling goes on ?

#### ericgibbs

##### Well-Known Member
what is MPPT ?

I'm guessing that I do not need straight 17.5 volts to charge a 12 volt battery and so there being a good 25 % over voltage a decent switch mode controller will conver the 4-5 volts extra into extra current making it a bit more efficient. ok so I can't connect the battery straight to a smps as it still needs to be "charge controlled" what sort of charge controlling goes on ?
hi TC,
If there isnt an internal blocking diode, then an external shottky will lose another 0.45V.
You could use a shunt reg but these are wasteful.

There maybe some decent controller designs on the web.

I would be interested on seeing your results when you have it running.

#### Thunderchild

##### New Member
well the panels came with a 10 amp standard diode (I suppose just for the sake of it) I'd prefer to used a skottky one.

If I'm to build my own I need to know the "logic" of charging batteries, I'm sure it can be done with comparators and possibly some digital logic (ok ok a pic can do the lot but my pic skills go as far as knowing the wonders they could do for me if I knew how to program them).

As for the diode well, if i was designing my own I'd be using the panel to power the SMPS first so that surely would act as a block anyway from the battery discharging into the panel. So I'd step down the voltage hopefully increasing the current by about 20 % and charge the battery via the appropriate "logic" which as far as i know is when "x" voltage is reached its charged but I'm sure i need to know more than that....

#### ericgibbs

##### Well-Known Member
well the panels came with a 10 amp standard diode (I suppose just for the sake of it) I'd prefer to used a skottky one.

If I'm to build my own I need to know the "logic" of charging batteries, I'm sure it can be done with comparators and possibly some digital logic (ok ok a pic can do the lot but my pic skills go as far as knowing the wonders they could do for me if I knew how to program them).

As for the diode well, if i was designing my own I'd be using the panel to power the SMPS first so that surely would act as a block anyway from the battery discharging into the panel. So I'd step down the voltage hopefully increasing the current by about 20 % and charge the battery via the appropriate "logic" which as far as i know is when "x" voltage is reached its charged but I'm sure i need to know more than that....
hi,
Do you need any help with a charger design, I have used 12V SLA 7AH and 20AH battery chargers on a number of projects.?

#### nickelflippr

##### Member
TC said:
What is MPPT?
I believe it is what you are trying to describe, in that excess panel to controller charge voltage is turned into increased current. Maximum Power Point Tracking Charge Controller

well the panels came with a 10 amp standard diode (I suppose just for the sake of it) I'd prefer to used a skottky one.
You are correct in thinking that a properly designed charge controller would do away with the external panel mount diode.

ecgibbs said:
hi,
Do you need any help with a charger design, I have used 12V SLA 7AH and 20AH battery chargers on a number of projects.?
Curious about a programmable type myself, and would start another thread if TC has no interest.

#### Hero999

##### Banned
The solar cells self limit the current, you could probably safely short circuit them and the current won't be high enough to do any damage.

As long as the batteries can handle the constant current then I don't see the problem. The solar panels I have connected up to my batteries give 23V each or 46V both in series when nothing is connected but the voltage drops when the batteries are connected.

If the batteries can't handle the current then you need something to limit the battery voltage. This is a problem I'm trying to solve myself, the LM317 will probably work and so will a comparator connected to a relay to disconnect the cells when the battery voltage exceeds a certain level.

#### Thunderchild

##### New Member
hi,
Do you need any help with a charger design, I have used 12V SLA 7AH and 20AH battery chargers on a number of projects.?
so what is SLA ?

basically i want to make as much use of the power availablr as possible

#### Thunderchild

##### New Member
so basically the output needs to track the baterry voltage and be just a little over than in real life applications

#### Hero999

##### Banned
so basically the output needs to track the baterry voltage and be just a little over than in real life applications
That's exactly what happens if you connect the solar panel directly to the battery. The trouble is you need to ensure the battery voltage doesn't rise above a certain point to prevent venting.

SLA, just means Sealed Lead Acid battery and means you don't have to worry about filling it with water. Most SLAs have a recombination system to react any hydrogen produced with oxygen to form water thus prolonging the life of the battery and limiting the venting of explosive gasses. The trouble is more hydrogen tends to be produced at higher voltages to it's good to limit the voltage to 2.3V per cell when float charging.

#### wombweller

##### Member
Hi all

I am following this thread with interest as I have thought about solar cells as an alternative power supply and charger.

I have a shed full of electric clocks that use very little power to make them run so I too would like to trickle charge an 12v SLA battery safely and productively.

Would the solar trickle charger stay connected all the time and if yes does this mean when I connect the load up to the battery it will take the power from both the battery and the solar panel in other words how do we separate the connection so it's only the battery that's being drained?

Is it possible to have say a bank of two batteries and use a battery swapper circuit that only trickle charges one battery at a time and when one battery is in use IE. connect to supply to my clocks it's not being charged until required? or am I over complicating things?

I found this on youtube any good?

I look forward to the outcome of this thread as like I say there must be good and bad methods to connect up the Solar charger to the batteries.

Cheers Mark

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