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hi guys i need solar charge controller for 6v 4.5 ahr battery

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gunjar

New Member
hi guys ,

i need a 6volt 4.5 ahr battery
solar charge controller circuit for led based emergency lamp. can anybody please help me out of this.
 

Hero999

Banned
What's the open circuit voltage from the solar panel?

What's the output current from the panel?

A simple LM317 regulator set to 6.9V will do, as long as the panel voltage is above about 9V.
 

Hero999

Banned
This will work as long as the panel has a built-in diode and an output voltage of >9V.

This circuit will leak 266µA from the battery when it's dark so if it isn't going to be charged regularly then you'll need to add a blocking diode, increase the output voltage by0.6V and the supply voltage by 0.6V.

Vout = 6.9V
R1 = 4k7
R2 = 18k*
8572-lm317t-voltage-regulation-circuit.gif

* You might want to consider using a 15k fixed resistor plus a 5k trimmer so you can adjust the voltage to exactly 6.9V, test with a 1k dummy load.
 

Hero999

Banned
Yes, but don't forget you have a huge battery connected to the output, which can happily absorb 5mA.
 

Mr RB

Well-Known Member
But the 5-10mA does vary a little with load, AND it only goes through R2, not R1 so it messes up your voltage divider. The way they get around it is a bit clunky, they specify a max value for R1 which makes a minimum current through the voltage divider, which gives almost good enough voltage regulation... ;)
 

Ghosty_Ghoul

New Member
But the 5-10mA does vary a little with load, AND it only goes through R2, not R1 so it messes up your voltage divider.
That's not true at all, it does not mess with the voltage divider. Reducing the value of R1 reduces the current through R2 and providing the ratio of R1 to R2 remains the same it's fine.

The regulator will work properly as long as the output current is >5mA, this is the reason for the maximum resistance for R1. You can use a higher value resistor if you like, but you'll need to ensure the load draws enough current.

The problem with having high resistor values is that Iadj flows through R2 which increases the output voltage slightly and makes it less stable. If you account for Iadj in the resistor calculation, it makes it recovers some accuracy but still isn't as good.

See page 18 of the datasheet, for a circuit that uses use 1k2 for R1
https://www.electro-tech-online.com/custompdfs/2009/08/LM117-3.pdf

This is all explained earlier on in the datasheet.
 

audioguru

Well-Known Member
Most Helpful Member
The more expensive LM117 can use 240 ohms for R1 because its max operating current is 5mA. The LM317 needs a max of 120 ohms (when its Vin - Vout voltage is 40V).

The operating current flows through both resistors when there is no other load.
 

kchriste

New Member
Forum Supporter
A simple shunt regulator will work if the solar panel doesn't have the headroom for a linear regulator IC.
 

cphaworth

New Member
Can I use the LM317 to effectively boost voltage from 6.5VDC to 13-14? I have a small home-built solar panel that I'd like to use to charge a 12V battery. If so, what resistor combination would be most effective? I have looked at spec sheets, and am having difficulty deciphering the jargon.

I am new to electronics, and would appreciate any and all help.
 

Noggin

Member
Can I use the LM317 to effectively boost voltage from 6.5VDC to 13-14? I have a small home-built solar panel that I'd like to use to charge a 12V battery. If so, what resistor combination would be most effective? I have looked at spec sheets, and am having difficulty deciphering the jargon.

I am new to electronics, and would appreciate any and all help.

No, you'll need a switching power supply to boost the voltage. Check out www.national.com and use the WEBENCH Designer on their home page. It'll give you a few options that you can do. Or you can try +5v to +12v converter (but I didn't look at it enough to see if it'll work with a 6.5v input though I suspect that it will)
 

pmadithya

New Member
Hi,

I have a Solar Panel having rating
5 Watt,
V(open circuit) 21.6 Volt
I(Short circuit) 0.32 Amps
V(mp) 17.3 Volt
I(mp) 0.29 Amps
Please suggest a suitable Charge controller to charge my 6 Volts 4.5 Ah battery.
 

audioguru

Well-Known Member
Most Helpful Member
The solar panel voltage is much higher than the battery you want to charge. Then the extra voltage will cause A LOT OF HEAT!
Maybe you can use a complicated Switched Mode Power Supply to reduce the voltage from the solar panel without making much heat.

Geez. You paid exra for the extra volts on the solar panel. Then you must pay more for a circuit to reduce the volts.
Why not use a solar panel with the correct volts instead?
 

Mr RB

Well-Known Member
You could just connect the solar panel direct to the battery, it provides 0.3A which is only 0.07 C (less than 0.1C) which is usually considered safe enough for direct lead acid battery charging.

If you get heaps of sun (and are not drawing power from the battery) you could add some type of shunt drain regulator across the battery terminals to keep terminal voltage below 14v. But if the battery is powering something regularly that may not be needed.
 
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