Power supply design help

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arecssor

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hi,
i want to design a power supply which can drive an led array (30 parallel led module each module consists of 4 series led connected with 56 ohm resistor)i want to drive led panel like this , i tired to build one using 7812 and lm 317 but the 7812 is heating itself continuously so can anyone suggest me a solution for this to avoid this .
 

Stating the voltages [input and output] and current would help.

Did you use a heat-sink?
 
yes , i used a heat sink am using 24v 7 ah battery as power source (12 v 7 ah in parallel ).
also let me know if i want to regulate the power to derive normal atmega 8 from this power source how can i do that , i tried to down the 24v to 12 using 7812 then i used 7805 to down further the voltage to 5 v to drive the microcontroller , but when it is running 7812 is heating up,so it will not be a stable model i think so i need suggestion to overcome this
 


Hi
Try LM2576 based regulators which are more efficient in compare with the linear one !

Best Wishes
Goldsmith
 

arecssor said:
yes , i used a heat sink am using 24v 7 ah battery as power source (12 v 7 ah in parallel ).
Click to expand...

I think you mean...........using 24v 7 ah battery as power source (12 v 7 ah in series ).

So you get 24V from the batteries, then want to drop the voltage to 12V for the LEDs?

You never provided the current [amperage], but you are wasting a lot of power that way.
 


Power design for led lighting

hi,

am using 12v 7 ah battery to power 13 led modules used for led lighting , i want to know is it possible to power these 13 panel from this 12 v 7 ah battery using a simple resistor network or using series resistor ?

the each panel structure is as follows
4 led connected in series with a series resistor of 56 ohm , 30 modules of this type series led are paralleled to form a 120 number led network

so the total current required is 20 mA * 30 UNITS = 600 mA , 12V for one panel

let me know the most feasible professional approach to power these panels from this 12v 7 ah battery ,
i tried to use two 12v 7 ah in series to make 24v then i used a 12 v regulator to power the panels , also let me know your remarks about this method, is it a feasible method or not.
 

Curiously you are scheduling the thread anew without referring to the valuable previous answers. Did you drop your own thread?
 

thank you for your response i missed your answer,since am powering it from 24v (two 12v,7 ah in series), i have to regulate it to 12v am i right otherwise high voltage will burn the led, if i use 12v 7 ah single battery if battery drops to 10 the panel will not work since each sub module ( series of 4 led require 4 v to operate).can you provide energy efficient simple method for it?
 

You are correct about the supply voltage varying, especially for a lead-acid, battery.

Not knowing the Vf of the LEDs, I can not say if they won't work or just dim at the low voltage range.

The total current draw is 13 panels * 600mA ? 7.8A

There are high current versions of the 7812 that use external high-power transistors. Do a search.

You will still need a HUGE heat-sink.
 


You MUST define the following;
1) LED model #
2) battery type or model # or chemistry and Ah capacity.
3) charger type or V specs.
4) how long without charger and dim tolerance.

If using two std chargers in series on flooded cell then the voltage will be 28.4V
If planning to keep on charger and run off battery in case of power failure then slight dim is allowed.

Assuming not SLA I would design around 23V battery cutoff for 0% SOC and string directly off batteries and no regulator.

Untll you specify 1) Vf typ is 3.2V which will fit 7 LEDs in series + series R ~ ESR of LED

That always works for me.

Alternative is use 5 cell x3.7V LipO batteries with Laptop charger at 19V and use string of 6 with 0R directly off Lipo with float charger.
Cheap and reliable and also no hot regulators or series R. Lipo is much flatter V than lead acid. I funiversal Laptop charger is 19.5 , it may still be acceptable current or add 0.5V drop R.

The current limiting R NEVER has to be higher than that Vf of one LED( unless running horrible unregulated supply shared by other loads) and if V+ is high enough, R can be zero (0) Ohms with voltage matched to string voltage.
 

DEAR...
So you get 24V from the batteries....
You never provided the current amperage, but you are wasting a lot of power that way.
 
Last edited by a moderator:

Orson Cart said:
Really a switch mode regulator is the way to go here...
Click to expand...

A switch mode regulator is more efficient
But
really the entire approach needs to re-thought. It should be re-designed entirely with the power source in mind.
 

How can I do that , all what I want high bright led panels ,the panel construction can't be changed because it is very difficult to re assemble all led connections , the circuit can be modified, so provide me a bit st solution to run this with minimal power loss and max possible battery back possible with normal 12v 7 ah ups battery
 

The total current draw is 13 panels * 600mA = 7.8A

Is that correct?

So your 7AH battery will last less than one hour.

Is that ok?

What is the voltage across the resistor [in the LED panel]?
 

A switch-mode converter with a variable output voltage that runs from 24VDC will allow you to vary the output voltage from 10V to 14 V say to set the brightness, as it is efficient, your 2 x 7aHr 12V batts (in series to provide the 24V) will provide enough energy for nearly 2 hrs of operation.
If you recharge your batts every day they will last about 3-6 months before they seriously degrade in capacity.
 

hi thank you for your time , please let me know if i want to get back up of two weeks , how can i do that , which kind of battery will help me to do that ,
what will happen i remove the 56 ohm resistor connected in series with the each four series led in led panel,
it will help to reduce the loss but what about the safety of led panel ?


thanks in advance
 

7.8 amps x 12V = 94 watts, assuming a 90% efficient converter from 24V, the cuurent draw from a 24V battery is 4.34 amp.
4.34 amp for two weeks is 1458 ampere-hours of 24V battery, weighing approx 800kg.

for operation of 12 hrs per day only, only 700Ahr required, 400kg.
 
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