Go Down

Topic: Converting 5v to 12v using an LM2577 - all i get is 4.8v? (Read 7 times) previous topic - next topic

dc42

If you are switching the door strike, the current will presumably drop to 0 when it is off?

Do you really need to run the whole thing from 5v? Why not run it from a 12v supply instead and derive the 5v for the Arduino from the 12v? My guess is that the voltage to the door strike is not very critical and doesn't need to be regulated.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

idiotjohn

Right yes you make a good point.

The issue is I'm trying to make it solar powered, and powered by AA batteries (trying to avoid a huge lead acid battery).

I have worked out (page 18) the maximum value for Rc is (750 x 0.21 x 12^2) / 4^2 = 1417.5 Ohms, so the 1k should be right?

ill continue trying to figure this stuff out.

John

idiotjohn

okay so heres what ive got -

Rc <= (750 x 0.21 x 12^2) / 4^2
    <= 1417.5 Ohms (so I will use a 1k)

Cout is the greater of these two equations

Cout >= (0.19 x 220 x 1000 x 0.21) / (4 x 12)
       >= 182.875

Cout >= (4 x 1000 x (4 + (3.74x10^5 x 220))) / (487800 x 12^3)
       >= 380.45

Therefore Cout is more than 380.45 so I can use a 1000uF cap?

Cc >= (58.5 x 12^2 x 1000) / (1000 x 4)
    >= 33.696 (??? not sure what this means?)

John

dc42

How about 10 x 1.2v NiMh AA cells? I'm assuming the door strike is only operated for a small fraction of the time, otherwise the capacity of AA cells will be too small. Or a small SLA battery? The only disadvantage I can see is that you will need to connect more solar panels in series to get 12v to charge them.

If you have a large current load on the 5v supply then you might want to use a switching regulator to get 5v from 12v efficiently, otherwise you can use the linear regulator already on the Arduino.

If you stick with the LM2577, then I suggest you connect the door strike permanently to the regulator output, and switch the input to the regulator circuit using a PNP power transistor. That way, the regulator always has a load of 210mA (making the design easier), and draws no current when the door strike is off.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

idiotjohn

Yes the strike is only on for 2 seconds every time someone enters the door from the outside, so the 4 x AA's should have been enough. I suppose using 2 solar cells in series and a small SLA would just make it so much easier to do.

Perhaps i'll give up on the idea of using AA batteries.

John

dc42


okay so heres what ive got -

Rc <= (750 x 0.21 x 12^2) / 4^2
    <= 1417.5 Ohms (so I will use a 1k)

Cout is the greater of these two equations

Cout >= (0.19 x 220 x 1000 x 0.21) / (4 x 12)
       >= 182.875

Cout >= (4 x 1000 x (4 + (3.74x10^5 x 220))) / (487800 x 12^3)
       >= 380.45

Therefore Cout is more than 380.45 so I can use a 1000uF cap?

Cc >= (58.5 x 12^2 x 1000) / (1000 x 4)
    >= 33.696 (??? not sure what this means?)

John


I make it:

Cc >= (58.5 * 12^2 * 1000e-6) / (1000^2 * 4) = 2.106 * 1e-6 ~= 2.2 uF
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

idiotjohn

Don't worry!

Sorry for wasting your time, ill just use a 12v solar panel and a small lead acid battery.

Fortunately I found a reasonably small solar panel, so yeah.

Thanks for helping me! Ive learned a lot anyway :)

John

dc42

That's a shame, I was looking forward to hearing that you'd got the step-up regulator working! But using a 12v battery is certainly a simpler solution, unless you also have a large current draw from ~5v.

Good luck!
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

parmares


michinyon

The digital output of the arduino is not going to provide enough current to drive this,

If you have a very robust 5V supply available,  you could probably use this device to create 24 volts.   You could then use a relay to switch the 24V to the valve.   You can get suitable relay modules where the input can be driven by an Arduino output.

You would need to check what the operating current of the valve is,  to make sure you can provide enough current to drive it.

Go Up