Help ! need info on a switch for Blu-Ray Project

[thejunkmonger]

Well I still haven't received any of the main components to build my Blu-ray yet and i'm already having a crisis.
I'm going to use Dr.Lava's Flexdrive 2 to run the diode @ about 80ma if that is a good figure that's what I could figure out by reading tons of posts. The battery will be a cr123 secondary cell from dx 3,6 volts but it charges up to 4.2 I think. My question is if I'm putting out 80ma at the diode how many ma am I pulling from the battery I need to know because the switch I have laying around here that I wanted to use for the project is only rated at 0.5A @125v.

Any help would be appreciated.

 

[chido]

Re: Help ! need info on a switch for Blu-Ray Proje

If you're putting in 80mA than you're pulling 80mA too.

 

[thejunkmonger]

Re: Help ! need info on a switch for Blu-Ray Proje

If you're putting in 80mA than you're pulling 80mA too.

Um your not convincing me chido.

 

[climbak]

Re: Help ! need info on a switch for Blu-Ray Proje

I'm not sure about the lavadrive, but if you don't have any resistors or anything that flows current in parallel to the diode then whatever the current passing through the diode is what will be passing through the rest of the circuit. I am guessing the lavadrive has a protection diode and a cap in parallel somehow similar to the ddl style driver. The cap won't flow any current after a very short time depending on capacitance and the protection diode won't flow current unless the polarity in the circuit is reversed. someone more familiar with the lavadrive will be able to say for sure about that though.

 

[danq]

Re: Help ! need info on a switch for Blu-Ray Proje

I think if the circuit is 'boosting' voltage, the current draw from the batteries will be greater than the LD current.

The power input vs output will be dependent on circuit efficiency.

For example, at 90% efficiency, to get output of 4.5V @80mA:

power out = V[sub]out[/sub] x I[sub]out[/sub]: P[sub]out[/sub] = 4.5V x .08A = 0.36 Watts
power in = P[sub]out[/sub] / efficiency: P[sub]in[/sub] = 0.36 Watts / 0.90 % = 0.40 Watts
I[sub]in[/sub] = P[sub]in[/sub] / V[sub]in[/sub]: I[sub]in[/sub] = 0.40W / 3.6V = .111A = 111mA

 

[Bionic-Badger]

Re: Help ! need info on a switch for Blu-Ray Proje

That switch can handle 62.5 watts (not milliwatts). You have nothing to worry about.

 

[thejunkmonger]

Re: Help ! need info on a switch for Blu-Ray Proje

I think if the circuit is 'boosting' voltage, the current draw from the batteries will be greater than the LD current.

The power input vs output will be dependent on circuit efficiency.
For example, at 90% efficiency, to get output of 4.5V @80mA:
 power out = 4.5V X .08A = 0.36 Watts
 power in = 0.36 Watts / 0.90 = 0.40 Watts
 if V[sub]in[/sub] = 3.6V then I[sub]in[/sub] = 0.40W / 3.6 = .111A = 111mA

Now here's an answer I like Thanks danq even though I can't really understand it. so the switch is good then?

 

[phenol]

Re: Help ! need info on a switch for Blu-Ray Proje

That switch can handle 62.5 watts (not milliwatts).  You have nothing to worry about.

Well, the power the switch disspates is calculated as this: Psw=RclosedI[sub]sw[/sub]^2. 0.5A is the max continuous current the contacts can handle, whereas 125V is the max voltage across the open contacts. During power-up there could be a surge current above 0.5A (charging caps, etc) but with lava's drive there shouldnt be a problem.
62 watts of heat would severely melt the switch and set things on fire.

 

[danq]

Re: Help ! need info on a switch for Blu-Ray Proje

Now here's an answer I like Thanks danq even though I can't really understand it. so the switch is good then?

if you like 'em incomprehensible I could easily make less sense

just edited it to make it I hope a little clearer what the calc factors are.

DanQ

 

[thejunkmonger]

Re: Help ! need info on a switch for Blu-Ray Proje

[quote author=thejunkmonger link=1210851899/0#6 date=1210854757]Now here's an answer I like Thanks danq even though I can't really understand it. so the switch is good then?

if you like 'em incomprehensible I could easily make less sense  

just edited it to make it I hope a little clearer what the calc factors are.

DanQ[/quote]


LOL it's not what you wrote Dang it's my math deficient brain.

 

[IgorT]

Re: Help ! need info on a switch for Blu-Ray Proje

You don't have to worry about the switch. The current draw will be higher than the current through the LD, but not that much. It will be less than double the current through the LD with a full battery, and slowly INCREASE to close to double the current as the battery voltage drops.

Since your switch is rated at 0.5A, you have nothing to worry about at all.


I once had to make a switch to dump 200A from a capacitor bank into a huge coil in a split second. Any normal switch would melt instantly. The switch i made melted slowly through the thick copper rod, untill it had a "dent" half the diameter deep. After that i replaced it with a circuit, that was meant to handle 6A CW, but could take the "little" extra current because of the short duration of the pulse.

Now that was fun! Death on contact, if someone should decide to touch the capacitor bank...

 

[thejunkmonger]

Re: Help ! need info on a switch for Blu-Ray Proje

You don't have to worry about the switch. The current draw will be higher than the current through the LD, but not that much. It will be less than double the current through the LD with a full battery, and slowly INCREASE to close to double the current as the battery voltage drops.

Since your switch is rated at 0.5A, you have nothing to worry about at all.


I once had to make a switch to dump 200A from a capacitor bank into a huge coil in a split second. Any normal switch would melt instantly. The switch i made melted slowly through the thick copper rod, untill it had a "dent" half the diameter deep. After that i replaced it with a circuit, that was meant to handle 6A CW, but could take the "little" extra current because of the short duration of the pulse.

Now that was fun! Death on contact, if someone should decide to touch the capacitor bank...

Shrinking coins Igor? If you could just figure out how to make gold ones bigger we would be set.

 

[IgorT]

Re: Help ! need info on a switch for Blu-Ray Proje

Shrinking coins Igor? If you could just figure out how to make gold ones bigger we would be set.

My coins, or rather my money is shrinking "all by itself" due to this nice hobby..

A gold inflating device would be nice to have.. I could trade it for a laser, no? :