Had to Google what a variac was.. not suitable for my project, unless they do an smd version
I'd planned on dropping the voltage a little, dont really want to just dissipate it but hey, if it works it works right?
Think I'm going to test out the linear volt control idea, trying for the least losses.
I've read the LT1084 is a more efficient regulator, and to keep it small maybe some BU208D npns paralleled up?
If anyone can point me in the direction of an efficient, small/smd size linear volt regulator schematic with a momentary switch trigger I'd be great full of the assist.
Hello again,
Sorry to say, there is no such thing as an 'efficient' linear regulator. Linear regulators by their very design are not efficient as dr pepper pointed out, except in the most rare case when the input voltage is not much higher than the output voltage such as in an LDO (low dropout regulator) but that also must have an input voltage that is not much higher than the output voltage. To make this point clear, lets look at a few examples. Since the key point here is input voltage vs output voltage we'll look at a few cases of input and output voltage. The load current will be the target load current for this project, 50 amps.
In all cases the power lost is:
PL=(Vin-Vout)*Iout=(Vin-Vout)*50
and the power out is:
Pout=Vout*Iout
and the power in is approximately:
Pin=Vin*Iout
and the efficiency expressed as a fraction (0.60 means 60 percent) is:
Eff=Pout/Pin
[1] Vin=10.1v, Vout=10v, PL=(10.1-10)*50=0.1*50=5 watts,Pin=10.1*50=505 watts, Pout=10*50=500 watts, Eff=500/505=0/99
[2] Vin=10.2v, Vout=10v, PL=(10.2-10)*50=0.2*50=10 watts, Pin=510, Pout=500, Eff=0.98
[3] Vin=11v, Vout=10v, PL=50, Pin=550, Pout=500, Eff=0.91
[4] Vin=20v, Vout=10v, PL=500, Pin=1000, Pout=500, Eff=0.50
Note how bad #4 is because there is a large input/output voltage differential.
Note that #1 is not that bad at all though.
This means that if you can adjust the input voltage to the regulator to be just a *little* bit higher than the output, you can keep efficiency up.
This is why i suggested the variac and full wave rectifier, if that can work in your app.
Some power supplies are built with a switching regulator at the front end so you dont have to adjust the voltage to the linear manually.
Give this some thought and figure out what you think you want to do.