Ok so Amazon seller messed up and sent me the wrong ac to dc converter. So while Im dealing with that, I decided to make something work myself. I have a box of lm317t voltage regulators and looked up how to wire it and used a couple calculators to figure out which resistors I need. R1 is 100 ohms and R2 is 2170 ohms. Using these I should get 28v out (running a dc motor of 24v and a fan for cooling and possibly some leds). I have remade this circuit 3 times triple checking it after its done and every single time Im getting 46v out. My hair is turning grey(er) trying to figure this out.
Ive never really drawn a schematic before but im triple triple sure its wired to the "correct" schematic shown on multiple sites. Anyways heres my horrible attempt at drawing my board (I drew this exactly how its wired up, never mind the colors on the resistors, i just used something close to whats actually on them, I know their values because I used a meter).
I looked at another google search because the first one told me the LM317T was good up to 60v which is why I decided on using it.
I saw your first reply, about the .01 caps, i dont have those because theyre not shown on any of the examples ive seen?
Ill do a voltage divider to lower the voltage to acceptable range for the 317T. But as it didnt (yet) short out, shouldnt it be at least close to what the calculators calculated?
But there's another problem and that's power dissipation. (It's thermally limited and it might have to be thermally calculated.) The power (heat) dissipated by a linear regulator is calculated as the voltage "dropped" across the regulator X the current through it. You didn't tell us the current rating for the motor but 20V X 1 Amp would be 20 Watts and the regulator will overheat and shut down.
For motors you'll need a switchmode DC-DC converter. These can be nearly 100% efficient so they don't generate nearly as much heat.
Its only .18 amps. And I am going to pass the 28v through a buck converter for the motor but wanted a little extra for running the fan and some lights, ect...
Voltage dividers don't work with "power". They only work with (low current) "signals".
The load is in parallel with the "bottom" resistor in the voltage divider. That lowers the effective resistance, lowering the voltage. And when the load changes (such as turning-on a motor) the voltage will change.
There is no load on this circuit yet. Im making this to get the voltage to an acceptable range for my buck converter (since amazon messed up and sent me 12v converter instead of 24). Theres more to add to this circuit, this is just the first problem ive encountered.
