Hi Leslie,
Looks a little complicated for me? Why do you use a voltage regulator?
The regulator is not working as a voltage regulator. Its a current follower set at 50ma. This requires only one resistor and is less complicated..
How this works is
Vref/I=R
Vref is the reference voltage set in the IC, I (current) is what you want the the IC to output. R is the answer to what resistor you use to tie between output pin and adj to get you constant I current..
As the load is subjected over R the voltage drops to adj dropping the voltage to the output causing a constant current despite the input voltage, input current and resistive load.
So vref for the lm317t = 1.25v
1.25v/.05a = 25 ohm.
We use a 25 ohm resistor between the adj and output and draw our current from the resistor output and adj.
The relay has 7 different types not spelled out very well in the data sheet. So the coil rating part can be confusing.
24v 480ohm 50ma is what the circuit was designed for.
I have a 12v coil.
The better relay for the 48v pack is the 24v rated coil. So the circuit I made works if you can get the 24v coil relay.
The coil will draw 104ma at 50v, too much, so we put the lm317t in current follow config not voltage regulation config, in there to stop the 100ma.
By resisting half the current we resist halve the voltage to the coil as well.
Let me introduce you to ohms law.
E= Volts
I= Current amps
R= Resistance
W= Watts.
Some math.
v/r=I
24v/480ohm=0.05 amps OK!
^^^This is fine for the relay
50v/480 ohm= 0.104 amps, Ouch!
^^^This will blow the relay.
See as the pack discharges the current decreases to the relay coil. What ends up happening if you set the coil good to work at 50v at 40v its starved and shuts down. If you set the coil to work good at 24v when the pack is full the current to the coil is too much and it burns it out.
Normally the 48v pack sits at 50v max when resting full charged. But we need 24v for our coil switch.
We can rely upon the coil resistance to distance the circuit load so the regulator only has to resist 50ma down from the 100ma at 26v drop.
More math.
26v*.05 amps= 1.3 watts. That's pretty good.
The beauty of the current follower regulator; in this circuit, no matter what the voltage is, as long as its above 24v, it will give 24v @ 50ma from 60v, all the way down to 24v. It doesnt matter what voltage the said device needs. Say you had one lamp to run at 10v at 1amp with a 30v input. With a current mode reg you could run a 20v lamp at 1 amp on the same circuit. Voltage doesn't matter no more, great hey!. Oh and I almost forgot, this little IC in current follow mode can take the inrush that those controller caps can cause and whip it tame. This is not good for inrush with a regulator in voltage reg mode. The LM317t has a max current of 1.5 amps As you know large caps can demand more peak current than you require when charging from 0v, 0v is seen as a short circuit until they get some energy into them. This can overload the IC in voltage regulation mode as soon as you switch her on.. Current reg mode is sweeeet for a precharging the controller or creating resistance to charging caps over the coil terminals to delay the relay switch, if you want to take it thus far..
The LM317t has a voltage rating of 37v drop from the input to the output, any more and its toast. every thing is checking out by the math. 26v drop from 50v and 36v drop from 60v.
Everything seems to be working to plan in the circuit. Looks like I nailed it to the floor.
Unfortunately I have a 12v coil, this sucks seriously as I have to bump down to 12v at 100ma, this is much more of a challenge. I can still test the math to the above with my relay.
I will show you some pics because I pull my power box out tomorrow to try install a switcher reg . I have a precharge delay on the FRA4 and I run the whole controller logic through the lm317t and LM338 regulators.
I switch on, a little bit of current charges the controller caps then whack the relay kicks in. Zero arc switching....
