Works full range but then as soon as I stick the probes the see what my amperage is, it trips again.
The PC PSU has its 0V rail grounded and *MUST* *NOT* be modified to remove this ground for safety reasons. ...
Works full range but then as soon as I stick the probes the see what my amperage is, it trips again.
I suspect that you are connecting the probes in parallel to the circuit. If you do that with the multimeter set up for measuring current, you are essentially shorting the output and that's why it trips.
You have to connect your multimeter in such a way that all current flows through the meter itself. For example, disconnect the wire that goes to one leg of the LED, then connect one multimeter probe to the wire and the other to the led. The multimeter then completes the circuit and all current passes through it.
I suspect that you are connecting the probes in parallel to the circuit. If you do that with the multimeter set up for measuring current, you are essentially shorting the output and that's why it trips.
You have to connect your multimeter in such a way that all current flows through the meter itself. For example, disconnect the wire that goes to one leg of the LED, then connect one multimeter probe to the wire and the other to the led. The multimeter then completes the circuit and all current passes through it.
This also struck me as a possible cause.
I would also ensure that there is a good size (at least 5 Watt, 10 W even better) dummy load on the +12V output. PC supplies do not like to operate with too little load.
The PC PSU has its 0V rail grounded and *MUST* *NOT* be modified to remove this ground for safety reasons. ...Why not? It's a flyback SMPS with transformer isolation between the primary and secondary side. Do you trust this transformer less than any other? Is there some other good reason you would like to share?
You don't need any current limiting resistors for an LM317. The circuit attached to the output of the LM317 (the load) is what determines how much current is used. Something else is not right with your set up.
Disconnecting the earth from the primary side of the PSU is unwise as it probably has a filter capacitor network that will put a significant mains frequency leakage current onto your 0V rail.
Disconnecting the earth from the primary side of the PSU is unwise as it probably has a filter capacitor network that will put a significant mains frequency leakage current onto your 0V rail.
I would however suggest making the supply into the LM317 regulator circuit switchable between 0/12V and -12/12V as the extra input voltage will double the dissipation, seriously limiting the maximum continuous output current available at low output voltages.
the extra input voltage will double the dissipation, seriously limiting the maximum continuous output current available at low output voltages.
2. I may be better served in this case by a new LM350T that can supply a bit more current at the lower voltage setting. (I just got in 10 of them i had ordered a while back)
If you are concerned about over-current, you can use an extra LM317 with a low value resistor between Out and Adj as a current limiter. Connect its Adj terminal to the adjustable voltage regulator's input. (see Figure 43. 1A Current Regulator in its datasheet: http://www.ti.com/lit/ds/symlink/lm117.pdf
#tautech Yeah i almost ordered 10 of all three but my misses fussed a bit..... She says i'm just like a kid!LOL
Do you think the LM350T's will work ok? I was also thinken I could just move the larger 12v bundle (5 leads combined) and the matching ground bundle to my temporary input terminal to cover the added current draw while I'm testing things.