Ok, first quick look at changing the frequency of the LM2588...
100k pot on pin #1 (freq adj / shutdown), 'scope hooked up to pin #5, the switch pin. Alligator clip wire set is M.I.A., so couldn't get reliable current measurements. Either that or power it off the PSU and read the current from the display. Give me something to do tomorrow.
With the pot dialed around to 100K, sloppy waveforms on the 'scope. Barely recognizable 100khz signal coming thru.
Rotate the pot (decreased resistance) and I can see the frequency increasing, until I get about 3/4 the way around, and SNAP...the switch waveform gets clean, some bouncing, not much.
Not sure if that's a function of the iffy hold-knob on the 'scope though. Could be that's the perfect frequency and timing for the hold-off itself. And if I rotate the pot any farther, it goes into shutdown, just like it's supposed to.
Also, the frequency is about 208Khz at that "perfect point", a bit above the maximum stated in the datasheet, with "Rset" at about 8Kohm.
Even though I couldn't get a current measurement off the battery (due to missing alligator clip leads), while rotating the pot, the voltage on the output varies a few tenths of a volt, not much at all (cheap meter doing the reading for now), but more importantly, the A/C component of the output power starts out at about .6v at the lower frequencies and drops to about .1v when the waveform "snaps" into clear view at the higher frequency. Spikes disappear, everything looks a lot smoother. That might also be a function of the bandwidth at the input to the 'scope itself. (Tek 2246A)
And, the regulator heat sink didn't get above 65C during this run, without a fan. Before this, I had a 40mm fan blowing air across the heatsink to keep it from going into thermal overload shutdown @ >120C.
I'll take a video of the 'scope tomorrow while I'm messing with it.....if I get to it.
EDIT: On another note, regarding current measurement on the meter. Would I be better off measuring the current off the battery using the AC or DC mode? Maybe put the biggest cap I can find across the battery pack leads? It's not alternating current, but it's surely a varying current. Maybe, since I'm using a cheap meter, in this case I'd be better off rather than trying to directly measure the current, I'd be better off measuring the delta of the current measured at the various frequencies. For instance, I know I'm reading ~1.81amps using this cheap meter at 100Khz. If I run the LM2588 up to 200Khz and the current drops to, say 1 amp, throwing out the effects of frequency on the measurement, I'll at least know I'm pulling ~.81amps less than before (and even that .81 amps probably isn't correct either, but less is less, a lot less is a lot less, and so on)... I know I'll have the same problem using my bench PSU, current readout will vary, will the readout keep up? will it average? will it display garbage? Won't know 'till I try it.