Trouble Shooting Turbo Pump Controller

[Chad Ramey]

So I got the new ICs in this week and replaced both the SN7474 and the SN7400 that Alexi's Turbo Pump controller calls for. I began testing the pump today and encountered some odd results. I captured what is going on and posted it on youtube so you guys could see:

Any ideas on what is going wrong?

Thanks,
Chad

[Doug Coulter]

Two 24v regulators that put out 26v? Huh? Hopefully one puts out 5v for the logic, or it's time to buy more chips again.

I didn't see the leds that would show the circuit operation, which are shown in the schiz. If you want to debug things, you have to give yourself some help there.
Also, no scope traces, and I know you have a scope.

In other words, not enough info to do anything with -- we're not magic here, we need tools too! I can't tell polarity with my tongue, or tell what's going on without some more info, but it looks as though it just fired off one drive phase and quit, like nothing is changing with the pump rotation -- as if the hall sensor has no output or it's not making it to (and through) the chips.

Does the series R get warm? What are the voltages in various places (motor leads, logic states in the circuit). If it were in front of me, that's what I'd be checking, and since it's not, there's not much help that can be given. Don't mean to be harsh, but you have to give some (far) better info or I can't do much for you.

[Chad Ramey]

After probing around agian, I found that one of the leads was messed up and some things were wired in the wrong order. Now the thing seems to be running properly, it starts to spin up, gets pretty fast, then slows down. I'm working now on putting it under vacuum to see how fast it'll get. I guess it just goes to show that sometimes small stupid mistakes (proving to be somewhat common to me) can screw everything else up. Well, wish me luck, I'll be posting results (hopefully) tonight or tomorrow.


(Side note: the 26v is going directly through the resistor to the pump. The 5v for digital logic is provided by a separate voltage regulator.)

[Doug Coulter]

Right, it's generally something "simple", that is, in hindsight which takes time to acquire All this detailed tech stuff will definitely give you the gift of humility at some point.
Believe me, even after you get "good at it" -- you'll still pull some mistakes that seem extremely dumb after the fact, rarely do you make a "complex" mistake.

Yeah, you're going to need to have some vacuum to spin one of these guys up much. They tend to be pretty good turbines, and so do a lot of work if there's air there, and that driver won't provide much energy to do work with. You should be able to adjust to target RPM with a decent vacuum and a scope on one of the drives or the hall to measure the frequency. The pumping speed is a real big function of this, so you want fast, but not so fast it flies apart of course. IIRC the pump speed is at least a function of RPM^2 if not a larger exponent. I take advantage of that here in my fusor run modes, where at full speed it would be drawing too much power at the gas pressure; I run at about 1/4 full speed for that.