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In my temp controlled fan circuit, you can put a capacitor between the gate of the FET and the +12v line. 100uF is on full for about 1.5 seconds with my exact circuit and the pot in it's lowest setting and the NTC thermistor at it's coldest. Your mileage may vary.
Okay sorry at this is another dumb question but could I get one of those cheap soldering guns that's over hundred watts will that work for the copper pipe and MOSFETs?
Also, if I want to make the fan stay on longer at start up, would I increase or decrease the uF value of the capacitor?
Increase the capacitance. Also, it will be longer the lower you have the temp set pot tuned to.
And yes, you can use one of those cheap 100 Watt stained glass irons for this project. You can also supplement that with some torching. Maybe low low low setting and stick it in the copper pipe.
Mine is a Weller Expert 100/140 Watt soldering gun. Note that the tips burn up so fast that at ~$2 a piece you (I) will go through about $20 worth a month. I ended up just using solid copper house wire with mine. I don't know if you can do that with that one or not.
So you really think that will do a better job than the soldering station I have? I guess by pure wattage it should I mean it's more than double the watts. The thing that gets me is I paid about $100 for the soldering station I already own but the gun is only $30. I don't have a ton of experience with soldering, been doing it off and on for the past couple years, but the guys down at the hobby shop sold me on the station I have, said it would solder just about anything. Then again, in the RC hobby we are not usually soldering to 3/4" copper pipe.
The money for that soldering station you have went directly into it's temperature controlled nature. It is a far superior machine than the one your buying. HOWEVER.... As we have been learning Watts = heat. And your soldering station just doesn't have the heat output to heat up that whole pipe. The pipe will be able to lose 30+ Watts to the surroundings fairly easily. If you turned the iron on full blast, stuck it in the end of the pipe, then wrapped the pipe in insulation... Then maybe you could get the whole thing hot enough. When doing electronics one generally only wants enough heat to just melt all the solder, no more. Heat ruins a lot of electronic parts after all.
It's a good piece of equipment though, It will be excellent for anything other than the pipe. I wish it was mine
(P.S. That torch prolly puts out the equivalent of >500 Watts, far too much power for what we are doing)
Back to the fan topic briefly...I am thinking of using this to attach the thermistor to the heat sink. Anyone see any problems with that, or any better suggestions (less expensive suggestions...think mass production)? I wonder if I could just use regular 15 min epoxy.
You can use anything that won't melt when it gets hot. Supper glue, JB Weld, any two part epoxy, silicone gasket maker, lot's of different stuff. Something flexible is your best bet. Believe it or not, some flexibility and give is better when attaching too items to each others bare surfaces. Hard drying glues tends to crack and break free more often than not. Stronger glues generally have some flex. The best bond I have ever had with gluing two flat surfaces was silicone gasket maker. COULD NOT pry the damn things apart at all.
I am trying to think of a way to put an on/off switch in the mix and I want to make it so the load cannot be turned on without the logic being powered up first, because I think if I inadvertently plugged in the PSU without powering up the op-amps it would be bad news. Is there some way to put a switch to power on the op-amps in line with the load circuit itself, so that there will not be a complete circuit on the load side of things unless the op-amps are switched on? I don't think I really care about an on/off switch for the load itself, although a solution might include such, mainly I would just like to have the on/off switch for the op-amps and be sure I can't run a load through it unless they also have power first.
Actually, now that I think about it, if the op-amps are not powered on then no voltage would be being applied to the gates on the MOSFETs so wouldn't they essentially be turned off already, making my perceived problem irrelevant? In other words, I could plug the PSU into the load bank all day long, but since not voltage is being applied to the gates on the MOSFETs it will not draw any current until I plug in the op-amps and turn on the MOSFETs...is that correct?
Edit:
That being said, I think I will still put a switch for convenience to turn the op-amps off an on, but that will be very simple since, if my above statement is correct, I don't have to worry about incorporating in the main load bank into the switch, just a simple switch on the 12v op-amp power supply will do the trick.
In thinking about it the ac side might be better, that way the 24 volts will come up slowly. I hate to see you have to order another part, but better safe than sorry.
sorry for the basic question, but what do you mean by "inputs floating"? I have heard that term thrown around a few times in other threads and always wondered what it means.
Edit:
Guess I shouldn't be so lazy...I just had to do a google search, get it now. It means the inputs are not connected/tied to anything to pull up to the rail voltage or pull down to ground.
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