Yes, your calculation is dodgy.tlfong01 wrote: ↑Wed Feb 27, 2019 2:30 amDC12V 0.25A 3W Electromagnet Can Lift/Hold 2.5kg
Let me see. If 12V, 0.25A, 3W can lift 2.5kg, and power is proportional to square of current, your 6A should be able to lift (6 * 6) / (0.25 * 0.25) * 2.5kg = 1,440kg! Are you sure you want to lift that heavy, or my calculation is dodgy?
Thanks for the information, but from what I gather the FET is a way to control the current flowing through a device. Correct me if I'm wrong but can't a relay switch do the same thing with less complicated components? So what would be the advantage of using the FET system?mahjongg wrote: ↑Tue Feb 26, 2019 5:25 pm
Note, to keep the dissipation on the FET low, you need the FET to either be completely closed (no voltage between gate and source) or open (a large voltage between gate and source), that is why two transistors are used to drive the gate voltage, also with this circuit the FET is off when you turn off the RPI.
Using a diode that can switch fast enough to take the spike would be preferable to frying everything.
So does that mean the ones I have wouldn't work, or would they be safe enough to keep?
Burngate wrote: ↑Wed Feb 27, 2019 9:08 am1. Yes, your calculation is dodgy.
2. What it "can lift" is nothing to do with power.
3. The power used to maintain the current will depend on what the wire is made of - copper, probably in this case, hence the 2Ω quoted, and hence 72W for 6A.
4. But if he managed to get some superconducting wire, once the field is established no more energy would be required.
5. The magnetic field is proportional to the current, and the force is proportional to the field, so the force is proportional to current - not its square.
6. The force will also depend on the material it's pulling on, as well as the material of the core of the coil, and the size and shape and number of turns of the coil.
7. Not easy to calculate.
tlfong01 wrote: ↑Wed Feb 27, 2019 1:44 pmICL8038 Mid Low Frequency (450kHz) Sinusoidal and Triangular Signal Generator - ¥16
https://item.taobao.com/item.htm?spm=a1 ... 8114234655
I try hard - generally three or four tries before I'm happybut actually structured
Isn't that the opposite of concise? But I won't argue!and concise.
So much for my BSc (failed) education!PS - I found your post easy to follow, because you speaks middle school physics English. Too many guys here speaks hard to follow geek English!
Fast enough? We're back to the time constant(s) of the coil - L/R - and everything else.
jadel wrote: ↑Wed Feb 27, 2019 7:32 pmIt is a 10SQ045: http://www.senocn.com/data/PDF/10SQ030-10SQ100.pdf
Would it still work?
Burngate wrote: ↑Wed Feb 27, 2019 10:13 am1. How short is "short"?
2. We don't know the inductance of the coil, so we don't know the time constant L/R
3. What is the main cause of the death of a diode?
Assuming it's the maximum temperature that kills it, we would need to know its thermal capacity as well as how fast it can lose heat to the environment.
4. Using a diode that can carry the full current of the coil seems to be preferable to using a small one and hoping.
tlfong01 wrote: ↑Thu Feb 28, 2019 7:18 amThe problem is that we don't know the inductance of OP's electromagnet.
Once we have got the inductance, then we can calculate the energy stored in the coil, and select a flyback diode with the appropriate current limit, breakdown voltage, and thermal capacity etc, ...
Looks good to me.jadel wrote: ↑Wed Feb 27, 2019 7:32 pmIt is a 10SQ045, here's the data sheet: http://www.senocn.com/data/PDF/10SQ030-10SQ100.pdf