Mosfet Info Needed for Submarine Project

[Sigurthr]

I don't quite remember the quote but it goes something like: "To truly understand a thing is to be able to effectively and accurately explain (or teach) said thing".

In truth the fully on point (called Saturation) moves higher or lower from ~8V depending on how the fet is used and what voltages are where. There's a formula for it, but in practice most don't bother learning it or using it because 10V does the job reliably and most power switching applications have 12V available to send to a gate when needed. Knowing how to determine the saturation point becomes necessary when working with Bipolar Transistors (BJTs) because they work on current sensing and not voltage sensing like fets.

Anyway, I'm happy to be of help.

 

[hakzaw1]

wow

can money buy that kind of help??lol

I did not understand most of this but was impressed anyway--

Will you have Lazoor sights on yer speargun??

plz do send us some pics-

6 min at 100'
thats damn impressive too

best wishes ( stay safe)

hak


'SeaHunt' (B & W) is on here at 3 AM-

- so corny!!

and he is always diving alone-- wth?

 

[AUTO XX]

At depth you can hold your breath a LOT longer than on the surface, it has to do with how pressure affects the absorption of oxygen and the release of CO2. The only problem is, when you DO need air, you need it fast. Like, 5 seconds ago...

So the reliable fully ON voltage is 10v and there is next to no current so a diode won't work for voltage drop. What would happen if you just used a straight 12.6v other than the capacitance effect of the FET?
Like if you used a double switch that was closed to activate the gate and then shorted it out when it was released.

 

[Sigurthr]

A complicated switch mechanism to apply 12.6 to the gate and then disconnect and then short the gate to ground works perfectly. Just better hope the switch doesn't fail and connect 12.6 to ground! You know what happens when you short a lipo...

@Mike. Yeah, money will buy this kinda help, haha. I'm always for hire.

 

[MarioMaster]

I would think it would be much more difficult to waterproof a toggle switch, I much prefer your original idea of using a reed switch. That way it can be totally sealed and activate it with a magnet on your wrist or whatever. The resistor divider takes care of the gate pulldown when the reed switch is open. (or any SPST switch for that matter)

 

[Sigurthr]

Yep, go with the resistor divider and reed switch. Much better idea.

 

[AUTO XX]

Oh I absolutely am, was just using it as an example to understand the how and why.

 

[AUTO XX]

Necro update here.
Sorry for the delay, I had forgotten about this project and was just going through some old files when I found the pics/vid.
I didn't completely finish the project to my usual level but it certainly worked well for saving air.
I wasn't about to push the seals on the motors too deep but ~5 minute runs at 30' went incredibly well. First run video will be uploaded soon.

 

[AUTO XX]

T-t-t-triple post!
Yeah, last one. Thanks again guys!

 

[Sigurthr]

Very nice!