Diy - mosfet

[billy breach]

Hi All,

I Have build this MOSFET

from this website.

**retailers on forum**

But made some alteraion with the positive wire being joined at the trigger (as done by most mosfets) so there is only three cables.

1 small wire going to top of trigger.
1 x wire from bat and joined and trigger then onto motor
1 wire to mootor from mosfet

PROBLEM
=======

The problem I have is that when connected the motor runs all the time and when I pull the trigger the motor reduces speed (doesn't stop). The mosfet gets warm very quickly.

Can anyone suggest whats going on or what I need to do?




thanks
billy

[billy breach]

Re: Diy - mosfet

MOSFET
Under construction. This is it prior to soldering cables on and fitting heat shrink

[kejot]

Re: Diy - mosfet

well to me the diode looks wrong way round, so would run all the time, and when you pull trigger you are putting the load across the power, so would slow motor

[billy breach]

Re: Diy - mosfet

mosfet photo

[billy breach]

Re: Diy - mosfet

try turning the diode around? The diode is un marked except a gray band around the top

[balaclava ben]

Re: Diy - mosfet

the diode will have a polarity so switching it round may help solve the problem!

[Bachelarius]

Re: Diy - mosfet

That diode is only there for filtering spikes out and protecting the mosfet, you did use a TVS type 27v one, right? If its less than that, it will just be grounding everything over whatever it is rated at. Make sure you've also not accidentally bridged that cut off middle pin to anything as well.

Have you looked up the airsoft mechanics forums? It's where they designed this thing in the first place and have some HUGE threads on it and another one about the use of TVS mosfets, which I highly recommend you have a read of

[billy breach]

Re: Diy - mosfet

Hi guys,

I switched the diode. the motor still runs all the time but when you pull the drigger it get fasters.

It is a TSV diode as require in the drawing although i think its 18v

[Bachelarius]

Re: Diy - mosfet

should still not be firing constantly. It needs to be able to vent the high voltages, so make sure it points towards the negative pole or heatsink, like it is in the diagram.

If you are sure that the joins are ok and there are no odd cross-overs, you may well have a duff mosfet, who knows. Like I said, check that forum out for more info

[billy breach]

Re: Diy - mosfet

thanks for the website info mate. Yeah could be a duff mosfet.....I have heat shrinked all off it , the photo was prior to heat shrinking

[No1_sonuk]

Re: Diy - mosfet

I doubt it's the MOSFET. If it was duff, it wouldn't go faster when switched on.

Did you use the IRLB303y? I can't find data for it.

BTW: The grey bar on the diode show which end is the cross bar on the symbol.

[Twisted Fate]

Re: Diy - mosfet

try following described wiring he tells you to do , my old mosfet was pickie where the gate wire went so did what yours is doing

[Genista]

Re: Diy - mosfet

Do you have a multimeter so you can check out what voltage is going where? That would really help.

[StuartL]

Re: Diy - mosfet

It does sound like the diode is the root of your issue, or you've used the wrong MOSFET. You're going to need to take the heatstrink off anyway to fix it so do that and write down the exact part numbers on each of the components including the resistor colour codes. It's possible you were mis-shipped parts and the MOSFET may have a different pinout.

[Genista]

Re: Diy - mosfet

If you don't have a multimeter then you could remove the diode altogether to test.

It's only there to add protection. It would isolate the issue to either the mosfet or a manufacturing issue.