Home
JAQForum Ver 24.01
Log In or Join  
Active Topics
Local Time 07:52 07 May 2025 Privacy Policy
Jump to

Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me.

Forum Index : Electronics : Sensitive Mosfet in piclog circuit

Author Message
Cornelius

Newbie

Joined: 26/12/2008
Location: Norway
Posts: 27
Posted: 10:05am 26 Dec 2008
Copy link to clipboard 
Print this post

Just made the basic part of the piclog v1.2 (volt measurement and dumpload circuit), and it's working fine.

Except that i can't get the hang of Mosfets, apparently...

I'm using a P80NF55 from an old inverter, which are similar to the P40N10, except for the V/A. (55V, 80A)

I've connected Source to v-, Drain to relay (and relay to V+), and Gate to Out2 on the Picaxe via a 100Ohm resistor.
The problem is that the Mosfet are very sensitive on the Gate; just touching it with my finger turns on the Mosfet, and when Out2 goes low, the relay stays on...

Is there something i miss here? I assume the mosfet are pictured with the front facing me in the drawing of the piclog, so the pins are G, D, S.
 
GWatPE

Senior Member

Joined: 01/09/2006
Location: Australia
Posts: 2127
Posted: 11:04am 26 Dec 2008
Copy link to clipboard 
Print this post

Hi cornelius,

You should connect a pulldown resistor to the mosfet gate and ground, if you use any sleep functions on the picaxe.

If you have omitted the protection diode across the relay, then this can potentially lead to failure of the mosfet, from the back emf when the relay is turned off.

Gordon.
become more energy aware
 
Cornelius

Newbie

Joined: 26/12/2008
Location: Norway
Posts: 27
Posted: 02:27pm 26 Dec 2008
Copy link to clipboard 
Print this post

Yes, i do use a pause for 1 sec. in the code after sending data to the comport. (Without, Sertxd would send 10-15 times/sec., since i do not use any Count command yet.)

I see in the circuit for the Picaxe based Windmill Controller/Charger, that a 100k pulldown resistor are used. Would this be suitable for the logger too? (I'll probably test before anyone answers though... )

Cornelius
 
Cornelius

Newbie

Joined: 26/12/2008
Location: Norway
Posts: 27
Posted: 03:58pm 26 Dec 2008
Copy link to clipboard 
Print this post

Now i've added a 100k pulldown resistor, and it's working excellent now! (Also added the diode to the relay. I'm aware of the need for a diode over the relaycoil; just taking one step at a time... )

Thanks, Gordon!

But alas; i've no windmill to use this piclogger on - yet... But it's a work in progress. I wrote a Diary on it over at Otherpower...:
7 feet Windgen

Excellent chips, these PicAxe's...
 
Print this page


To reply to this topic, you need to log in.

The Back Shed's forum code is written, and hosted, in Australia.
© JAQ Software 2025