Anyone know how NPN transistors work? - Page 3 - Fuelly Forums

Click here to see important news regarding the aCar App

Go Back   Fuelly Forums > Tech, Troubleshooting and Repair > General Maintenance and Repair
Today's Posts Search Click Here to Login
Reply
 
Thread Tools Display Modes
 
Old 10-11-2008, 01:53 PM   #21
Registered Member
 
GasSavers_BEEF's Avatar
 
Join Date: Apr 2008
Posts: 1,831
honestly, I would replace it with a tiny little relay. they pull next to no current and you can get them with a 12 volt coil. go to radio shack and spend a buck or two.

it is much better than having to worry about the thing burning out and not having lights. don't reinvent the wheel. they have been using relays in cars for years.

ground one side of the coil and run the ignition wire to the other side of the coil, good to go.
__________________

__________________
Be the change you wish to see in the world
--Mahatma Gandhi



GasSavers_BEEF is offline   Reply With Quote
Old 10-11-2008, 01:54 PM   #22
AMX
Registered Member
 
Join Date: Mar 2008
Posts: 44
Country: United States
Quote:
Originally Posted by itjstagame View Post
Hmm, well 33k ohm still makes it hot as all hell pretty quickly, so, hmm.
Have you calculated the power being dissipated in the resistors? What wattage are you using? Try going to an increased wattage resistor.
__________________

__________________
AMX is offline   Reply With Quote
Old 10-11-2008, 02:15 PM   #23
Registered Member
 
theholycow's Avatar
 
Join Date: Apr 2008
Posts: 6,624
Country: United States
Send a message via ICQ to theholycow Send a message via AIM to theholycow Send a message via MSN to theholycow Send a message via Yahoo to theholycow
Quote:
Originally Posted by BEEF View Post
don't reinvent the wheel. they have been using relays in cars for years.
That's not reinventing the wheel...that's just using the appropriate tool for the job. Relays are for switching large loads. Transistors are for switching small loads (or some non-switching jobs like amplification).

Don't use a sledgehammer to pound a finish nail. A transistor is the right tool, keep at it until you get tired of trying, THEN use the sledgehammer.
__________________
This sig may return, some day.
theholycow is offline   Reply With Quote
Old 10-11-2008, 03:05 PM   #24
Registered Member
 
GasSavers_BEEF's Avatar
 
Join Date: Apr 2008
Posts: 1,831
you do ralize that you can get a relay that is as small as a pencil eraser. I am not talking about a huge device.

he is trying to engineer a system within his vehicle to work with somewhat unknown values. if they were known then things wouldn't be getting warm.

there are a million ways to get where you want to go. the question is which is the best for what is available. a relay (very small one at that) will do the job and nothing else has to be taken into consideration.

also, fets are used to switch large loads. variable speed motor drives have been using FETS in their output stages for a while now. field effect transistors rated for 1200 amps(each one weighed about a pound and a half ). that is a pretty big load.

honestly, either way would work but the question is how much time do you want to invest? have fun figure it out or just buy a relay (the little one).
__________________
Be the change you wish to see in the world
--Mahatma Gandhi



GasSavers_BEEF is offline   Reply With Quote
Old 10-11-2008, 03:37 PM   #25
Registered Member
 
VetteOwner's Avatar
 
Join Date: Mar 2007
Posts: 1,546
Country: United States
I say go with the relay...

multimeter wont measure amps because of 3 things:

1. you didn't switch the leads (most have to switch the red lead to the amps/ma socket)
2. blew the fuse because you didn't break the circuit to measure something
3. cant measure current (havent seen one but do know of some crappy ones that cant)
VetteOwner is offline   Reply With Quote
Old 10-11-2008, 03:57 PM   #26
Registered Member
 
theholycow's Avatar
 
Join Date: Apr 2008
Posts: 6,624
Country: United States
Send a message via ICQ to theholycow Send a message via AIM to theholycow Send a message via MSN to theholycow Send a message via Yahoo to theholycow
Quote:
Originally Posted by BEEF View Post
you do ralize that you can get a relay that is as small as a pencil eraser. I am not talking about a huge device.
I did not realize that. I've only ever seen the ones that are about 1 inch, cube shaped, and a few about half that size.

The pencil eraser-sized one still has moving parts, but it sounds pretty cool. Where does one find them, and how much do they cost?

Transistors are found in any junk electronics being discarded and are free, of course.
__________________
This sig may return, some day.
theholycow is offline   Reply With Quote
Old 10-11-2008, 05:45 PM   #27
Registered Member
 
VetteOwner's Avatar
 
Join Date: Mar 2007
Posts: 1,546
Country: United States
if you know where to look you can pick relays up like candy at a junkyard....lets just say i got enough to last a lifetime

i wouldn't worry about size of the relay cuz its most likely going to be shoved up in the dash anyways
VetteOwner is offline   Reply With Quote
Old 10-11-2008, 09:23 PM   #28
Registered Member
 
GasSavers_BEEF's Avatar
 
Join Date: Apr 2008
Posts: 1,831
radioshack

Model: 275-233
Catalog #: 275-233

(didn't think the link to the search would show up right)

this is just an example of one. the current that they can handle may be the biggest drawback and yes they are supposed to be mounted in a PCB but so is the transistor that is being used. I think that current through the device may also be making it hot.

transistors are used for switching but the reason they use them for switching is usually for #1 no moving parts but #2 their switching speed is much faster. the second one goes along with the first but it doesn't have much to do with the size. a solid state relay is just a transistor (be it a big one) in a package that fits in a relay socket. it does have all the resistors and other good stuff built into a neat little package so you don't have to do anything but plug and go. they last longer because of the less moving parts which makes them very valuable in industry.

also, those boards that you can find the transistors on, look at them more closeley and you may find relays on them too. most are square and long (the small ones) maybe a qtr to a half an inch square by about 1 inch long. two pins on one side (the coil) and 2 or 3 pins on the other side (the actual contacts) they are used more than people realize in electronics. not necessarily computers but definitely for controllers. old PLCs used them for their outputs. they were very low current though. that may be a problem with them though in this application.

*edit* the way I see this is a low-tech problem with a high-tech answer. that is the reinventing the wheel thing. you want a switch to flip off so that the lights won't come on when the car is off. a relay is simply a switch. flip off the switch to the coil and the contacts open. low-tech but effective. nothing to figure out (other than current capcity you would need) if you use a 20 amp one, you have nothing to worry about but you can figure that out and use an appropriately sized one if you care that much. I guess also remember to use one with a 12VDC coil but that goes without saying.

*edit again*
http://relays.tycoelectronics.com/datasheets/OMR.pdf
here is one from mouser. this pdf shows a lot of things. it shows physical size but it also shows maximum switching rate. these things get really small but also the current handling is small as well. a lot of good data on this data sheet. I wouldn't use this relay but you see what I am saying about relays being small.

sorry for the book ^^^
__________________
Be the change you wish to see in the world
--Mahatma Gandhi



GasSavers_BEEF is offline   Reply With Quote
Old 10-12-2008, 05:13 AM   #29
Registered Member
 
theholycow's Avatar
 
Join Date: Apr 2008
Posts: 6,624
Country: United States
Send a message via ICQ to theholycow Send a message via AIM to theholycow Send a message via MSN to theholycow Send a message via Yahoo to theholycow
Great work, BEEF!

As I was reading it, I got to this part...
Quote:
*edit* the way I see this is a low-tech problem with a high-tech answer. that is the reinventing the wheel thing. you want a switch to flip off so that the lights won't come on when the car is off.
That's when I realized that using a relay or transistor is probably more than necessary, due to an idea that I got:

The headlight switch gets power from somewhere and puts that power through a relay which powers up the headlights. Why not just change the source of the switch's power? You could just tap a wire that's only on when the car is on. This avoids needing any relay or transistor, because you're using that big honkin' ignition switch that's made to control exactly this sort of thing!

According to http://www.bulldogsecurity.com/New%2...stiva91-93.htm OP's Festiva could use the Black/White (ignition) or Blue/Red (accessory) wire from the ignition switch harness. The only gotcha would be if the headlight switch runs on the opposite polarity, which is a distinct possibility...that would pretty much break this idea.
__________________
This sig may return, some day.
theholycow is offline   Reply With Quote
Old 10-12-2008, 06:28 AM   #30
Registered Member
 
Join Date: Jul 2007
Posts: 280
Country: United States
Nope, doesn't matter if it runs in the opposite polarity, the headlight switch could switch positive or negative side of the coil, doesn't matter and making that positive controlled by ignition will fix the problem in either case. But I already outlined above why I'm not doing that.

And thanks for all your thoughts, that small relay is a cool idea and quite easy to use. I may just do that. I don't want a big transistor because I'm not under the dash, I'm in the steering column, no room. But the small one will work. I'd just prefer solid state if I've got a million of them. To me it feels like the right solution and to me it seems stupid to give up because we just doing know what we're doing. It should be the thing used for the job we just don't know how.
__________________

itjstagame is offline   Reply With Quote
Reply


Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
What is this stat? cavale Fuelly Web Support and Community News 1 09-03-2008 08:23 AM
Another diesel burner GasSavers_Jeece Introduce Yourself - New member Welcome 0 06-16-2008 08:47 PM
Visual representation of airflow behind car landspeed Aerodynamics 6 12-04-2006 02:58 PM
Gaslog entry blues Spule 4 General Discussion (Off-Topic) 5 10-25-2006 07:03 AM
Whats your concentration factor. zpiloto General Fuel Topics 15 09-30-2006 05:28 PM

» Fuelly iOS Apps
» Fuelly Android Apps
No Threads to Display.
Powered by vBadvanced CMPS v3.2.3


All times are GMT -8. The time now is 05:39 PM.


Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2024, vBulletin Solutions, Inc.