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Car Forum / Driving, Maintenance, Tuning / Maintenance and Repair / February 2006Building a transistor starter interrupt. - 90 Honda
I notice that on some new automotive security systems there is a starter interrupt that uses a transistor instead of the usual relay to disable power to the starter solenoid. A small current is supplied to this transistor and the car can be started. It's usually located at the starter solenoid. Usually I use a relay to disable the solenoid but I noticed that even the biggest stock relay leaks current. It leaks because when I start the car using a relay the car won't start. But when I bypass the relay it starts fine. Where can I obtain these unique transistor? Thanks > I notice that on some new automotive security systems there is a > starter interrupt that uses a transistor instead of the usual relay to [quoted text clipped - 6 lines] > > Thanks mouser.com You are describing dirty connections. Using electronics instead of electro-mechanical is still subjected to the dirty connection. Relays don't leak' current, dirty connections or contacts can fail to pass current. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) > I notice that on some new automotive security systems there is a > starter interrupt that uses a transistor instead of the usual relay to [quoted text clipped - 6 lines] > > Thanks > You are describing dirty connections. Using electronics instead of > electro-mechanical is still subjected to the dirty connection. > Relays don't leak' current, dirty connections or contacts can fail to > pass current. Thanks. You guys are correct, relays don't leak current. The word I was looking for was resist current. Will the transistor resist more or less current compared to the relay? What is the name of this transistor if I were to find one at mouser.com? Thanks > > You are describing dirty connections. Using electronics instead of > > electro-mechanical is still subjected to the dirty connection. [quoted text clipped - 7 lines] > > Thanks I have a funny feeling you are using a relay on the main battery power line to the solenoid? Usually the cut off relays are on the solenoid trigger line and a standard 30A Bosch relay will work perfectly for that. The current is really low there. That type of relay will not pass starter current, it will arc out internally. I replaced my headlight switch with a stock Bosch relay and my lights went an amazing bright white in color. The Bosch relay has 'way' less resistance in it than the new GM headlight switch I have in there. No relay, electronic or mechanical will work well with bad connections to it. I prefer to use crimp connectors with solder in them and heat shrink on top for corrosion resistance because most of my wiring is open to the weather and occasional underwater use. I am not well versed on totally electronic relay types, sorry. That was someone else posting about them, I still like the simple Bosh style ones. Mike 86/00 CJ7 Laredo, 33x9.5 BFG Muds, 'glass nose to tail in '00 88 Cherokee 235 BFG AT's Canadian Off Road Trips Photos: Non members can still view! Jan/06 http://www.imagestation.com/album/pictures.html?id=2115147590 (More Off Road album links at bottom of the view page) Do transistors resist more current than relays? Yes they do, however there has been some development on power devices such as MOSFETS, IGFETS, and smart power devices as yet to be in widespread general use. You could use a relay driven via a transistor with a reverse connected diode across the coil to absorb the switch off transisents. Bobscar Do transistors resist more current than relays? Yes they do, however there has been some development on power devices such as MOSFETS, IGFETS, and smart power devices as yet to be in widespread general use. You could use a relay driven via a transistor with a reverse connected diode across the coil to absorb the switch off transisents. Bobscar > > You are describing dirty connections. Using electronics instead of > > electro-mechanical is still subjected to the dirty connection. [quoted text clipped - 7 lines] > > Thanks Mouser may not carry what you need. Put ST780C06L0 or ST780C04L0 into Google. One of those should handle the current. > I notice that on some new automotive security systems there is a > starter interrupt that uses a transistor instead of the usual relay to [quoted text clipped - 6 lines] > > Thanks I doubt you actually know much about how an interrupt works when you don't understand the way a vehicles alternator works. Reference your earlier post. Maybe you should take some classes in electronics first. "I have been thinking of a good way to prevent stranding myself from a dead battery. It happened twice. Once at a beach from leaving my lights on. The other was at a college campus which the stereo and the dome light ran down the battery. Unlike the beach, the college campus have lots of helpful students with beat up cars that have jumper cables. Now, I have a new idea. Once my battery runs dry, I remove my alternator belt and wrap a rope around the alternator pulley. I then pull the rope so it'll turn 10 revolutions per pull. I keep doing this for about 20 times. What is the possibility that this will supply enough charge to start the car. If not, can somebody think of a clever idea to start an automatic?" > Usually I use a relay to disable the solenoid but I > noticed that even the biggest stock relay leaks current. It leaks because > when I start the car using a relay the car won't start. This is complete nonsense. Relays don't "leak" current. And the biggest "stock relay" I can think of is <ta daa> a Ford starter relay and those buggers can carry 200+amps (the whole draw of the starter MOTOR, not just the solenoid). > But when I bypass > the relay it starts fine. Where can I obtain these unique transistor? Put down the $1.50 Harbor Freight crimp tool, and step AWAY FROM THE CAR. Ford relay is a baby compared to the ones we have on our fire engines. The relays for the booster reel drives and the primer pump look like Ford units on steroids. They have 3 connections. Two in from the batteries and one HEAVY one out to the primer or they reel. They can take 400 amps BUT they only handle about 1/4 of that normally.  SignatureSteve Williams > > Usually I use a relay to disable the solenoid but I > > noticed that even the biggest stock relay leaks current. It leaks because [quoted text clipped - 9 lines] > > Put down the $1.50 Harbor Freight crimp tool, and step AWAY FROM THE CAR. |
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