• Welcome to our site! Electro Tech is an online community (with over 170,000 members) who enjoy talking about and building electronic circuits, projects and gadgets. To participate you need to register. Registration is free. Click here to register now.

Help configuring NPN Amp switch for 12V Relay

Status
Not open for further replies.

stuhagen

Member
The transistor has nothing to turn it off. Add a base-emitter resistor, try 1k.
Cool, can you maybe jot down a quick drawing on the this? I can only picture a 1K resistor from Pin #7 of the LM311 to ground?

Also, in regards to the relay, it does state the it requires a minimum of 1 Amp current. So maybe the TIP31 can 't handle that? Also, the relay's are outside of my box and I run wires to them.

I will try those other options as noted above.
 

audioguru

Well-Known Member
Most Helpful Member
A 1k resistor from the base of the transistor to its emitter will turn it off quickly. You don't need a schematic showing it. Connecting a resistor from the comparator to ground is different and won't do anything to turn off the transistor.

The relay coil is 90 ohms. With a 12V supply it draws 12V/90= 133mA.
The contacts of the relay are probably silver plated and need a minimum load of 1A to cause a spark to break through the black corrosion film of silver.
 

stuhagen

Member
A 1k resistor from the base of the transistor to its emitter will turn it off quickly. You don't need a schematic showing it. Connecting a resistor from the comparator to ground is different and won't do anything to turn off the transistor.

The relay coil is 90 ohms. With a 12V supply it draws 12V/90= 133mA.
The contacts of the relay are probably silver plated and need a minimum load of 1A to cause a spark to break through the black corrosion film of silver.
Sorry, I forgot there was a diode after Pin#7. I will try putting a resistor "after" the diode, and at the base to ground. Since the specs state "min recom'd current of 1 amp" then this makes sense.
 

stuhagen

Member
A 1k resistor from the base of the transistor to its emitter will turn it off quickly. You don't need a schematic showing it. Connecting a resistor from the comparator to ground is different and won't do anything to turn off the transistor.

The relay coil is 90 ohms. With a 12V supply it draws 12V/90= 133mA.
The contacts of the relay are probably silver plated and need a minimum load of 1A to cause a spark to break through the black corrosion film of silver.
Actually, I am curious to know why this may help when this circuit works fine in my bench test 12V generator and not on the car's voltage..installed?
 

audioguru

Well-Known Member
Most Helpful Member
Actually, I am curious to know why this may help when this circuit works fine in my bench test 12V generator and not on the car's voltage..installed?
An open-circuit base of a transistor turns off slowly and picks up interference that might turn it on when it should be off.
 

stuhagen

Member
Revised Drawing

I thought I would throw out 1 more drawing here before I mofidy it. Just in case one of you "guru's" see's something amiss.

So the theory is the car runs stock at 9V to the FP. At 4000rpms the car computer sends a 4.5-5.0V signal and kicks out 12V to the pump. At this time, the LM311 switchs the relay to initiate the other boosted 18V power source. The other relay on the left is used to power up the voltage booster once the car starts so it is always "on" and ready to be switched over. I was told a diode is needed from the power source here.

Overall power supply voltages run anywheres from 12.2v to 14.3v depending on initial startup or cruising.

Stu
 

Attachments

stuhagen

Member
Well, tonight I started all over. Made a new board and everything. Bench test, it works perfectly. Install it, it doesnt. Here is a few things I did that I didnt try before.

On initial starting of the car, it is producing 14.4V. The relay is oscillating and holding right at about 7.2V which is the relay's minimum operational voltage. So I start to think that maybe this comparator circuit isnt liking this higher voltage. So I make a voltage divider to drop the incoming voltage to about 11V. Well, the relay quits chattering now, but the comparator doesnt seem to make the transition with the 5V trigger voltage.

I have tried different resistors, and I tried the base to emmitter 1K resistor in both configurations, and still doesnt work. What I mean is I tried these combinations with the dropped down voltage and the normal 14.4 voltage.

So I am giving up............ BUT.......I have one thought and here it is..........
When I bench test this, I cannot leave the "input" open. I have to supply it 2.0V. Now, when I want to "trigger" it with the new "input" of 5.0v, I cannot just apply a 5.0v voltage to what is going in there now at 2.0V. I have to actually remove the 2.0V signal, and "then" apply the 5.0v signal. Which of course it works.

So now, where I am coming from, is when it is in my car it has a 2.0v signal "inputing"..So my idea of simulating the 5.0v signal was to apply a 4.5V (3 ea 1.5V batteries) V signal to the current car's 2.0v signal. Maybe when I am applying this test 4.5v signal, on top of the 2.0v signal, I am not really getting a true 4.5V signal to the comparator. Like paraleling the voltages and no really getting the comparator its real 4.5V to trigger it?? Maybe I really need to go out on the road and let the signal change to 5.0v to really see if this is the problem>
 

slotcar330p4

New Member
Hi,

what kind of power supply are you using,

I don't see a stable power supply in your schematic,

If you are using just the power supply of the car ( battery and alternator) then you need to add some filters in the powerline from the car. The powerline of a car is a hazard, lots of spike's.

the LM311 can do with +5 volts, add the 7805 to the schematic ( and some capacitors) to feed the LM311 only and you be fine en put the R1 and R2 allso to +5 volts ( might have to change their values ).

greetings,

slotcar330p4
 
Last edited:

stuhagen

Member
Hi,

what kind of power supply are you using,

I don't see a stable power supply in your schematic,

If you are using just the power supply of the car ( battery and alternator) then you need to add some filters in the powerline from the car. The powerline of a car is a hazard, lots of spike's.

the LM311 can do with +5 volts, add the 7805 to the schematic ( and some capacitors) to feed the LM311 only and you be fine en put the R1 and R2 allso to +5 volts ( might have to change their values ).

greetings,

slotcar330p4
I think this seems to be the problem as you say. It is car battery/alternator power.

What do you mean by "add the 7805 to the schematic"? What is a 7805.
What do you mean by +5V is OK. Do you mean that I can reduce the LM311 supply down as low as +5V?
You have suggestions on what the RC Circuit might look like for this voltage input scheme? Is the voltage divider I came up with not complete, and I should add a capacitor somewhere?
The R1 and R2 seems to be OK because it does supply a good 3.3V reference voltage. (i.e. non-trigger is 2.0v and "trigger" is 4.5v..so 3.3v is a good reference)
Stu
 

slotcar330p4

New Member
Hi,

a 7805 is a small voltageregulator, input greater than +8 volts and output +5 volts / 1Am so that is more than enough to power the LM311. your reference voltage is not stable, and therefor no good reference.

what program do you use to draw circuit diagram, I normally don't draw diagrams, but make them straight in Lochmaster 3.0 ( english ).

and a TIP: if I don't know a electronic part,I google it with "XXXXX datasheet", it works most of the times.
 
Last edited:

stuhagen

Member
Hi,

a 7805 is a small voltageregulator, input greater than +8 volts and output +5 volts / 1Am so that is more than enough to power the LM311. your reference voltage is not stable, and therefor no good reference.

what program do you use to draw circuit diagram, I normally don't draw diagrams, but make them straight in Lochmaster 3.0 ( english ).

and a TIP: if I don't know a electronic part,I google it with "XXXXX datasheet", it works most of the times.

Radio Shack sells these for $1.59~!. Are you sure that an "output" of +5V is sufficient and will not interfere with the 2.0v-4.5v input/reference voltages?
Do they make one of these that outputs a bit more than +5V? Or is this not needed.

I do not use programs for circuitry, I do id free-hand~! I am sure I can work out how to install the 7805.

Stu
 

slotcar330p4

New Member
Hi,

I am positive.

but you might have to reconfigure some of values of the resistors.

Can you draw a circuit diagram for me please, so I can see if you got the whole picture?

I will look for a circuit drawing program to make a drawing myself

greetings

slotcar330p4
 

stuhagen

Member
Hi,

I am positive.

but you might have to reconfigure some of values of the resistors.

Can you draw a circuit diagram for me please, so I can see if you got the whole picture?

I will look for a circuit drawing program to make a drawing myself

greetings

slotcar330p4
Just look in some of my past posts, I have several diagrams there on circuit boards, and the whole layout plan.

I checkied into regualtors, and the only issue that I see is the the relay requires a minimum of like 7.8v to energise the coil. So maybe a +5v regualtor might not provide sufficient V output to fire the relay. I see that there is a LM117, which is an adjustable one via a small circuit and a pot. There is a 12V regulator, but it states I need a minimum of 14.4V as the "input" voltage. I wouldnt have enough V-in to cover this. So unless they make like a 8v or 10v regulator, I may been to go with as adjustable one to dial in the correct voltage.

Stu
 

slotcar330p4

New Member
hi,

you're right, but the relay should be powered straight from the +12 volts just in front of the input of the 7805, then it will be just fine.

greetings,

slotcar330p4
 

Willbe

New Member
FWIW
car batteries are charged at 13.3v (summer) to 15.5v (winter). Above 16v will boil off the electrolyte.
Open circuit voltage for a fully charged battery with the surface charge bled off (leave the headlights on for ~one minute) is 12.76v.
:eek:
 

rezer

New Member
Just look in some of my past posts, I have several diagrams there on circuit boards, and the whole layout plan.

I checkied into regualtors, and the only issue that I see is the the relay requires a minimum of like 7.8v to energise the coil. So maybe a +5v regualtor might not provide sufficient V output to fire the relay. I see that there is a LM117, which is an adjustable one via a small circuit and a pot. There is a 12V regulator, but it states I need a minimum of 14.4V as the "input" voltage. I wouldnt have enough V-in to cover this. So unless they make like a 8v or 10v regulator, I may been to go with as adjustable one to dial in the correct voltage.

Stu
Look into the 7809 or 7810 regulator. The drop-out voltage is 2V.
http://pdf1.alldatasheet.com/datasheet-pdf/view/173533/UTC/LM7809-TA3-G-T.html
 

Hero999

Banned
FWIW
car batteries are charged at 13.3v (summer) to 15.5v (winter).
I thought it was the other way round; doesn't the cell voltage increase with temperature?
 

Willbe

New Member
I thought it was the other way round; doesn't the cell voltage increase with temperature?
I think it has to do with how fast the battery will accept charge, and this is higher in the winter, so the regulator is set to take advantage of it.

Bosch, in their book on auto elec. stuff, has a weird-looking chart that shows charging current vs. engine speed vs. driving habits, etc. It seems to come down to keeping as much charge in the battery as long as you can without unduly shortening battery life.

Our Subaru seems to have cut this scenario pretty close for all the city driving we do. So far I haven't had to jumpstart this jalopy, but we came close once.
 
Last edited:

stuhagen

Member
OK I think I may be on the right path now. When originally designed for the 3.3 ref in V, that was based on a typical 12V supply. Well, when the car first starts up, it is actually outputting 14.4V. So this meant that my voltage divider was actually pumping in 4V to the comparator. Too close to my trigger voltage. Plus, the unstable car's voltage was too much for the LM311.

I have now inserted a 7805 to run the LM311 on regulated 5V. I have inserted a 3.0v Zener diode to keep the reference voltage too 3.0 v steady. I think this should do the trick. I havent made the new board yet, but I am sure this will fix it. I know it worked on 12V bench, so it should work. I will advise once it gets done.

Now I am working on a 0-5v linear adjustment circuit which I have over in another thread. This also will work off the cars voltage, and trigger a relay. So a lot of this has been a great help in uderstanding. I am still unable to find the correct resistance values when terms such as "Rh..Rs..RL are used.........more reading I guess.

Stu
 

stuhagen

Member
Well, after many attempts to get this to work, it isn't going to happen. Not sure what this issue is with the Vsrc input, but it isn't providing a signal that the comparator cannot recognize.

When I install this unit in the car, it operates perfectly when using a bench voltage generator. While the car is idling, with a 2V generated to the circuit, the car maintains its 9V to the fuel pump. The relay is in its N/C position. I crank the generator to 4V and the relay triggers and I am now seeing 16v to the fuel pump. Drop it back to 2v and it turns the relay back to 9v. I go to replace the generators supplied voltage with the cars computer 2v and it triggers immediately to 16v at idle. I can remove the 2v source wire all together and it does nothing. If I removed the Vsrc wire on the bench test, it shuts down the relay and it goes dead. I have actually gone out and logged the computers supply, and it is a very flat 2V then a 4.15V at the elevated rpms. So I know it is doing what it is supposed to do.

I talked to a friend who knows these cars well, and his only thought was this 2V/4V computer signal is really a "duty cycle" voltage. Now I don't know what this actually means, but whatever it is, it is not enough for this comparator circuit to recognize and operate as it should. If I owned an oscilloscope, I could look at what this is. If anyone has an idea on how to make this a viable voltage reference I will be all ears. This friend did suggest an OpAmp possible to amplify this. I then could change my Ref voltage up to adjust to this. But I am not sure if this is the answer or not. I need to read up on what a "duty cycle" voltage supply really is. I have attached a drawing I made with notes if anyone is interested.

Stu
 

Attachments

Status
Not open for further replies.

Latest threads

EE World Online Articles

Loading
Top