Then I can run my relays directly off it, correct?

You probably could.

I wouldn't. Why?

According to datasheet Voh at 15v Vcc could be as low as
12.5V (drop of 2.5V). If @12V Voh is 10v (a drop of 2.0V)
and if your relay (just guessing) requires say 9V as an absolute
minumum to turn on, it may not turn on reliably or worse
yet, chatter.

12V @ 85 ohm = 141.2mA

Take it easy on that I.C.
No need to run it at 70% of its rated capacity, even
though it will only be high for "a second".

Transistor would allow "emergency" use of any
556, including a CMOS version.

Transistors are rugged, reliable, simple to design circuit for,
plentiful, cheap.....

Whichever way you go protection/flywheel diodes are a must have.

Next answer:
For a "small signal" transistor (such as 2N2222),

For a quick and dirty value of the base resistor take
load resistance (relay coil) X 10. (When supplying
base with approx same voltage as collector).

Pulldown resistor (Base to ground) = base resistor X 10
Needed because Vol is not 0 and you need to make sure
transistor is turned off.

These values are not arrived at in the "most scientific"
method, there are formulas for this stuff that will
produce the "correct" values, but will do fine to get you started.

Edit: I'm glad to see you checked to see for yourself the paltry
source current of original 556 you had chosen.

 

You probably could.

I wouldn't. Why?

According to datasheet Voh at 15v Vcc could be as low as
12.5V (drop of 2.5V). If @12V Voh is 10v (a drop of 2.0V)
and if your relay (just guessing) requires say 9V as an absolute
minumum to turn on, it may not turn on reliably or worse
yet, chatter.



Take it easy on that I.C.
No need to run it at 70% of its rated capacity, even
though it will only be high for "a second".

Transistor would allow "emergency" use of any
556, including a CMOS version.

Transistors are rugged, reliable, simple to design circuit for,
plentiful, cheap.....

Whichever way you go protection/flywheel diodes are a must have.

Next answer:
For a "small signal" transistor (such as 2N2222),

For a quick and dirty value of the base resistor take
load resistance (relay coil) X 10. (When supplying
base with approx same voltage as collector).

Pulldown resistor (Base to ground) = base resistor X 10
Needed because Vol is not 0 and you need to make sure
transistor is turned off.

These values are not arrived at in the "most scientific"
method, there are formulas for this stuff that will
produce the "correct" values, but will do fine to get you started.

Edit: I'm glad to see you checked to see for yourself the paltry
source current of original 556 you had chosen.

The second 556 I found has a true 200mA sink/source. Ohms law says my DPDT only pulls 65mA. Would it be acceptable to tun those direct (my intentions). That's only a 32% load for one second.

As far as the relay actuation voltage,

Manufacturer Part #: 782XBXC-12D

Nominal Input: 12VDC
Nominal Resistance: 160Ohm
Coil Pull In Voltage (DC): 80% of Nominal
Coil DropOut Voltage (DC): 10% of Nominal

So Pull-in is 9.6 volts, drop out is 1.2 volts.

That's not accounting for the inline diode feeding it, which drops output voltage by .6 volts. So I need a minimum 10.8 output volts to engage it. I don't think that will be a problem, though.

http://www.mouser.com/catalog/specsheets/850-0210.pdf

 

The second 556 I found has a true 200mA sink/source. Ohms law says my DPDT only pulls 65mA. Would it be acceptable to tun those direct (my intentions). That's only a 32% load for one second.

http://www.mouser.com/catalog/specsheets/850-0210.pdf

and when you NEED to replace it quickly and can't get the high output ones, a transistor will allow a wider substitution range of useable chips.


I felt that point needed repeating.

 

You have come this far. Go get a 555 timer or three and we will do this neat trim and proper. The math exercises you just went through will serve you VERY well in the coming change.
We are going to use transistors. They will 'switch' the relays on and off.

Also:

According to datasheet Voh at 15v Vcc could be as low as
12.5V (drop of 2.5V). If @12V Voh is 10v (a drop of 2.0V)
and if your relay (just guessing) requires say 9.6V as an absolute
minumum to turn on, it may not turn on reliably or worse
yet, chatter.

 

For a "small signal" transistor (such as 2N2222),

For a quick and dirty value of the base resistor take
load resistance (relay coil) X 10. (When supplying
base with approx same voltage as collector).

Pulldown resistor (Base to ground) = base resistor X 10
Needed because Vol is not 0 and you need to make sure
transistor is turned off.

So between output and base is 1600 ohms, between base and ground is 16Kohm? Emitter to ground and Collector to load?

Do I still need the extra in-line diode with the transistor? Or just the coil jumper?

Something I just thought about, yea the transbrake is an inductive load (solenoid) with no diode, but do I need a diode across the coil of the relay that I'm connecting to the Tbrake wire? (the trigger relay)

 

(The +12 here is for the launch control, not the power for the box)

 

So between output and base is 1600 ohms, between base and ground is 16Kohm? Emitter to ground and Collector to load?

We can do better than the "quick and dirty" X 10 method.
We want to make sure that switch (transistor) turns on
"hard and fast".

For 2n222A transistor:
When collector current is 75 mA (relay coil @ 160Ω @12v)
Base current should be 7.5mA (Collector current / 10) for
using transistor as a switch.

Vbe (Voltage base to emitter) from datasheet is ≈ .9V.

OUTPUT voltage from 556 @ 12v Vcc is ≈ 10v (guess from datasheet)

So to get base resistor:
(10V-.9V)/.0075=1213

1.2K should be fine

Pulldown resistor from base to ground 10K-12K.
Pulldown to make sure that transistor turns off
fast and completely (your Vol from 556 is not 0, remember).

Something I just thought about, yea the transbrake is an inductive load (solenoid) with no diode, but do I need a diode across the coil of the relay that I'm connecting to the Tbrake wire? (the trigger relay)

If it is easy to get to/install every relay should (opinion) have one.
That being said, there are relays all over the place that won't have them. You probably can't get everyone, get the ones closest to your circuit.

Do I still need the extra in-line diode with the transistor? Or just the coil jumper?

I don't think so. Only the one "connected backwards" across
the relay coil should be needed.

One thought on the relay. "ice cube" relays are not as easily
gotten in emergencies as regular "Bosch type". For space saving
consider "PCB mount", but not easily replaceable.

 

We can do better than the "quick and dirty" X 10 method.
We want to make sure that switch (transistor) turns on
"hard and fast".

For 2n222A transistor:
When collector current is 75 mA (relay coil @ 160Ω @12v)
Base current should be 7.5mA (Collector current / 10) for
using transistor as a switch.

Vbe (Voltage base to emitter) from datasheet is ≈ .9V.

OUTPUT voltage from 556 @ 12v Vcc is ≈ 10v (guess from datasheet)

So to get base resistor:
(10V-.9V)/.0075=1213

1.2K should be fine

Pulldown resistor from base to ground 10K-12K.
Pulldown to make sure that transistor turns off
fast and completely (your Vol from 556 is not 0, remember).

If it is easy to get to/install every relay should (opinion) have one.
That being said, there are relays all over the place that won't have them. You probably can't get everyone, get the ones closest to your circuit.

I don't think so. Only the one "connected backwards" across
the relay coil should be needed.

Well consider that we have an electric fuel pump, electric water pump, 2 electric fans, transbrake, shift solenoid, that's 4 electric motors and 2 inductive coils. Then relays to drive all of them. So there are a total of 4 electric motors, 2 large coils, and at least 4 relay coils. None of which have protection diodes......

One thought on the relay. "ice cube" relays are not as easily
gotten in emergencies as regular "Bosch type". For space saving
consider "PCB mount", but not easily replaceable.

I was wondering if I should get get the 5 pin DPST standard-form relays myself. The only difference, is that the ice cube relays are 160Ω coil, the bosch style are 85Ω. The ice cubes actually fit pretty well right now, the bosch's would actually be loose, even with velcro to hold them. The ice cubes fit almost perfectly.

 

I was wondering if I should get get the 5 pin DPST standard-form relays myself. The only difference, is that the ice cube relays are 160Ω coil, the bosch style are 85Ω. The ice cubes actually fit pretty well right now, the bosch's would actually be loose, even with velcro to hold them. The ice cubes fit almost perfectly.

2n2222 can switch up to 1A (1000mA). 500mA is
probably a more practical (read: reliable) value.
A relay coil of the types mentioned so far do not
even approach this level.

Either way style is a choice as long as operating
parameters are met.

 

2n2222 can switch up to 1A (1000mA). 500mA is
probably a more practical (read: reliable) value.
A relay coil of the types mentioned so far do not
even approach this level.

Either way style is a choice as long as operating
parameters are met.

Well I was intending to just do a direct feed, that's why I went with the ice cubes, since they make ohm's law. But the transistor method is more reliable, so i'll probably pull it all out and re-solder it with those put in. I'm still going to get the NE556 timer. Hopefully this will be the last set of revisions.

So I need two 1.2-1.5Kohm resistors, two 2N2222's, and 2 bosch 5 pin relays? I have 2 10K resistors already.

 

So I need two 1.2-1.5Kohm resistors, two 2N2222's, and 2 bosch 5 pin relays? I have 2 10K resistors already.

Recalculate base resistors based on load (resistance), if
you change relays (1.2K is based on 75mA collector current)
(which is based on 160Ω relay coil).

Pulldowns (10-15K) won't need changed.

 

Recalculate base resistors based on load (resistance), if
you change relays (1.2K is based on 75mA collector current)
(which is based on 160Ω relay coil).

Pulldowns (10-15K) won't need changed.

When collector current is 140 mA (relay coil @ 85Ω @12v)
Base current should be 14mA (Collector current / 10) for
using transistor as a switch.

Vbe (Voltage base to emitter) from datasheet is ≈ .9V.

OUTPUT voltage from 556 @ 12v Vcc is ≈ 10v (guess from datasheet)

So to get base resistor:
(10V-.9V)/.014=650

(12V-.9V)/.014= 800

Vbe stays constant I assume?

So I need two 650-800ohm resistors, two 2N2222's, and 2 bosch 5 pin relays? I have 2 10K resistors already.

 

When collector current is 140 mA (relay coil @ 85Ω @12v)
Base current should be 14mA (Collector current / 10) for
using transistor as a switch.

Vbe (Voltage base to emitter) from datasheet is ≈ .9V.

OUTPUT voltage from 556 @ 12v Vcc is ≈ 10v (guess from datasheet)

So to get base resistor:
(10V-.9V)/.014=650

(12V-.9V)/.014= 800

Vbe stays constant I assume?

So I need two 650-800ohm resistors, two 2N2222's, and 2 bosch 5 pin relays? I have 2 10K resistors already.

Looks good.

Pay attention to pinout on them transistors.
Breadboard a trial if you can.

 

Looks good.

Pay attention to pinout on them transistors.
Breadboard a trial if you can.

I have to be done by Tues- relatives arrive on wed, leave sunday, then we're sending the car off for 2 weeks sunday night for headers, get it back and send the axle off to get rebuilt, and tearing down the engine and trans while the axle is off. Would prefer to have it done before we send it off so I can test it, otherwise it'll be till january before I can test it again.

transistors- http://www.mouser.com/ProductDetail/ON-Semiconductor/P2N2222AG/?qs=sGAEpiMZZMtvtNzZ3W%252bLwDFLbhmxBhTpM8WFDZBeQEo%3d

11K resistors- http://www.mouser.com/ProductDetail...=sGAEpiMZZMu61qfTUdNhG2ZPHRPE95IicrKL3RjtkWM=

750 resistor- http://www.mouser.com/ProductDetail...GAEpiMZZMu61qfTUdNhG%2bDQRbLcOBw9i2UqtYZjfLE=

 

I have to be done by Tues-

I don't know if you are ordering online
or picking it up local.

If you have a local store such as
even Radioshack open on Sunday you
could pick items up tomorrow.
You may have even better choices in larger towns.
(Don't count on staff to know many details)
(Impress them gals by using their computer to check Datasheet).

Many readily available "small signal" transistors will
do. (2N2222, 2N4401, and others).
(Quick check of Ic MAX (collector current) and hfe(current gain))

Resistors don't need to be 1 watt.
1/2 watt would be plenty, 1/4 watt good enough.

Exact values not necessary, you have some tolerance.
(Tolerance is one reason for a sound design.)

 

I don't know if you are ordering online
or picking it up local.

If you have a local store such as
even Radioshack open on Sunday you
could pick items up tomorrow.
You may have even better choices in larger towns.
(Don't count on staff to know many details)
(Impress them gals by using their computer to check Datasheet).

Many readily available "small signal" transistors will
do. (2N2222, 2N4401, and others).
(Quick check of Ic MAX (collector current) and hfe(current gain))

Resistors don't need to be 1 watt.
1/2 watt would be plenty, 1/4 watt good enough.

Exact values not necessary, you have some tolerance.
(Tolerance is one reason for a sound design.)

I do will-call over at mouser, it's nice and cheap. Radioshack doesn't know jack, doesn't carry jack, and is expensive, I dont have any other retailers.

Who said overbuilding was a bad thing? (especially when pennies are the difference)

So what I picked out will work?

 

So what I picked out will work?

Yes, good to go.

 

Yes, good to go.

Here's everything I've got ready to order

1x http://www.mouser.com/Search/Produc...virtualkey62000000virtualkey893-896H1CHC12VDC

1x http://www.mouser.com/Search/Produc...virtualkey62000000virtualkey893-896H1CHC00112

2x http://www.mouser.com/Search/ProductDetail.aspx?R=294-750-RCvirtualkey21980000virtualkey294-750-RC

2x http://www.mouser.com/Search/ProductDetail.aspx?R=294-11K-RCvirtualkey21980000virtualkey294-11K-RC

2x http://www.mouser.com/Search/ProductDetail.aspx?R=P2N2222AGvirtualkey58410000virtualkey863-P2N2222AG

Am I missing anything?

 

Here's everything I've got ready to order



Am I missing anything?

Spares, in case of mishap.

Pick good quality (well known namebrand) relays if you can.
Switching small signals reliably requires good contacts and
reliable coils.