voltage drop

[audioguru]

Hi Nigel,
To drive his motors and LEDs he doesn't need the relays
anyway! :lol:

 

[George L.]

oh....

what resistor is to high... the 10K?

is there something wrong with the 180 ohm resistors because that is what you suggested.

i flipped the battery, capacitor, and diode

correct now?

thanks,

George

 

[audioguru]

Hi George,
Good, you have the circuit drawn correctly now.
The value of the 10k resistor is much too high because if the transistor has its lowest guaranteed gain of only 60 with your 60mA load, then 1mA must flow through the 10k resistor to turn-on the transistor. Ohm's Law says that 1mA through a 10k resistor requires 10V across it. Your transistor would never turn on!
With the PNP transistor, the 10k resistor had nearly the entire supply voltage across it.

If you use a 220 ohm resistor or a piece of wire instead of the 10k resistor, the max voltage at the emitter will be only about 7.9V with a 9V supply. With the PNP transistor circuit the relay got about one volt more. Learn about the differences between a common emitter circuit (the PNP one) and a common collector circuit (the NPN one) and look at the transistor's datasheet.
If you use 180 ohm voltage dropping resistors, the voltage across each relay will be only 4.6V with a 9V supply. (I said to use 180 ohm resistors with the PNP transistor circuit where the relay got 1V more). When the battery voltage sags to 6V over its life, the relay's voltage will be only 2.85V and won't work. With 100 ohm voltage-reducing resistors the relays should still work when the battery voltage is 6.35V. Look at the relay's datasheet.:lol:

 

[George L.]

ok...thanks(circuit is done)

I can probobly handle the rest of my project

thanks for helping, everyone!

George :wink:

 

[George L.]

Audioguru you said....

"To drive his motors and LEDs he doesn't need the relays anyway!"

I could use transistors, but I don't know how to use transistors instead of a relay.


George

 

[audioguru]

I don't know how to use transistors

We have noticed. :lol:

 

[George L.]

that is condisending, i would talk back, but I don't have time

 

[ljcox]

George,
I suggest that you look at circuits posted on this forum and look at sites such as www.discovercircuits.com

If there are any you don't understand, ask us to explain.

Len

 

[George L.]

thanks ljcox

 

[George L.]

Hello,

I have run into another problem, (two actually)

The first one is that the three relays I am trying to activate at the same time are turning off one by one instead of all at the same time. They go off one by one with the time interval of less then a second between each one going off.

Is there a way to fix this?

also... the relays do not activate when I use my "almost dead" battery its voltage is 7.81 V.

Audioguru said that is should work up to 6.35V

if anyone can help please do

thanks,

Geroge

 

[audioguru]

Hi George,
A fairly complicated Schmitt trigger circuit will activate all the relays at the same time. They turn off one at a time now because your new circuit reduces their voltage very slowly and they are all a little different from each other.

[quote Audioguru]With 100 ohm voltage-reducing resistors the relays should still work when the battery voltage is 6.35V.[/quote]
Did you use 100 ohm voltage-reducing resistors? With your 150 ohm resistors the relays will turn on when the battery voltage is above 6.9V, with 180 ohm resistors above 7.35V.
The battery's voltage should be measured when the circuit is trying to turn on the relays.

You didn't post the relay coil's resistance so i was just guessing. You also didn't post the relay's manufacturer's name nor the model of the relay so I couldn't lookup its spec's. Relays that I have used are guaranteed to activate with a coil voltage of 75% of their rating, 3.75V for your 5V ones.

Maybe the transistor's current gain is shot from abuse. :?:

 

[George L.]

Audioguru,

here is the site for the relays I have:

https://www.allelectronics.com/cgi-bin/category.cgi?category=500&item=RLY-625&type=store

the relays have 130 ohm coils ... I guess this changes all the calculations

I am using 100 ohm resistors and the 220 ohm for the base

the battery voltage when the relays are activated is 6.6V

(I can hear a slight click inside the relays with the "almost dead" battery, but the relays are not activating. )

the transistor is probably ok, I have only been using it for a few minutes of operation.

thanks,

George

 

[audioguru]

Hi George,
There 's the problem. The relays have about half the resistance that I assumed! They eat batteries. Also, the transistor's current gain is less with such a high current.
Four AA alkaline cells in series for a 6V battery will work well without any voltage-reducing resistors and last much, much longer than a little 9V battery. They cost less too. :lol:

 

[George L.]

Audioguru, I am using a 2N3904 NPN transistor

I attached the circuit that is up to date

do I still keep the 220 ohm resistor for the base?

also, could you please explain why I don't need any voltage reducing resistors any more and how you got 220 ohms.

thanks again,

George

 

[audioguru]

Four AA alkaline cells in series for a 6V battery will work well without any voltage-reducing resistors

Hi George,
Your schematic shows a 9V battery.
With a 6V battery, the transistor will drop about 1V when it is fully conducting, leaving 5V for your 5V relays.

Your circuit doesn't need the 220 ohm resistor. Your circuit will work about the same with it or without it. It is there to protect the transistor in case you accidently short the relays. Replace the 220 ohm resistor with a piece of wire. Connect the 220 ohm resistor in series with the pot to prevent it from smoking if it is turned down. :lol:

 

[George L.]

Hi Audioguru,

I changed the circuit (I really want to keep the 220 ohm base resistor :wink: )

Is the 220 ohm in series with the pot. there so the pot doesn't get damaged?

With the 6V battery, the circuit should work until the battery drops to what voltage.

also 8) .... I am planning to run two of these circuit at the same time, one circuit with three relays and one circuit with only one. Could I run both of the same battery, or do they need seperate.

thats about all.

thanks,

George

 

[ljcox]

Hello,

I have run into another problem, (two actually)

The first one is that the three relays I am trying to activate at the same time are turning off one by one instead of all at the same time. They go off one by one with the time interval of less then a second between each one going off.

Is there a way to fix this?

also... the relays do not activate when I use my "almost dead" battery its voltage is 7.81 V.

Audioguru said that is should work up to 6.35V

if anyone can help please do

thanks,

Geroge

George,
The reason the relays release at different times is because there is a spread in their release currents. Your circuit has no threshold and so the collector current reduces slowly hence each relay releases when the current through its coil falls below its release current.

All components have a spread in their characteristics. For example a 100k +/- 5% resistor has a spread of 5k. So if you buy 10 of them, their resistances will be spread between 95k and 105k.

As I said in the PM that I sent you some time ago, you need a Schmitt Trigger (such as the 40106 or you could use a 555) to do the timing - this will prevent the relays releasing at different times. Also, if you read what I said when I posted my suggestion, you will note that my circuit suffers from the same disadvantage.
In order to solve the voltage issue, you need to remove the resistors in series with the relay coils and instal a "low drop out" voltage regulator which has an output voltage of 5 Volt . Then your circuit will work down to whatever voltage the regulator drops out at.

Len

 

[George L.]

ljcox,

I never saw your PM. How do I check if I got it?

I only have acsess to a radioshack for my supplies. I know they have a 555 timer IC, we could use that to fix the problem like you said. They also have a 5V regulator.

thanks ,

George L.

 

[ljcox]

You should receive an email saying that there is a PM waiting for you.

Alternatlvely, click on the Private Messages button at the top of this screen just under "Electro Tech"

The regulator needs to be a "low drop out" type in order to maximumise the battery life.

Len

 

[George L.]

how can I use the 555 timer IC to stop the relays from going off one by one.

thanks,

George