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Relay?

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kchriste

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If you are worried about current consumption of the relay, use a set/reset type. They only need current when you change their state.
 

BrownOut

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what is the min current required to make a relay work?
Because i'm a using a very low current ( in uA / less than mA) circuit, parallel to which i want to use a relay that switches my Domestic Power Supply.
Depends on the relay.
 

MikeMl

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what is the min current required to make a relay work?
Because i'm a using a very low current ( in uA / less than mA) circuit, parallel to which i want to use a relay that switches my Domestic Power Supply.
The power required to operate the coil of a relay is quite large, even for a "sensitive" relay. Look at this page. It lists several sensitive 12Vdc relays with a coil resistance of 700-800Ω, meaning that it takes ~15mA to pull them in.
 
The power required to operate the coil of a relay is quite large, even for a "sensitive" relay. Look at this page. It lists several sensitive 12Vdc relays with a coil resistance of 700-800Ω, meaning that it takes ~15mA to pull them in.
So, what can i do now? my load current is very low. i hav already buil a circuit on it, wat can i do now? i require this relay to switch the domestic power supply, it seems like not possible since my circuit current is too low uA???!!!!!!!!!!
 

kchriste

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Like I said, "If you are worried about current consumption of the relay, use a set/reset type." If your current source can only supply uAs then use a capacitor to store the power and dump it into the set or reset coil of the relay. The relay only needs a very short burst of current to turn it on or off.
 

BrownOut

Banned
So, what can i do now? my load current is very low. i hav already buil a circuit on it, wat can i do now? i require this relay to switch the domestic power supply, it seems like not possible since my circuit current is too low uA???!!!!!!!!!!
Physics can be a cruel master. There's nothing anyone can do about your circuit but you. Sometimes, you just have to start over.
 

colin55

Well-Known Member
r.vittalkiran - - - - That's why you should start to learn a bit more about electronics - - I have never been asked this sort of question in 35 years from any student. They all seem to realize a relay takes more than microamps to operate.
 

alphacat

New Member
As kchriste said, why not using a capacitor to latch/unlatch the relay?

The relays i've seen, required 15msec of applied power in order to change their state.
 

KMoffett

Well-Known Member
what is the min current required to make a relay work?
Because i'm a using a very low current ( in uA / less than mA) circuit, parallel to which i want to use a relay that switches my Domestic Power Supply.
Can you post a schematic (or sketch) of your circuit?

Since you already have "domestic power" available, can you just add a wall-wart to power a relay, and a MOSFET or transistor (or 2) to drive it from your µA source?

Ken
 
Can you post a schematic (or sketch) of your circuit?

Since you already have "domestic power" available, can you just add a wall-wart to power a relay, and a MOSFET or transistor (or 2) to drive it from your µA source?

Ken
i dont want too use transistor here... brief circuit is given below,
not sure of using wall-wart, because it may lead to electric shock??!
 

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BrownOut

Banned
Wall warts are safe. They use a transformer to isolate the output from the mains.
 

KMoffett

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Your circuit will never work as shown. There is barely enough current in you water detection loop to turn on a transistor, let alone a relay. As BrownOut said, a wall-wart is isolated and perfectly safe for your purpose.

You may want to Google: water liquid detector alarm circuit
There are tons of circuits that do what you want...and most of them work. ;)

Ken
 

MikeMl

Well-Known Member
Most Helpful Member
Besides, this is the fourth thread he has started. I already showed him how to turn on a fet (and switch a load like a relay) three threads ago...
 
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Like I said, "If you are worried about current consumption of the relay, use a set/reset type." If your current source can only supply uAs then use a capacitor to store the power and dump it into the set or reset coil of the relay. The relay only needs a very short burst of current to turn it on or off.
Sir, you mean that i have to use a capacitor, but capacitor blocks DC rite?, can i have a simply diagram, so that it will make me understand...I may be preety silly for u all, but i'm still learning
 

kchriste

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Sir, you mean that i have to use a capacitor, but capacitor blocks DC rite?
It also stores DC. So you can charge it slowly at a uA rate and release the charge much quicker at a ma rate.
, can i have a simply diagram, so that it will make me understand.
A very simple diagram would be like this:

When the switch is up, the cap is connected to the supply via a current limiting resistor. This slowly charges the capacitor up. When the switch is down, the cap is connected across the relay coil and supplies the needed high current to activate it briefly. A latching relay only needs a short pulse to switch states.
 

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