## The bleeder resistance

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triaco
Posts: 19
Joined: Fri Jan 31, 2014 5:05 am

### The bleeder resistance

Hi,

I've got a circuit like this:

My question is how can I match the bleeder resistor at BEST ?
There are formulas for that, but with my multimeters I can forget it; leakage current required etc...

Thank you.

DaveJ
Posts: 9
Joined: Fri Jul 26, 2013 10:03 am

### Re: The bleeder resistance

The FSS1 relay is a solid state relay. I don't think you would need a bleeder resistor in parallel with it.
This relay doesn't have a coil in it so the transistor doesn't need any protection from high voltage spikes when the relay is switched from on to off. That is when you usually use a bleeder resistor in parallel with a relay.
I am thinking that if you wanted to restrict the current flowing through the relay to 15mA you would use a resistor in series with the relay. at 5v you would use Ohms LAw to work it out E = IxR
therefore 5/0.015 = 330 ohm resistor. That would allow only 15mA to flow through the transistor.
The other way you could do it would be only allow the transistor to conduct 15mA by using the correct base resistor size.

triaco
Posts: 19
Joined: Fri Jan 31, 2014 5:05 am

### Re: The bleeder resistance

DaveJ wrote:The FSS1 relay is a solid state relay. I don't think you would need a bleeder resistor in parallel with it...
We are talking about two different topics, that in fact are confusing in theory.
In my case, yes you might need that bleeder resistor.
Anyway, I have already TUNED my circuit and runs for months without a hitch.

eric_1050
Posts: 5
Joined: Sat Aug 30, 2014 11:50 am

### Re: The bleeder resistance

Hello I know you have your project working,

But you do not need a bleeder resistor in parallel, you need a diode reverse bias across any coil to discharge any high volts back EMF the coil releases when power is removed from the coil, your project might work all right but it is safer to add the diode. In you flick through any project article in a electronics magazine you should see such a diode across any thing that has a inductance load.

To read more on bleeder resistors, where the purpose is used to discharge capacitors AFTER any electronic appliance has been turned off. To read more go to
http://en.wikipedia.org/wiki/Bleeder_resistor and read the part I added in many months ago "Electrical regulations"

angusgr
Freetronics Staff
Posts: 853
Joined: Tue Apr 09, 2013 11:19 pm
Location: Melbourne, Australia
Contact:

### Re: The bleeder resistance

Hi eric,

The load in the example shown is the Solid State Relay input which is not inductive like a normal relay coil, therefore no need for a back EMF/flyback diode.

The confusion may arise from the term "bleeder resistor". I think a more suitable term for the schematic shown in this thread is a "pull-up resistor". Thanks for the link to the page with explanation on the bleeder resistor term.

Angus

eric_1050
Posts: 5
Joined: Sat Aug 30, 2014 11:50 am

### Re: The bleeder resistance

Yes I had no idea what is inside the square box, the Impedance given distorted my response.

garyg58
Posts: 78
Joined: Wed Dec 27, 2017 12:51 am

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