I need a simple Polarity Reversing Circuit

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GuitarZombie

Joined Oct 31, 2014
11
I need a simple Polarity Reversing Circuit. It can be adjustable or can cycle on and off equally for a minimum of 60 seconds to a maximum of 5 minutes. I am alternating + and - on two 30V DC electrodes.

I have a DPDT 12 v relay RS 275-0206 that I would like to use.

Basically all I have to do is cycle the relay on and off automatically. I do not need an on switch. I have a variety of wall power supplies ranging fro 5 to 18 and 30 VDC.

I do not necessarily need a timing adjustment.

Given a reasonably simple circuit, I can build one. If I only had a party light that strobed in the time range I need, I would use that (LOL).
 

Alec_t

Joined Sep 17, 2013
11,637
This should give you about 2.5 mins on, 2.5 mins off. Change R1 to adjust the timing.
Note: long delays like this with a 555 are subject to errors in timing due to electrolytic capacitor leakage current (which can vary with age and temperature).
RelayDriver.gif
 

Thread Starter

GuitarZombie

Joined Oct 31, 2014
11
That's great! is there a chart or something where I can get all of the values of the diode? Plus I am assuming the voltage of a 555 is 5 volts. is that correct?
 

Thread Starter

GuitarZombie

Joined Oct 31, 2014
11
Thank you all! I didn't see the value of the diode and I had no idea a 555 worked on 5 - 15! Thanks again! I'll et you know how it turned out.
 

Alec_t

Joined Sep 17, 2013
11,637
The diode (just about any silicon diode will do) is there to supress the high voltage spikes which would otherwise occur when the relay coil switches off. If you omit it the 555 may die.
 

ScottWang

Joined Aug 23, 2012
6,933
If using a light current relay around 30mA then 555 is ok, otherwise using a transistor to drive the relay is better, and I like to do this way.
 

Thread Starter

GuitarZombie

Joined Oct 31, 2014
11
OK I got the diode, and the 555 will be only pulling the coil. The relay is 12V so According to ISB123 it should work (5-15V). The current of the coil is ? But I have found sites that say Nonmetal Current: 75mA - but I am thinking it is a typo but I have seen this on several sites. The relay will fire a separate power source. At $1.00 per 555, I'll probably try it as drawn, seeing I just got the components.
 

Thread Starter

GuitarZombie

Joined Oct 31, 2014
11
Well it didn't work. I am thinking that the current of the relay killed the 555. (It is a 555CN - but the pins are identical). I also used a microsoft wall supply that said 12V DC but when I metered it, it read 15.7 (within the spec of the 555). Can someone show me how to add a transistor to fire the relay - I'll need a schematic and component numbers (values). Thanks so much, when finished, I'll share my cool application. Oh and the 555 never heated up that I could feel.
 
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ScottWang

Joined Aug 23, 2012
6,933
You may choosing the Fig-01 diagram as below, same Rb or less that it depends on the current of relay, two pins of +V and Q1_C connecting to the coil of relay, and the diode(1N4001~1N4007) in parallel with relay, the negative of diode connecting to +V, the positive connecting to Q1_C.
+V → (-)diode(+) → Q1_C.

Or to google "ne555 pwm bjt drive relay", or to see the second circuit as this.


 

Alec_t

Joined Sep 17, 2013
11,637
the current of the relay killed the 555
It may have. And any spikes above 15.7V wouldn't show up on a conventional DMM.
Is it a LM555CN, or a LMC55CN? The latter has a 15V absolute maximum rating and certainly can't provide enough current to drive a relay.
Here's a mod of the circuit to use a transistor to drive a relay.
RelayDriver2.gif
 

Thread Starter

GuitarZombie

Joined Oct 31, 2014
11
Thank you for being patient.
I apologize for not being electrical literate. I can follow directions, but one should not assume that I know anything other than figuring out the orientation of diodes and capacitors and how to solder and follow directions. I have incorporated figure 1 as you mentioned. Does this schematic look correct?
 

ScottWang

Joined Aug 23, 2012
6,933
I'm not sure why you always forgot the diode, the diode is to protect the bjt for back emf of relay, just remember to in parallel a diode with the coil of relay, and the negative of diode connecting to Vcc.
The Rb is connecting to Pin 3 of ne555, and the (+) of relay is connecting to Vcc.
 
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