Relay chatter when battery dies

Discussion in 'General Electronics Chat' started by Smoke_Maker, Jul 5, 2009.

  1. Smoke_Maker

    Thread Starter Active Member

    Sep 24, 2007
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    I am running a load (6 amps) off a deep cycle battery that has a low voltage sense circuit on it. The problem I am running into is when the battery is going dead around 10.80 volts the relay starts to chatter on and off.

    What I am looking for is a way to keep the relay from reengaging when the voltage rises because the load was disconnected.

    I have a voltage window detector MC64161, but what I am really looking for is a way to shut off the load to the battery when it go's to something like 11 volts, so I don't over discharge it.
     
  2. russ_hensel

    Well-Known Member

    Jan 11, 2009
    818
    47
    You might get away with something as simple as a series resistor. Tiral and error to see if it works.
    Note that the hold current ( and voltage ) for a relay is less then the pull in current so this can work if the voltage does not bounce up too much when the load is removed.
     
    Last edited: Jul 6, 2009
  3. Jsw123

    Active Member

    Jun 20, 2009
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    0
    You mat be able to set up the relay to hold. This way you will have to manually reset/start it after battery drainage.( your relay will have a start button) Many relays come with auxilary contacts these can be used to hold.
     
  4. R!f@@

    AAC Fanatic!

    Apr 2, 2009
    8,754
    760
    Post your schematics

    Rifaa
     
  5. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    Here is a circuit I recently built to disconnect a load from a 12V battery when the battey becomes discharged.
    The pot adjusts the trip point and is adjusted with this formula:
    TP=((Vcutoff)/(151.1KΩ)X51.1KΩ, TP is the voltage adjusted at the testpoint or TP. In my case the load current can be up to 20A.
     
    Last edited: Jul 6, 2009
  6. Smoke_Maker

    Thread Starter Active Member

    Sep 24, 2007
    126
    15
    Thanks k7elp60, I should have gone with a opamp but decided to try and get voltage detector MC33161 to work, I have it configured as a window detector with a really clean set points but it turns back on as soon as the load is turned off. I see in your schematic that there is no way to keep it from turning on again also.

    I created a schematic in PCB last night but I can't get it out. I will recreate it in Eagle and post it, be right back.
     
  7. Smoke_Maker

    Thread Starter Active Member

    Sep 24, 2007
    126
    15
    Here is the schematic, what do I need to do to make it like a one shot or put more hysteresis in it?
     
  8. k7elp60

    Senior Member

    Nov 4, 2008
    478
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    In my circuit the opamp circuitry is always monitoring the applied voltage. When the battery gets charged to the trip point it turns the powermosfet on again, supplying power to the load.
     
  9. Smoke_Maker

    Thread Starter Active Member

    Sep 24, 2007
    126
    15
    So what I think you are saying is, that it has enough hysteresis to prevent the MOSFET from turning on until the battery is recharged.?

    I will try to breadboard that circuit this weekend, to see if it will fit my need.
     
  10. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    Im not sure if there is enough hysteresis, the circuit is built and being tested now. My circuit has an intermittent load and hopefully the 47uF capacitor in parallel with the 47KΩ resistor will give a little hysteresis. In testing with a bench power supply. When the PS was adjusted to the trip point the load was disconnected. When the PS was adjusted above the trip point the load reconnected. I may have to redue the circuit with some hysteresis.
    But looking at your circuit with the MC33161, it can be programmed so that the two open collector transistors can be programed to do what you want. I would continue to use a pullup resistor from pins 5 & 6 tied together. You could continue to use the relay, use a transistor driver for it, if necessary. If you use a NPN driver transistor, connect one side of the relay to Vcc, the other side to the collector of the transistor. The emitter to ground, and a resistor from base to pins 5&6 of the MC33161. Program the MC33161 to be high out when the upper voltage is reached and low when the lower voltage is reached. Be sure and use a diode in parallel with the relay coil to discharge the coil counter emf when the relay deenergizes.
    To get the hysteresis you want you need to use two seperate voltage dividers for the two inputs. This will make it a true window detector and then the two trip points could be a great difference.
     
    Last edited: Jul 8, 2009
  11. Smoke_Maker

    Thread Starter Active Member

    Sep 24, 2007
    126
    15
    After rereading the data sheet for the MC33161
    http://www.intusoft.com/onsemipdfs/mc34161.rev5.pdf

    The only configuration I can see working as needed is figure 23, pin 5&6 will go high when the low set point is crossed during discharge and will not go low until a negative voltage is reached, so all I need to do is invert the signal out of pin 5&6.

    Dose this look doable.
     
  12. k7elp60

    Senior Member

    Nov 4, 2008
    478
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    I think the circuit of figure 16 with out the dashed line LED and resistor.
    Connect the base of a PNP to the output of the MC33161, the emitter to Vcc, and the collector to the high side of the relay. Then the relay would be energized between the two voltages.
     
  13. Smoke_Maker

    Thread Starter Active Member

    Sep 24, 2007
    126
    15
    After I posted the reply and went to bed it hit me that it won't work. Think about the how a lead acid battery acts, when you remove the load the voltage rises to a higher level, thus chatter.

    I think what I need is a one shot or could I set up a opamp to turn off at 11 volts and not turn on again until it see 14 volts (turn off means low)?
     
  14. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    I think you are correct. I have a circuit of a 555 timer that only uses the trigger points to control the output, and of course it latches. If you like I can post the schematic.
     
  15. Smoke_Maker

    Thread Starter Active Member

    Sep 24, 2007
    126
    15
    Yes, please do. I would like to light a LED when the battery hits 11 volts and the LED not turn off until the battery sees 14 volts, but I don't how to configure the opamp.

    I started reading a tutorial on opamps as a brush up.
     
  16. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    Here is the circuit with the 555.
    I breadboarded it and it worked great. I put a 220 resistor in series with an LED on pin 3 and one the voltage went down to the lower trip point the LED stayed on until the input voltage reached the uppper trip point. Upon application of power when the voltage was above the upper trip point the
    LED flashed very quickly, but stayed off.

    P.S. I live about 150 miles from Las Vegas.
     
  17. Smoke_Maker

    Thread Starter Active Member

    Sep 24, 2007
    126
    15
    I bread board the circuit and it's not quite what I need. the output pin transition from low to high at the set point as the voltage is lowered.

    What I want is a circuit that is high between 14 volts down to 11 volts and then go low at 11 volts until the voltage rise above 14 volts.

    In other words, the battery starts out at 12.6 volts and the green LED is on, when the voltage drops to 11 volts the green LED go's dark until the voltage rises above 14 volts again and then the LED turns on again, then repeat.
     
  18. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    I think if you add a single NPN transistor on the output of pin 3 as an inverter the circuit will do what you want.
     
  19. Smoke_Maker

    Thread Starter Active Member

    Sep 24, 2007
    126
    15
    I used a 57k for the R1 and 32k for R2. I only got one transition from high to low going from 5 volts up to 18 volts.

    I can't find the window 11 volts to 14 volts.
     
  20. k7elp60

    Senior Member

    Nov 4, 2008
    478
    69
    I rebuit the circuit and found upon further testing it really didn't do what we both wanted. I made some changes and this is the results:
    On application of power at below the upper threshold the LED and the relay were off. Increasing the voltage of the power source to at or above the upper threshold the LED came on and the relay was energized. If the applied voltage was reduced to near the lower threshold the LED went off and the relay deenergized. Disconnecting the power and reappling with the power below the upper threshold the LED stayed off and the relay didnot energize.

    I also tried the circuit with the CMOS and the normal versions of the 555. Notice the 100uF capacitor on the input rails. Without it the circuit still was intemittent on
    occasion.
    Hope this helps.
     
    Last edited: Jul 13, 2009
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