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Latching Relay Redux

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JLuckey(at)pacbell.net
Guest

Posted: Wed Jun 27, 2012 9:23 am Post subject: Latching Relay Redux

Back in 2011 there was some discussion of new latching-type relay/contactors that might be suitable for use as master relays.  

   

I remember at the time looking at the spec sheets & pricing of some of those devices and they seemed available & reasonably priced.  

   

I google search earlier this week failed to turn-up any devices that were reasonably priced and they seemed to have huge lead times.  

   

I want to consider using such a device but if they are difficult to get, I won’t bother.  Does anyone have a source(s) for such a device?  

   

TIA  

   

   

   

Jeff Luckey  

   

       [quote][b]

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 27, 2012 10:02 am Post subject: Latching Relay Redux

At 12:21 PM 6/27/2012, you wrote:

Back in 2011 there was some discussion of new latching-type 

relay/contactors that might be suitable for use as master relays.



I remember at the time looking at the spec sheets & pricing of some 

of those devices and they seemed available & reasonably priced.



I google search earlier this week failed to turn-up any devices that 

were reasonably priced and they seemed to have huge lead times.



I want to consider using such a device but if they are difficult to 

get, I won't bother.  Does anyone have a source(s) for such a device?



   If your design incorporates this, or any other

   uniquely crafted product, you're presented with

   both 'spares' and 'unconventional operations'

   issues. If the design goal is to reduced energy

   consumption in the battery contactor, you could

   craft a duty-cycle controller that drops the

   contactor excitation to about 1/2 say 1 second

   after you energize it. More than enough to keep

   it closed yet drops heating (energy consuption)

   by 75% or so.



   Then you can use ANY contactor in the constellation

   of similar devices while. What's more, with a

   alternate feed path to an E-bus, risks to mission

   for failure of your energy conservation device are

   covered by the same Plan-B that covers main

   alternator failure. The airplane's controls are

   consistent with legacy philosophies and no new

   spares issues are created.



   Bob . . .

JLuckey(at)pacbell.net
Guest

Posted: Wed Jun 27, 2012 12:02 pm Post subject: Latching Relay Redux

Bob,



All good points, many of which have been discussed on this forum.



I'm currently doing a more academic analysis (you know, when you are stuck

in traffic) as to how such devices might improve a system design (if at all)

but, if they are difficult to obtain then I think the point is moot.



BTW - a "pull & hold" circuit seems to me to be a non-starter - putting a

bunch of 'exotic' circuitry in the critical path of the coil circuit to

accomplish such a trivial task seems to me to be counter-productive.  If you

are counting milliamps then your system probably has bigger problems.

-Jeff



--

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Jun 27, 2012 12:48 pm Post subject: Latching Relay Redux

 	  Quote: 	
		  BTW - a "pull & hold" circuit seems to me to be a non-starter - putting a

 bunch of 'exotic' circuitry in the critical path of the coil circuit to

 accomplish such a trivial task seems to me to be counter-productive.  If you

 are counting milliamps then your system probably has bigger problems. 	


    That philosophy is core to this product from Tyco



   



   which not only offers a sealed atmosphere environment

   for better high voltage handling but an after-engagement

   duty-cycle managed for reduced power consumption. But

   it's about a $135 device as I recall.



   One of the drivers for installation of the E-bus was

   to eliminate the 0.7A draw of a battery contactor

   during alternator-out operations. That much current

   would run several radios . . . but might seriously

   impact a design goal for battery-only endurance to

   exceed fuel endurance. Trivial task? It's a matter

   of degree . . .



   Exotic? About $6 worth of Radio Shack parts

   will do it and it doesn't increase risks. But

   if one has a Rotax 18A or SD-8 excited airplane

   the wasted watts become more critical than when

   you've got 60A alternator with 40 to burn. So

   one could choose to achieve similar performance

   with a plain vanilla contactor and DIY duty-cycle

   management.



   Hardware capable of very fancy footwork is becoming

   less expensive while consuming less power. The things

   one could put in a 25 year-old VariEz lit up with

   an SD-8 were very limited . . . not so much today.



   It's all inter-related and as mentioned earlier,

   related to mission, hardware, full up vs.

   endurance loads, battery sizes and PM protocols.

   So if latching battery contactor is more a 

   attractive than a duty-cycle managed device, you

   are ultimately responsible for the formulation

   of design goals and techniques used to meet them.

   The basket of bits-and-pieces with which the big

   picture is painted is huge . . .



 

   Bob . . .    [quote][b]

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Thu Jun 28, 2012 7:51 am Post subject: Re: Latching Relay Redux

Attached is an untried circuit to reduce contactor current using PWM.

The TC648 costs less than $2.  It will start up at 100 percent duty cycle to pull in the master contactor.  Then it will hold with PWM at reduced current.  The progressive transfer type switch will normally be operated in the center position but can be full up to bypass the PWM circuit.

http://ww1.microchip.com/downloads/en/DeviceDoc/21755b.pdf

Joe

Contactor PWM.pdf

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_________________
Joe Gores

JLuckey(at)pacbell.net
Guest

Posted: Thu Jun 28, 2012 8:51 am Post subject: Latching Relay Redux

Joe



As I have mentioned in previous posts, I'm not a big fan of adding complex

circuitry to the coil circuit of the master contactor.  I think it makes the

system less reliable for very little benefit.



However, I do like the way the switch is wired in that schematic with the

bypass circuit.



-Jeff



--

bobmeyers(at)meyersfamily
Guest

Posted: Thu Jun 28, 2012 10:44 am Post subject: Latching Relay Redux

Just a note,



I got one of these Tyco EV200 for use in my Sonex with an Aerovee Volkswagen conversion with a 20 amp alternator.  I got mine on eBay for about $60 three years ago and they seem to be in that same ballpark today on ebay.

I went from a measured contractor draw of 0.7A to 0.13A.  The product is very robust and the amperage savings can almost operate my EFIS. 

 Bob Meyers



Flight testing completed, now flying Sonex N982SX. Web Site Index http://N982SX.com

 

 



 [quote][b]

Tundra10

Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario

Posted: Tue Jul 03, 2012 1:59 pm Post subject: Latching Relay Redux

Joe,



Not shown in your diagram is the spike shunting diode on the contactor  

to protect the FET.



Jeff Page

Dream Aircraft Tundra #10



 	  Quote: 	
		   Time: 08:51:57 AM PST US

 Subject: Re: Latching Relay Redux

 From: "user9253" <fran4sew(at)banyanol.com>



 Attached is an untried circuit to reduce contactor current using PWM.

 The TC648 costs less than $2.  It will start up at 100 percent duty  

 cycle to pull

 in the master contactor.  Then it will hold with PWM at reduced current.  The

 progressive transfer type switch will normally be operated in the  

 center position

 but can be full up to bypass the PWM circuit.

 Joe



 --------

 Joe Gores

user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Tue Jul 03, 2012 6:38 pm Post subject: Re: Latching Relay Redux

Good point, Jeff.  My mistake.  I added a diode.  Keep in mind that I have never built this circuit.  So there is no guarantee that it will work.  The TC648 operating frequency of 30HZ can possibly be increased with a smaller value of C5.   The TC648 is designed for use with fan motors which have inertia.  The off time period is not a concern with fans but is a concern with contactors that could drop out.  If my math is correct, the off time period at 25 percent duty cycle is 25ms.  This might be too long and allow the contactor to drop out.  The diode will delay the drop out.  Will a capacitor in parallel with the contactor coil also help to delay the drop out?

Joe

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_________________
Joe Gores

Tundra10

Joined: 14 Jun 2010
Posts: 102
Location: Scarborough, Ontario

Posted: Tue Jul 03, 2012 7:12 pm Post subject: Re: Latching Relay Redux

Has anyone considered this voltage doubling circuit ?  It was the Circuit Cellar EQ question in Issue 248 March 2011.



The theory behind the circuit is that while the contactor is off, the capacitor charges to 12V.  When the switch is turned on, the positive of the capacitor is 0V, so the negative side becomes -12V.  The transistor now conducts, applying 12+12=24V across the contactor coil, closing it.  The capacitor quickly discharges and the transistor switches off, leaving 12V across the contactor coil.  12V is probably enough to keep the contactor closed and at half the current of a 12V contactor.



Once the flight has begun, the failure mode is down to the contactor, the switch and one diode, which is the same component count as the standard circuit (The spike shunt diode is not required for this circuit, since the current from the coil serves to charge the capacitor faster).



The article did not propose values for the components, so it is quite possible that the capacitor would need to be impractically large.



Jeff Page

Dream Aircraft Tundra #10

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user9253

Joined: 28 Mar 2008
Posts: 1927
Location: Riley TWP Michigan

Posted: Mon Jul 30, 2012 6:07 pm Post subject: Re: Latching Relay Redux

I received this email today from Chuck (quoted below) in reference to my circuit "Contactor PWM.pdf " to reduce contactor holding current.

http://forums.matronics.com/download.php?id=32370

 	  Quote: 	
		  Hello Joe 

I built the circuit with one change. I replaced R1 with an adjustable 0-25k ohm pot. Works great, just dial in the PWM for the right duty cycle with R1 for the particular contactor being used.

Thanks Chuck

_________________
Joe Gores

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Aug 01, 2012 5:03 am Post subject: Latching Relay Redux

At 09:07 PM 7/30/2012, you wrote:

 	  Quote: 	

I received this email today from Chuck (quoted below) in reference 

to my circuit "Contactor PWM.pdf " to reduce contactor holding current.

http://forums.matronics.com/download.php?id=32370

 > Hello Joe

 > I built the circuit with one change. I replaced R1 with an 

 adjustable 0-25k ohm pot. Works great, just dial in the PWM for the 

 right duty cycle with R1 for the particular contactor being used.

 > Thanks Chuck

   I recommend that the power saving duty cycle

   be set for not less than 50%. This cuts average

   voltage to contactor by 50% . . . hence average

   current by 50% and total power dissipated by

   75%.

   While a 12v contactor will stay energized at

   voltages of 2v or below, you want to make sure

   that the contactor stays closed down to battery

   end of life at 10.5 volts or so. 50% at 14 volts

   with alternator running gives you 7 volts to hold

   the contactor . . . 10.5 translates to 5.25 volts

   or thereabouts . . . probably as low as you want

   to go. 75% reduction in lost energy is pretty

   substantial if you're in a battery-only operational

   mode . . . or struggling to make the most of an

   8A alternator.

   Bob . . .

   Bob . . .

klehman(at)albedo.net
Guest

Posted: Wed Aug 01, 2012 7:22 am Post subject: Latching Relay Redux

Is that 75% power reduction correct??



I would have guessed that a 50% duty cycle gave full voltage and full 

current for 50% of the time in a pulsed resistance circuit resulting in 

a 50% power reduction. Not sure about an inductive coil contactor though.



Just asking but intuitively I would not have averaged the voltage and 

applied the I squared power calculation to this.



Ken



On 01/08/2012 9:02 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		   

 <nuckolls.bob(at)aeroelectric.com>



 At 09:07 PM 7/30/2012, you wrote:

> 

> <fran4sew(at)banyanol.com>

>

> I received this email today from Chuck (quoted below) in reference to

> my circuit "Contactor PWM.pdf " to reduce contactor holding current.

> http://forums.matronics.com/download.php?id=32370

>

> > Hello Joe

> > I built the circuit with one change. I replaced R1 with an

> adjustable 0-25k ohm pot. Works great, just dial in the PWM for the

> right duty cycle with R1 for the particular contactor being used.

> > Thanks Chuck



 I recommend that the power saving duty cycle

 be set for not less than 50%. This cuts average

 voltage to contactor by 50% . . . hence average

 current by 50% and total power dissipated by

 75%.



 While a 12v contactor will stay energized at

 voltages of 2v or below, you want to make sure

 that the contactor stays closed down to battery

 end of life at 10.5 volts or so. 50% at 14 volts

 with alternator running gives you 7 volts to hold

 the contactor . . . 10.5 translates to 5.25 volts

 or thereabouts . . . probably as low as you want

 to go. 75% reduction in lost energy is pretty

 substantial if you're in a battery-only operational

 mode . . . or struggling to make the most of an

 8A alternator.



 Bob . . .

nuckolls.bob(at)aeroelect
Guest

Posted: Wed Aug 01, 2012 9:32 am Post subject: Latching Relay Redux

At 10:20 AM 8/1/2012, you wrote:

 --> AeroElectric-List message posted by: Ken <klehman(at)albedo.net>



 Is that 75% power reduction correct??



 I would have guessed that a 50% duty cycle gave full voltage and full current for 50% of the time in a pulsed resistance circuit resulting in a 50% power reduction. Not sure about an inductive coil contactor though.



 Just asking but intuitively I would not have averaged the voltage and applied the I squared power calculation to this.

 -----------



  Excellent question . . . and yes, consideration of

  contactor inductance paralleled with a diode

  is critical to the analysis.



  When to the bench and set this up:



 [img]cid:.0[/img]



   This test setup produced the following data:



 [img]cid:.1[/img]



   If I go to 100% duty cycle, this El Cheeso,

   Stancore/RBM contactor draws 0.9 amps 14.6 volts.

   Dynamically, the coil current (Yellow trace) shows

   some ripple  at the switching frequency but averages

   just under 0.5 Amp.



   In the mean time, the power supply is showing a

   load of just 0.21 amps or about 25% of the full-on

   current draw. 



   If I put a 15 ohm resistor in place of the\

   contactor, the 100% current goes to the expected

   1 amp. At 50% duty cycle, the peak current is still

   1 amp with average current falling to the predicted

   0.5A . . . hence 50% duty cycle produces only 50%

   reduction in power in the resistive circuit.



   The L/R time constant of the inductive circuit

   prevents achievement of full current during limited

   on-time. The diode prevents current from falling

   to zero during off-time.



   After one hour, the outside temperature of the

   contactor was not too hot to sustained touch . . .

   Waayyy cooler than contactor operatied at 100%.



 

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Aug 01, 2012 7:33 pm Post subject: Latching Relay Redux

At 12:30 PM 8/1/2012, you wrote:

 	  Quote: 	
		  At 10:20 AM 8/1/2012, you wrote:




Is that 75% power reduction correct??



I would have guessed that a 50% duty cycle gave full voltage and 

full current for 50% of the time in a pulsed resistance circuit 

resulting in a 50% power reduction. Not sure about an inductive coil 

contactor though.



Just asking but intuitively I would not have averaged the voltage 

and applied the I squared power calculation to this.

-----------


	


   P.S. just for grins, I thermocoupled the contactor

   and let it stabilize for over an hour. Got a 120

   F shell at 50% duty cycle for a 40F rise.



   Let it run 100% duty cycle to stabilization and

   got a 180F shell temperature for a 100F rise.

   At that temperature, the 100% duty cycle current

   draw was down to .6 amps from the cold start at

   .9 amps. This copper temperature coefficient of

   resistance rise in coil accounts for the less

   than 4x temperature rise for 4x the dissipated power . . .



   This means that a cooler contactor uses the power

   you supply it more efficiently by running a

   lower winding resistance. I.e. ampere turns

   of magnetic flux that is more proportional to

   applied voltage because the coil is cooler.



   By the way, here's one approach to fabricating

   a "contactor cooler" . . .



http://tinyurl.com/bolkoyc



   On power up, both capacitors are discharged.

   The 10uf holds down on the comparator pins

   2,6 for about 100 milliseconds thus holding

   the output pin 3 HI, turning the FED on hard

   and energizing the contactor with full voltage.



   The 10uF charges up in 100-200 milliseconds

   thus allowing the 555 to 'hum' at about 200Hz

   and 50% duty cycle. The diode and RC network

   across the contactor coil should be mounted

   right to the contactor terminals. All other

   components can be remotely located but close

   proximity to contactor is best.



   Bob . . .

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