Relay Power Dissipation Reduction 2

[itsmoked]

I have this 12Vdc relay that I unfortunately have 14V to operate. It can take it but jeez it gets warm.. It's also in a small enclosure that warms up more than would be ideal.

I can stuff in a dropping resistor that will lower the relay's temp but will, of course, do nothing for the box ambient because the same power will be dumped in the box.

So I thought I'd try cycling the power to the relay fast enough that it can't respond. That way I could essentially PWM my way to less average power use in the relay.

So I added a little routine that cuts the power off to the relay after 5ms for 1ms then turns it back on.

Damned if that relay doesn't drop out in 1ms!!! Dang.

Thought you guys would find it interesting.

Here's the relay:
OJE-SH-112DM,000
OJE_series_relay_data_sheet




Keith Cress
kcress -

http://www.flaminsystems.com

 

[btrueblood]

I can recall working in a clean room helping to install small thrusters on a spacecraft. We would purge helium (from the fuel tank on the s/c) through the valve during some operations, to help keep the thruster clean. To know when the solenoid valve was opened, the crew kept a small AM radio playing, and the burst of static gave them auditory feedback that the valve had been actuated.

 

[VEBill]

Thus is explained some of the 'alien signals' from space. ;-)

 

[waross]

Here's an off the wall solution;
The pull-in may not be that serious, the I²RT will be so small. After pull-in you want to use some method to reduce heating.
How about switching a Peltier effect cooling module in series with the relay? Put that voltage difference to good use!

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[itsmoked]

What with a beer holder too?

I went with the DC solution; 470uF cap in parallel with a 1.2k resistor. Worked like a charm. I can just barely, after an hour, feel a just-detectable rise above ambient on the relay case instead of a reflexive finger yanking rise like it was before.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[waross]

What with a beer holder too?

Now that's real "out of the Box Thinking!" Grin

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[VEBill]

Of course, a Peltier effect "cooling module" has a heating side too. So it'll obviously have a net increase in the total power and the total heat. The only way they work for cooling is if they're carefully installed half-in and half-out of the box. Even then, they need a fair amount of power.

 

[itsmoked]

That and they fail in 5 years. Peltiers have horrid dependability issues.

Keith Cress
kcress -

http://www.flaminsystems.com

 

[OperaHouse]

Don't get too enamored with ultra low hold in current. Had a customer that required a very low current self powered go nogo current relay. By hand selecting sensitive relays I could meed the spec. This wasn't much of a problem because we used that 12V relay in a dozen other products and there was always an abundant supply to select from. Some lots were 90% ok and others about half were acceptable. Those that weren't were quite high in current. Better have a pad to solder on another resistor if you aren't conservative.

When you run at really low currents the relay becomes very sensitive to any mechanical shock. A little tap and they will open up. That said, I added a relay at my camp to connect a second set of batteries. The relay drew 190ma and I PMWed it down to 31% or 60ma. That was about as low as I could go. Possibly because of low inductance running at 490Hz. I would suggest using a schottky diode not only for speed but because the forward voltage can be a good part of the low voltage hold in. Here is a sample of the two added lines of code to implement the current reduction.

// CHARGING OF SECOND BATTERY & RELAY POWER SAVE

if (battery < 14000) PWM11 = 0;
// DISCONNECT second battery Set PWM to zero

if (battery > 14400 && PWM11== 0) PWM11 = 255;
// CLOSE RELAY OK to charge second battery

if (PWM11 > 80) PWM11 = PWM11 - 1;
// Decrement relay current down to 1/4 power

analogWrite (11,PWM11);
// Output PWM to pin #11

 

[itsmoked]

Didn't realize relays could be that different. I'm not too worried about it because these relays are rated to stay closed down to 0.6V and I'm still feeding them about 6x that. These things are also screwed to walls so no mechanical shock issues either.

Keith Cress
kcress -

http://www.flaminsystems.com