Which Is The Most Power Savvy Relay?

[becrux]

Hi Isaac,
From what I've read here it seems as if you are most concerned about triggering an alarm when your system goes into an alarm state. For this purpose the most power savvy relay is possibly no relay at all. Think of the alternator light on your dashboard. The 'hot' side is wired to the ignition. The 'ground' side is connected to alternator output. When alternator output is plus, there is no alarm. When it goes to zero, there is a path to ground and the light is illuminated. (There is often a diode to prevent alt light from glowing faintly when output is higher than ignition voltage.) in my setup, the alt light 'ground' is connected to the regulator alarm terminal. In alarm state (not charging, overheating, etc.) i get a light, which also triggers a buzzer.
Of course your alarm circuit could include a relay which is not energized until the ground side gets grounded (hence zero power draw), but you might not even need one, depending on the power needs of your alarm. The diode might still be a good idea, but I don't have one unless it is internal to my regulator.
Make sense?

[nigelmercier]

Originally Posted by isaacchacon

I am unsure about the resistance of the elk912...

You said it yourself: ELK912 : 0.030 amperes @ 12V

V=IR, so R=V/I = 12/0.030 = 400Ω

[ebaugh]

I've used a few of these:

Slim Line Industrial Control Power Relays for Sale at ICD

Spec'd at 850 ohms at 12V. Nice form factor that mounts to DIN rail.

[nixsee]

How about building an "economizer" for these relays with an RC (Resistor capacitor) circuit. I did this for my main loads contactor because I didn't want to splurge on an expensive gigavac one and got a cheaper, less efficient one off Amazon.

It can be quite complex to specify the parts perfectly, or you can just use a much bigger capacitor than needed and approximate the resistor/try a few different ones.

I forget the details now, but it reduced the draw from something like 0.5A to 0.2. I could have been more aggressive, but I didn't know all the specs and figured that the best I could hope for was an extra 0.1A.

I've actually been thinking of setting something similar up for the 5 automotive relays that im using for various hvc/lvc controls that are driven by my HPBMS and Junsi Powerlog (which I'm using as my solar controller). I think in total they are draining about 0.5A, so I'm going to see if I can somehow install an RC circuit into the main circuit that feeds all the relay coils and hopefully it'll reduce that draw.

I'll try to dig up the articles I found that were useful and post them here later. But essentially the resistor drops the voltage of the circuit, and thus the continuous watts used, and the capacitor gives an initial boost to trigger the coil. The parts cost like $4 at any electronics store (or online I'm sure).