High current through relay without switching

I’m looking at drawing a variable current through a relay. The majority of the time, the current would be under the rated current for the relay. However, the current will spike up to 5x the rated current for the relay for several seconds at a time. During this time, the relay would never be switched - it would always be conducting only. Would this be ok? Is there a way to tell if a given relay could handle this, aside of testing it to see?

Welcome to the Digikey tech forum. It may be possible to run a higher carry current than the rated switch current for short periods of time. However, the resistance of the relay will also create more heat while the current is high and can cause issues depending on how hot it gets. I would suggest using a relay with a higher current rating, one that is capable of handling the high current spikes. If you provide us the specifications on the relay you’re using and the amp readings of the current spikes we can search for an option that may meet your needs.

Hi Steve. The current would typically be around 20A, spiking to 85A for a second or two during peak events. The voltage will vary between 12VDC to 30VDC. Weight is a major factor - the relay needs to be as light as possible. Coil voltage between 5-12VDC would work. The peak current events are almost always shorter than 1-2 seconds. There is lots of airflow around the device for cooling.

You can take at these options to see if one may work for you, Power Relays, Over 2 Amps | Electronic Components Distributor DigiKey You’ll need to verify the contact form, mounting style and weight to see if one will work for your application.

Hi fam891,

Running 5x the rated current for a second or more is pretty extreme, whether it is switching or not. If it doesn’t destroy the relay immediately, it will likely significantly shorten its life. What are your expectations for lifetime?

To be more helpful, it would be useful if you could tell us which relay, specifically, you are considering. Then we could at least look for more technical data which might give more insight into how it might behave under such circumstances. Additionally, then we would have a frame of reference to compare to any other relays to see if there is one with higher current ratings which may still fit within your physical requirements.

The one I was going to test is below. It’s a 20A relay. Normally, I would never use a 20A relay for these types of loads, but this is a special use case in that I don’t need to switch the current, just conduct the current. If I could get 200+ hours out of it, I would be happy.

I found one relay that may be better suited for your application.
Click here for F9629-ND.
This is a 12VDC coil, SPDT, can handle 70A normally.
The Datasheet has this information:
Relays are rated based on a steady state resistive load. De-rate
according to the type of load.
Motor load: Inrush can be 5 to 10 x steady state current.
Solenoid load: Inrush can be 10 to 20 x steady state current.
Incandescent lamp load: Inrush can be 10 to 15 x steady
state current.

Hi fam891,

That type of automotive relay David_1768 identified seems better suited to the application, though they are quite a bit heavier. I didn’t see the mass of the Littlefuse relay mentioned, but a similar one from CIT with PC mount pins, the A31CSP12VDC2, weighs about 46 grams.

You didn’t specifically state that you needed an SPDT relay, though the one you pointed out is an SPDT. On the outside chance that you only need an SPST relay, you might want to take a look at the Omron 39-G8PM-1AW7RDC12BYOMR1-ND. From the datasheet, it has a continuous current rating of 60A @ 20°C (derated to 40A @ 125°C) and it is explicitly rated for 120A at DC14V for 2 mins. It is quite small and only weighs about 7.6g.

This one should work perfectly, and I don’t even need to push the limits of the product (where’s the fun in that?)! SPST is all I need, and this is smaller than the one I had previously chosen. Thanks, David!

Thanks to everyone for their help in finding this relay. Much appreciated!