[Phidgets] Question of relay max current(DC) -- PhidgetInterfaceKit 0/0/4

[BruceHsin]

Hi Phidgets member,

Good day, Could you help a question. We had bought a relay was PhidgetInterfaceKit 0/0/4.
Regarding max DC current limit, the Electrical properties is show max 7A.
But the product introduction is show 210W for DC, and Relay Lifespan is estimated on 28Vdc/10A(will reduce life).

So which one should I refer to for its real current? if we use it on 8V/10A, is it recommended?
Thank you.

Best Regards
Bruce Hsin

[mparadis]

Even though 8V/10A is only 80W and well below the maximum power rating, running at 10A instead of 7A would cut the lifespan in half (80000 actuations vs. 40000 actuations) according to the graph.

That being said, the graph probably only goes all the way to 10A because the AC max current is 12A. This 7A DC specification was taken directly from the datasheet for the relays we used to make the 0/0/4, so I wouldn't recommend running them higher than 7A DC.

[BruceHsin]

Hi Mparadis,

Thanks for your reply.
Do you have recommend relay product, it can used at 10A~12A(@8V, and 7A@14V)? And the wire connector size can use about 8 AWG size.

Another question, if we still keep the PhidgetInterfaceKit 0/0/4, but use 2 channel to split the current of 10A. is it recommended?
Thank you.

[mparadis]

You could use the REL2103, which can switch 30V DC at up to 10A. If you need to go above 10A there is a certain way you can wire it to permit up to 20A (see "Using the SRC Terminals" in the user guide). Each REL2103 only switches one channel, so you'd have to get multiple of them and connect them to a VINT Hub or another Phidget with digital outputs.

If you use two channels of the 0/0/4, I don't think it would prevent damage to the relay. My understanding is that the majority of damage to mechanical relays occurs when the relay is just making or just breaking contact (high current causes an arc to form in the air gap during the break, which degrades the metal of the contacts over time). Since you can't guarantee that both of the channels switch at the exact same time, one channel would still be momentarily getting the full 10 amps of current for long enough to cause extra wear on the contacts.

[BruceHsin]

Hi Mparadis,

Thanks for your reply.
As I know, because the Relay is just consider high current when the relay is just making or just breaking contact. If we keep low current(<7A) on switching, using should be no problem?

And I had check the relay (HF3FF/005-1ZST(257)) contact rating is 10A/28VDC(is meet our require 10A@8V). Does relay have any protection if continue current over 10A? Switch disconnected (burned out)?
Thank you.

Best Regards
Bruce Hsin

[mparadis]

If you use more than one channel to split the current and you keep it below the maximum when switching, it should be fine.

I'm not sure what the failure mode of the relay is when used above the specified current for extended periods of time. It's possible the switch inside the relay would stick, or maybe the contacts attaching it to the PCB would de-solder. In any case, I don't recommend using relays outside of their specifications.