Panasoinic relays for PLCs


#1

I am wondering if this relay:

https://www.digikey.com/products/en?keywords=255-5324-5-ND

requires flyback protection. It says it is specifically designed for use with PLCs, and has such a low coil current requirement it can be directly switched with a microcontroller. Does it have built-in flyback protection, or should that be added externally? Thanks.


#3

Hello @couldabin,

I did speak with my product manager and he stated the following.

It doesn’t require flyback protection. They use a permanent magnet in these relays to lower the coil currents for these relays. The magnet serves two purposes, lower coil current to trigger and act as a eliminator or squasher for back EMF spikes (even though it is very small due to the smaller currents due to magnet). So the permanent magnet is your friend and eliminates back EMF diodes. This is true for most PCB relays under 10A. Higher current contacts will require it.

Thank You


#5

Thanks, but when I asked if it required protection, what I meant was does using it require protection (for the rest of the product). I looked at the documentation, and I don’t see that the issue is addressed. I was hoping you could tell me whether this relay generates enough flyback voltage that protection to the source pin is required.


#6

From what I understand from the previous posts, the relay can run directly from the PLC I/O, as it is designed to do, with little or no EMF spikes. There is isolation between the coils and the load contacts. Load devices are intrinsically protected from the operation of the coil.


#7

Yes, I got that from one of the responses. But I couldn’t tell from the last reply (or was it a sermon?) whether I was being told that protection from the relay was needed.


#8

@couldabin I may have missed it, but I see no explicit mention in the datasheet that this relay contains any features to protect a driving agent against the effects of the relay’s coil inductance. Assume that none exist, and proceed accordingly.

I suspect that one probably could make it click by direct-driving it from a microcontroller I/O pin, but would strongly advise against it; experience has shown that to be a Generally Bad Idea (for Reasons) and the FET & diode needed to “do it right” cost only pennies.

This page contains a good bit of information on relay-related matters, and might be one you’d find informative.


#9

Thanks much for this – it’s very helpful. When I placed my order yesterday for two of these relays, I included several diodes, some to put in parallel with the motor, and some to isolate this relay. (I’m presuming that a combination of regular and zener in series for the relay is the best way to preserve the life of the relay contacts while containing the flyback voltage.)


#10

You’re quite welcome–though as for “the best way to ___” the best answer I can offer is “It Depends…”

A structure such as the one below might be a good staring point. It 'aint the only way, and might not be “best” for your particular case. If you want to add some sort of protection for the relay contacts, that’s another topic altogether. (“snubber” would be the magic search term there.)

In either case, the previously-linked resource page and (and it’s suggested references) should offer you a decent explanation of the considerations and trade-offs involved.

image


#11

(post withdrawn by author, will be automatically deleted in 24 hours unless flagged)


#12

Thanks. The page was helpful. I plan to err on the safe side.