[exmadscientist]

> to avoid wearing out one side of the rectifier inside the PSU

If you are seriously worried about this then the whole thing is trash. Either the design is marginal or it is not. You cannot possibly switch a relay fast enough to make a difference here (and have the relay survive).

[cyberax]

I'm worried about long-term thermal wear from uneven heating, so I switch the current direction once a day. Simply because that's the maximum time I can set on a time delay relay that controls it.

[exmadscientist]

Don't bother. That's not how these things fail, and one day is so so far beyond the thermal time constants involved that it's not doing anything useful. You would have to switch on timescales of seconds to minutes to do anything meaningful, and that would kill your relay in short order.

If you are truly close to the design failure point of the rectifier, it's not safe to run at all. (You are almost certainly not.)

If you are worried about the fact that you're only using one element of a multi-element package, again, it's a nonissue. We do this all the time. It's often cheaper to add a second bridge rectifier to get a single diode than it is to add another BOM line item for the "proper" part. As long as that diode isn't operating near absolute maximum ratings (it probably isn't), it doesn't matter that there are or aren't three more in the box.

[butvacuum]

note: its the additional component and its knock on effects that are the cost- not the half cent diode.

aka- you add a diode, now you have to add procurement, warehousing, extra time on the pick and place, possibly a more expensive/larger+slower one as well(so even more time), then you have wastage, labor for keeping the machine fed...

[cyberax]

I removed it to see what happens :)

The reason I added it in the first place is because I've seen failures from uneven PCB heating. It's not the components themselves fail, but radiators get unglued and PCBs can get damaged.

[Dylan16807]

I don't understand what you're saying.

If you're specifically worried about wear, then you could switch once a month and it would be enough.

[exmadscientist]

Silicon rectifiers don't wear out.

(At least not on timescales relevant to individual humans.)

So hearing that makes me get suspicious that something else is going on.

[Dylan16807]

I'm also suspicious of the idea of that part wearing out, but if it doesn't matter at all then there's no reason to call things trash.

Your other comment says: If you are truly close to the design failure point of the rectifier, it's not safe to run at all. (You are almost certainly not.)

Well there's no reason to assume it's close to the failure point.

Think of it this way: Draw the line in the sand for where you'll approve the design, but just barely. If someone is running a diode close to that line, then it's not trash but trying to improve longevity isn't crazy either.

[exmadscientist]

The point is that the dance with the relay doesn't move the needle on design acceptance. If it is acceptable with the relay, it will be acceptable without the relay, because the component stresses will be the same.

So if it is unacceptable, it is unacceptable, and needs to be fixed. I said "trash" because it's going to become trash, and with luck just the power supply. Hope there's a fuse inline! Input rectifier failures tend to take down other stuff without one.