1
\$\begingroup\$

I have an old kitchen range hood whose lighting suddenly stopped working. With my limited knowledge and capabilities in this field, I was able to access the PCB just to see that the power relay is severely burned through.

Based on the ID I found out that the original piece was manufactured by Fujitsu (item no. FBR-161SED012UHB-T, datasheet here) and has unfortunately been discontinued. I have done a bit of research myself and found a replacement.

Everything is the same as the original piece, except for these three parameters:

Coil power: 400 mW (new) vs. 360 mW(old)

Current rating - N.C. position only: 5 A (new) vs. 7 A (old)

Casing: Fully sealed (new) vs. Flux free (old)

Matching parameters are: shape & size, pin location, switching current and voltage, SPDT configuration, 12 VDC coil voltage etc.

My question therefore is - would this be a proper replacement piece or should I keep looking further to match the specs completely? I have absolutely no feeling whether 40 mW of coil power difference is a dealbreaker. As I mentioned before I am a complete rookie, so any advice is highly appreciated.

EDIT: The lightbulbs are 10 W halogens with G4 connection (2 simple pins). I am adding some photos below:

Circuit with burned relay

Schematic

Back side PCB

Relay closeup

\$\endgroup\$
9
  • \$\begingroup\$ We may be able to get a better idea of the coil power issue if we can see a photo of the surrounding circuitry; there may be hints based on the circuit that's driving the coil. Additionally, do you know what wattage lamp is connected to this relay? (doing so would allow us to evaluate whether the decreased current rating is a dealbreaker) \$\endgroup\$
    – nanofarad
    Jul 9, 2022 at 19:58
  • \$\begingroup\$ Can you give a link to the datasheet for the old one so we can compare it with the datasheet for the new one? (Also, the old one is available, but might be difficult to buy.) \$\endgroup\$
    – Andrew Morton
    Jul 9, 2022 at 20:17
  • \$\begingroup\$ What bulbs (type and power) are used in the lighting that the relay switches? \$\endgroup\$
    – Andrew Morton
    Jul 9, 2022 at 20:18
  • \$\begingroup\$ Thanks a lot for your feedback, I have added the requested information in my original post. It is fitted with 2x 10W/12V halogen bulbs. @AndrewMorton wow you certainly know where to look! :-) I see they have min limit for orders, I am afraid I'd be good with one piece for roughly 4 EUR. \$\endgroup\$
    – J. Hrstka
    Jul 9, 2022 at 20:25
  • 1
    \$\begingroup\$ I think halogen bulbs tend to have high inrush current, so even though steady state they are only drawing 1.67A (20W/12V) it may be worth replacing them with G4 LED bulbs if switching to the new relay \$\endgroup\$
    – ks0ze
    Jul 9, 2022 at 20:44

1 Answer 1

Reset to default
2
\$\begingroup\$

The coil wattage is minimally different. 33 milliamps vs 30 milliamps. It's unlikely that any driver circuit would care.

The reduced switch rating is a problem. 2 Amps lower rating is significant for any large load. If you measure the current across the relay pins and its anywhere near 5 Amps, then it will not be suitable. Keep in mind that in-rush current may be much higher and you may not see that with a multimeter. And that some loads change over time or with heat. So it may start at n Amps but increase to n+1 amps.

Edit: since your load is 830mA per bulb or 1.667A. Halogen bulb inrush is rule of thumb 3 times or more the operating current. So a 5 Amp relay is barely at the rating. I wouldn't use it.

As suggested by @ks0ze if you switch to lower load LED bulbs then a 5 Amp relay will be fine.

\$\endgroup\$
5
  • \$\begingroup\$ Passerby thank you for your input. I have seen a 16 A version of the same relay available. Based on your answer, would it be sensible to opt for that model to provide some extra margin for the in-rush current? \$\endgroup\$
    – J. Hrstka
    Jul 9, 2022 at 23:05
  • \$\begingroup\$ @J.Hrstka That would be perfectly reasonable, yes. It doesn't matter if the rating is too high (unless it's a very low-current, low-voltage application, which this isn't), only if it's too low. \$\endgroup\$
    – Hearth
    Jul 9, 2022 at 23:09
  • \$\begingroup\$ @J.Hrstka yes but a suggestion in the comments is to switch to led bulbs. Which is a much better option to be honest. Switch the bulbs and your fine with the 5 Amp relay you found. \$\endgroup\$
    – Passerby
    Jul 10, 2022 at 4:09
  • \$\begingroup\$ If I understand it correctly, a LED bulb replacement for 10 W halogen is around 1.2 W rated. Meaning that for the same voltage, we get roughly 8x smaller current and therefore 8x smaller risk of reaching the threshold during the in-rush instance? In any case, I will stick to the originally proposed relay alternative and shop for some proper LED lights with G4 fitting. Thanks a lot for your help guys! It is always refreshing to learn something new :-) \$\endgroup\$
    – J. Hrstka
    Jul 10, 2022 at 11:31
  • \$\begingroup\$ @J.Hrstka yes. A smaller current draw and almost no in-rush current to worry about. \$\endgroup\$
    – Passerby
    Jul 10, 2022 at 17:55

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.