silent relays - Page 1
Forum section: electronics / general

author: akis
author_rank: Frequent Contributor
timestamp: April 26, 2014, 08:23:50 pm
content: I presume encapsulated reed relays make a clicking noise just like ordinary coil relays?I have been using successfully the LH1510AT - fantastic and silent, but now the current requirements have increased and it will not handle it anymore, I need 500mA instead of 200mA and at 70V AC and 10 times audio frequency.There are a few but cost like £10 each. It seems 60V is the magic voltage and over 60V things become very expensive very quick. Any suggestions?

author: calexanian
author_rank: Super Contributor
timestamp: April 27, 2014, 04:56:54 pm
content: Do you mean mechanical noise? Or electrical noise? Generally small reed relays don't make much mechanical noise. The bigger they get the more the may make, but its not something I have been on the look out for over the years. Electrically there is not much difference from a reed and a normal relay.

author: akis
author_rank: Frequent Contributor
timestamp: April 27, 2014, 05:54:25 pm
content: I meant mechanical, audible noise (click, click, click). I have some miniature OMRON and other relays and they do make an audible clicking noise even though fully sealed. Are the reeds just as loud ?

author: qno
author_rank: Frequent Contributor
timestamp: April 27, 2014, 08:14:49 pm
content: The 60 volts is probably the safety voltage.Above 60 V a new range of qualifications and tests need to be done.These are expensive.These relays are usually only used in low power low voltage applications so ther is no need for UL or VDE CE markings.Just try.

author: akis
author_rank: Frequent Contributor
timestamp: April 27, 2014, 08:48:51 pm
content: OK I will follow that advice. I imagine to test 4 chips for like a few hours and see if they are still alive.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 28, 2014, 06:06:38 am
content: You might also consider SSRs, if applicable. The main differences are, I think, the dramatically higher leakage and capacitance; the slow switching may actually be helpful in some cases (less chance of EMI).Tim

author: akis
author_rank: Frequent Contributor
timestamp: April 28, 2014, 07:44:56 am
content: My first post was badly phrased, I am already using SSRs. The LH1510AT is an SSR. They have quite some leakage especially at higher frequencies and some are better than others so you have to buy a bunch and choose the make that performs best.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 28, 2014, 08:03:50 am
content: Oh, well then! (I hadn't checked the part number or anything..)Why is the mechanical noise a problem? Can it be ignored? Turned into a feature? (I personally love the sound of an oscilloscope or calibrator clicking away, but I don't know what kind of stuff you're working with.) Isolated, damped?Examples might include routing a "U" in the PCB, around the relay, to provide some springiness away from the main board, then damping that with some foam rubber pads; and further damping the rest of the board with more of the same, or using rubber isolation washers around the screws/standoffs (give or take grounding requirements and such), etc. Steel or plastic covers, with acoustic damping, could provide additional attenuation.Tim

author: akis
author_rank: Frequent Contributor
timestamp: April 28, 2014, 08:36:51 am
content: Hi Tim, judging from the OMRON miniature relays I have here, I would say you can hear them clicking from the other room, and they are not mounted on anything. They are more silent inside an enclosure. The device I am making will have 2 or 4 relays switching once every 1.5 seconds and I would need to sleep or relax with it near me. I have bought some Reed relays may be they make less noise than the normal electromechanical ones - they are also double the price for 1/10 or 1/20 of the current! I have also bought two SSRs the CLARE LCA710 (60V, 1A, 0.3 Ohm) and the Vishay VO14642AT (60V, 1.2A, 0.18 Ohm) and will test to see if they can handle the loads and the relatively high frequency of AC (200 KHz). These SSRs have a high capacitance and leakage and they sometimes let a lot through. I tested the leak at 200KHz on a 10K load on many SSRs and got leakage voltages from 3.84% to 10%. I attach a table of results for who cares:Code:Solid State MOSFET RelaysModelCompanyVleak% at 200KHzLoad Current mALoad Voltage VOn Resistance OhmCoil/LED Current mAPS7360-1ANEC10906004110G3VM-351AOMRON3.84100350357.5LCA110CLARE4.5120350231PS7141E-1ANEC3.3333333331204002510PVT412PbFIR5.625140400275LH1500ATVishay5.95150350201ASSR-1218-001EAVAGO2006015ASSR-1228-002EAVAGO2006015LH1510ATVishay6.25200200125ASSR-5211-001EAVAGO21.32352941200600105AQV257Panasonic2502002.65AQV255Panasonic3501001.85PVA1352NIR37510051G3VM-61B1OMRON5004821.6AQV212Panasonic550600.835PVD1354IRno AC5501001.55LCA710CLARE1000600.35VO14642ATVishay1180600.185AQY275Panasonic13001000.235AQZ205Panasonic20001000.235AQV252GPanasonic2500600.0355

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 28, 2014, 12:14:35 pm
content: Obvious question... why are you switching 200kHz at nearly an ampere so frequently? Why not disable the inverter? Or use multiple inverters, if it's a common-rail sort of thing. A good reason there aren't many products to do this is, because people don't do it this way, there's something better.1.5 seconds is pretty frequent for relay use, probably just getting into the decade range on wear. Probably not a problem over, say, a couple years continuous duty, but for something hi-rel, you'd want to look for a better way.Tim

author: akis
author_rank: Frequent Contributor
timestamp: April 28, 2014, 01:12:00 pm
content: The system is like this: sine oscillator fed from two 12V batteries producing 200KHz at 8Vpk ---> push pull current amp ---> transformer 1:7 RM12 N87/N97 core ---> relays ---> Channel_1 and Channel 2 isolated loads of 80R each. The relays disconnect the loads from the secondary of the transformer. The primary of the transformer is like a 1.75R load to the amplifier, around 18-20W spent on the primary.Two transformers would be very bulky and expensive (RM12 cores) and I'd still need to switch them on and off alternatively.I could have two oscillators, two power amps, two transformers and somehow switch the oscillators on and off or disconnect them from the power amp, so there I could use the smallest relays, except I'd need double the bulky components (transfofmer, power transistors, heat sinks), plus the power amp would be drawing current all the time even when not switched on, which would be worse for the batteries.(I am not an electric/electronic engineer so the above design has been put together semi-randomly).

author: mzzj
author_rank: Super Contributor
timestamp: April 28, 2014, 04:19:53 pm
content: Compared to "normal" mechanical relays the reed relays are silent or nearly silent.