where can i get a quiet automotive relay?

I just built and installed an intermittent wiper circuit for my rear, but although it's working correctly, the 30/85/86/etc relay I got from PepBoys (A2C Part# 775) is unpleasantly loud when it releases.  It wouldn't be a problem for lock/unlock or engine start functions, but for intermittent wiper control, the noise occurs at the beginning of every wiper cycle and is impossible to ignore.  I've tried wrapping it in heavy felt, but it made only a minor improvement.

I don't know if there are other manufacturer's 30/85/86/etc relays that are reasonably quiet (which would be preffered since that's the installed socket) or if I have to go to something else entirely, but if there's a much quieter SPST NO relay out there that doesn't cost a pile, I'd love to learn about it.  (The rear wiper fuse is 15A.)

i am an idiot wrote:

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Turn your radio and amps off, do you still hear the noise?   If the noise goes away with radio and amplifiers off, install a diode across the relay as depicted in the following link.   Any 1 amp diode will do.  Radio Shack will have one. https://www.the12volt.com/relays/page5.asp#ctm   Disregard the diagram in the link.  Only pay attention to the diode.  The Banded end of the diode must attach to the positive wire.

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Yes, this is with the radio off -- it also did it during my bench testing before install, which is when I wrapped it with felt.  I hoped it might actually be OK installed, but unfortunately no.  The noise is specifically mechanical -- I can hear the spring vibrate.  The engagement is a reasonably survivable click (mechanical again), but the release is just a bit much.

91stt] wrote:

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ry a solid state relay, no click at all.
check digikey.com to see what fits your application

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Thanks, but the highest SPST NO socketed solid state relay current capability I see there is 3A.  A bit low for driving a motor with a 15A fuse.

trevors wrote:

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91stt] wrote:

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ry a solid state relay, no click at all.
check digikey.com to see what fits your application

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Thanks, but the highest SPST NO socketed solid state relay current capability I see there is 3A.  A bit low for driving a motor with a 15A fuse.

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Oh yes, and the unit price is $43.52, think I'd better stick to mechanical.

KPierson wrote:

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How much current do you need?  Reed relays and transistors are both silent.  Depending on how much current you need one or the other should work.

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I don't know the actual current requirement, it's a motor fused at 15A.  I imagine the current needs will tend to be higher on icy/snowy weather than at present.  Yes, I could add a power transistor and another driver I suppose, but I'd prefer to avoid the heat and stability issues in driving high current, and a winter motor stall could be deadly.  A mechanical relay is both a simpler and more reliable solution.

I'm not used to reed relays being high current capable, and wiper motor's can present unfriendly loads, but still, I'll take a look.

trevors wrote:

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KPierson wrote:

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How much current do you need?  Reed relays and transistors are both silent.  Depending on how much current you need one or the other should work.

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I don't know the actual current requirement, it's a motor fused at 15A.  I imagine the current needs will tend to be higher on icy/snowy weather than at present.  Yes, I could add a power transistor and another driver I suppose, but I'd prefer to avoid the heat and stability issues in driving high current, and a winter motor stall could be deadly.  A mechanical relay is both a simpler and more reliable solution.

I'm not used to reed relays being high current capable, and wiper motor's can present unfriendly loads, but still, I'll take a look.

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I see 3A at the high end of the reed relay spectrum -- doesn't look good to me.

Thanks for the inputs and to wrap up so far,  Outside of identifying a reasonably quiet automotive relay, I can always tackle a homebrew solid state replacement that could plug into the 30/85/86/etc socket and hopefully include a stall current limiting mechanism of some sort, but I'd really prefer to go with a quieter relay.

I'm hoping people who specify parts and do installation work professionally will have a sense of which relays are louder and which quieter, and in what applications they'd be inclined to use one versus another.  I tend to doubt all 30/85/86/etc relay manufacturers develop the identical quality product, and if there're relatively premium versions that perform more quietly (say for Escalade quality installations :)) I'm hoping to learn of them.

KPierson wrote:

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Perhaps you can get a weatherproof relay and mount it under the hood?

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Yes, relocating the relay to the other side of the firewall would be a solution.  Darned shame to have to do though -- all that additional wire length.  I guess -- if all else fails :(!

i am an idiot wrote:

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Felt will no nothing to deaden the sound.   Have you thought about Dynamat? 

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Not any old felt but the high density stuff has been traditionally used for sound deadening as well as padding.  It did take the edge of the sound, but it definitely remains too loud.  I have some eDead which did a great job of kiliing speaker sourced vibrations in my xB door panels.  I've debated whether I should give that a whirl, or just accept the hint the felt test gave me.  Of course, I can't apply eDead to the base of the relay -- that's where the pins are (I was able to put one layer of felt down there).

The "click" of the relay is made by three things - the size of the contacts, the amount of current the coil pulls (and thus the strength of the magnetic coil, and the strength of the return spring.

If you go with a 15A relay your contact size will be smaller, so a higher resistive coil can be used and a lesser return spring.  To my knowledge all 30A bosch style relays are loud - I have never seen a "quiet" one.  I just read a thread somewhere where an installer wrapped a relay in dynamat and it was still too loud.

If you go with a Mosfet get one with an isolated tab (assuming 12v output) and bolt the tab to a ground ground in the car - this will allow you to use the car as the heat sink and should elminate any concerns of heat.  Also, as dualsport alluded to, try to find a mosfet with an extremely low on resistance.  I think this path is definately worth a try as it is fairly cheap and easy and will definately get rid of the noise.

howie ll wrote:

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How about a modified 508d (remove the pot and use a rotary pot instead for the delay or better still, one of the Vellerman kits, either variable wiper delay specific, or a timer device. again though not sure about the current handling, 15amps seems high, any one tried to measure the current draw whilst holding on to the wiper?

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Thanks, but my timer/control circuit module is functioning as desired and mounts perfectly in the available space with its own wiring harness -- I'd prefer not to have to scrap it and start again.  Everything is cleanly mounted wihin the steering column shroud and if it wasn't for that darned noisy relay, it would be perfect.

I'm sure the 15A fuse selection is based on worst case protection of the wiper motor.  It's quite possible normal operation doesn't exceed 3 to 5A.  Stall conditions can cause a considerable increase in current.

I've thought up a pretty simple NPN final output two transistor replacement possibility that includes current limiting, but it does steal a volt or so from the motor under  normal conditions.  Not sure how much impact that loss would have.

dualsport wrote:

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It sounds like you have prior experience with working with solid state- so you might reconsider a power transistor.
If your application here is simply switching power on and off, rather than a continuously variable output, it's much easier on the transistor, because it'd be operating in the saturated region, where it actually dissipates relatively low power, even if you're driving it with 20A. The on resistance of power MOSFETs is pretty low, so when it's on, the power is current squared multiplied by the on resistance.

Power transistors are used for continuously variable blower motor control, which draw in the range of 20A; and they do have a hard time when the speed is throttled down to half power, because then the power is divided equally between the motor and the transistor. Lots of heat there to deal with.

With your wiper application, it spends little time in the middle region of the transistors operating area, so it won't heat up anywhere as much as with a variable blower speed control. Should be easy to heat sink it sufficiently to keep it cool.

If you can work out your setup to use a low side drive, it'd be better, because N-channel transistors tend to be better in regard to the on resistance.

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Yes, bipolar transistors are old friends of mine.  I've a little experience with FET types, but I'd have to reaquaint myself with their circuit configuration.

Yes, the application is pure ON/OFF and I have bipolars in my parts box that could be used for this application.  I think I'll just limit the current to something under 10A and then just see how things go.  I'll have to think about the MOSFET idea though, it is interesting, just need to include stall current protection.

Guess it's not looking too good for mechanical relays at this point :(!  Thing that's niggling is the factory front wiper internittent column switch I'm using has an internal relay that's perfectly quiet!  And that 25A fused motor drives two wipers, both with larger wipe radii than the rear.

KPierson wrote:

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The "click" of the relay is made by three things - the size of the contacts, the amount of current the coil pulls (and thus the strength of the magnetic coil, and the strength of the return spring.

If you go with a 15A relay your contact size will be smaller, so a higher resistive coil can be used and a lesser return spring.  To my knowledge all 30A bosch style relays are loud - I have never seen a "quiet" one.  I just read a thread somewhere where an installer wrapped a relay in dynamat and it was still too loud.

If you go with a Mosfet get one with an isolated tab (assuming 12v output) and bolt the tab to a ground ground in the car - this will allow you to use the car as the heat sink and should elminate any concerns of heat.  Also, as dualsport alluded to, try to find a mosfet with an extremely low on resistance.  I think this path is definately worth a try as it is fairly cheap and easy and will definately get rid of the noise.

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dualsport wrote:

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$1.25

Inexpensive enough to experiment with-

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Thanks fellows :)!  So those relays are called Bosch style and what I've got is what I can expect!  OK, that's good info and eliminates some wondering.  Looks like I'm going solid state, but I'll try to package the circuit so it can plug into the standard Bosch connector.  That permits easy function restoration should something go amiss.

Always wondered what I'd end up using my supply of 2N3055 TO-3's for, looks like an opportunity to me :)!  Though I'll probably also look into the MOSFET solution as well.

dualsport wrote:

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Keep in mind the Vce (sat) spec for the 2N3055 shows 3V at 10A, so you'll have quite a bit more heat to contend with. At 4A, it'll drop 1V, for 4W heat dissipation.

Since you already have a stockpile of them, you may as well give it a try it to see if it'll work out.

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Yep, the 2N3055 has a high saturation voltage, but it's also a TO-3 which means I'll have to mount it to a plate (probably mount the power tab PNP driver to it as well).  Originally picked up the 2N3055's for Dynaco Stereo 120 repairs, but I've still got four and given typical battery voltage climbs to around 14V when the vehicle's running, I think I can spare the saturation voltage (the intermittent works fine on 12V).  The duty cycle is less than one second in ten, so I'm not worried about normal operating heat.  My only concern is if the motor were to stall.

Yep, I'm gonna give it a shot -- got the circuit finalized and concept bench tested -- nice and clean on the scope.  Now just need to resolve the heatsink/circuit board/mounting/wiring issues -- those and fabrication are usually the time hogs :(.

Just want to say thanks for the help.  I now know better than to hunt for a quiet auto type relay :)!  I found a couple unmarked TO-3 NPN's in my stash and decided to use one of those instead of a 2N3055 -- so they're saved for another day :)!  I included motor stall protection and here's a photo of the completed module (hopefully, it displays OK).   The wiper control is now dead quiet :)!

Oh yes, I tried tightly bundling the mechanical relay and socket in heavy felt like a little football, and the upper frequency sounds are killed, but the lower frequency content still makes it easily audible.