Special double relay needed - Page 1
Forum section: electronics / beginners

author: Braveheart Jerry
author_rank: Newbie
timestamp: February 12, 2025, 11:12:06 pm
content: Amateur DIY’er looking for some help finding the correct custom specialized relay for my car, and drawing a wiring diagram that I can follow to wire up the equipment in question. 12v system and the pump being added could draw up to 30 amps (oem equipment being retrofitted after the fact without all the oem wiring harnesses and relays) oem uses relays and a 30 amp fuse for the same equipment.I am adding a headlight washer pump to the car. I need a double relay if I am not mistaken to make the pump work under the following conditions:1) the headlights are on2) when the windshield washer pump is activated via the dash switch-In addition to the above I want the headlight washer pump to operate on a timed circuit for between 3-10 seconds (will decide exactly after some trial and error)-also want the headlight washer pump to have a timer that will not allow it to work again in succession after the initial trigger for 10 minutes.The objective is to have a short wash on the headlights and then a pause even if I decide to wash the windscreen multiple times in short succession.Any help finding a relay to purchase would be great help and a wiring diagram on how to connect all the workings would be very helpful.I am going to splice into the headlight wire and the windshield washer pump wire for the connections and run positive negative from the battery and chassis.

author: JustMeHere
author_rank: Frequent Contributor
timestamp: February 14, 2025, 04:25:25 am
content: Use 2 relays?

author: kripton2035
author_rank: Super Contributor
timestamp: February 14, 2025, 08:04:40 am
content: a small microcontroler like a pic or a small arduino. the arduino will be easier to program if you're not familiar with microcontrollerstwo inputs from the headlights and windshield pump (lowered from 12v to 5v or 3v)and a relay piloted by the microcontroler, who also do the timing.

author: Zero999
author_rank: Super Contributor
timestamp: February 14, 2025, 08:40:06 am
content: You've got two time delays. It's possible to use off the shelf timer relays, or build your own (555 timer), but using something which is programmable is a good idea.If you have zero programming/micro controller/electronic experience then I would suggest a Programmable Logic Controller (PLC). It's essentially a small computer, with an array of inputs and outputs which can be programmed to turn on or off. It won't be able to switch 30A loads directly, so you will still need relays. The only downside is most PLCs are designed for 24V industrial controls, but there are some 12V models available.A PLC can normally be programmed with a graphical language such as ladder logic or function block diagram, which are easier to understand for those who are more familiar with schematic drawings, rather than text based languages.It turns out that PLCs which will work off 12V are fairly common.https://uk.rs-online.com/web/p/plcs-programmable-logic-controllers/9176370?gQT=1https://uk.rs-online.com/web/p/plcs-programmable-logic-controllers/2825512https://www.amazon.co.uk/Hyuduo-Programmable-Controller-Industrial-Computer/dp/B09MMZR913I would opt for a known brand, Siemens, Eaton, Allen Bradley etc. rather than that Chinese one from Amazon.

author: Braveheart Jerry
author_rank: Newbie
timestamp: February 14, 2025, 04:09:22 pm
content: Really appreciate your reply. I had a look at some arduinos online and they look a little intimidating for my abilities. I can follow instruction very well but feel a little intimidated by dropping the voltages building an arduino and putting it all together to control the headlamp washer motor. I would need a lot of instruction or maybe someone who is willing to build it for me and I can just install in the car.

author: Braveheart Jerry
author_rank: Newbie
timestamp: February 14, 2025, 04:48:54 pm
content: Thanks for your help. I had a look at the PLC controllers and they seem pretty complicated. Would it just be a matter of connecting the wires to the correct input pins and output pins and then figuring out how to set the parameters of this pins on the controller?I would like to know some specifics for off the shelf timer relays. Think that might work simpler. Think it might also be less costly too. If the relay would allow the wiper switch to activate the pump while it is depressed manually (say for a couple seconds)and then after the wiper switch is let go activate the delay timer so any subsequent pushes of the wiper switch would not operate the pump for say about 10min that would be sufficient to work for me. Basically removing one of the time circuits out of the equation. This would make it so that when the pump is operated via the switch through the relays for a couple seconds manually it would then go into a delay where the pump couldn’t be operated again for say ten minutes. Any ideas welcome?

author: Kasper
author_rank: Frequent Contributor
timestamp: February 15, 2025, 08:18:57 am
content: Quote from: Braveheart Jerry on February 14, 2025, 04:48:54 pm2 timer relays in series ought do it. Each is activated by one of the inputs. Both need to be activated for power to get through to the pump. 2 timers should work, but this latest plan with just one timer should be easier.Have you found a timer relay you like?

author: Braveheart Jerry
author_rank: Newbie
timestamp: February 15, 2025, 10:22:05 am
content: I have not found a timer relay that would be suitable for my task of operating the pump. Any help to locate a suitable one would be appreciated.Revised plan would be to have one relay work when the lights are on, then in series the second relay would be some sort of timer relay that would allow the pump to operate initially when the momentary screen wash switch was depressed for a couple seconds and then the timer relay would go into a delay off position where it wouldn’t operate sequentially for say ten minutes.The car manufacturer has a 30amp fuse and some relays in their oem circuit. 30a seems a lot for a small headlight washer pump.Help finding the right component timer relay for my job and a quick wiring schematic would be super helpful. As a novice I am getting to the limits of my knowledge but could easily follow some simple direction to get the job done myself.Thanks in advance for the help.

author: BeBuLamar
author_rank: Super Contributor
timestamp: February 15, 2025, 01:11:24 pm
content: The PLC would be easiest although it tends to be on the expensive side. I looked at Automation Direct and the Click series is good for the money but doesn't run on 12V. The Direct Logic series which would run on 12VDC but even the cheapest DL05 (which is used to be very cheap) is now more than $200. It's possible to do it with relay and timer relay but it's not cheap as you need quite a good number of components.

author: NE666
author_rank: Frequent Contributor
timestamp: February 15, 2025, 02:43:57 pm
content: Personally, if I were doing it and wanted the logic complexity that your OP indicates, I'd use a Rapsbery PI with a suitable relay board, and program a basic state machine to drive it (in C, or Python). I'd leave out the 'hold off' timer aspect, and instead just have it count the number of times the windscreen is washed since engine start - something like "wash lights on first activation, then only every two or three activations thereafter" (which is what my Volvo does).If that doesn't sound like you, to you, then I'd suggest reducing the complexity of your requirements to the bare minimum that can be implemented with a single timer relay: Use a timer relay to control the length of the wash, and just accept that it will operate when the lights aren't on (if the screen is dirty enough to want washing, your lights will be too anyway, so why not?) and each time you wash your screen (if it's not clean yet, then probably neither are your lights). Not perfect but much, much easier and cheaper to implement.

author: Kasper
author_rank: Frequent Contributor
timestamp: February 15, 2025, 04:35:28 pm
content: I had a quick look for timer relay. Found some with big list of features but not rated for 30A.If you cant find one then chose between PLC, arduino, 555 timer or something else.PLC is handy for automation and control.Arduino is not too hard and very powerful. Can do all sorts of things.555 is pretty simple.Whatever you chose, protection is needed, automotive power has big voltage spikes that will damage your circuit if you don't include adequate protection. Not a big hurdle, those cheap little cigarette plug - USB adapters manage to survive.

author: kripton2035
author_rank: Super Contributor
timestamp: February 15, 2025, 05:02:01 pm
content: a Pi is completely overkill for that... a small pic or atmel chip is plenty sufficient.a PLC is completely overpriced.or even thishttps://www.aliexpress.com/item/1005006053150372.htmland don't forget you have to make the device "automotive compliant" that is completely waterproof and vibrationproof.this could be the most difficult part of the project !

author: Braveheart Jerry
author_rank: Newbie
timestamp: February 16, 2025, 11:56:19 am
content: Quote from: NE666 on February 15, 2025, 02:43:57 pmThis is exactly what the oem BMW circuit does. It counts the number of wash cycles since the lights were turned on and allows the headlight washer to operate once every 5 momentary washer switch cycles. This sounds like the best way to do it so what components are needed? 1 raspberry PI? One or 2 relays? And kind of other voltage stabilizing devices? Any other components? Obviously a waterproof box or maybe I can find room behind the glove box inside the car? I love everyone’s suggestions but being a beginner might need a little more help with either a set of detailed schematics or even someone who might be willing to build me something for a small fee. Welcome all you input. Thanks