How to convert a remote relay to pass through power - Page 1
Forum section: electronics / beginners

author: RooEEV
author_rank: Newbie
timestamp: February 23, 2021, 08:49:57 pm
content: Hello everyone,I bought a small remote relay circuit. I press the button on the remote and it closes the relay momentarily. The device is powered by 4v-12v and it works perfectly. I'm using a 3.7v lipo to power it. The problem is, I cannot figure out a way to have a single battery powering both the remote relay and the end device (which also runs on 3.7V) that I want to switch on remotely. I have to have a second battery powering the end device and this adds bulk, weight and complexity. Can anyone suggest a way I could solve this?I have tried running a wire from the negative of the remote relay's battery to the negative of the end device's negative and also a wire from the positive of the remote relay's battery to one of the yellow wires, then the other yellow wire going to the positive of the end device's positive terminal, hoping that when I activate the relay, it would close the circuit and power the end device. But it did not work. I have attached a photo of the remote relay circuit.

author: Terry Bites
author_rank: Super Contributor
timestamp: February 23, 2021, 10:35:01 pm
content: I dont think that's possible. It loooks like you want the remote to power up the relay board. Sort of chicken and egg?If you can run one wire then why not two and power it. If you can do that then what's the use of a remote?

author: Manul
author_rank: Super Contributor
timestamp: February 24, 2021, 01:25:31 am
content: Quote from: RooEEV on February 23, 2021, 08:49:57 pmActually what you did seems correct, so I'm not sure what is problem. Do you have a multimeter? Are you sure the contacts are closing? Does any voltage come to the device or no?Some devices may have an issue if the wires from battery are too long. And you definitely increased the length. That could be issue, but it is not very likely.Also it is possible, that the end device causes a current surge at turn on and the relay unit fails, because voltage drops too much. It seems it is supposed to work from minimum 4V, so one lipo cell is kinda below the minimum spec already.Quote from: Terry Bites on February 23, 2021, 10:35:01 pmI'm quite sure OP wants to power the relay unit and somethird partydevice together from the same battery. Not the remote.

author: Ian.M
author_rank: Super Contributor
timestamp: February 24, 2021, 03:14:14 am
content: The relay module is specified to work with from 4V to 12V on its VIN terminal, with respect to GND. A single cell nominally 3.7V LiPO will only be over 4V when freshly charged and unloaded. For 99% of its discharge life it will be below the minimum voltage for the module. I can't find a datasheet for the relay itself, but LCSC have datasheets for very similar relays in the same series with from 6V to 24V coils, and they all have a 'Max Operate Voltage' which should be read as max (i.e. worst case)mustoperate voltage, i.e the minimum coil voltage at which all relays of the type will pull in at of 65% of their nominal coil voltage. For a 5V coil this would be 3.25V. There's probably a little drop in the driver circuit - lets 'handwave' that as 0.15V, assuming they've been cheap and used a BJT driver transistor. Therefore there is a high risk it will stop operating (i.e switching on) when the battery discharges to 3.4V. It may well fail above that voltage if the driver electronics has a higher minimum. As the commonly accepted end of discharge voltage for LiPOs under light load is 3.0V per cell, "Houston, we have a problem"!Its this sort of willfully ignorant sh!t that results in95 kg drones dropping out of the sky at airshows...To do this right, you've either got to power that module from a 2S LiPO pack or fit a low quiescent current boost module*between a single cell LiPO and it, to to keep its supply voltage in the specified range.Once you've got it properly powered, connecting a load controlled by it to the same battery should be as simple as ignoring the existing connections the the battery and adding a series circuit of its COM and NO#contact pair and the desired load, which *MUST* *NOT* exceed 20A inrush current.* e.g.https://www.sparkfun.com/products/10255# Assuming you want to minimize off state current consumption, you use NO because that's the one that's open with the relay coil not powered.

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 24, 2021, 08:29:19 am
content: Quote from: RooEEV on February 23, 2021, 08:49:57 pmthis will work for sure if your relay has enough voltage on the coil when ignited3.7V is really limit (as relay have 5V coil, he neds in ideal world 5V, in unideal 0.7+5==3.5VBUT if they put some voltage regulator to 'create' those 5V for relay coil/micro, that regulator neeed a little more voltage to make 3.5V for coil relay. you're at that limittest with 12V battery or ps and in will work for sure IF the relay is good (i mean the NO contact close correctly)to be clear concerning the wiring:Battery + >> red wire and yellow wire (relay IN)Battery - >> black wire and load negativesecond yellow wire (relay OUT)>> load positive

author: Ian.M
author_rank: Super Contributor
timestamp: February 24, 2021, 12:47:52 pm
content: Good point, Perieanuo.A badly designed relay module would put the relay supply through a LDO regulator. However as the rest of the board is likely to be running at 3.3V, so a separate regulator would then be needed for the relay, with significant dissipation when the relay is on at max supply voltage. A smart designer would PWM the relay coil, adjusting the duty cycle to maintain an average of 5V, which removes a LDO + its caps from the BOM, allows operation down to a lower voltage and is also more energy efficient. On any MCU with spare code space, a PWM peripheral and an ADC input, that's nearly 'free' to implement as the only additional cost per unit is a two resistor potential divider.If the LDO starts to drop out at 300mV across it, that would raise the undervoltage threshold to around 3.7V, loosing the use of half the battery capacity if no boost converter was used to maintain the supply in its specified range.

author: RooEEV
author_rank: Newbie
timestamp: February 24, 2021, 04:27:46 pm
content: Thank you everyone for the replies. Your comments helped me think I understand more about the problem. I think it is a voltage sag issue.The third party device is an internal circuit from an arc lighter (those things that produce a high voltage continuous arc, designed for igniting a gas kitchen stove). I want to trigger the arc lighter remotely to launch fireworks from a safe distance. I got it working perfectly with two separate 1S lipo batteries - one powering the relay module and the other powering the arc lighter. The relay triggers the momentary switch on the arc lighter and it lights the fuse. But when I wired it up in the way I described above, with a single 1S lipo battery, the arc lighter will not produce an arc, though it will light its LED showing it has power. And I can hear the relay closing when I trigger it remotely. So even with the little battery being under the load of both devices, the relay appears to operate normally but I suspect that the battery voltage under that combined load might be too low to power the arc lighter and can only manage to provide enough power to light the operation indicator LED. But I'm not sure if this is the problem.Another piece of the puzzle is that under the above mentioned wiring configuration, when the relay switch is open, there is still about 1v going to the arc lighter, which is worrying.

author: Caliaxy
author_rank: Frequent Contributor
timestamp: February 24, 2021, 05:14:53 pm
content: Quote from: RooEEV on February 24, 2021, 04:27:46 pmI think you are right. Since generating the arc is a very short event, I'm wondering if a big capacitor (mounted in parallel with the battery) would help provide the extra-energy when needed. Can you provide more details about the arc lighter module?

author: RooEEV
author_rank: Newbie
timestamp: February 24, 2021, 05:42:47 pm
content: Quote from: Caliaxy on February 24, 2021, 05:14:53 pmI don't know much about it but I got it on amazon and it runs on a small, 200mAh 1S lipo cell. This is a similar device:https://www.amazon.ca/Rechargeable-Flameless-Electronic-Windproof-Ignition%EF%BC%8C/dp/B08LMV1CCS/ref=sr_1_24_sspa?dchild=1&keywords=kitchen+arc+lighter&qid=1614188496&sr=8-24-spons&psc=1&spLa=ZW5jcnlwdGVkUXVhbGlmaWVyPUEyM0tHQkw4NUJPVlYxJmVuY3J5cHRlZElkPUEwNjc2NTI0RzlYWDFHSEtPSDNMJmVuY3J5cHRlZEFkSWQ9QTAyMTQzMTlXMjlQUkZYRFdTR0wmd2lkZ2V0TmFtZT1zcF9tdGYmYWN0aW9uPWNsaWNrUmVkaXJlY3QmZG9Ob3RMb2dDbGljaz10cnVl

author: Ian.M
author_rank: Super Contributor
timestamp: February 24, 2021, 06:06:52 pm
content: Hacking together and using a wireless remote pyrotechnics igniter reasonably safely requires a *LOT* of knowledge, and quality components appropriately specified for safety critical applications.I wouldn't trust that relay module not to operate if a CBer driving past hits their PTT switch, or if someone clicks their garage door opener etc. Also for a Chinese radio controlled relay module, what guarantee do you have that there aren't other transmitters with exactly the same code (if it even bothers with coded transmitter and receiver pairs)? Consider what could happen if random interference or another gadget's remote nearby, using the same wireless RC chipset, fires it while you are setting up the next firework in line! At best you'd need clean underwear . . . .Worst case: It could very easily make you a Darwin Award candidate.If you are going to use a wireless link for something safety critical it needs to be securely encrypted end-to-end so random or malicious signals cant trigger it and to have link integrity monitoring so you can get advance warning if it is being jammed by interference.Have you considered using hard-wired single use 'electric matches' operated from a console with a secure locking safety switch an adequate safety distance from the pyrotechnics?If you want to discuss using the wireless relay module with other loads that aren't an immediate safety hazard, we are quite happy to help . . .To get a better idea whats actually going on, you'd need to scope the voltage across the LiPO on your bench to view the instantaneous voltage drop, with just the relay module, just the gas igniter, and with both together.A 200mAH small LiPO from a consumer gadget build down to a price, may well be already on the bleeding edge of its max permissible discharge rate (current) with only enough margin for battery aging to minimize warranty returns. To have any hope of it working reliably with the additional load of the relay board with the relay pulling coil current, you'll probably need a larger LiPO, e.g. an 18650 cell. You may well be best off hacking a cheap dollar store single cell USB powerbank to tap its cell for the load and to supply the relay module from its boosted 5V output.e.g. one like this:https://hackaday.com/2016/12/21/cheap-powerbank-logic-and-teardown/N.B. more expensive powerbanks are likely to have auto-poweroff and wont stay on if only a light load like an Arduino or your relay module are connected, so aren't suitable. The type I linked provides 5V on its USB A socket all the time, so long as its got charge left, pulsing occasionally to keep the voltage up if no load is connected.

author: RooEEV
author_rank: Newbie
timestamp: February 24, 2021, 07:35:27 pm
content: Quote from: Ian.M on February 24, 2021, 06:06:52 pmWith respect, in my opinion you are somewhat over-reacting and I think the "darwin award" implication is unnecessary and perhaps disrespectful. I live on a 100 acre rural plot with a 60 acre plot behind it. The small family fireworks event will take place in the Summer in the middle of a large field, approximately 600m from the nearest road. The probability of someone being within range of me with the same coded remote and to be pressing their remote during the approximately 60-90 seconds I will have the arc lighter positioned on the end of the fuse is low enough for me to not fear such a scenario.And let's say the worst case happens and someone tresspasses within range, pressing a PTT radio or garage door opener that happens to be similar enough in transmission code to trigger my relay while it is powered on and already positioned on the fuse, the arc will just ignite the fuse seconds before I have begun running away, in which case it's no different to lighting it with a match. The intention of this device I'm putting together is to increase safety by getting me away from the fireworks before being ignited, rather than me lighting it and then running away. And I believe it achieves that. I do not believe the effort and complexity of an end to end encrypted communication link is warranted for this project but thanks for your other suggestions and links. your idea about using the circuit from a cheap 18650 power bank is a very good one. I have a few such $5 cylindrical power banks in a box.

author: Ian.M
author_rank: Super Contributor
timestamp: February 24, 2021, 08:00:05 pm
content: If you are firing one firework at a time, and add a manual lockout switch in series with the igniter + a warning LED before the switch, so you can see if its getting triggered unexpectedly without it actually firing, and *ONLY* close the lockout switch as the last thing you do before promptly retreating to a safe distance, assuming common sense and a reasonable sense of self-preservation, odds are you wont experience any 'brown trouser' events. The potential for a Darwin Award starts if you are trying to use several devices like this to fire multiple fireworks in sequence, as without an adequate single point lockout system one could get triggered behind your back while you are setting up another. I've seen a display where the whole lot went up at once with the pyro-techs running for cover. Fortunately no injuries. The display was quite impressive for 30 seconds, but no-one bothered sticking around for the remaining ten minutes allocated for the ex-display on the programme!

author: RooEEV
author_rank: Newbie
timestamp: February 24, 2021, 08:19:32 pm
content: Quote from: Ian.M on February 24, 2021, 08:00:05 pmI'm not using several remote relay devices at once for multiple triggers. So, I don't think I'm worthy of the Darwin award this time. Yes, I have a physical switch in there which keeps the arc lighter disconnected from its battery until I have everything set up and in position. Then I flip the switch, walk back to my family and remotely ignite the fuse for one rocket at a time. And I agree, no one wants brown trousers, unless one happens to prefer that shade or corduroy.My next step is to consider your suggestion of the power bank circuit and see what I can make with that. Failing that I will just have to keep it in its current form which has two separate batteries. That 1V reading on the arc lighter circuit's input terminals when the relay is open has me confused though. This relay module just might not be able to function the way I want it to, with the single battery powering both devices.

author: Ian.M
author_rank: Super Contributor
timestamp: February 24, 2021, 08:42:27 pm
content: Quote from: RooEEV on February 24, 2021, 08:19:32 pmDon't knock cords or moleskin trews, or people who prefer more subdued colors. However there's something questionable about anyone who prefers *that* shade of off-brown!QuoteIt seems the relay may be leaky. Most hand-held DMMs have 10Meg input resistance on voltage ranges so it only takes 100nA of leakage to read 1V with no other load present. With the load disconnected, and COM fed from your positive supply (same as the module), see what voltage you measure across a 10K resistor connected from NO to supply negative/ground, when the module is activated. If its significantly non-zero, you've got a problem!

author: RooEEV
author_rank: Newbie
timestamp: February 25, 2021, 01:22:00 am
content: [ Specified attachment is not available ] [ Specified attachment is not available ]Quote from: Ian.M on February 24, 2021, 08:42:27 pmI have a rather lovely pair of brown corduroys. Just for clarity, they were brown when I got them. I did not add any pigment of my ownThanks for helping me try to figure this out by the way. I appreciate it. I have no formal electronics education - I've just been tinkering with things since I was a kid.I'm a bit confused about the leaky relay. The 1v leakage is only present when I have the configuration like this (I attached a new image). But when measuring the two yellow wires without the arc lighter wired into the circuit the relay is breaking the circuit as it should. But clearly there is leakage going from the positive of the relay module to the yellow wire on the other side that should be disconnected by the relay. Since it's a physical switch I don't understand how power is getting to the other side of it it. I was thinking that because this module is not designed to be powered by a battery and also provide pass through power from the same battery to the load, then this is just user error. And maybe I need to add another component to make this work as a single battery solution. It's not a big deal for the arc lighter project but if I can solve this I would love to use the same setup for other things, again requiring only one battery rather than the end load device needing its own power source. Lights, motors and so on.

author: RooEEV
author_rank: Newbie
timestamp: February 25, 2021, 03:10:51 am
content: I tried a different configuration (see attachment). This time I connected the battery to both the relay module and the arc lighter and connected the two yellow wires to either side of the momentary switch built into the arc lighter. Before, I had bridged the momentary switch and was activating the arc lighter by applying power to the terminals. The new version seemed like it was the solution, as it was working. But within a few minutes the battery was dead (1.9v). I put in a new lipo battery and within a few minutes of just sitting there it drained to 2.2V. So two lipos were killed. Now I'm back on a dual battery setup.

author: Ian.M
author_rank: Super Contributor
timestamp: February 25, 2021, 03:46:45 am
content: Your earlier circuit layout looks OK and is what I would use if the battery was capable of supplying sufficient voltage and current for both devices, and if I'd bypassed the igniter switch so it starts operating as soon as power is applied to its battery contacts. I believe the remaining issues will resolve when you mod it to run the relay module itself from 5V from a cheap powerbank.There *SHOULDN'T* be *ANY* leakage through open relay contacts of a real electromechanical relay (solid state relays are a different matter), however when you are dealing with dirt cheap made in China crap, you don't know how they've managed to f**k up the design or production, or compromised on materials attempting to save half a cent! e.g. it could have moisture from a board washing process trapped inside the relay, or contamination on the board causing track to track leakage.Another possibility is that the igniter has a largish capacitor across its power input. When power is disconnected, the igniter briefly runs off the capacitor, discharging it till the voltage is too low for the igniter to do anything, then the capacitor holds the remaining voltage for a considerable time.Try running it, check for the mystery 1V, then disconnect the wire from the relay to the positive terminal of the igniter, and check whether you've still got the mystery 1V at the relay terminal or if its at the igniter terminal. If the latter, short the igniter positive terminal to its negative one for a minute or so, then disconnect the short and check if the voltage has gone or is much reduced. If so my theory about an input capacitor in the igniter is confirmed, and you can stop worrying about the mystery voltage as its *NOT* due to leakage current through the relay.Edit: You posted the new circuit as I was writing this. It also looks OK and I would expect it to work, given (as before) a suitable battery for both.With your new results its looking increasingly like a problem with a leaky relay. If it lets enough current through to partially turn the igniter on (but not enough to function correctly) , it could be expected to discharge such a small battery rather quickly. The test I mentioned earlier with a 10K resistor would help narrow down the cause of the problem.

author: perieanuo
author_rank: Frequent Contributor
timestamp: February 25, 2021, 02:13:28 pm
content: Quote from: RooEEV on February 25, 2021, 03:10:51 amyou gotta respect the arc generator power supply specs, also it may be possible that the relay 'eats' some voltage if it's low-cost (you may loose bat normally under 1 V on contact relay)if you are handy, just put some standard 12V/7Ah battery with voltage regulator with specs within spark igniter demands, then you're bullet proofwhat voltage/current is that igniter specs? so we can propose some power supply that get the job done without glitches