12v Timer Relay

[andys]

Ok seeing as there are some very knowledgeable electrical people on here I wonder if anyone can help with this. My van has an electric water heater as standard that is switched by one of those ubiquitous round 12v switches, but I want to do away with this switch and have one that will stay on for, say 2o mins, and then turn itself off.

Thing is, even though the element is rated at a fairly weedy 300W (it's still enough to give enough piping water for one shower), if I've done my maths right it's pulling 25A and I can't seem to find a timer circuit or relay that can switch that current safely. Any suggestions for what I could use, or even if my calculation is crap and it's not pulling that high a current?

I want to crack this so it will mean there's much less chance of me forgetting and draining my leisure battery, but also the next step after that would be to wire in a GSM switching box so I could switch that circuit, via another relay, by sending a text to turn the hot water on.

 

[Pauly]

If you use a 30 or 40 amp standard relay to switch the main feed you can use any device to trigger the relay as the rating wouldn’t matter so any timed relay/gsm trigger could be used to control it ??

 

[Dellmassive]

what @Pauly said.

300w @ 12v is 25amps. . . . . (w = v x a)

so any 25amp or above 12v relay will work

example here with a loom and fuse >

https://www.amazon.co.uk/Wiring-Har...1199510&sr=8-1-spons&keywords=12v+relay&psc=1



then the timer part can be anything you like. . . .

like this 12v timer with case>

https://www.amazon.co.uk/KKmoon-Aut...UTF8&qid=1531199664&sr=8-6&keywords=12v+timer




the idea being like pauly says that you use the existing rocker switch to trigger the 12v timer . . . this will then be used to switch the bigger relay on/off . . . . which in turn switches your 300w load.



Note: basic automotive electrical safety and knowledge will be required to hook it all up.. . . . . so if your not sure . . . . . . take it to someone know knows what there doing.

 

[andys]

Ah great, thanks guys, so I was just making it unnecessarily complicated by trying to combine both functions in one.
I’m fine with the wiring, just couldn’t work out how to achieve what I wanted as I could only find combined timer relays rated at 10A. I want to replace the switch with a push switch and an LED that is only on when the water heater is on so am going to take the LED feed, via a resistor, downstream on the timer circuit. I would rather use a momentary switch so need to find a timer that will latch on when pushed once.

Edit: actually if I’m reading it right, that timer can latch with a momentary switch. Ordered it and will have a play

 

[travelvolts]

Why not just use an ignition switched relay and only have the heater on when driving. It would be far kinder to your battery too. I assume that you are using a Surejust 22 litre model?

 

[andys]

Why not just use an ignition switched relay and only have the heater on when driving. It would be far kinder to your battery too. I assume that you are using a Surejust 22 litre model?

I did initially consider that but I recalled all the times I'd needed to use it when the engine wasn't running and realised it wouldn't be practical. I don't know what make it is, it was installed by Westfalia and is covered by insulation, I'd be surprised if it was 22L though, it doesn't look big enough but I'm not great at estimating size. It looks about the volume of one of those big Nescafe tins.

 

[mmi]

Got this one VBESTLIFE Hot DC12V Delay Timer Switch Timing on/off Relay Module 0~60minutes 30A Load 250VAC/30VDC-in Relays from Home Improvement on Aliexpress.com | Alibaba Group a couple of days ago for my experiments.
Pleasantly surprised with build "quality" - at least looks good, solderings look good, etc.
Stand-by current 6mA, when relay activated 80mA. Not bad/huge investment... delivered to the mailbox
I would expect it to be available also through ebay, amazon...

 

[Dellmassive]

Like it... looks good that one. =)

 

[mmi]

Some more fun with the gadget linked above when used "in-line" in 12 Volt circuit.

A self-de-energizing 12V timer.

Taking advantage of "Function 1" described in the instructions.
By setting it up as in the picture when momentary switch is pressed the relay will close (and power up also the timer itself) and remain closed for the set period of time. When time is up the relay will release and thus remove the power feed to the timer itself (eliminating the 6 mA standby current). The diode is useful preventing a short surge to load through the switch when the switch is initially pressed. However if using a switch of same rating as the relay, the diode can be omitted (just wired directly instead).

 

[andys]

Ok, I have a slightly different issue that I'm trying to solve with a relay that has me stumped. What I need is some sort of mechanism that will latch a circuit closed for a set period at the first trigger of an intermittent pulse from a different circuit. All the relays I have/can find on ebay need a continuous voltage to the trigger and will pulse the output if the input is also pulsed. Is that possible with any sort of relay/solenoid? Does my explanation even make sense?

 

[mmi]

Ok, I have a slightly different issue that I'm trying to solve with a relay that has me stumped. What I need is some sort of mechanism that will latch a circuit closed for a set period at the first trigger of an intermittent pulse from a different circuit. All the relays I have/can find on ebay need a continuous voltage to the trigger and will pulse the output if the input is also pulsed. Is that possible with any sort of relay/solenoid? Does my explanation even make sense?

Just to clarify, do you mean that the set period starts specifically and only at the first trigger and possible subsequent triggers should not "restart" the timer again thus extending the switch off? (The latter case would be an easy one )

 

[andys]

Just to clarify, do you mean that the set period starts specifically and only at the first trigger and possible subsequent triggers should not "restart" the timer again thus extending the switch off? (The latter case would be an easy one )

Ideally the output would be latched only while the input was pulsing, but it would be workable in the latter case you mention as a very short time period continually reset by a pulse would still effectively give me what I want.

 

[mmi]

Ok – using the before mentioned (10 Aug) programmable relay LINK
I like this relay package as the timing is a kind of digital one instead of analog resistor/capacitor circuit. The timing resolution is one second but is fixed and set up using solder spots. It also has a couple of functions which change its functionality - two of them below (both just tested and verified , thanks for inspiring challenge)


Proposal 1:

Triggered by first positive pulse. Will stay switched on programmed period starting from the first pulse. Subsequent pulses won’t extend the time. Retriggering possible only after programmed period has expired and trigger input has been low.

Diodes in the setup isolate the other circuit from relay circuit.

​

Proposal 2.

Triggered by first pulse (contact closed). Each following pulse (contact open-contact closed) will restart the period thus the relay stay switched on programmed period from the last pulse. The trigger input must be either just a switch or isolated (no common ground) voltage supply (about 10mA) thus the proposal to use a separate relay (the current less than 1mA in the "orange circuit").​

​

Happy to answer any questions...

 

[andys]

Ok – using the before mentioned (10 Aug) programmable relay LINK
I like this relay package as the timing is a kind of digital one instead of analog resistor/capacitor circuit. The timing resolution is one second but is fixed and set up using solder spots. It also has a couple of functions which change its functionality - two of them below (both just tested and verified , thanks for inspiring challenge)


Proposal 1:

Triggered by first positive pulse. Will stay switched on programmed period starting from the first pulse. Subsequent pulses won’t extend the time. Retriggering possible only after programmed period has expired and trigger input has been low.

Diodes in the setup isolate the other circuit from relay circuit.

View attachment 29040​

Proposal 2.

Triggered by first pulse (contact closed). Each following pulse (contact open-contact closed) will restart the period thus the relay stay switched on programmed period from the last pulse. The trigger input must be either just a switch or isolated (no common ground) voltage supply (about 10mA) thus the proposal to use a separate relay (the current less than 1mA in the "orange circuit").​

View attachment 29041​

Happy to answer any questions...

Outsatnding! Thanks
The trigger current is around 200 mA so would the first one be best? I've just ordered that relay but it'll take a couple of weeks to get here.

 

[mmi]

Outsatnding! Thanks
The trigger current is around 200 mA so would the first one be best? I've just ordered that relay but it'll take a couple of weeks to get here.

Good. I would think that the 200 mA is enough to serve the initial current rush when the relay initially pulls as it is served through the relay circuitry, so the first one might be simpler to implement. The first one also removes all the power from itself when the time is up thus no standby current).
In normal mode the relay pulls 6 mA at standby. 80 mA when activated.

EDIT (16.10.2018): Checked the surge when relay pulls. Surprisingly almost none - seems to be quite well designed gadget for the price.

80 mA @ 11.0V
90 mA @ 12.5 V
105 mA @ 15.0 V
Measured using both 100 ms and 1 ms integration time - so should have covered any high energy surges.​

Next test would be the actual relay contacts - probably just keep using and let the time tell...

 

[andys]

Good. I would think that the 200 mA is enough to serve the initial current rush when the relay initially pulls as it is served through the relay circuitry, so the first one might be simpler to implement. The first one also removes all the power from itself when the time is up thus no standby current).
In normal mode the relay pulls 6 mA at standby. 80 mA when activated.

Thanks again, I'll let you know how it goes.

 

[andys]

Good. I would think that the 200 mA is enough to serve the initial current rush when the relay initially pulls as it is served through the relay circuitry, so the first one might be simpler to implement. The first one also removes all the power from itself when the time is up thus no standby current).
In normal mode the relay pulls 6 mA at standby. 80 mA when activated.

EDIT (16.10.2018): Checked the surge when relay pulls. Surprisingly almost none - seems to be quite well designed gadget for the price.

80 mA @ 11.0V
90 mA @ 12.5 V
105 mA @ 15.0 V
Measured using both 100 ms and 1 ms integration time - so should have covered any high energy surges.​

Next test would be the actual relay contacts - probably just keep using and let the time tell...

I've finally got a day off work spare to do van stuff today so I've had a go at this and I just can't get it to work. I've checked all connections several times, checked the diodes, and ensured they're the right way round. If I bridge the signal output and +12v on the relay then the auxiliary siren and strobes power up fine.
All I can think is that the pulse is not long enough or powerful enough to act as a trigger, but the specs of the output (it's a Clifford alarm) quote a 200ma output.

To make matters worse, I've done something to my back lifting the driver seat out of the van and can't straighten up

Got a bit more of the work done to carbon fibre my door mirror covers though so the day hasn't been a total washout. Now laying flat on the sofa.

 

[mmi]

I've finally got a day off work spare to do van stuff today so I've had a go at this and I just can't get it to work. I've checked all connections several times, checked the diodes, and ensured they're the right way round. If I bridge the signal output and +12v on the relay then the auxiliary siren and strobes power up fine.
All I can think is that the pulse is not long enough or powerful enough to act as a trigger, but the specs of the output (it's a Clifford alarm) quote a 200ma output.

To make matters worse, I've done something to my back lifting the driver seat out of the van and can't straighten up

Got a bit more of the work done to carbon fibre my door mirror covers though so the day hasn't been a total washout. Now laying flat on the sofa.

Hmm.. sounds like the Clifford thingy is not supplying voltage/current. Perhaps it has only relay type output which can handle (but doesn't supply) the mentioned 200mA? Any spec sheet to look at?
To trigger this relay even very short pulse (<0.1s) should be enough.
Hope your back gets better soon.

 

[andys]

Hmm.. sounds like the Clifford thingy is not supplying voltage/current. Perhaps it has only relay type output which can handle (but doesn't supply) the mentioned 200mA? Any spec sheet to look at?
To trigger this relay even very short pulse (<0.1s) should be enough.
Hope your back gets better soon.

This is the page from the installation guide. The output highlighted is the one the installer told me to use and I think I've seen the problem, it's a switched negative not positive. Is that the issue?


Thanks, I've tried a trick my sister in law told me a while back, shower jet on the area as hot as you can stand it and then switch it to cold and keep alternating the two. The spasming it causes seems to free it off. It's only temporary though, Im going to be getting out my car and walking from the car park like quasimodo tomorrow.

 

[mmi]

This is the page from the installation guide. The output highlighted is the one the installer told me to use and I think I've seen the problem, it's a switched negative not positive. Is that the issue?

Yes... the switched negative definitely won't work. It obviously doesn't put out positive pulse being just a current sink.

I'm on travel now so can't verify now if/how we can exploit the Batt neg-line of the relay within the 200mA limit. I'll get back on this...