Author Topic: GSM remote control of a 12V circuit  (Read 780 times)
merc
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GSM remote control of a 12V circuit « on: October 13, 2022, 07:47:12 AM » Author: merc
As posted to another thread, I need to power off/on an eletric fence remotely. Its supply is powered by a 12V/60Ah AGM battery so the easiest thing to do is disconnect that powering.
Looks like a independent car heating GSM controller (the pdf manual is in the Czech language, sorry) could be an affordable solution and does exactly what I need. Using an SMS code it can power on or off a 8V to 30V circuit and confirm the final status in a reply.

What's quite discouraging is its power consumption up to 4.8W (max Icc on 12V is 0.4A ). Being powered 99% of time, it would eat out the battery soon.
The electric fence pulse supply (AKO Mobil Power AN 5500) has a power consumption of 112 to 440mA depending on the fence length and amount of vegetation discharging it. I assume our value being usually closer to the lower bound.
What kind of OPTO-MOS relay do I need to switch on/off the low current pulse supply and minimise the consumption of the GSM switch at the same time? Thanks.
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Medved
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Re: GSM remote control of a 12V circuit « Reply #1 on: October 13, 2022, 10:54:24 AM » Author: Medved
The question is, whether the 4.8W is maximum peak power, or the average one.
Knowing GSM transmitters could have max RF power 2W, with 50% efficiency of the output stage that could lead to the 4W, which would suggest the 0.4A is the peak power during transmitting, so the average would be way lower.
Because I have no idea, what the 5W would be used for, when normal phones using 3.6V 1Ah battery tend to last nearly a week on a single charge, so average consumption of barely 30mW. With a limited converter efficiency at such light load, we may be talking about roughly 100mW from the 12V...
To know for sure, you would have to try it out.

Otherwise using a normal complete cheap "dumb" phone would consume way less (allow only selected number to "receive calls", set it at "vibration only" and connect the control to the vibration motor output)...

For controlling the load you won't need any "OptoMOS", few small bipolars and a single IRFZ44 switching the power to the HV generator would be good enough. Definitely use some higher power MOSFET, as the 120mA could be the average consumption, but the peak would be in a few A-range.
« Last Edit: October 13, 2022, 10:56:55 AM by Medved » Logged

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merc
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Re: GSM remote control of a 12V circuit « Reply #2 on: October 13, 2022, 03:36:08 PM » Author: merc
Thanks! I don't know so much about electronic components and their parameters so I'd probably prefer a ready-made "box" - just to wire and use it.
Looks like this F5305S module should do the trick...? The non-PWM terminals, of course.
My only concern is that the GSM module "Digital Out" voltage is input Vcc, which is the AGM Battery voltage and this could be more like 14V when fully charged. The F5305S has control voltage of 3.3..12 V so the 14V could be too much.

Good point with the peak current. I've noticed a sparkle on the battery terminals while connecting the HV generator so there indeed must be a peak in the moment of connecting to a DC supply.
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Medved
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Re: GSM remote control of a 12V circuit « Reply #3 on: October 14, 2022, 01:03:12 AM » Author: Medved
The module: The control part is just a series resistor with the optocoupler LED, so it is just a matter of not overheating it. An extra series resistor will do the trick.

However when the GSM is already switching the high side, the MOSFET connection is way easier:
You need two resistors in the 1..10kOhm range and the MOSFET (IRFZ44 or any of similar strength; standard, not th "logic drive" type).
One resistor you connect as the "load" for the GSM module (there should be nothing in series with it, not even any LED or so; if you want that, connect it separately with its own resistor).
The second resistor is in series with the MOSFET gate (normally the MOSFETs withstand up to 18V, but not any spikes above that, the resistor separates that).
The MOSFET is connected by its source to the minus, gate via the resistor to the GSM output and the drain is the negative power connection for the fence generator.
Positive power to the fence generator is connected permanently.
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merc
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Re: GSM remote control of a 12V circuit « Reply #4 on: October 15, 2022, 09:58:11 AM » Author: merc
Thanks, Medved.

On Monday, I'll hopefully get the GSM module from a guy selling it new for a half price. In the smart age with all those "Alexas" etc. it's an obsolete piece of tech anyway. An overnight average load test with a 2000mAh battery pack should tell the actual consumption of the device. The pasture might have a bit weaker GSM signal though.
I haven't managed ordering the MOSFET part yet (the e-shop had some problems) but it shouldn't add too much to the GSM module consumption...
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marcopete87
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Re: GSM remote control of a 12V circuit « Reply #5 on: October 16, 2022, 05:57:15 AM » Author: marcopete87
Hi, you can also opt for a latch-unlatch relay with a controlling circuit and forget about voltage spikes.
https://it.rs-online.com/web/p/rele-di-potenza/1762937

However, if you are concerned about battery drain, you should add some solar panel with a charge controller in order to charge your batteries during day.
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merc
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Re: GSM remote control of a 12V circuit « Reply #6 on: October 18, 2022, 12:06:22 PM » Author: merc
Hi, yep - low battery drain is crucial. The MOSFET part should arrive tomorrow (the e-shop messed up the shipping so it's been a bit delayed).

The consumption of switch itself (in the picture) is negligible. Powered from an 8x AA Eneloop pack (1800mAh?) for almost 24 hours (including some test switchings and status reports) and batteries seem still almost full, according to their voltage.
Looks like those 4.8W is just a special constellation like transmitting on a very weak GSM signal + holding such a relay + digital input connected.
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merc
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Reporting almost discharged battery « Reply #7 on: October 27, 2022, 09:40:37 AM » Author: merc
The GSM remote control for the electric fence was installed last weekend and works fine.
Used GSM module (pdf manual available only in the Czech language, sorry) has a terminal called IN1 I haven't used yet. When connected (3.5mA) to GND (or disconnected from GND), it can send a text message about the change.
This is a pager feature - as the primary use of the module is cars, I assume people use it for intrusion alarm.

Anyway, I'd like to use this feature for reporting battery discharge. When AGM battery voltage drops to 12.2, the HV pulse source shows that by flashing the red indicator during the pulse. (Meaning: I'm still working but don't forget to replace the battery soon.)
I'm not going to tamper with the HV source but I'd like to find a way to connect IN1 to GND (or disconnect connected, if that is easier) if the battery voltage drops to a similar level. Is there an affordable component (also not drawing too much from the battery) that could do that?
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Re: Reporting almost discharged battery « Reply #8 on: October 27, 2022, 11:17:10 AM » Author: Medved
You may use TL431 with two resistor divider to set the threshold and then a resistor to set the load current...
If I remember well, the TL431 datasheet is showing such circuit...
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Re: Reporting almost discharged battery « Reply #9 on: October 27, 2022, 02:06:51 PM » Author: merc
Thanks, looks promising. I'll look into that.
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marcopete87
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Re: Reporting almost discharged battery « Reply #10 on: October 27, 2022, 06:09:21 PM » Author: marcopete87
Hi, i think you should continue the old topic instead of opening a new.
However, you should definitively add a sort of recharging option (like some solar panels).
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merc
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Re: GSM remote control of a 12V circuit « Reply #11 on: October 28, 2022, 08:14:14 AM » Author: merc
Okay, that was a separate (while related) question. Somebody joined the topics anyway.

If moderators have so much time, I think they should rather focus on enforcing picture upload policy (like 10 shots of the same fixture - just go 7 or 8 upload pages back). ???
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Rommie
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Re: GSM remote control of a 12V circuit « Reply #12 on: October 28, 2022, 09:08:01 AM » Author: Rommie
@ merc - Regarding multiple uploads of the same fixture etc., we do try, but it's difficult sometimes to convince people.

As for two topics on the same thing, it really depends on how old the original topic is. If it hasn't been commented on for several months/years, then I would say start a new one. If the previous one is relatively recent, it's probably better to add to it as it will be fresher in people's memories.
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merc
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Re: GSM remote control of a 12V circuit « Reply #13 on: October 28, 2022, 12:51:34 PM » Author: merc
Ok. I just didn't like merging my topics (as if it was a real problem) without asking me. I believe PMs work and if you asked me, I wouldn't say no. Let's forget about it. :angel:

Best regards,
:mv:
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