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crazy72

External power supply to a fibaro door sensor. Crazy idea ?

Question

Hi 

Am i crazy if I want to connect an external power supply to the fiabr door sensors ?
The idea is to use the sensor with the battery so in case the power has gone off the sensor will continue to work. 
Required: 
- rechargeable battery 14250
- This one to provide 220V-5V 

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- It will be connected to this one to have a recharge module and not overload the battery

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For less than 10 euros we have a powered z-wave door sensor with backup power supply. (extender function not available)

What do you think ?

Thanks
Chris

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I'm not sure if this battery is prepared to work in environment where charging and discharging are in the same time... It will work, but the battery probably will be dead in a few months.

You'd better use some UPS, but I'm well awarded that it is hard to find something this small and cheep.

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I thought about this years ago and then realise that all i wanted was a door or window sensor that was hard wired, so i just wired it into my alarm system, expanded the zones and used the alarm system to power my door and window sensors using the universal sensor on each, i also added temp sensors too. I could just buy another alarm and install a massive battery as a backup if need be but the door and window sensor with batteries is just a pain to maintain. 

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There is a user that soldered the battery terminals of the Fibaro motion sensor to a DC power cable. I don't see why it can't be done to a door sensor. You just need to know the voltage and amperage required.

Just translate this page in Google 

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Strictly speaking, that battery charger will take your battery to 4.2 V and that is a bit too high (spec: 3.6 V) for the Z-Wave SoC. You could add a silicon diode (between battery and sensor) to drop about 0.6 volt.

 

A second issue with using a "generic battery charger" is that it will keep the voltage of your lithium cell too high, reducing its life span. But I do not have a clue by how much. Those chargers are meant to be disconnected from the cell after a full charge. You should get the actual chip number of that board, but I can tell you about 95% of boards I've seen are based on TP4056 (or a clone of that chip).

 

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Careful when you order cells, you can buy either 3.3 V (LiFePO4) or 3.6-3.7 V (other chemistries).

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  • Inquirer
  • Yes, most probably risks are higher than results.

    I will remove the original 14250 battery and I will connect with wires 2 rechargeable Panasonic in parallel 18650 (6800mah). They are relatively cheap and they should last at least 5 years.

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    16 minutes ago, crazy72 said:

    I will remove the original 14250 battery and I will connect with wires 2 rechargeable Panasonic in parallel 18650 (6800mah). They are relatively cheap and they should last at least 5 years.

    Sounds like a plan, I love it ;-)

     

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  • Yes, the new plan is a good 26650 

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     . It's a good battery and it should last 5/6 years.

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    1 minute ago, crazy72 said:

    Yes, the new plan is a good 26650 

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     . It's a good battery and it should last 5/6 years.

     

    Maybe. It says "NOT protected! Don't buy this unless you know what you are doing!"

     

    Without protection, the sensor is going to drain the battery below 3 V and then you might want to be careful when you try to recharge it. Not that you would often have to recharge it ;-)

     

    Just saying for those users that do not have a lot of experience with lithium rechargeable cells...

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    Keeps us informed. My battery of my door sensor is empty after 3 weeks because the place where it is installed is sometimes under 0º. Very expensive solution like this.

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  • Yes I considered pro and pros but it's something I can manage. When the sensor stopped to work I checked the voltage and was 2.9V, not so far from the voltage the protection circuit reacts (3V). 

    At 10% is still 3.2V.  So yes, the idea is to re-charge the battery when the system is showing 10% and I should be in the safe range.

    If temperature is under 0 it's hard to find a battery that will last for long, but at least with these you can recharge them, or keep far from the sensor in a protected and isolated environment.

    Edited by crazy72

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    @crazy72 I agree with what you say, I was trying to tell other users to be a bit careful. If you use wires thinner than about 0.5 mm2 those will act as a fuse. ;-)

    You probably have a nice, intelligent charger anyway... Like this one...

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    Reading this i started to think about those:

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    But they are not for D/W sensor though :(.

     

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    Nice idea (though you sacrifice capacity with that integrated charger). And indeed... thats CR123

     

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    EDIT:

     

    I think the issue with rechargeable 14250 is low capacity. I've never tried one, but I'd say most are about 250 mAh while a genuine ER14250 boast 1200 mAh.

    Edited by petergebruers

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    im using 2 Panasonic NCR18650B batteries in series with a Regolabile Buck Converter DC DC Step Down, 24V a 12V 9V 5V 3V to bring down the amps and voltage.  it allows for Input voltage: 4.5V to 28V; Output voltage: 0.8V to 20V

    Edited by matt1981
    edit

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    17 minutes ago, matt1981 said:

    im using 2 Panasonic NCR18650B batteries in series

    You mean..."in parallel"?

     

    18 minutes ago, matt1981 said:

    with a Regolabile Buck Converter DC DC Step Down, 24V a 12V 9V 5V 3V to bring down the amps and voltage.  it allows for Input voltage: 4.5V to 28V; Output voltage: 0.8V to 20V

     

    If I were to make a UPS-like solution, that is probably how I'd do it. I'd set the voltage to 3.8 to 3.9 V. As a rule of thumb, that would reduce the stored capacity to about 1/3 to 2/3 of its rating, but the cell should live longer. Or... use a much more sophisticated charger IC but I can't think of any specific IC. Texas Instruments lists about 200 different ICs :-D

     

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    1 hour ago, crazy72 said:

    At 10% is still 3.2V.  So yes, the idea is to re-charge the battery when the system is showing 10% and I should be in the safe range.

     

    Yes, safe, but not (very) good for the cell.

     

    I do not have much experience with cells left alone for 5 years and drained < 3.2 V :?

     

    I do have bunch, that drained to 1 V and they survived, but with reduced capacity (25 % to 50 % of spec I think).

     

    From reading a lot about batteries, I'd say cells degrade below that 3.8 -3.9 V level (which seems counterintuitive because of the nominal 3.6 - 3.7 V spec,, but 3.8 is the recommended voltage for storage charge, that is about 50 % of rated capacity). Because it will sit a very long time at about 3.6 V you might want to charge it much sooner, say below 3.4 or 3.5 V. I don't know how much % that is an a D/W sensor though, but I guess it might be as high as 50%.

     

    Random discharge curve, taken from Richtek site 

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    battery-discharge.png.be75a9fff0b77c062259c186da703bad.png

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    @petergebruers from the graph, 3.8 to 3.9 V looks like the "sweet spot". from what i can tell "series" and not parallel in this case, is better being i only double the volts, but keep the same amps of 3400mAH.  this way, when i use the reducer it's having to reduce the the volts from 7.2 in this case to 3.9v and drop the amps from the 18950 battery of 3400mAh to roughly 700 mA. correct?

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    I thought you were going to use the regulator to charge the cell. But you mean... a regulator between 2 cells in series and the sensor. So you are not going to attach a charger permanently? That is OK (I thought it was part of the exercise :-))

     

    If you connect them in series, you get 7.2 V nominal and 8.4 V freshly charged. So you need to drop that voltage. I agree. However...

     

    You would want a low quiescent current regulator, so an typical "3V3 ebay board" would not work because they are based on AMS1117 clones (and they probably have an LED because these cheap boards need a minimum load, don't remove it!), so they need 10 mA (order of magnitude). That will drain your battery too fast.

     

    You can find very low current regulators, based on XC6206 (or more likely: a clone of that...) without LED, less than 10 uA (real TOREX: 1 uA) - BUT unfortunately max input voltage is only 6 V and the clones I have do start to draw excessive current above that... If you have toyed with "Arduino sensors" that are based on 3V3 chips, your sensor board probably has one of those 3V3 clones to make it 5V compatible. See if you can find a chip marked "662K", that is the code of a Torex 3V3 regulator.

     

    A Holtek HT7333 (or HT7333-1 with revised specs) would do the trick, less than 7 uA quiescent and input up to 12 V. But I have not seen boards based on this voltage regulator. They're still available in TO-92 package so that is DIY friendly. I have never tried the HT7333 in this application, because I would not do it like that.

     

    Actually, no, I would not put them in series. Just use the cells in parallel. Maybe add a diode in series to go from 4.2 peak voltage to about 3.6 V. I use LiFePO4 cells, they are 3.3 V nominally and 3.6 V so I do not have this issue. It probably won't fry without that diode but it is out-of-spec.

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    On 3/28/2018 at 7:19 PM, Sjekke said:

    And any idea’s how I can external isolate my ER14250 :?:

     

    You mean... Improve performance? Especially at low temperatures?

     

    Yes, I might know how to do that... This is how I use "cheap" = "high internal resistance" cells. I add a LIR2032 coin cell in parallel. It has a lower resistance, so it provides bursts of current when the sensor transmits. Not really low temperatures, we had about -5 °C in Belgium for a few nights. That yellow component is a 50 mA PolyFuse. EDIT: that polyfuse does not perform a function in this particular application, you best leave it out. I reused the wires + connectors from another project, and it was easier to solder to the PCB than that thin wire.

     

    IMG_20180206_095740.jpg.64447cb6d2b2c79eecae6bb40b90ff9d.jpg

    Edited by petergebruers

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    @petergebruers could you get a close up of the wires you soldered to the sensor?? the user that opened this thread pogo something, was going to add the charger the batteries. that sounded like more trouble than it was worth... 

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