your opinion for NiMh battery chargers

[sfiga69]

I purchased some WiFi thermostatic valves (TRV603) powered by 3 AAA batteries which have a battery life problem.
In 15/20 days the batteries are completely discharged and the valves go offline and are no longer reachable remotely.
I have tried different brands of batteries but the lifespan does not exceed 20 days.
I did some tests and it works correctly with a voltage between 3.2v and 5v.
Considering that:
- they are installed in unattended rooms
- that power outages may occur for a duration not exceeding 10/15 minutes.
- when the power supply returns they must be put back on line manually

Since there are power outlets nearby, I decided to use AAA NiMh batteries with charge regulator as per the attached diagram.
Do you think the schottky diode circled in red can cause problems?

Thanks for your opinion

PS I've been powering a valve with the attached diagram for 10 days, doing operation simulations and there don't seem to be any problems but I'm interested in your opinion.

[Old_but_Alive]

why not try rechargeable Alkaline AAA batteries they give 3x1.5V = 4.5V

and claim 8800 mAH ( probably a total lie), but they work for me in my laptop mouse

you would need a charger of course, unless you get the lithium with USB socket

or lithium  https://www.aliexpress.com/item/1005004995221539.html?spm=a2g0o.productlist.main.21.39c855ffwMgXk9&algo_pvid=123cc867-063a-44fe-80ae-9125ab0d0de0&algo_exp_id=123cc867-063a-44fe-80ae-9125ab0d0de0-10&pdp_npi=4%40dis%21GBP%219.15%219.15%21%21%2111.32%2111.32%21%402103251f17167897442396752e66ee%2112000031283679561%21sea%21GB%21135358991%21&curPageLogUid=hzWSSXoYuqKI&utparam-url=scene%3Asearch%7Cquery_from%3A

or

https://www.aliexpress.com/item/1005006106825346.html?spm=a2g0o.productlist.main.1.625a49dcwmQ9T3&algo_pvid=b6c5b4c0-14ee-4478-8f7e-bbaba284603e&algo_exp_id=b6c5b4c0-14ee-4478-8f7e-bbaba284603e-0&pdp_npi=4%40dis%21GBP%2116.62%2116.62%21%21%21149.20%21149.20%21%402103249617167900070653118e339d%2112000035778591098%21sea%21GB%21135358991%21&curPageLogUid=IK9Ey298mWYg&utparam-url=scene%3Asearch%7Cquery_from%3A

[Manuel]

I think that's a developed buggy product.

WIFI takes lotta NRG, BT >=5 should be better for sure or ZIGBEE (alexa)

But maybe the control work all the says often.....so it can also be firmware oriented the issue...

Personally I can not accept such short life in a product battery powered.

Remember then that rechargeables has lower voltage vs alkaline / lithium.

Lithium 1.7V, Alkaline 1.6V, Rechargeable 1,2V generally.

Try to change the product going to BT possibly.

this is just my personal suggestion.

For not WIFI or BT check : Eurotronic Comet Plus Set 4 700151 (AMAZON i think)

ZIGBEE: Qiumi, Zigbee TRV

take care,
X!

[DarthPic]

why not try rechargeable Alkaline AAA batteries they give 3x1.5V = 4.5V

and claim 8800 mAH ( probably a total lie), but they work for me in my laptop mouse

you would need a charger of course, unless you get the lithium with USB socket

or lithium  https://www.aliexpress.com/item/1005004995221539.html?spm=a2g0o.productlist.main.21.39c855ffwMgXk9&algo_pvid=123cc867-063a-44fe-80ae-9125ab0d0de0&algo_exp_id=123cc867-063a-44fe-80ae-9125ab0d0de0-10&pdp_npi=4%40dis%21GBP%219.15%219.15%21%21%2111.32%2111.32%21%402103251f17167897442396752e66ee%2112000031283679561%21sea%21GB%21135358991%21&curPageLogUid=hzWSSXoYuqKI&utparam-url=scene%3Asearch%7Cquery_from%3A

I use this kind of 1.5v usb rechargeable battery too and they work very well.
I have them in mouse , radio, in my old photo camera and in my telescope too (8 of them !)
And like Old_but_Alive said , don't trust them on the mA/h they give , my AA battery are between 1300 to 1500mA and the AAA are in the 800-900mA.

Cheers

[sfiga69]

The valves are installed in a mountain apartment where, in winter, I go to spend some weekends.
You understand well that if I find a temperature below 10° it is not pleasant.
So, to save on heating costs, the valves always remain in anti-freeze mode and are then adjusted remotely as needed so that I have an acceptable temperature when I arrive.
From research on the internet I see that all those who have this type of valve, of any brand/model WiFi or Zigbee, have the same problem: alkaline batteries empty in 10/15 days.
I can insert any type of battery but if they are empty 2 days before my arrival I cannot adjust them remotely.
For this reason I thought of the circuit I posted, where the valves are normally powered at 5v (via AC)  and, only in the event of a power failure, they are powered by rechargeable batteries which are maintained at around 1.4v by the CN3085.
In the event of a power failure they are powered via diode D2 at 1.4x3-0.4=3.8v and considering that the NiMh discharge curve is quite flat, they still have a few hours of autonomy.
So my only doubt is related to possible malfunctions of the charge regulator due to diode D2

[pickit2]

have you thought of using a small Solar Panel to charge your batteries.

[sfiga69]

have you thought of using a small Solar Panel to charge your batteries.

It's an option I've thought about. I just have to check, given that the exposure would be north, whether the exposure allows the batteries to be recharged.

[Manuel]

Depending on electronic usage, solar could be the best option.

I agree.

take care,
X