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Topic: Servo turn ON and OFF to save battery power (Read 1 time) previous topic - next topic

boylucky

Hi, I would need your help with correct control of following servo motors:

Servo Motor

As it is going to run on batteries and will operate only lets say twice per day I would need to save battery then. I was thinking to connect the power supply via some transistor. Please can you help me to find correct power control transistor or some other solution for these servo? As I got info it is drawing current even when it is not operate. Even when the servo is detached in arduino code it is taking current. I need to keep the project running on batteries for long time as it will only turn on and off the water valve once a day. That is why I need to control ON and OFF the current going to the servo. I do not want to use solenoid valve as it is taking current all the time the velve is open. In my case it can be about a hour a day. Which would leak to much power. I see the servo as the best option, but I need to find the correct power control for it.

Thanks in advance for your replies.

dongjee33

Does it can solved by turn on it when it use or 1 hour per 10 minute operate with on/off transistor controlled by arduino or timer IC chip?

boylucky

I am sorry, but I do not understand what you mean. I need to turn the servo on for about 1 second to open the valve. Then it waits 1 hour and then it will again power on the servo and will stop the valve + then power off the servo for 1 day. So I think that the transistor would be probably good solution. But as I never used transistors for power control yet, I asked in this tread what would be the best solution.

boylucky

Please, any help with this topic? I also found some solid state relay which could be used for example model G3MB-202P. What do you think about such solution? I need to cut off all current to the servo (and also to the switching device - transistor, SSR relay etc) to keep battery life as long as possible.

boylucky

Or what about some H-Bridge. But I am not sure with any of the device if some current is also leaking when not powering the servo.

MorganS

#5
May 29, 2018, 06:00 am Last Edit: May 29, 2018, 10:18 am by MorganS
That SSR can only switch AC loads. It can never switch off DC.

Get a regular relay. Preferably on a driver board or shield.

An H bridge will work but is unnecessary. There is also a big risk that you will destroy the servo with reverse polarity.

A single P-type mosfet (one quarter of an H bridge) can work but it requires more construction skills.

I like to use high-side switching chips designed for automotive uses. BTS5012 or BTT6010 are great but a little complex due to the current-feedback features. BTS716G is good as it could switch 4 things.

Make sure that when the servo is off that you don't attempt to output anything on the Arduino pin connected to the servo. Make the output LOW or make that pin an input temporarily.
"The problem is in the code you didn't post."

boylucky

Hello MorganS,
thanks a lot for your post. Based on your info I would go the way with regular relay or some of the high-side switching chip. I already search for some suitable relay but as the Arduino pin can only give max of 25mA per pin I need to find some suitable one to be able to switch the load at this small current (ideally running on 1,8 V :o) which I thing is not possible at all). I saw some board with optocoupler to be able to give more current for the relay to be switched on. But I am not sure if there is some small power consumption of such things when the load is off. As the aim is to have the device running for a long time only on batteries. Next thing is that I am running the arduino (or better ATMEG328P-PU chip) at the smallest configuration possible and with 4 MHz external oscilator on 2AA batteries. It communicate via NRF24L01+ device then. Currently I am able to run such device without problems but now I need to add this power switch for the servo which will have its own power supply again from batteries. I see that the BTS and BTT chips which you recomend run on 5V if I am correct right?

MorganS

I'm sure there are high-side switches available for such low voltages. The BTS types are best for very large currents at 12-28V.

What servo do you have which runs on 2AA batteries? Most of them get very weak below 5V because they prefer 6V.
"The problem is in the code you didn't post."

boylucky

I do not have servo for 2AA batteries. That is currently the power source only for the ATMEGA328P-PU with the NRF24L01+ module. I am going to power the servo with separate power source which is most probably going to be 4 to 6 AA batteries. The server I will drive is here.

It is right, that I can power up the BTS or BTT with this power source too, and only switch the load on and off with the arduino powered up with 2 AA batteries. Not sure if the BTS or BTT can use the logic of 1,8 V to switch on and off.

By the way I have one more idea. Probably not the best solution from electronics point of view but I will try to describe here. I have some power bank at home which is designed to provide 5V with 10000mAh of capacity. If I would connect it with the servo motor then it should be able to run for about 100 days in lets say stand by mode. I mean it could operate for 90 days if I would not run the servo motor (just powering it up as it is taking 4mA when not running if I am correct). The problem but in this case also an advantage is that the power bank switch off automatically when the powered device is not taking enough current on the supplied USB port. It means when the servo need to take the power from the power bank, the power bank should be first wake up by some current, and then just turn the servo as needed. After that the power bank will again turn off when no current on the USB port. I already tested with my power bank and looks ok. So no I just have to find a way how to wake up the power bank to provide power source for lets say 2 seconds to turn the servo. I was thinking to just connect an optocoupler with some resistor to simulate an power requirement. This would be driven by the ATMEG328P chip. I was also thinking to use this power source from power bank also for the ATMEG328P chip. My idea was to connect there an supercap (I have one for 2,5V with capacity of 10F) which would just take the power from power bank (via some diode to reduce the voltage from 5 to 2,5 V) and then will supply with this power the ATMEG chip which will be mostly in sleep state. I am sure this is not the best idea ever  :) but I will probably try as I have all the components at home.

Anyway I would prefer some more easier solution in form of a simple board with the BTS or BTT and ATMEG+NRF. But I would need some help probably to design it. Maybe it could be useful for others in the world of Arduino too  :)  as a solution for IoT with servo needed projects.

What do you think MorganS?

MorganS

I think if it is useful as a general-purpose board then you should already be able to buy it. What does Google find for you? Why are those options unsuitable?

Yes, the driver chips will work with low voltage logic. Unfortunately you have to read the datasheet very closely to find out how low.

The power bank idea sounds promising.
"The problem is in the code you didn't post."

jremington

#10
May 30, 2018, 03:53 am Last Edit: May 30, 2018, 03:57 am by jremington
Pololu has a good selection of electronic power switches with manual and digital inputs. The Mini LV seems perfect for your project

boylucky

Hi Jremington,

thanks a lot for your post and Pololu power switches. The Mini LV looks really good. I will probably order one for testing. I just need to ask you if I understand correctly the wiring there. If I am correct then I should apply the voltige for load to VIN and GND pins. In my case it means 6AA batteries which will power the servo. If I correctly red the documentation then the consumption is 210 mikroAmps per 1 volt. In my case it will be about 1,5 mA. In case I would not use this power switch, then the power consumption of servo should be 4mA. It means I can save about half of the current when in idle mode lets say. It is not bad but I expected a bit more. Anyway like I said I would like to test the Mini LV anyway. So thanks for your info in the post.

jremington

#12
May 30, 2018, 04:50 pm Last Edit: May 30, 2018, 04:54 pm by jremington
Quote
If I correctly red the documentation then the consumption is 210 mikroAmps per 1 volt.
That is in the ON state, and most of that current is due to the on board LED. The OFF state current should be negligible.

It is easy to remove the LED or the current limiting resistor, just swipe it off with the tip of a hot solder pencil.


boylucky

Thanks Jremington for explanation. My mystake that I wrongly understand it before. Then it should be really a good solution for my project I think. I am going to order one for testing. Thanks a lot for your help. I will share the experience later here when tested.

Thanks both of you guys.

boylucky

Hi all,
I already got and tested the Pololu Mini LV power switch advised by jremington here in this post. It works perfectly and it is exactely what I was looking for. I have now first prototype of the watering system for the garden. Valve is automatically opening by the servo when watering needed. It communicate via NRF24L01 with the main node where Sigfox LPWAN module is also connected. Then the information about irrigation is transfered to the interent. Everything is designed to work on low power mode just with AA batteries to be able to use this system on places without external power source. I am looking forward to test it soon in the real environment.

Thanks for your help in this post.

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