Is there a need for a UPS

Information, updates, questions, issues regarding BWS CAR PS project.
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fuusob
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Joined: Thu Jan 10, 2019 3:56 am

Is there a need for a UPS

Post by fuusob » Thu Jan 10, 2019 9:42 pm

I am new to raspberry pi and the bws car PS. My question is does the bws car ps act like a ups when the car is turned off? If so how long can it keep the pi running? Or should the bws PS be wired to an always live wire or a switched wire like the accessory power? Finally, in either case is there a need for a UPS? If so could you use a 5000ma or so power bank as a UPS for the pi?

Thanks

BlueWave
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Posts: 394
Joined: Tue Sep 18, 2018 6:30 am

Re: Is there a need for a UPS

Post by BlueWave » Fri Jan 11, 2019 11:30 am

The BWS CAR PS is not UPS. It is power supply which can detect if ignition has been turned on/off. Then, by signal wire connected to the RPI GPIO, it provides this information to the RPI. Base on that, scripts execute safe shut down of the RPI. When the ignition is on, then the RPI boots.
The board is always connected to +5V. This allows to keep e.g. time and date in RPI. Current transient is only 0.72mA. With BWS CAR PS you do not have to care about RPI turning on and off.

You can also use power bank or UPS however you have to care about proper battery loading, and remember to charge it in case you is not used for a while. Capacity of power bank depends on you power consumption, you have to make the power budget calculation on your own.

Hisma
Posts: 36
Joined: Wed Nov 28, 2018 9:38 pm

Re: Is there a need for a UPS

Post by Hisma » Fri Jan 11, 2019 7:22 pm

So .72mA is the transient current draw of the BWS Car PS? That is very very low, surprisingly low. Is it something you guys measured with testing?
Also, you mention that the pi provides a constant +5V to the pi. So while the Car PS only consumes .72mA, the pi has to be consuming a certain amount of energy as well, in order to be in a "ready to wake" state, correct? Just curious what the total power consumption would be when you account for the transient current of both the pi and the BWS Car PS. I tried to find this data online but couldn't find it.

BlueWave
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Posts: 394
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Re: Is there a need for a UPS

Post by BlueWave » Fri Jan 11, 2019 10:04 pm

We have found some photos from measurements, maybe not the best quality but you can see the results :)

We have measured BWS CAR PS connected to power supply and disconnected from RPI, and got result of 0.723 mA:
PS_.jpg
PS_.jpg (215.67 KiB) Viewed 210 times

With BWS CAR PS connected to power supply and connected to RPI which was turned off, we got 0.0735 A (~74 mA ):
Rpi_PS_.jpg
Rpi_PS_.jpg (233.7 KiB) Viewed 210 times

Hisma
Posts: 36
Joined: Wed Nov 28, 2018 9:38 pm

Re: Is there a need for a UPS

Post by Hisma » Fri Jan 11, 2019 11:32 pm

Perfect, thank you. So roughly 74mA pulled at idle when you include the pi.

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