Hello.
I’ve been using this power timer with a raspberry pi zero quite successfully for a while. However when it stopped being reliable and stopped working altogether, I looked more closely and of course it supplies around 3.5V output to your microcontroller. My Pi Zero doesn’t like that, it wants its 5V to run its internal regulator, especially when I ask it to supply hdmi to my monitor for debugging and to run a camera. Any ideas? A 5V version or a simple converter perhaps come to mind? Im using it to power down my controller between taking pictures for a very long time lapse camera system.
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Hi Tony,
The power timer is more or less a timed switch rather than a voltage converter, so it will feed through whatever voltage your battery is outputting (you could even use a 5V battery bank/phone charger)
If your battery can supply enough power for the Pi and to power the converter a setup like this should work well.
(This is assuming that the grounds are linked inside of the converter)
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Righto. Im feeding 5V to the ‘nano power timer’ module, and whipping out my trusty multimeter Im seeing 5V at the input line and 3.5V at the output line. So maybe something is dragging the voltage down? Im using a common ground. I see you have a ‘converter’ stage in your diagram. Whats that?
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Hi Tony,
It’s possible you may have maxed out the current supply available so the output voltage has dropped. What is the rating of the power supply are you feeding into the nano power timer?
Can you send us a photo of your setup so far? We’ll need to know why that voltage drop is occurring before you can add a converter and have it work effectively.
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OK, more information. Im feeding it to a fairly minimal Raspberry Pi Zero, however diconnecting the +5V power in, Im measuring 5V on that wire now, not 3.5V. So something is dragging it down, or Ive bricked my Pi somehow. Im powering from a 1A PowerBoost module with a 2A USB charger attached. The batteries pretty flat, I’ll also try giving it a good charge.
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Hi Tony,
Would it be possible to send through a photo of your setup?
A couple of questions:
- Are you able to power your Pi from just the Powerboost module?
- If not it sounds like your LiPo might be limiting the power (either the internal resistance or something else)
If you also have your USB PWR connected you’ll see some strange results, I’d make an adapter cable from the power timer into the USB so you don’t skip the onboard polyfuse on the PI
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Hi Tony
The interesting bit is that it ran OK for a time then deteriorated to the point it stopped altogether. Then you say the battery is flat.
What that indicates to me is your primary supply is not up to it. I think what has happened is that over a period the battery is making up the shortfall That is supplying the current demand that the 5V supply can’t. Eventually it has gone flat and there is no longer enough current to power your load (RPi, camera etc).
What happens here is that the primary supply voltage (5V) is converted down to charge the battery then this (including the battery) is boosted to 5V for the outside world (RPi etc).
Now firstly your primary supply has to provide enough current to power the load AND keep the battery charged. If the battery is low this can be substantial.
Secondly every time you convert, in this case twice, you lose a bit. Conversion efficiency can be anywhere between 80% and 90%.
To summarise if you want 1A at the output the current requirement at the input will be quite a bit larger, especially with a flat battery. I would advise when establishing your needs you assume a flat battery, this being worst case.
Some of these units bypass the battery when 5V is connected I think. I don’t believe this one does as the battery has to be present for it to work. That snippet of info is from the Adafruit web site.
I have just been through this sort of thing in another thread but will do it again.
Say your required load current is 1A. @ 5V this is 5W
Say boost efficiency is 85% you will need 5.9W at the boost input.
@ 3.7V (battery voltage, could be 4.2 while charging but I always err on the safe side) this equates to 1.6A .
Say the required battery charging current is 500mA.
Add this to the 1.6A required for the load and we have 2.1A or approximately 8.8W.
Now this is at a voltage between 3.6 and 4.2 so this as been converted from the input 5V.
If we assume 85% efficiency and 4.2V again we finish up with an input of 10.4W which @ 5V is about 2.1A
All this is rounded up and leaning towards worst case which I think you should really do. But you can see that the output of 1A can easily escalate to 2A or more so I think with your scenario I would be looking at least a 2A or even larger 5V input supply.
Cheers Bob
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You may be onto something there Robert.
Easy enough to check.
Ta
Tony
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