I did suggest one some time ago. The Pololu U3V70F5 which I think would do your job. This choice was ticked off by Trent of CoreElectronics as being OK. This has good documentation and even graphs of performance under various conditions. If you haven’t investigated this that is not my fault but I had made this suggestion in reply to your original request. You haven’t indicated whether you have looked at this device or not so we don’t know what the state of play is there.
Irrespective which device or brand you wish to use all the statements about input power (or current) are valid. In a nutshell if the input source can’t supply the required power neither can the output.
But you say you know all of this so I really have nothing new to offer. If the above suggested unit does not suit you will probably have to do exactly what I would . Search for what is available or someone might know of another suitable unit without a search.
Cheers Bob
I have that unit on order, since a little after it was suggested, to try it. It will be here tomorrow, then I can validate that choice.
In the meantime I have been trying to work out why the three different boost boards that all say that they should do what I want to do dont work, that’s all.
It works as expected and can power the pi4 and screen from the built in USB, no problems from the 18650s that I have been trying on the other boards.
Not so happy days though, when running off battery all good, but when you plug in the charge cable while running, it kills the output. Same for disconnecting the charge, kills the output.
So there is another board off the list.
Yes yes, I understand that it wasnt the recommended Pololou board as recommended, but I do have one of the two battery 18650 battery holder power boards that @Trent5487676 suggested.
I did not know that so will apologise. At least that unit has graphs pertaining to conversion efficiencies and currents available on Cores description for the product so one has a fighting chance of doing the right thing. The conversion efficiency of this device seems quite good at over 90% for a 3.3V in 5V output. As always you still have to provide enough power in for your required power out.
Do you have a convenient means of measuring your current requirement at 5V. I have a little USB device that connects into the line with a male and female USB connector. Mine is a Ruideng AT34 and is very useful. Displays Voltage across the line and Current through it with a capability of some Amps, can’t remember how many off hand but several anyway. Also lots of other things like mAhr and mWhr over time, useful for checking power bank or battery capacity etc, even current temperature, load resistance, all sorts of things. Very useful device.
Hard to say without having them in front of me. The fact that all of them are the same would suggest that you have insufficient input power. Or if they are the same brand it is not impossible they are not designed properly or the most likely scenario is very scarce information so you are not able to use it as the designer secretly intended.
This lack of data is all too prevalent these days. Some suppliers have none at all or at best provide only the data sheet for the main chip on board and nothing at all about the device as a whole. As far as these converters go if the conversion efficiency is published it is a plus but better than nothing at all I suppose. On the other hand others even provide a schematic and a good description of the device so you can make your own decisions.
I generally try to steer clear of things that have useless or no information and pay a bit more for something I can evaluate better.
Cheers Bob
I do not have such a device, could be handy to look at.
Seeing as I now have the DFRobot boost board doing as intended, I definitely have had the required input capacity as that known board is delivering as it says.
The fact that the 2 other boards that I have dont do what they say they should, I do agree, random Chinese boards without specs are useless and it’s best to use known brands with, as you say, published specs.
However, it’s pretty cheap and easy to test the no-names and see if they work, it’s just problematic and time consuming.
Very handy. Well worth the investment. There are several different flavours and prices around but I have found that one to be pretty good and dead easy to use. In fact it sits pretty permanently on the end of a USB power cable so I can see immediately if something is amiss.
Good to hear. That problem solved.
Mostly not so cheap at the end of the day, especially if your supplier is in China. Their postal system sucks. I know I am retired but old habits die hard and I tend to put some sort of value on time (I am 86 and might not have much of it left) so mostly I don’t see the extra few dollars as a deterrent to buying local with better supported brands.
Good result anyway.
Cheers Bob
That is concerning to hear, I’ll make a note to test the next unit that we receive with the electronic load and see if this is a fault with yours or a result of the design from the manufacturer (we’re out of stock at the moment).
The device has two distinct modes - charge and boost, and it does not do both simultaneously. That is implied in the description page, and confirmed in the datasheet: “In the absence of an input source, the MP2636 switches to boost mode through the MODE pin to power the SYS pins from the battery.”. The reason is that it is difficult for the charging circuitry to determine the correct state of charge of the battery, and therefore to apply the correct charging voltage, if the battery is under load. As mentioned above, proper evaluation of the capabilities of the device is as important for the humble power supply as it is for the more sophisticated components, The information is available, but sometimes needs a little hunting down.
12v wont work for me as I need it to be super portable so that I can have the Pi running and move it around before I can set it up hook back to the main battery.
I have it limping along at the moment using a USB power brick that handles passthrough, and it works, but it’s a small, old, crusty powerbank that’s really low capacity.
Just as an idea as to what I’m doing so that it might make a bit more sense to people.
I am amateur astro photographer and have built a Pi powered camera dolly that has full control over the camera and motion of the slider, pan and tilt axis.
The Pi is a WiFi hotspot and we wrote a set of web pages used to kick off python scrips and get previews from the camera.
Next month I am shooting overnight at the Australian Compact Telescope Array and there is no wireless devices allowed.
We’ve coded in the ability to turn wireless and bluetooth off, but it requires the Pi to be kept powered on other wise it turns back on again.
I need to be able to keep the Pi running for an hour or so to give me enough time to get into the facility and then setup enough to plug in my car battery.
yep, I just wanted to make sure that there wasnt any possible way that the radios would be on, I thought that there might be a small period of time that they were on before it turned them off on boot.
I have a touchscreen on the pi that auto boots to the control webpages so the whole thing is controllable without the wireless.
Not a very good pic, but the screen is on top of the pi that is in a case.
The whole thing is almost as small as I can make it, so there really isnt much room at all, and the idea is that it can all be carried in one piece.
Being able to carry that contraption into the car and out again while using an external battery is problematic.
USB powerbanks are great and would be good, but finding ones that have passthrough power and dont turn off when you unlug the charge power from them are really difficult to find.
Bloody hell, it’s getting expensive trying to find something that works
Here’s another one to add to the ‘does not work’ pile.
FYI for anyone still interested, this battery shield works great, powers the Pi 4 and Screen without issue, and maintains USB and pad power output when you connect the external power to charge it, HOWEVER as soon as you remove the external power it shuts down.
It’s frustrating that none of the boards anywhere list this sort of function, but I cant figure out the use case for these boards that you can not use them while starting or stopping charging.
OK last ditch idea. @Robert93820 or anyone else, would it be possible to use capacitors to hold enough charge to smooth out the 5v @2A for about 3 seconds so that the battery bank switching is smoothed enough to output a continuous output?
Yeah thanks for that, it does look like the PiJuice would work for me, a little fiddly to fit with my custom PiHat that uses all GPIO, but it might fit.
It is a LOT more than I wanted to spend on the solution, however if it works, which I have no doubt that it would, then it may be the right solution.
Thanks
The test was a success, I can confirm the Pi stays powered regardless of charging, and can be powered on and off with the button on the HAT. Let me know if there’s any extra info you want clarified.
The Pijuice only uses i2c, and that’s a bus, so you should be ok to use it with your custom HAT:
As for the cost - I get the hesitation, it’s about as much as a whole new Pi! It does include a battery and software though.
The docs are a little hard to get to, but very in-depth:
