SparkFun Forums

[Mr6510]

Hi,
I have an autonomous boat project that amongst many other systems, uses an OLA for some logging. My power system on the boat consists of three independent 12.8v LiFePo4 batteries that will each be driving a 5v/8A regulator (so three independent batteries + reg systems), that will then be diode OR'd and powering various sub-systems. So the output of that power system will be somewhere between 4.3 and 4.7vDC depending on the diodes I use to do the OR'ing.
Now my question is, can you see any issue with me powering my OLA by connecting that 4.3-4.7vDC to its Vin pin? My theory is that its high enough to drive the OLA's onboard v3.3reg but low enough that it should not backfeed a USB computer port if I plug a USB cable in to configure it.
I have read and re-read https://learn.sparkfun.com/tutorials/op ... -guide/all and also looked at the schematic and I think I'm on the right track.
What do you think? Am I missing something?
Thanks,
Paul

[PaulZC]

Hi Paul,
I think the main issue will be that the 4.3-4.7VDC source will drag down the USB 5V when you connect it.
I really don't recommend trying this... You may end up releasing the magic white smoke - from your computer!
Best wishes,
Paul

[Mr6510]

Hi Paul,
I kept investigating how to get this working and now have success, so I thought I'd share it here in case it helped anyone else out.
My boat has a power rail that runs at about 5.3v (long story) and if I insert a diode between that rail and Vin on the OLA, then it drops the voltage applied to Vin to about 4.6v or thereabouts.
So when the OLA is powered only via Vin, it runs fine, the 4.6v is plenty to drive the downstream circuitry on the OLA.
When I then insert the USB-C thats connected to my Mac (if I want to see OLA console or program it) then the USB 5v takes over seamlessly as is > 4.6v. At the same time the diode I have on Vin blocks the USB5v from "pushing back" against my boat supply AND because the Vin is at 4.6v and has a diode inline it does not pull down or interfere with the USB 5v.

It's pretty simple in that the diode is doing all the work, and its been running for quite some time now, so I think its looking good.
Cheers,
Paul J

[PaulZC]

Hi Paul,
Good to know - glad that's working for you - and thanks for letting us know.
Best wishes,
Paul