VOXL2 Mini Power Requirements

[bendraper]

I noticed the disclaimer in the docs that stresses the Voxl 2 Mini only gets 3.8V power supply and I just had a couple follow up questions.

1. Can the mini alternatively receive power only through the USB - C port (5V)?

2. Can the mini operate normally on 3.3V (a more standard value)?

3. What is the best way (or any way) that you'd recommend to step down 5V to the required 3.8V? The power adapter provided by ModalAI looks like it would not function on 5V as it requires a minimum of 2S supply?

Thanks!

[Vinny]

Hi @bendraper

1. No. External power is required for our configuration
2. No. We generate a 3.3V on-board, so if you provide 3.3V, that power rail will be reduced impacting functionality.
3. V2 Mini was designed to mimic being powered from a 1S standard battery, at nominal state-of-charge, hence 3.7V/3.8V. In theory, yes, 1S cells go down to 3.2V, but that is when the battery is discharged, so practically speaking 3.45-3.5V is the true limit to keep the system happy.
   We have a version of our power adapter set for 3.8V, and it regulates just fine over the full 2S range.
   https://www.modalai.com/products/mdk-m0041-1?variant=44759397073200

Hope this helps!

[bendraper]

@Vinny Thanks Vinny!

[bendraper]

@Vinny The documentation says that the Voxl Mini requires 6A inrush current capability. Is that true? Just looking for alternative BEC's for our system because in our system we only have a 5V and 12S supply at our disposal. Looking at the following component specifically https://www.amazon.com/DSN6000AUD-Converter-Regulator-Photovoltaic-Generation/dp/B09BDXZSRZ

[Vinny]

Hi @bendraper
Sorry I missed this message.
6A in-rush is for Voxl2 for certain. We have not characterized the drop-off point for V2-mini, but it will be marginally less (not much) since we have less support circuits.
I would not try anything less than 4-5A. However, that said, our "official" response would be to use our power module, which has been characterized over hundreds-of-thousand (yes, 100K+) hours of use in high stress applications.
Let us know if you try this experiment.
Thanks!
Vinny

[bendraper]

@Vinny Unfortunately I will not be able to get the 7.4-22V input the ModalAI BEC requires so I'll try the one from the link i sent above. Rated for 4A so it will hopefully suffice

[Alex Kushleyev]

@bendraper Since the power module for Voxl2-mini is outputting 3.8V, I believe applying 5.0V input to it should be just fine, since the dropout at full load should not exceed 1.2V which would be the margin in this case.

Right, @Vinny ?

However, you would need a pretty good 5.0V source as well.

Alex

[Vinny]

@bendraper @Alex-Kushleyev
Yes, 100%. At full load, you need to maintain only about 200-300mV of dropout. So, anything above 4.2V (fully charged 1S) will work. In a pinch, we've cascaded these off a 5V supply if battery is not available.
The 6Amps is for the output of the power module we have (our constraint)... if you have less than 6A available, you can always do the power conversion math and add ~20% efficiency loss and you'll be solid.
So, for example, we want 6A at 3.8V, with ~10-20% efficiency losses.. that translates to about
[3.8 * 6 *1.2] = 27.4W. Therefore, at 5V, you only need 27.4/5=5.4amps. If you want to provide higher voltages to reduce the current even more, the cutoff for 4A yields about 6.8V.
So, if you must use that Amazon link you sent, and then you use that to feed our 3.8V power module, simply set it for any voltage above 6.8V and you should be good to go.
Hope that makes sense.
To be clear, do NOT provide 6.8V directly to the VOXL 2 Mini input. That is fixed 3.8V. But, you can use our module https://www.modalai.com/products/mdk-m0041-1?variant=44759397073200 and feed that AMZN module as the supply set at 6.8V or higher up to 28V.

Again, you can also try that module directly at 3.8V with 4A direct to VOXL 2 Mini and see if you boot reliably. But, I'm not sure how well it would work at full loads. Be careful what you use here. That module has all the earmarks of caution written all over it!! The "specs" written below it and in the description photos are very contradictory and unclear. Do not forget you are trying to use a $1,200 device. The difference in $10 vs $70 for the most important aspect of any electrical system is worth it in my book. I'd hate to see you blow your board to save $60.

[Vinny]

@bendraper
Also, to clarify, where do you see this spec/written:?
" I will not be able to get the 7.4-22V input the ModalAI BEC requires"
I'm not familiar with that constraint so, I want to be sure wherever that is posted it is clarified...

[bendraper]

@Vinny Thanks for this info this is super helpful. I 100% agree about the last thing you said and if I can use the ModalAI power adapter then I definitely will. I got the 7.4V spec by assuming nominal 2S battery voltage to nominal 6S, which was probably a bad assumption. Even so, a 2S battery from dead to full charge is typically 6.4V to 8.4V so I figured 5V input was probably not sufficient for the power module as it was not in the range of 2S to 6S. Seems like this may not be the case though which is excellent