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Help with basic concepts regarding batteries


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Dear community,

I apologize in advance for my notorious ignorance on the subject... I'm in the process of building a rig for my new Blackmagic Pocket 4k and, rather than just copying whatever I see on YouTube, I'd like to understand how to properly distribute power from a battery source. Now, It's been a while since my physics classes in school but I've found some info online, though I still like to get other people's opinion on the matter.

So, a BMPCC 4K requires 12V of DC power (7,4V if connected via a dummy LPE battery)

Ideally, I'd also like to power my Tilta Nucleus Nano (5V) and, if possible, my Atomos Shinobi (6.2V-16.8V).

Now, I've seen some people power all of this from a single 14.8V V-lock battery. Obviously, this seems to work for them, but I wonder, is it really safe to use ONE battery for all of this?

One of my main concerns is that I obviously don't want to fry any of my devices, but then I see people connect a D-tap cable from the 14.8V battery to the 12V port on the Blackmagic. Does that mean that the camera only draws the voltage needed? When is the "risk" of damaging a device with a battery?

Or perhaps I'm just looking at this the wrong way and should focus instead on the current needed for each device, and then see if the sum adds up to the capacity in my battery?

On the other hand, I've also seen this adapter from Smallrig which transforms the 7.4V voltage from an NPF battery to 12V so that I can power up the camera. At a glance, it seems like a more cost-effective solution, as NPF batteries are much more affordable than V-lock. Is that something you would suggest?

Again, please pardon my ignorance. If you have some reading or articles on the matter, I'd appreciate it.

Cheers from Spain

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Generally, d-tap ports are unregulated unless specified otherwise. So whatever the battery outputs, that’s what comes out of the d-tap port. V-locks are nominally 14.4v, but after a full charge they can output more that that, 16-17v. You’ll definitely need some kind of step-down regulator for your 5v devices or you’ll fry them. There may be an existing cable with a regulator built-in, I’d check with Tilta.

Basically, you want to know how much voltage each device you are powering can safely handle, and also how much current it draws. Amps x Volts = Watts. Add up the Amps to see if your batteries can handle the total load. Most v-lock batteries will specify a maximum current draw, and also the watt-hours (how many watts supplied per hour, basically a run-time indicator).

Rencher Industries makes a d-tap voltage meter, which I find really handy for checking new batteries and d-tap plates : https://rencherindustries.com/products/micro-voltmeter

 

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  • 1 month later...
On 4/11/2021 at 8:57 PM, Satsuki Murashige said:

Generally, d-tap ports are unregulated unless specified otherwise. So whatever the battery outputs, that’s what comes out of the d-tap port. V-locks are nominally 14.4v, but after a full charge they can output more that that, 16-17v. You’ll definitely need some kind of step-down regulator for your 5v devices or you’ll fry them. There may be an existing cable with a regulator built-in, I’d check with Tilta.

Basically, you want to know how much voltage each device you are powering can safely handle, and also how much current it draws. Amps x Volts = Watts. Add up the Amps to see if your batteries can handle the total load. Most v-lock batteries will specify a maximum current draw, and also the watt-hours (how many watts supplied per hour, basically a run-time indicator).

Rencher Industries makes a d-tap voltage meter, which I find really handy for checking new batteries and d-tap plates : https://rencherindustries.com/products/micro-voltmeter

 

Dear Satsuki,

Thank you for your message and pardon for my late reply. I got busy soon afterwards and forgot about the topic I started!

I undestand. Also, the 2-pin port on the BMPCC 4K accepts 12V-20V according to Blackmagic's manual, so it should be fine. I couldn't find the amps the camera needs, but I found it requires 22W to function, so that means with a 95Wh battery I'll get 4,3 hrs of runtime.

I couldn't find the amps for the Nucleus Nano, but I think it will be safe to assume it won't be something a 95Wh can't handle. 🙂

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