Stalled Possible VR Backpack : S4M with Hot-Swappable battery pack

Choidebu

"Banned"
Original poster
Aug 16, 2017
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I spent some time in LTT forum the other day explaining some battery stuff to this guy, when I got this idea...



As some of you may know, I am developing battery powered portable PC in S4M-C. It's self-contained: internal brick, pack charging, seamless switching on mains loss, and all that kind of stuff, just like a laptop.

Meanwhile people just want their VR backpack a reality.

A VR backpack doesn't have to do all that stuff - it just needs juice. Imagine:
  • AMD R5-1600 or R5-2600x
  • GTX 1660Ti up to RX 5700 / RTX 2060
  • HDPLEX 400W DC-ATX
  • 2x Mini-Box's Y-PWR cascaded (3 inputs)
  • 6S3P 200Whr+ High-Drain battery packS
  • External HDPLEX 400W AC-DC
  • 6S Balance Charger (Imax B6 etc)
The first 5 in the case, plus the rest and extra pack(s) into a backpack.

On the low-end, minimum requirement for VR this setup will consume maximum about 220W, and on the other side of the scale - 300W.
In that case 200Whr+ pack would only last an hour, an hour and a half tops, but what if we can just hot-swap them mid-play?
This is with a good, high drain 18 cells ~3200mAh each. Want less DIY solution? We might be able to fit this 22.2V 10Ah LiPo in its place.

How does it work?

The key is Y-PWR. This device accepts two inputs and outputs only one with higher voltage, or switches them if their voltages are close enough. Cascade 2 of them, and we got 1 DC input, and 2 hot-swap battery input. The output goes straight to wide-input 16-24V (more like 14-28) HDPLEX 400W DC-ATX.

So you run a VR rig with one pack, no dc input. 1, 1.5 hr later, that pack ran low, we put another pack in, sliding and pushing the old pack out. In the process at one point, these two connects at the same time to the Y-PWR, and Y-PWR detects that the new pack have higher voltages therefore switches power input to the system to the new pack. Old pack is now offline, and out she goes. You now have another hour or so.

You want to do non-VR, normal tasks? Just prop her on your desk and plug the external brick. Meanwhile your packs can charge away.

What we need:
  1. Cut the front and the back for pack entry and exit.
  2. Design a magazine-style Pack holder, with two parallel spring loaded contacts. Maybe some lock-and-release mechanism.
  3. Design a battery pack case that exposes its power leads by copper plates.
  4. Buy lots of packs (well, at least two)
  5. Profit!
Why S4M? Why not other cases?

Frankly I don't care. I'm familiar with it so my brain is tuned to its dimensions, what's possible and whatnot.
Maybe anyone have better ideas? Sentry? RVZ03?
 

ExplodingWaffle101

SFF Lingo Aficionado
May 11, 2018
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If you did it smartly, would you even need to use 2 Y-Pwrs? What I mean is that connecting the battery packs in parallel (while they're swapping) doubles the capacity, not the voltage. It shooould work as long as 1 is always connected.
 
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thewizzard1

Airflow Optimizer
Bronze Supporter
Jan 27, 2017
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Burning through one battery per hour is going to stink, regardless of how many batteries you have.
You'll need higher efficiency, lower power requirements and larger batteries.

I'm willing to be you can get good enough VR with 150W power input, and a wider-input 12v supply (dc:dc for automotive use) using a 3S/4S 300/400Wh cell, and better battery lifespan using higher capacity cells, or swapping to LiFePO4 or Li-Ion of an equally higher rating.

Second to that, using 2-5c rated cells are lighter than 10+C rated cells - You don't need anything more than 2C for your requirements, and that extra power rating comes at the cost of WH/g ratings.
 

Choidebu

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Original poster
Aug 16, 2017
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If you did it smartly, would you even need to use 2 Y-Pwrs? What I mean is that connecting the battery packs in parallel (while they're swapping) doubles the capacity, not the voltage. It shooould work as long as 1 is always connected.

No. What happens when you parallel a 16V battery, a new 22V battery, while connected to load? The new pack is going to charge the old one, while simultaneously powering the load.

Second, momentary spark when you first connect a battery to its socket. This can send high voltages through, possibly damaging upstream devices. It's fine when everything is not powered, not so when everything's connected.

Regarding 2 Y-PWR, the second one is just for convenience of being able to plug dc brick. You can always require people to remove battery to use the dc jack as input.
 

Choidebu

"Banned"
Original poster
Aug 16, 2017
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Burning through one battery per hour is going to stink, regardless of how many batteries you have.
You'll need higher efficiency, lower power requirements and larger batteries.

I'm willing to be you can get good enough VR with 150W power input, and a wider-input 12v supply (dc:dc for automotive use) using a 3S/4S 300/400Wh cell, and better battery lifespan using higher capacity cells, or swapping to LiFePO4 or Li-Ion of an equally higher rating.

Second to that, using 2-5c rated cells are lighter than 10+C rated cells - You don't need anything more than 2C for your requirements, and that extra power rating comes at the cost of WH/g ratings.

How many hours you gonna do VR anyway with ~5 kg strapped to your back?

And the battery size I propose is completely due to the fact I used S4M as baseline of how small it should be.

The main idea is to make an easy to use hot swap system without leaving your VR session. Battery size, while related to enclosure design, can be arbitrarily chosen based on how much space you have.

Why automotive wide input? Like, 6 to 40 V? Hdplex is already wide input 16-24V.

If you notice I didn't state what specific batteries to get. And yes, we need >2C. Do the math. 300W over 16.5V (lower bound) is already 18A - that's 6A per cell. And we don't want to restrict people from wanting more power, do we?

I'm not talking high drain battery as something of a unicorn here, apologies if I sound like it, because many LMC 18650 cells (not the 29e) are already capable of it. LiFe and RC LiPo cells, they're commonly high in specific power anyway.
 
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Choidebu

"Banned"
Original poster
Aug 16, 2017
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A <=2C batteries would make sense in a carefully thought out usage scenarios and fixed installation. I myself am considering using 29Es on roadrunner.

Let's agree that a "backpack" isn't a backpack per se? And we are talking about sub 300W here... It's just strapping your case to your back. You can use anything - frames, actual backpack, baby carrier etc.