Backpack VR Gaming Rig! (Step 1 - Planning)

[STS1985]

Hey folks,

Im doing some prelim research before buying parts for a custom VR backpack rig. DC-DC is how Im hoping to power the rig. Id like the option to run either off battery, or DC in wired mode if needed.

Hoping to run 1070 ITX and an I5 6600T in a Mini-ITX case. Any ideas on what the realistic power consumption may be. PC Part Picker says Im looking at 249W. Im flexible in both the GPU and CPU, realistically all I need is to meet recommended specs for VR (https://www.vive.com/ca/ready).

With all that being said, Im a bit unsure on what PSU to choose.

Do you believe either of these has an advantage?
300W PICOBOX - https://www.aliexpress.com/store/pr...wer-Supply-PICO-DC-DC/211500_32705436355.html
250W HDPLEX - http://www.hd-plex.com/HDPLEX-250W-Hi-Fi-DC-ATX-Power-Supply-16V-24V-Wide-Range-Voltage-Input.html


Does anyone have experience running DC off battery power, any tips/suggestions?
Battery Options:
http://www.bixnet.com/bp300.html
http://www.bixnet.com/xp280dc.html


Thanks for any info you guys may have, SFF + VR Backpack is a new venture for me!

Tenative PC Part Picker list of components: http://ca.pcpartpicker.com/list/Lfv4NN

**CPU** | [Intel Core i5-6500T 2.5GHz Quad-Core Processor](http://ca.pcpartpicker.com/product/khgPxr/intel-cpu-bxc80662i56500t) |-
**CPU Cooler** | [Noctua NH-L9i 33.8 CFM CPU Cooler](http://ca.pcpartpicker.com/product/xxphP6/noctua-cpu-cooler-nhl9i) | $48.99 @ Newegg Canada
**Motherboard** | [MSI B150I GAMING PRO AC Mini ITX LGA1151 Motherboard](http://ca.pcpartpicker.com/product/bwcMnQ/msi-motherboard-b150igamingproac) | $138.98 @ DirectCanada
**Memory** | [Corsair Vengeance LPX 16GB (2 x 8GB) DDR4-3000 Memory](http://ca.pcpartpicker.com/product/...-2-x-8gb-ddr4-3000-memory-cmk16gx4m2b3000c15w) | $112.99 @ NCIX
**Storage** | [Samsung 850 EVO-Series 250GB 2.5" Solid State Drive](http://ca.pcpartpicker.com/product/3kL7YJ/samsung-internal-hard-drive-mz75e250bam) | $119.99 @ Memory Express
**Video Card** | [Gigabyte GeForce GTX 1070 8GB Mini ITX OC Video Card](http://ca.pcpartpicker.com/product/...0-8gb-mini-itx-oc-video-card-gv-n1070ixoc-8gd) | $503.99 @ NCIX
**Other**| S4 Mini Chasis| $185.00

 

[Kmpkt]

250W is probably a fair guess and certainly a fair number to work from. As far as which DC-DC board to choose, I'd definitely go with the HD Plex. Numerous people have had quality issues with the Pico Box products here. Anything I've managed to break from HD Plex, Larry just sends me another unit immediately. The service with him thus far has been awesome. As far as power goes, perhaps something like this would make life a tad easier for you?


42,000 mAh should give you a couple hours of VR goodness at 250W if I'm not mistaken.

 

[hardcore_gamer]

42,000 mAh should give you a couple hours of VR goodness at 250W if I'm not mistaken.

48,000 mAh is specified at the voltage of a single cell. Actual Wh rating of PLUG is 199.8 (It's given in the FAQ). With 199.8 Wh capacity and 250W load, you'd get less than 48 minutes of usage.

 

[iFreilicht]

At 250W, it'd probably be easiest and safest to use an e-bike battery, those come in many different sizes and up to 600Wh or more. They do have quite a bit of weight to them, though.

 

[lhl]

You might want to look at this old thread of mine: https://smallformfactor.net/forum/threads/ono3-pelican-1430-to-s4-portable-vr-workstation.423/

or my final writeups from earlier this year: https://randomfoo.net/2016/05/30/diy-backpack-vr-system

I also have lots of information on setting up a DC-DC power system including some tips for not hurting yourself.

 

[lhl]

42,000 mAh should give you a couple hours of VR goodness at 250W if I'm not mistaken.

The way this battery is being marketed is very misleading. They claim 42Ah, but that's based on multiplying 16 x 3000mAh 18650 cells, which if they're the Pana/Tesla batteries as claimed have a 3.7V nominal voltage. They make a rather dubious claim of 199.8Wh (that'd be 4.7V, which is ridiculous).

If it were 200Wh you would max get under an hour of usage (less under heavy load realistically), but you also need to consider that if you're plugging in AC you will an additional conversion loss from DC to AC, and then from AC to DC in a power supply. Of course, that's all a lie anyway. At max you'd have 155.4Wh (3.7x42). One other red flag of course is they claim the weight, with all electronics (AC-DC converter, BMC, plugs, casing, LCD/LEDs) is <1kg. The best Lipo batteries alone (no case, no electronics, bare) are hard-pressed to push 180Wh/kg currently.

For those of you wanting to learn more about battery powering PCs, consider reading the guide I wrote on just this topic: https://randomfoo.net/2016/04/14/building-a-battery-powered-pc

 

[hardcore_gamer]

The way this battery is being marketed is very misleading. They claim 42Ah, but that's based on multiplying 16 x 3000mAh 18650 cells, which if they're the Pana/Tesla batteries as claimed have a 3.7V nominal voltage. They make a rather dubious claim of 199.8Wh (that'd be 4.7V, which is ridiculous).

It is misleading. However, they're claiming the cell voltage to be around 4.2 V, not 4.7V. Although 4.2V Li-Po batteries exist, I'm not sure how long they hold that voltage before the sustained load droops it to 3.6.

 

[lhl]

It is misleading. However, they're claiming the cell voltage to be around 4.2 V, not 4.7V. Although 4.2V Li-Po batteries exist, I'm not sure how long they hold that voltage before the sustained load droops it to 3.6.

4.2V is the max voltage for most LiPos but power and energy calculations (W, Wh) are calculated against nominal voltage because the voltage drops as the battery is used (you can get down to about 3V before you start really thrashing the cells/exploding your batteries). Think about it as the height and area under the curve.

So, re-reading with a fine tooth comb:

• They specifically say they are using Panasonic cells - "We used the same battery cells you’d find in a TESLA car" - that would be some variation of Panasonic NCR18650Bs which are pretty standard 18650 Li-on batteries with a 3.6V nominal voltage and a 3000mAh rated capacity (16 x 3000mAh = 48000mAh) so far so good
• As a stretch goal, they talk about increasing to 54,000mAh - so upgrading to the 3400mAh version, also fine
• They make a travel version, which they specify, again, correctly as 42,000mAh/151Wh ($235) - 42Ah*3.6V = 151.2Wh for those doing the math at home. They just use 14 instead of 16 18650s. No shenanigans
• Now here's where it gets a bit questionable. The $250 Pro is 48,000mAh, which doing the same basic math is 172.8Wh (just over the 100-160Wh pre-approved air travel limit), but that number's not mentioned in the rewards. At the bottom in the FAQ they explicitly claim 199.8Wh - they get that number presumably with upgraded cells (w/ the "54000 mAh" version using 16 3.7V/3400mAh 18650s you would indeed get 199.8Wh). This requires that they double their funding in the next 11 days - presumably if they don't hit that they use the regular cells and you get 173Wh, hence why they don't explicitly list the Wh in the rewards?
• That's all in the fine print. Where they are *definitely* being misleading is with the "48,000 mAh" in ginormous fonts, presumably to get people to compare it to power banks (fine), but that's at 3.6V nominal - you can get 20000mAh USB power banks for $30/pop (~4x cheaper) so what you're really paying for is the inverted AC power. Now, they say "48,000 mAh and 250 WATTS" in big bold text but what and people may make the assumption they're talking about the same thing, but they're not. They are talking about the aforementioned 172Wh capacity, and then up to 250W on the AC inverter, which (lets give them a huge benefit of the doubt and say they are converting at only a 10% loss), at 250W would give you a whopping... 37 minutes power. In practice, I'd bet you at high wattage it'd be significantly lower.

Anyway, they're not making the worst claims ever and it sort of does slot in as a good product between stuff like the GZ Sherpa 100 / Bienno BP120 and the Yeti 400 Lithium, but you will also get a much bigger bang/buck if you do a bit of your own legwork. If you're just looking for capacity, a 4S (14.8V nominal) 16000mAh Lipo battery will give you 237Wh at just $50. That gives you $200 to figure out your electronics. (If you're battery powering a PC btw, you will definitely want to just go DC-DC).

 

[hardcore_gamer]

So the 199.8 Wh is a stretch goal, but still they're claiming it in the FAQs. Typical crowd-funding campaign, I guess.