wolfwings: (Default)
[personal profile] wolfwings
The pouch it has to fit in, batteries and all, is currently just barely able to fit a 10-cell 2x5 AA battery holder, and the 0.5" thick circuit board that slips in beside that and is almost exactly (down to the mm) as large as the battery holder's flat side.

The parts work, and they work well, but they're cumbersome (especially recharging 10-20*2200mAh AA's after an outing/con) so I'd like to switch to fewer but higher-power-capacity cells powering it. Either 1 or 2 10000mAh-ish NiMH D-cells. I have no interest, nor do I care about discharge rate, I top this off just before use so self-discharge rates are not something I care about.

And yes, I realize that 1*D would end up roughly half the effective duration of my AA pack now, the convenience of having a single big-ass battery I can fumble even with paws on versus battery holders I need to get a screwdriver out to pry the batteries loose would be worth it to me.

The output is feeding a large parallel bank of LEDs (between 10 and 30 depending on 'compile time' configuration of the rest of the suit when being put on) w/ one micro-fan in my direct breathe path, so power draw does vary slightly but not appreciably once it's powered on and is very stable.

The components are all rated for 12V, I'm running them at 9-10V to reduce heat and brightness to more reasonable levels for longer sessions in the 8+ hour range, run at a full 11.5-12V things get uncomfortable in the head after about 2-3 hours and the lights blow out mosaic-sensor digital photographs quite badly due to the brightness.

So my rough technical specs that I'm looking for as a contract-project I'm willing to pay $100-200 for someone willing to design and prototype a proof-of-concept of this for me since it's beyond my technical skills and learning the technical knowledge to do it is beyond my time available:

DC-to-DC regulator that takes your choice of rechargeable battery source and outputs 9-10V@1A for 4+ hour runs without component failure, without any active or 'finned' cooling solutions, pure fanless passive, while fitting inside of a roughly 2"x2.5"x1.5" box w/ rounded (NOT sharp) corners, and which can have the battery changed out when discharged to extend runtime.

If the battery technology for your design requires low-voltage cut-outs for safety and/or a hard case, I'd consider including those in the design as part of this project/RFQ/etc. I.E. Please don't offer to do this w/ LiPo unless you can fabricate the case/design the safeties as well.

A basic 'short circuit cutout' is expected since this will operate in a damp/humid/hot environment due to sweat and what-not.

I'll pay additional for some kind of battery gauge being included, a LOT additional if it can have a remotely-mounted LCD showing actual voltage from the batteries. I have plenty of space inside the head, and there's sufficient-to-extreme levels of backlighting occuring already so a naked LCD panel is very readable inside the head polarized as black digits on a clear background.

My budget range I have estimated is $100-200 for the design side, +50-100% if it includes some sort of remote-mountable battery meter depending on complexity and detail level of the readout that provides.

Note that is not to deliver a finished product, just for the design work including a bill-of-materials to make one, a first milestone if you will. I'll pay additional at that time for one to be produced and assembled, or take the construction step elsewhere if you're not interested in doing that but only want to do the design work.

Thoughts on battery packs

Date: 2012-01-25 12:57 am (UTC)
texxgadget: (Default)
From: [personal profile] texxgadget
Gauging battery level by voltage leads to disappointment.
You need to frequently re calibrate by load testing and then index that to voltage, but
this calibration doesnt last long.

An interesting statistic is that fully charged, a 12 volt battery is well over 12 volts.
In the case of lead acid chemistry, 12.5 volts is dangerously close to permanent damage to the battery and 12.0 volts you ARE doing permanent damage.
Technically a 12 volt lead acid battery is totally dead at 11.5 volts.

A 01.1 v change in a battery down at in that area is a MAJOR change, no matter what chemistry you are using.
When you get up around 40 volts, a tenth of a volt isnt so bad.

Other battery chemistries will have different numbers but similar situations.

Another thought, ALWAYS put a thermal circuit breaker in your battery pack to stop fires & explosions before they start as well as burn control.
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