News flash: Fuel cell even more forgettable than I thought!

The other day, I concluded that the Medis 24-7 Power Pack fuel-cell gadget-charger wasn't a very interesting product, based on its specifications. The spec sheet didn't make it look as if the fuel cell could do anything you couldn't do with much cheaper conventional batteries.

I'm now indebted to blogger Techskeptic, a man after my own heart except less lazy. He, as he mentions in the comments for the original Medis post, actually bought some Medis power packs and tested them thoroughly.

The results are explained in great detail in Techskeptic's final testing report, replete with the kind of graphs that I only bother to make when I'm testing something completely hilarious.

Techskeptic tested three Medis Power Packs, and found that they actually managed to deliver only about nine to 13 watt-hours into real loads. Medis claim twenty watt-hours in their literature, and it's that figure on which I based my own unimpressed response.

So these things actually appear to be even worse than they seemed.

The lousy real-world performance could be due in part to Medis optimistically listing the amount of energy the fuel cell actually (sorta-kinda) delivers on the sticker, rather than the amount of energy that makes it out of the Power Pack, down the cable and into the device you're charging. There's a DC-to-DC converter, you see, that takes the very low output voltage of the fuel cell (less than one volt) and boosts it to a gadget-charging level. And that converter turned out to be only about 70% efficient at best. Into a one-watt load, it dropped to about 60%.

So Techskeptic concluded that the Medis device didn't even beat a pack of six alkaline AAs. Actually, you'd probably get better results than the fuel cell if you hooked a similar voltage-booster up to a single humble D battery.

(Little kits to make that sort of converter, usually to allow you to replace low-capacity 9V batteries with beefier but lower-voltage cells, have been around for ages. Here's one that'll boost the output of two cells to 9V; I'm sure I've seen single-cell versions as well, but can't find one right now.)

So Medis' numbers would appear to be, at best, sort of like the old gross horsepower measurements that told you how much power a nude engine - no transmission, no air filter, no exhaust system, no alternator, no nothin' - on a test-stand once managed to deliver. This did not have very much to do with the amount of power that would make it to the rear wheels of a car powered by the same model of engine.

4 Responses to “News flash: Fuel cell even more forgettable than I thought!”

  1. Techskeptic Says:

    Thanks dan! I've never been written up before!

    Some finer points:
    I did not test the latest and 'greatest' units that came off the fully automated line. There is no way to know which ones come off that line. further they have flip flopped back and forth whether to not they have made any actual improvements to the device.

    There is plenty of fuel to accomodate the losses from the DC converter in the unit. Their problem is that the fuel and electrolyte don't get utilized well due to the design of the box. I have no idea if they took my suggestions on how to fix those problems.

    Doesnt matter, even if they get what they claim its still a huge expensive box that puts out a ridiculously low amount of power.

  2. Nikola Says:

    Maybe it's different down under, but aren't car HP's (at least in NorthAmerica) still power-at-the-crank? My Subaru WRX is rated at 227HP, but it's usually dynoed at 180ish at the wheels...

  3. Gareth Pye Says:

    Nikola, depends on the car. Some of your higher power cars have been known to quote power at the wheels because they don't like to quote stupidly high numbers. Also it lets them get out of direct comparisons.

  4. VMax Says:

    It's still power at the crank, but it's net rather than gross - i.e. when they measure it, there's a standard inlet with air filter, exhaust, alternator etc etc connected. Gross measurement (which was used until sometime in the 70s I think?) is just the engine on a sort of life support system.

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