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Thread: Batteries for Evohome

  1. #21
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    I wonder if you could somehow use a thermoelectric generator to recharge batteries, although I guess the amount of power they output would be too low.

  2. #22
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    Lovely idea - slap a TEG on the radiator and keep the batteries charged. Only problem is what do you do on a cold day when the batteries are flat - you need a hot radiator to open the valve - but you can't get heat unless you can open the valve and there is no electricity...

  3. #23
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    Quote Originally Posted by Old_Codger View Post
    Lovely idea - slap a TEG on the radiator and keep the batteries charged. Only problem is what do you do on a cold day when the batteries are flat - you need a hot radiator to open the valve - but you can't get heat unless you can open the valve and there is no electricity...
    Obviously it would charge some rechargeable batteries with several months worth of battery life... such as the NiMH that are already supported by the HR92...

    As long as the average power supplied by the peltier device was greater than the average power draw of the HR92 it would work. And if it's <2.6mA that is not much, even for a peltier device. And with all that hot surface available I don't see why it wouldn't work.

    Two problems though:

    1) Many radiators don't have a sufficiently large flat area to adhere a peltier device to, at least on the rear side, due to all the bumps and fins and you wouldn't want it on the front for appearance reasons.

    2) The major problem though is what do you do with the cool side of the peltier device ? To generate power you need a heat sink to cool the cool side. Often that literally is just a stuck on heatsink. If the device was attached to the rear of a radiator in the gap to the wall this heatsink would have great difficulty in attaining a significantly lower temperature than the radiator side of the device - thus no power generated, as only a difference in temperature generates power.

    On the front side of a radiator it could radiate IR into the room to cool itself so it would work a bit better but still be an eye sore. So in theory it could work but I suspect heatsinking of the cool side is the challenge, aside from adding cables and some gizmo stuck to your radiator. In the end changing batteries every 2 years is a lot easier!

    A perhaps easier approach would be a very small solar panel. They will produce some output with indoor lighting and will receive some indirect daylight as well. This could be enough to average over 2.6mA but might still be an eye sore.

  4. #24
    Automated Home Legend paulockenden's Avatar
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    Seems like a lot of hassle (and additional ugliness) when changing a couple of AAs every two years is hardly a major chore or expense.

  5. #25
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    Quote Originally Posted by paulockenden View Post
    Seems like a lot of hassle (and additional ugliness) when changing a couple of AAs every two years is hardly a major chore or expense.
    My thoughts exactly.

    I guess the APS90 power supply is for commercial installations where they don't care about the ugliness of an extra wire and don't want to rely on someone being responsible for following up low battery alerts.

    But how often is Evohome used in business or commercial installations I wonder ? It doesn't really seem it's intended market, unless we're talking about relatively small SOHO businesses with just a few rooms, community centres, those kind of places...

  6. #26
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    Quote Originally Posted by DBMandrake View Post
    Obviously it would charge some rechargeable batteries with several months worth of battery life... such as the NiMH that are already supported by the HR92...

    In the end changing batteries every 2 years is a lot easier!
    Oh I agree entirely,it just seemed like such a fun idea. No doubt someone will develop something like it one day perhaps long thin devices that replace a fin which would provide the necessary cold sink? Until then I'll keep changing the batteries...

  7. #27
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    Quote Originally Posted by paulockenden View Post
    Seems like a lot of hassle (and additional ugliness) when changing a couple of AAs every two years is hardly a major chore or expense.
    Every year. In one case every 3 months and almost always dead on 3 months.

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