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Thread: 12v LiFePO4 -charge controller - powered by PV and TEG

  1. #1

    Default 12v LiFePO4 -charge controller - powered by PV and TEG

    Hello, I'm building a micro house (120 sqft) and I'm going to power it up with a thermo-electric generator and solar.
    I'm definitely going with LiFePO4, and tentatively settled on " LiFePO4 Battery: 12v 20Ah (240Wh) with controller for Solar Power Storage (24.0) " from batteryspace.com
    My plan is to pair the battery and controller with a 40Watt solar panel, the whole setup will run around a little over 300$.

    Here is where I'd like some help:

    I'm sure that I can feed TEG power (15V at 1A per unit, aiming for 60W after 15W prototype) into the LiFePO4 charge controller no problem so long as I don't exceed the controller's 120W limit, the machine should treat it just as if it were a partially shaded solar panel...
    BUT I'd like to be able to supply the controller with the TEG at 15V and PV at 17V or so at the same time, and that seems like it might be a problem.

    I think I understand that the battery in such a system acts to buffer the power supply when drawing 12V, but I'd really like to find out how to draw directly from the controller in times when power is abundant (the wood fire raging, sun is shining, the modest battery is already full) -otherwise it just seems like this would be unnecessary wear on the battery and possibly a bottleneck, not to mention the 20% loss of charge-to-battery-to-load. So how can I have automatic switching between battery charging, direct power to loads, and draw from battery when loads exceed power generated???

    Basically I want the controller to do what I'd do if I could just stand there and micromanage:
    Firstly: Run lights, pumps, radio, etc. from TEG and PV power sources.
    Secondly: Send excess capacity to battery
    Thirdly: Draw from battery when incoming supply is insufficient.

    Any well meaning help is appreciated, the better the more of course. ;-)

    Details unnecessary for the questions for those interested:

    The appeal of TEG is that I can generate electricity whenever I'm burning wood for heat, long periods of bad weather are not going to run my batteries down so long as I don't mind keeping a fire, and keeping the cool side cool will synergize very well with water heating.

    I realize that this isn't a lot of power capacity but the battery and controller fit with the small scale of the building, are very light, can be upgraded to 120W solar, can add more identical batteries, and as the whole setup is weatherproof I'll be able to re-purpose the whole system outdoors for a repeater, area light, small pump or other uses if I decide to upgrade later.

    So basically I'm fine with it, want to get into LiFePO4 and am not interested in getting a bunch of lead acid batteries, light weight and long life is key, this project might well get hoisted up in the air to become a tree house before it's all over after all.
    Last edited by eh4; 02-27-2012 at 01:26 AM.
    The brighter the light, the darker the shadow.

  2. #2

    Default Re: 12v LiFePO4 -charge controller - powered by PV and TEG

    Did you find some answers to your questions and build this project? I'd be interested in how it tuned out.
    Lantern Light Output Comparison Review:

  3. #3
    Join Date
    Jul 2015

    Default Re: 12v LiFePO4 -charge controller - powered by PV and TEG

    Hi. I'm close to plan a similar system for my house, just bigger. I'll use 8 aluminum rods to extract the heat from the stove. They will be protected from direct fire, being covered in ceramic inside the fire channels. I will control the fire tunnells automatically to keep a temperature of the rods below 300 celsius or maybe slightly higher, results after calculations of thermal flux. TEGs will be the 300 celsius type. They will be mounted between the rods and a water tank circulation pipe. The electricity produced will be captured in LiFePO4 batteries to compenste for cloudy weather. My plan for fotovoltaics is with 6 panels 250w each, producing approximatively 10-15W each on clouds. From the stove a 2-3kW thermal flux can be easily produced. TEG may reach 8-10% efficiency at a good temperature difference. A 150W power production for a few hours will be just fine.. I will update you about project next year.

  4. #4
    Flashaholic* Steve K's Avatar
    Join Date
    Jun 2002
    Peoria, IL

    Default Re: 12v LiFePO4 -charge controller - powered by PV and TEG

    isn't this going to depend on what the controller will let you do?

    I've worked with a large battery charging system that took power from a 3kW solar array and charged the battery packs. The loads operated from the battery bus. Pretty basic and very robust. The battery packs were nicad, so properly charging them just meant knowing their voltage and temperature. With lithium, I'm not sure that it can be that simple, which is a disadvantage.

    Perhaps you can provide details on how the charger/controller operates?

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