Battery Charging from TEG

Discussion in 'The Projects Forum' started by doof205, Oct 9, 2013.

  1. doof205

    Thread Starter New Member

    Oct 9, 2013
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    Hi All, my first post here but looks like a good active electronics forum.

    I'm building a Thermoelectric Generator-powered camping stove much like the Biolite stove if anyone's seen it. Basically a camping stove with a TEG that powers a fan to drive air into the combustion chamber.

    I've got it working using a basic circuit whereby I use a 9v battery to drive my fan at the start and then switch to the TEG as a power supply once the temperature is such that I'm getting enough current to drive the fan.

    This setup is fine but what I'd love is a built in rechargeable battery so I don't have to keep changing them. I really don't know much about battery recharging and so i'm reading up on it but wondered if i could get any help here.

    So, i'll have a battery to run the fan 'til the stove is warmed up, then I'll want to switch to TEG power and I'll want any extra power to charge the battery...how easy / difficult / complicated is this?

    Thanks for any help.

    Lewis
     
  2. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Some are easier than others, and it depends on how fast you need to charge them. So tell us more about what you have. Do you know the fan voltage and current? What is the output of your TEG and regulator if you have one? How long does the battery need to run the fan before the TEG can take over? How long will it burn typically?
     
  3. doof205

    Thread Starter New Member

    Oct 9, 2013
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    Sorry, more detail would help wouldn't it.

    The fan is 12v 0.2A

    The TEG - http://dx.com/p/f30345-high-temperature-power-generation-thermoelectric-cooling-module-white-179466

    Max. working voltage: 5.2V (@120'C)
    Max. short circuit current: 1320mA (@120'C)

    So the TEG will output a max of 5v but will change depending on temperature obviously. I suppose I'll need to modify the heatsink to get close to that figure during normal operation. We can assume it'll be outputting anything from 0V up to 4.5V provided. As for current, i'm not sure how the short circuit current relates to output current with the TEG.

    I've been using a cheap circuit that I bought to up the voltage from 9v from the battery to 13v for the fan.

    The battery should probably be able to power the fan for 10 minutes at most, once it's running it will burn for any amount of time so I'd need overcharging protection. Normally I'd expect a minute or two on battery power then 15 minutes+ on TEG power.

    Hope this helps, thanks.
     
  4. ronv

    AAC Fanatic!

    Nov 12, 2008
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    I'm no expert on these, but I think you will need more than one to get the desired result. I think you may expect .7 amps at 2.5 volts from a single one (hard to tell from its spec.) But lets say you had 2 - about 5 volts at .7 amps.. You could then use say 10 AAA rechargeable batteries good for .5 amp hours at 12 volts. You could then but a cheapie constant voltage constant current boost regulator from e-bay and set it to 50 ma at 14.1 volts. It may not totally recharge it every time but would save a fancy charger ic. Do you need such a large fan? Are you trying to run anything else besides the fan?
     
  5. doof205

    Thread Starter New Member

    Oct 9, 2013
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    I'm not sure sure whether the fan is a suitable size at the minute as I've only managed limited testing. I was actually thinking it might be on the small side.

    I'm not running anything else apart from the fan just yet but would like to copy the Biolite and have a 5v usb output at some point. That will come at a much later stage though. I think you might be right with this TEG not being enough. How can I test the max output current of something like this?

    Would it just be a case of applying 14 volts to the batteries to recharge? I guess with 10 at 1.5v each you'd be at 15v max and so when charging from totally flat it'd get up to 14 volts and then be equalised (i'm really guessing with all of this!)
     
  6. doof205

    Thread Starter New Member

    Oct 9, 2013
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