Peltier Element -> 5v

[Trax]

Hi,
I wanted to build some simple USB charger from a Peltier Element and 2 CPU fans I head laying around, I get around 3v at 500 mA max.
Thats not great but something.
Now I need some simple yet effective means of making 5V out of it.
I would normal just buy some converter module but this is supposed to be a scrap build so no buying of new parts

Could anyone recommend me some simple circuit to make a suitable converter my self with standard parts?

Cheers
Trax

[f5r5e5d]

a not obvious need for the converter is for low ripple current in the Peltier - ripple current kills the Peltier's efficiency by pumping heat both directions

[Alex30]

What model number is the peltier?

EDIT
Just to clarify, are you powering the fans attached to the peltier in order for the peltier to produce power which you will use as a USB charger? What's the point?

[Trax]

I have no model number its some no name without any printing on it.

I would in the ideal case power the fans with th Peltier Element but I don't know if I will get enough energy out.

[rob77]

peltier has a terrible efficiency as power generator.. so don't know if it's worth it... some time ago i was considering to build a "winter camping charger" - boiling water on one side (heated by fire/stove) and snow/ice on the other side of the peltiers... but never built it because of the poor efficiency (despite the fact that it would have a nice delta and lot's of heat transfer to be converted into electricity)

[Alex30]

I would in the ideal case power the fans with th Peltier Element but I don't know if I will get enough energy out.

If you plan on using the peltier on the heatsink to power it's own fans to cool down the heatsink while having surplus power for a USB charger, you are barking up the wrong tree as you are trying to make a system that is more than 100% efficient with a petlier device that is typically as poor as 10% efficient or less if you have a cheap ebay one.

A peltier must have a lot of delta T to produce any meaningful power, which means an extremely hot surface on one side and a humongous heatsink on the other, note that if it is being used for generation you are effectively insulating the hot side by using this setup.

If you wanted to produce a proper USB charger out of a peltier you would probably start by deciding what you are attaching it to and having a reasonable datasheet for the peltier (if possible). When you know what kinds of hot temperatures you expect, you can work out your heatsink properties (which should not be using fans as you lose your small margin of efficiency straight away). With that known you can work out your expected delta T and use that information along with your datasheet or other typical datasheets to determine what kinds of voltages and current you will expect.

Once you have that I would recommend doing something like a buck-boost regulator that has 90% or better efficiency so that you can squeeze every last bit of the little amount of power you are generating. You will probably need an undervoltage lockout as well. As previously stated you will need to pay extra attention to your input ripple on your buck-boost otherwise you will destroy your peltier after a few hours\days.

This is not the kind of project you can just throw together if you wanted to have a useful charger. If you are going for just a learning exercise then do it anyway but don't expect to have something thats very useful and don't expect your peltier to last very long if you go for a buck-boost approach without lots of design work for your input ripple filtering

[Trax]

Why should the fans need as much power as the Peltier generates, you can run such a setup also completely without a fan just with less yield.

thats what i want to build: http://biolitestove.com/products/biolite-campstove
just in small cheep and not as powerfull.

[Alex30]

That peltier has been specifically designed for high temperature, for example the typical peltier you find on ebay is this the TEC1-12706 but that one will only stand a max temperature of 138 degrees. You'd have to shop around to get a specialised peltier for this purpose that could withstand hundreds of degrees, which often don't come cheap.

As I said before designing a circuit for using power generated by these low efficiency devices requires a lot of work and really isn't straight forward. I'd say having a fire on the hot side of the peltier is pushing the technology to the extreme. If you wanted to play with power generation, I would think smaller unless you're prepared for at least a few months of designing and spending lots more money than what that stove is worth. $130 aint bad for that stove in my opinion.

[mrpackethead]

I have seen Peltiers on the exhaust of a large diesel truck.  Lots of delta T there.