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# transformer question

#### Archane

##### New member
Has anyone tried to use a transformer to step down the voltage and ste up the current in a circuit? I'm looking at this because I want to fit my LD and a small peltier in the head of a flashlight. The pelt feeds on current not volage so I need to pump up the current.

I'm trying to find a way to split a circuit into 2 parts to power them seperately since I know that if I send 800ma through the LD I might as well start buying a new one =) my goal is to get 3v to both the pelt and the LD but get 250ma to the LD and around 500-800 to the pelt.

#### rog8811

##### New member
Do transformers work the same on DC? Not sure just something in the mists of time that raise that doubt......

Regards rog8811

#### Archane

##### New member
I believe the only real difference in the AC/DC transformer is that the once for AC are designed so that the occilating wave in Hz is passed through to the other side as well. DC doesn't have this so there is no need for this fuctionality.

#### Gazoo

##### Active member
Archane,
How small is your peltier? Mine are 4 watts and only require around a volt, or less than 180ma's, to keep the diode just below room temp.

#### pseudonomen137

##### New member
Its possible but you need AC. If your input is DC and you need a DC output, you'll need to convert it to AC and back, which could be a real pain in the butt. (transformers work based on changing magnetic flux, which means the current must be changing/alternating)

#### philguy

##### New member
Physics 101: Transformers will only work with AC!
If you put DC through it, all it is is a resistor.
Using DC, you need to chop it up to get AC.

Also, if voltage decreases so does current. And if you connect the pelt to your battery, the voltage should (afaik) cave in to the point where max battery current fits the pelt resistance.

Basically, a transformer differentiates your current, and the derivation of a zero slope (=dc) is zero.

#### Archane

##### New member
the spec sheet only gives me max values
watts 4.5-5
amps 2.1
voltage 3.75-4.1
module resistance 1.54-1.74
these are depending on hot side temp

I have run it at 3v and around 200ma and with a good heat sink the cold side would hit 55 degrees with an ambient temp of around 77 to start with. i'm working on making something that will help make the pelt fit around the aixiz module since just setting it on it won't work(not enough surface area touching)

i'm just trying to get ideas to make the LD last longer and handle higher amps safer.
I'm gonna hit up Radio Hack on my way home to get some basic parts to add and test with(without an LD or pelt) to get some numbers flowing first.

#### Gazoo

##### Active member
Even at that low a current and 55 degrees, it will most likely condensate depending on the humidity. Nevertheless, you only need it to be a little cooler that the ambient temp with the diode running.

#### Archane

##### New member
It's just an idea I had while trying to find ways to run the whole setup on a single switch without needed to use a ton of batteries.

If you think that the circuit DDL made can handle running both (most likely with alittle modification) then i'll go with that.

#### philguy

##### New member
What you could try would be a smaller pelt, or cutting it up as described in one thread.

Alternatively, use a voltage regulator that will accept your input voltages and 2+ amps output, and you can regulate the pelt down!

Also, as said before, you only need to make the diode cool, not cold. So an LM317 might be enough to do the job.

But it all depends on your voltage and current source - lithiums will make the experience a nicer one that carbon-zincs for example

#### Archane

##### New member
i'm using 2 CR123 lithiums, lord knows I don't want to spend a kings ransom on AA's for the rest of my life =)

#### Gazoo

##### Active member
Archane said:
It's just an idea I had while trying to find ways to run the whole setup on a single switch without needed to use a ton of batteries.

If you think that the circuit DDL made can handle running both (most likely with alittle modification) then i'll go with that.
I am sure Daedals circuit could handle both, but you might run into problems keeping the current to the LD and the peltier independent. It would be best to run with two independent circuits. Also keep in mind you need a minimum of 6 volts sustained using Daedal's circuit. I have noticed many people trying to run it with 4 batteries...this is a no go. Even 2 cr123's
isn't the best idea IMO. However 2 rechargeable lithiums should work out great.

Of course, the other option is to use a regulator with a lower drop out voltage.

#### philguy

##### New member
2 CR123As, if the 3,6V are taken, shouldn't they work fine? 8.4V (dropping to 7.2) should be enough voltage?

As far as the circuit, use two LMs - that way, if the peltier one fails, it won't take the diode down with it

No, but simply for current control, use two - that way, you can use temperature control on your peltier.

#### Archane

##### New member
well the CR123's I have are the 3v versions but I could get the 3.6 if I needed them.

My goal with this is to make a portal burning laser at around 250ma and keep it cooled to around 70 degrees all powered by 2 CR123 rechargable batteries.

I've even thought of making my own enclosure instead of using a flashlight(but whats the fun in that hehe)

#### Things

##### New member
ya a transformer WILL NOT WORK ON DC!!!,but peltiers don't require much to get cool!

#### philguy

##### New member
that idea occured to me, too, but if you don't have a small peltier, it will not be very pocket-friendly (as well as battery-friendly).

On the other hand, though - if you are building your own enclosure, you might also try NiMHs, htey should be able to sustain the current needed (not sure about that), and you can get higher capacities easier. What sucks is the voltage, so you'd need six AAs to get the voltage of two (3.0V) CRs. But you would have 2600mAh, not 800, and they wouldn't explode.

Not so sure about the usability of NiMHs, though.