# ac/dc conversion

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#### alec_t

##### Well-Known Member
What actually is Ripple? is that the fluctuation of voltage between say 9v-15v
Yes.

#### Dalork

##### New Member
Would there be a need for a heat sink for the bridge rectifier?

#### alec_t

##### Well-Known Member
Yes. The bridge will drop about 1.5V at your >4A current, so will dissipate 6W or more. Others on this forum would probably be able to recommend a suitable heatsink.

#### 4pyros

##### Well-Known Member
That would be fine, just try and get the heat sink attached to or out of a side of your enclosure.
That one does not have to be soldered either, you can use 1/4 inch disconnect crimp on terminals to attach to it.
Like this;

#### Dalork

##### New Member
I have 10s of 1000s of different types of crimp terminal/connectors, they are always so damn handy (also have a good selection of crimping tools etc) so that will make it dead easy for trying and swapping out if need be.

I have some small boxes somewhere in the shed I might be able to use to house things but they are plastic so I'm guessing attaching the heat sink to the side wont be of much advantage. I have a hot knife attachment for my soldering iron though so could slice in venting or even enough so the heat sink is fitting outside of the box. Looking at the image of that rectifier the heat sink is just held to it with a screw I think. Sould I use a thermal paste between the rectifier and heat sink also? I have several types of TIM's already (from playing about with computer GPU's/CPU's etc)

#### 4pyros

##### Well-Known Member
I would cut a slot down one side of the box just wide enough to slide the center part of the heat sink down and stick the last three fins of the heat sink on the outside.
That way you will keep the metal to metal contact. Heat will not go thru the plastic well if you have it in between the metal parts held with the screw.
Seal with silicone glue and you're done.
And yes the heat sink should have compound on it.
I would think it would come with some as an assembly.

#### tcmtech

##### Banned
Personally at 6 watts one of those bigger brick module type bridge units would not even need a heat sink.

If it was me I would just buy a pack of larger diodes and call it good enough.

If you don't mind the wait here is a 10 pack of 10 amp 1000 volt units from china for $2.18. **broken link removed** Or a 5 pack of 10 amp diodes from the US for$3.95 including shipping.

#### Dalork

##### New Member
How would I use/wire those and I think if I do this I'd like to do it so as it can handle a tiny bit more incase other lights or 12vdc devices are added later on down the track. So I think I'd also like to smooth out the ripple/regulate the current so it stay as close to 12vdc as possible. I'm thinking I might do this to my set-up as well as I have some LED strip lighting that only works on dc that I could then put outside and power off my 12vac unit.

It looks like either way I go about doing this it's well under $10 for a bit of fun and a easy place to start learning about all this kind of stuff. #### 4pyros ##### Well-Known Member Most Helpful Member How would I use/wire those and I think if I do this I'd like to do it so as it can handle a tiny bit more incase other lights or 12vdc devices are added later on down the track. So I think I'd also like to smooth out the ripple/regulate the current so it stay as close to 12vdc as possible. I'm thinking I might do this to my set-up as well as I have some LED strip lighting that only works on dc that I could then put outside and power off my 12vac unit. It looks like either way I go about doing this it's well under$10 for a bit of fun and a easy place to start learning about all this kind of stuff.

Ya us technical guys would not think twice about soldering up our own bridges.
I like the one you found on ebay.
And yes you can put more LEDs on it.
The transformer is 105 watts so you could put 5 more 10 watt LEDs on it.
That would be about 8.25 amps so the 10 amp bridge is just right.
Did you say you already have a filter cap?

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#### Dalork

##### New Member
I don't mind making up/solder my own bridge just a matter of I've no idea on how to do it yet lol. I've actually got a good temp controlled soldering station and also a nice portable gas unit with all sorts of tip that is very good to use (what I use normally). The ac stepping transformer my father-in-law bought is the 105va unit, mine I think was 300va or so from memory, both are same brand/ac type just different sizes.

May I ask, what's the difference in va to watts or what's va stand for?

Yeah a 4700uF 16V cap, but think a 25v was suggested as better option

#### 4pyros

##### Well-Known Member
what's va stand for?
It is volt amps, its about the same as watts, manly used to describe the power handling of transformers.
Yes you need a 25 volt cap it give you a good safety margin.
If you have two of the 16 volt caps and have room in your box, you could use them in series to give you a 32 volt cap.

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