Thread: Anyone try a Forward Converter?

Originally posted by magnetik:
<STRONG>Jeff, PressLab thanks very much for your explinations....

And since we are ****ing off the original tranny, the same winding ratios would work on ATX supplies designed for 240Volt Australian usage too, would it not?

How small is the final powersupply. Can you fit the re-designed transformer back into the ATX case shell..... maybe this is how the ARISE guys build their powersupply units!! hehehehe!

I guess if some schematics were posted, and the ferrite core could be purchased of the size required (it is a core, not a rod?) im guessing you would have the problem solved for us guys like myself still using a PS/inverter setup.....

this is exciting stuff... </STRONG>

Yeah, the transformer will work for the 240VAC ones as well. If your power supply is set up like mine, then the same transformer could theoretically work without any winding differences. For example, the old transformer had a primary winding of 41 turns (120VAC). Yours would probably be the same, if you have the switch in the back for 120/240, or if it says 'autoswitch'. If it is 240VAC only, it might be 82 turns on the primary. They basically just do a full-wave or half-wave rectification based on what the switch is set to.

The modified power supply is small enough to fit into the same microATX power supply case, although the fan needs to be moved up to allow the bigger transformer to fit. I just took out the funny looking fan, and replaced it with a regular case fan, if fit fine. When it is done a good dose of hot-glue will keep the pieces from rattling and breaking in the car.

The ferrite core is called the "E" core. It is two E's back to back like this "E3". There is a bobbin, like the sewing kind but square, that you wind the wire onto. The two E's then slide over the bobbin, and they touch in the center and outer edges. Sometimes the E core center leg has been gapped, so it doesn't touch in the middle. This allows a magnetic flux bias in the core without saturation. We don't need that with the Forward Converter, it just hurts the maximum flux capacity of the core. In a continous-mode flyback converter, there is a magnetic bias, therefore the core is probably gapped. Any power supply over about 200W is not a flyback, as those don't work well with that much power.

So to scavenge parts go with a nice beefy supply. I bought two, good thing because I broke one of the E cores getting it off! Good thing I had a spare.

I just did some testing, and at 7V I can do 60W (probably more, my 12V supply only does 11A) It is about 60-80% efficient, based on load (best efficiency is at about 50W load). I played with the frequency a little to get it better, but I think I can get more out of it.

I am thinking more and more on getting a better PWM chip that goes down to 6V or so and using the IRL540s. Any suggestions on a cheap flexible PWM chip with mosfet sink/source drivers?

Presslab

Presslab,
Can't believe your battery voltage drops that low. Working on cars through the years I've always read that your battery voltage should not drop below 10V during cranking otherwise this indicates a bad battery.

Is this voltage measured across the battery terminals itself?

Originally posted by Probedude_2000:
<STRONG>Presslab,
Can't believe your battery voltage drops that low. Working on cars through the years I've always read that your battery voltage should not drop below 10V during cranking otherwise this indicates a bad battery.

Is this voltage measured across the battery terminals itself?</STRONG>

It is measured at the PSU with an o'scope. It has ~15ft of #10 wire to it. The 7.5V transient is only some microseconds in duration, the resistance of the starter is very low during the initial moment you start it. That means high currents. After the initial moment, while still starting, the voltage looks to be about 11.5V or so.

Presslab

Originally posted by hornet:
<STRONG>If this really does work, and i get get it to work, i may have to worship the ground that you walk on.

Few questions. will it work for an AT (i cant see why not)

and what is the total cost for the transformation? (and the unit of currency )

cheer mate</STRONG>

It will work for the AT as long as you follow the turns of the original PSU. I bought a surplus power supply for my transformer, USD$7, but if you bought one new (2 E cores, and a bobbin) it should be about USD$20 at the most I'd think. The rest of the electronics might run another $15-20 or so.

Presslab