Need some DIY help looking for a BEC

[Ping]

I've had a piece of equipment break at work recently. It's a 200,000 dollar laser designator that apparently smoked a "battery eliminator" it was running. I got the idea of using a simple BEC circuit to replace it. The replacement cost for the officially supported solution is $3,000 and I really don't want to buy another one of these things. I've got the important parts of it, a cable with a cannon plug and crazy threaded battery shaped cap on the other.

All I need is to step down 12 volts (supplied from several Lithium batteries in series, and at a later date regulated 12volts from a lab power supply) to 3.6 volts (1 lithium cell). If anyone can point me to a schematic that would be great.

[rmteo]

What is the current draw of the device? A 12-3.6 DC-DC converter - or a linear voltage regulator (a BEC in R/C terms) can be less than $20 (or maybe even less $1). I can give you a part number if you provide the current draw info.

[Ping]

I will measure it and get back to you if I were to guess 1amp max draw. They included no official specifications with the designator.

[rmteo]

If it is 1A or less then a simple linear regulator would be the easiest and least expensive solution. There are many choices. Here is one for about $1:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=497-3456-5-ND

Put a heatsink on it as you will be dissipating about 8.5watts at 1Amp draw. Also, since you are needing a non-standard 3.6V output, you will want to use an adjustable output version.

Now you owe me $2,999.... :D :D :D

[Ping]

Man the government is getting scammed bad on this thing. I found the actual schematic today. I was looking up the various (now black and crispy) IC's trying to get an idea as to what went wrong.

Anyway in my search I found the exact schematic for this thing it was in the data sheet for the switching regulator the subcontractor didn't even pay to engineer this thing. Somehow this costs the government 3,000 bucks. So I decided to price the actual components on this thing. The most expensive bits are the LTC1159CS regulator ($9.00) and the two mosfets ($2.45 each).

So now I've learned a bit more of the specifics of what was in there in the first place I've determained what I should be looking for. I need a 3.3v/2.5A switching regulator. One of the mosfets failed and I'm unsure the cause so to be safe I'll probably double the requirments and look for a flat 5amp 3.3v switching regulator.
I think I'm just going to go purchase something off the shelf to replace it. I really don't feel like drawing and etching a PCB for this.

[rmteo]

Ping,

There are many off-the-shelf switching regulators out there that will work for you. Here is one for $11.70:
http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail?name=507-1162-ND

It will output 0.75-3.3V at up to 6A.

[Ping]

Thanks for the help! Maby your taxes will go down next year!

[Dan Baldwin]

Thanks for the help! Maby your taxes will go down next year!

Yeah! :rolleyes: That's gonna happen. :D

I guess we can always hope.


Dan