need help designing/building a variable DC power supply

[jeffisaviking]

Hi,

I’ve been dreaming about building an anodizing rig for titanium. For that, I need to build a variable DC power supply. It doesn’t really need to be able to go down to 0 Volts DC, 10v DC on the bottom end would be fine. On the Top end, I need at least 30v, and up to 120 is useful. Current limiting wouldn’t be a bad idea, and doesn’t need to be variable necessarily. 1A is plenty, and more is ok. It doesn’t have to be the most accurate or smoothest DC, but having a power supply I could use for future electronics projects wouldn’t be a bad thing. I’m going to be running DC through a fluid, so grounding I assume is important too.

I’ve got two challenges. One, high school electronics was half a life time ago, so my electronics skills are a touch rusty. And two, I can get a commercial power supply for $130ish, so I’d like to aim for less than that for the project.

I’m not against kits if that is a good route, or building it all from scratch if that makes sense. Thoughts?

Many thanks!
Jeff

 

[jeffisaviking]

Hi,

I’ve been dreaming about building an anodizing rig for titanium. For that, I need to build a variable DC power supply. It doesn’t really need to be able to go down to 0 Volts DC, 10v DC on the bottom end would be fine. On the Top end, I need at least 30v, and up to 120 is useful. Current limiting wouldn’t be a bad idea, and doesn’t need to be variable necessarily. 1A is plenty, and more is ok. It doesn’t have to be the most accurate or smoothest DC, but having a power supply I could use for future electronics projects wouldn’t be a bad thing. I’m going to be running DC through a fluid, so grounding I assume is important too.

I’ve got two challenges. One, high school electronics was half a life time ago, so my electronics skills are a touch rusty. And two, I can get a commercial power supply for $130ish, so I’d like to aim for less than that for the project.

I’m not against kits if that is a good route, or building it all from scratch if that makes sense. Thoughts?

Many thanks!
Jeff

 

[MikeMl]

What surplus stores do you have access to? Its all about what surplus (cheap) transformers you can find?

 

[jeffisaviking]

Surplus Center is up the street about an hour. They usually have transformers. I think they have one with a 35v 0.5 amp output, and I've got a 32v wall wart from an old printer I could use as well. Haven't seen deals on a variac locally.

 

[KeepItSimpleStupid]

Take a look at this for a possible start. **broken link removed** It doesn't quite meet your specs because it has a 1.5 A current limit.

You can use another LM317HV im series in a differnt way to get a variable current limit.

You may have to force cool it.

Abetter candidate might be a switching regulator. Constant current or current limit is useful for plating power supplies.

 

[engineernate2782]

Jeff,
How about a variable 0-120 VAC transformer and then a rectifier bridge to convert the transformer output to 0-120 VDC. The transformer would be the pricey part at around $100.00 but a rectifier is relatively cheap you could even build one with 4 diodes. This transformer would work for your purposes: Staco Energy Products Co. - 171 - Power Products - Transformers - Allied Electronics and it has an output of 1.75A.

 

[blueroomelectronics]

Please don't double post.

 

[KeepItSimpleStupid]

My post apparently disappeard. See the datasheet for the LM317HV. **broken link removed** You can use another configured differently for current limit. 1.2 to 57 volts @ 1.5 Amps.

Switching supplies are abetter option.

See www.National.com

 

[jeffisaviking]

Was looking through Ti's product catalog and found the TL783. Looks like it works a lot like the LM317, but can regulate from 0ish to 120 volts. Could I skip a transformer, use a bridge rectifier directly from the 120v AC, add filtering caps and the TL718 circuit, and get what I need? I assume I'd need a giant heat sink on the TL718. Or, and I trying to get too much out of that regulator?

 

[BrownOut]

Skipping the transformer might work, but it wouldn't be safe. You want a transformer to isolate your power from the mains for safety reasons. Transformer-less power supplies need to be insulated, and not expose the output connections.

One idea may be to find a 1:1 isolation transformer. But even that would give almost 170V peak. That's near 50V head voltage, might be a bit much.

For the range you're shooting for, you'll need to consider a two stage regulator scheme, where the 1st stage uses a chopper or switching regulation technique, and the 2nd stage uses a linear regulator. Trying to get that range with just a linear will be tough. Just think of the power wasted if you're dropping 120V down to 5V @ 1amp. You waste 115W and deliver only 5W.

 

[jeffisaviking]

Please don't double post.

Saw it posted twice and didn't see a delete function. Obviously didn't do that on purpose.

 

[jeffisaviking]

Thanks everyone. Time to camp out with a few reference books and see what I can come up with.

 

[jeffisaviking]

Thanks everyone. Sorry for the double post.