Power supply question.

Thread Starter

Fyreater21

Joined Oct 15, 2010
5
I am new here to this site. I probably have just enough knowledge to get me in trouble, so I decided to ask here for some insight and help. I am into amateur radio and have been able to get my hands on a transformer that has an output of 12V and 16V at 70Amps from 110 volt input. I am looking to design a power supply for my mobile equipment. :confused: I have been looking at circuitry and schematics but nothing I've seen even talks about this range of amperage. Do I own a door stop or is there a viable solution? If there is a solution, I would greatly appreciate schematics or a lead to finding a solution.
I am looking to be able to connect 4 pieces of apparatus to the supply and need a constant 13.8V. The amperage is important for the 200W amp, radios, and antenna tuner. (40 meter and 10 meter).

Thanks
 

R!f@@

Joined Apr 2, 2009
9,918
Welcome,
Amateur radios require lot of power but 70Amps ??? I think u are pushing this too far.

A 70A transformer will be as heavy as a welder. Ever seen this.

For radios, PSU are available.
Did u try googling
 

Thread Starter

Fyreater21

Joined Oct 15, 2010
5
R!f@@, Yea, I googled it, but the stuff comes up like a guarded secret. There 100 amp units 80 amp but no one seems to want to give up a schematic. The parts are not that expensive, even a STM 400V 90A Bridge rectifier is only $13.65. My problem is in designing an operational amplifier like an LM chip to handle the current. I would like to end up with a power supply that adjusts from +3 to +24 VDC.
 

Kermit2

Joined Feb 5, 2010
4,162
A simple shunt bypass type power supply would be easy to implement, for increased amperage you would simply add more shunt bypass transistors(4 should be enough) and put them on a BIG heatsink.

I KNOW that schematics for these power supplies are all over the web. Do some more searches @ www.images.google.com
 

someonesdad

Joined Jul 7, 2009
1,583
While I understand you've already purchased the transformer, another option would be to just buy a power supply such as this 500 W switching supply. It's certainly not as cheap as making your own (nor as fun), but it would get you running quickly.
 

marshallf3

Joined Jul 26, 2010
2,358
What he's trying to build isn't that hard, what I dread in situations like that is coming up with the heat sink.

From time to time you'll find BIG heatsinks on eBay at great prices, often these came from those Peltier coler refrigerators.

I've also been known to adapt almost anything aluminum or copper in combination with other pieces to make my own. I once hit a surplus sale on some website that had pallets full of older heatsink/fan combos that related to a CPU socket that wasn't really used anymore, however the heatsink/fan combos were still rather substantial. A rather hefty copper bus bar from an electrical supply surplus house + some thermal adhesive and I had quite the setup. I've used pieces of aluminum door threshholds from Home Depot as well but if you find a good souce of flat, thick copper it's worth jumping on - especially because so much has been melted down lately.

A shop that sells/supplies/rents/repairs welding equipment or anything having to do with charging "tractor batteries" (warehouse equipment) will probably have some old units that have bad transformers. Guess what's inside on the rectifiers? Huge heat sinks.

Also remember that a heat sink doesn't need to be flat and exactly cover the area you need to serve, heat moves and the idea is to get it into the air even if it has to take a few sidesteps in doing so.
 

Thread Starter

Fyreater21

Joined Oct 15, 2010
5
Pich, thank you. I know how to google, I was looking for a better idea. Guess I well have to use about 7-3055's paralleled and then work on keeping some head room voltage to avoid too much of a drop under load.
 

SgtWookie

Joined Jul 17, 2007
22,230
More than that.

Count on about 8A per transistor. More than that, and you're really pushing it. You're going to need 9 for the pass transistors, and at least 1 to supply their base current.

You're also going to need a LOT of capacitance for C1; 250,000uF or more.
 
Last edited:

R!f@@

Joined Apr 2, 2009
9,918
This is do able. If OP tries. I did made a 10Amp one and is pretty rugged.
Don't see why OP can't

I asked for his former rating to give him sum info from my part.

Op did not reply to tht
 

R!f@@

Joined Apr 2, 2009
9,918
I checked his link. OP, Are u referring to the 110V to 16V @ 70A transformer.

If u have bought it than I suggest u plan on buying the bridge and the filter caps
 
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