Astron power supply upgrade - Page 1
Forum section: electronics / beginners

author: C11MAN
author_rank: Newbie
timestamp: April 27, 2015, 07:15:25 pm
content: A few years ago I saved a large Astron 13.8v 50A linear power supply from a electronics recycling bin.(dumpster dive style). When I got it, its control circuity was removed so it was basicly a large heatsink with some BJT's on it, filter cap, diodes and the transformer. So I put together the best circuit that my 14 yr old self could. While today I know that it is horrendous it did serve me well through melting much nichrome wire and powering car audio equipment. Looking at it now, it has no protection ciruits, voltage sags under load, and spikes on load disconect. So its time to improve on it.My thought was to turn it into a variable power supply with both CC and CV. Taking inspiration from Dave's and others videos and my better electronics knowledge I think I could pull it off if I took the time. While only in brainstorming stage my current issue is how to do the current measurement? If I do a simple resistor, and I say go for a .5V drop, thats 25 watts dissipating across it at full current. To me that seems both a waste and my resistor would change value quite a bit due to increased temperature. Or do I use a premade shunt resistor but that would give me something in the 100-50mv range at full load right? Would that be too low to get accurate readings at low current? I am not looking for anything super accurate or close to it, but even +-100ma would be ok. I am more concerned about keeping voltage to a higher tolerance.Thanks for any help and for putting up with my first post!

author: mikerj
author_rank: Super Contributor
timestamp: April 27, 2015, 08:22:30 pm
content: You need to use a lower value sense resistor, and use a precision op-amp to amplify the error.You could also use one of theAllegro hall effect current sensors, though bandwidth is relatively limited.

author: picandmix
author_rank: Frequent Contributor
timestamp: April 27, 2015, 08:24:52 pm
content: Sure you will get a hundred replies with a hundred different ways you can assemble a suitable psu.First off, I would suuggest you post a pic of your existing linear parts and any details that may be printed on the tranformer such as voltages and current like VA etc so we can see exaclt what there is to work with.My opening suggestion would be to keep it simple and get one of these little regulators which coltrol both voltage and current etc.See this link and very detailed thread for initial detailshttp://henrysbench.capnfatz.com/henrys-bench/minghe-b3603-user-manual-table-of-contents/https://www.eevblog.com/forum/reviews/b3603-dcdc-buck-converter-mini-review-and-how-the-set-key-could-be-fatal/

author: rdl
author_rank: Super Contributor
timestamp: April 27, 2015, 09:05:04 pm
content: That's a 13.8 volt 50 amp linear power supply. I don't think it needs little 3 amp switch mode devices hanging off it, unless they will be used to power an accessory of some type.I believe most of these type (large linear) power supplies used 723 regulators with something like 3055 transistors for the power output.edit: Here is a page with some info that may be useful.http://www.repeater-builder.com/astron/astron-index.html