Friday, 23 December 2016

Clansman 24V SMPSU Build Started

With the transfer of the 4Ah 7S LiPO pack to its new home inside the metal cased 1Ah battery, that left the metal 4Ah battery case free to start building a mains PSU into.

There is one aspect of this which is of prime importance above every other consideration - Earthing!

This is a metal battery case. Its attaching to a metal radio. And im building a mains supply into it. I personally (dont know about the rest of you) like to live through my radio sessions. Plus, I learnt what mains voltage can do to a body at a very young age - having suffered a severe electrical burn aged only four, the scars of which I still have on the join between my index and middle fingers of my right hand, and the first knuckle of that index finger.

First task then, was to fit an IEC socket. The one chosen was salvaged from a piece of professional video coding equipment, and is not only fused but also contains EMC filtering.

This is installed very low into the bottom of the case, which did pose a tricky problem - how to fasten the nut underneath! The technique I used for that was to fit the nut, star washer, and the bolt through the hole, with another nut and washer on the outside. I could then adjust until the bolt only just was through the inside nut, and then tighten the outer nut up so that everything was in alignment and secure. I then used hot melt glue to secure the inner nut in place against the chassis, a sharp blade to cut away any glue over the hole in the nut where the bolt would come through. Once the glue was set, the outer nut was slackened, and the bolt withdrawn. Once the socket was in place, this bolt was then reinserted and very slowly and carefully tightened, so as not to disturb the glue until the star washer had a chance to bite and secure the nut.

The other nut and bolt of course I could reach to tighten. Those of you possessed of Action Man like Eagle Eyes might have noticed the other nut and bolt, in the bottom center. Here I used a drill powered wire brush disk to remove the paint etc from the chassis around another 3.5mm hole, and then added a cheesehead bolt, crinkle washer and nut, and tightened them to a damn good level of torque. Another washer and nut have been put on for safe keeping. This will be the Earth Binding Post, to which the SMPSU's earth terminal, as well as that of the IEC socket, will be bolted.

A good number of continuity checks were then made to this bolt from everything so far that had to be earthed.

From the outside, you can see that the socket is fitted off to one side. This, when the battery is attached to an RT-320 and the radio laid down for operating on a bench, will actually be at the top of the battery, and the Earth pin will be highest - exactly as you would expect to put the plug in.

The next problem, is what to do about the previously cut holes for the LiPo monitoring and charging. Ive decided the best thing here would be to expand this into one large square hole, and then mount, bolted behind it, a sheet of metal ventilation grill mesh, which luckily I salvaged off of some other bit of kit.

Once I have the grill fitted, there should be relatively little metal bashing needed. A few holes for bolts to attache the SMPSU, one for an LT fuse holder, one for an indicator lamp. Maybe one for an 'LT ON' switch, and perhaps an external 24V output.

No comments: