Feb 082020

So, lately I’ve been helping out with running the base at a few horse rides up at Imbil. This involves amongst other things, running three radios, a base computer, laptops, and other paraphernalia.

The whole kit needs to run off an unregulated 12V DC supply, consisting of two 105Ah AGM batteries which have solar and mains back-up. The outlet for this is a Anderson SB50 connector, fairly standard for caravans.

Catch being, this is temporary. So no permanent linkages, we need to be able to disconnect and pack everything away when not in use. One bug bear is having enough DC outlets for everything. Especially of the 30A Anderson Power Pole variety, since most of our radios use those.

The monitor for the base computer uses a cigarette lighter adapter, while the base computer itself (an Intel NUC) has a cable terminated with a 30A power pole. There’s also a WiFi router which has a micro-USB power input — thankfully the monitor’s adaptor embeds a USB power outlet, so we can run it off that.

We need two amateur radios (one for voice comms, one for packet), and a CB set for communications with the ride organisers (who are otherwise not licensed to use amateur bands). We may also see a move to commercial frequencies, so that’s potentially another radio or two.

I started thinking about ways we could make a modular power distribution system.

The thought was, if we made PDU boxes where the inlet and outlet were nice big SB50s, configured so that they would mate when the boxes were joined up, we could have a flexible PDU system where we just clip it together like Lego bricks.

This is a work in progress, but I figured I’d post what I have so far.

Power outlets on the distribution box, yet to be wired up.

I still need to do the internal wiring, but above is basically what I was thinking of. There’s room for up to 6 consumers via the 30A power pole connections along one side, each with its own 20A breaker. (The connectors are rated at 45A.)

Originally I was aiming for 6 cigarette lighter sockets, but after receiving the parts, I realised that wouldn’t fit, but two seems to work okay, and we can always make a second box and slap that on the end. Each has a 15A breaker.

Protecting the upstream power source is a 50A breaker. So total of the down-stream port + all outlets on the box itself may not exceed 50A.

The upstream and downstream ports are positioned so that boxes can just be butted up against each-other for the connectors to mate. I’ve got to fine-tune the positioning a bit, and right now the connectors are also on an angle, but this hopefully shows the concept…

The idea for maintenance is the box will fold out. Not sure if the connection between all the outputs on the lid will be via a bus bar or using individual cables going to the tie point inside the box just yet. Those 30A outlets are just begging for a single cable to visit each bus-bar style. I also have to figure out how I’ll connect to the cigarette lighter sockets too.

Hopefully I’ll get this done before the next ride event.