Power Subsystem

Power Subsystem

In my original design, the power subsystem had two pairs of connectors, envisioned as an input and an output, or use the one of your choice as the input. Intended for up to 16V DC and 7.6A total current and 3.8A constant on a single output.

I ran two power and ground buses off of the power connectors in loops and wired the two buses together to into multiple parallel paths allowing twice the current to reach any one point or just to help the power be cleaner.

Adding 4 medium sized capacitor positions (which I populated to 1000uF 35V caps), I was easily able to fire the 3A relays using my under powered 2A power supply. Since for a hobbyist or experimenter, this is a 'good thing' I also added multiple hole positions on the power and filters caps to make it easier for a variety of parts to work. This means anyone using this design can optionally add different capacitors depending on what they have on had or special requirements.

Then as part of bumping up to a rev 1.0 and trying to be more flexible for the hobbyist or developer, I added a third power connector in the output stage and made sure there was a power loop just for the output stage, connected to the inner power loop by just two runs marked for 'easy' cutting leaving three large capacitors in the output stage on and to help filter the timing stage. Then I added holes for 7805 or 7812 voltage regulator and a bleeder diode, to allow a higher voltage to be used in the output then 556 timers could handle. You either use two external power supplies, or a single power supply feeding the output stage and a regulator feeding the timing stage. Again, how this is setup depends on the exact needs, the board defaults to a single set of power with up to three connectors, but is designed to be modified to isolate the two voltages.

Next, I changed the track thickness of all runs from 1oz to 2oz, allowing any single output to handle up to 6.3A continous and a total current capacity of about 12.5A and even higher for surges. This helps if all four outputs needs to be run constantly at up to 3A each and reduces problems from surges. The cost increase for the thicker traces was barely noticeable and it made ALL the runs more durable, not just power/ground.

If more is ever needed, reinforce the runs with wire and watch the connector specs or solder the wires directly. The connectors I was using in my testing were rated for 15A, but I did allow for flexibility there, including slightly over sized holes & pads as well.

That leaves the final limiting factors to the selection of MOSFET, heatsink, and external power supply more so then then actual board design.

Next Steps ...

This improved design I've now had built in a small quantity beyond our modest needs in the hopes that the extras can be sold off on eBay during the next year or two to help keep my total costs down. If people do seem to find this useful and deplete my spare stock, I'm willing to order more and continue selling to help fund additional designs. But, being that this is a hobby of mine and I want other hobbyists to be able to benefit, the price stays low, around $5-$6 each PCB blank plus shipping here in the USA. No Chinese imports here!

I'll be posting a full set of schematics to what I've done so far and post the results of the final installation and testing as well as my next project. More docs as well, including infomration on all the optional jumpers, etc to make it easier for people to work with the design.