Saturday, 8 September 2018

Portable Power Supply

Some of you may know that I tinker around with solar power from time to time and that in fact my workshop is 'off-grid'. One of the features of a lifetime spent tinkering with stuff is a lot of spare bits lying around, so when a friend was looking for a lighting system for her allotment shed and summer house I thought I could come up with something quite easily.

I had a 86W panel and a small car battery knocking about (as you do - they were part of the evolution of my workshop solar power system), so I would not have to spend much money. I also had a simple panel controller, which essentially sense battery voltage & connects the panel if the voltage is below a set point and disconnects it when it goes above the set point - pretty basic; no MPPT here.

What I needed was something to unite it all into a simple portable unit. This came in the form of a bit of an old kitchen unit and some pine offcuts:

I used the little router to cut a slot at the back:

This accommodates the foot of the battery. I sized it to suit the largest battery I had, to 'future proof' it a little. You can see how the foot of the battery is trapped in the groove:

The other foot is trapped under this little bar, made from 3 mm cold rolled sheet and retained with two M6 wing nuts:

Here's the battery in place with the controller:

Here I've added a simple modified sine wave inverter. It gives 200 W at 220 VAC, so you can charge your phone from it.

Here it is with the wiring completed. The six terminals top left are for the solar panel and for two 12V outputs. Lower down, there is a higher current termination for main battery cable, voltage sensor and feed to the inverter.

The inverter provides 200W at 220 VAC - that's about an amp, which translates to about 20 A on the DC side; I can run a 60Ah battery for 36 minutes at that rate, assuming my maximum allowable discharge is 20% - with a deep cycle battery I could increase that, and the frame will carry larger batteries.

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