So last Friday morning, I was all fired up, looking forward to testing a slow cooker on the new bike box through the 240 Volt output.

You’ll remember I said that a slow cooker takes much less power than say, a kettle.  It does.  Whereas a kettle takes a full 13 Amps at 240 Volts -that’s a little over 3 thousand Watts, a slow cooker, on the other hand, takes a mere 200 Watts.

But doing the math, 200 Watts @ 12 Volts still draws 16.66 Amps.  This would completely drain a fully-charged, standard car battery of 50 Amp/Hours in 3 hours.  Not good.

I also found by experiment that turning the slow cooker on, even to ‘low’ made the inverter squeal in disgust, while my multimeter, rated at a mere 10 Amps had a not-so-quiet fit.  The leads to it got pretty warm as well!

So, a bit of a dilemma going on here…

…Enter a 400 Watt, 240 Volt mains lighting dimmer, freshly purchased from ‘Wickes’ -our not-so-local DIY store.  (B&Q, my preferred choice, hadn’t got any.)

I built a ‘rig’, consisting of a standard 13 Amp plug, a piece of wire, the dimmer switch and a spare 13 Amp mains socket.  I then connected it up so the new dimmer circuit was between the box and the slow cooker.  This meant I could ‘dim’ (i.e. Reduce the power to) the slow cooker by turning the ‘brightness’ up and down.  …Tremendous fun!

(…Of course, I felt completely safe doing this.  The slow cooker has no electronics to speak of inside it, so I wasn’t running the risk of blowing, say, a switch mode power supply by giving it lower power than it was used to.  Switch modes can get very, very upset if you try this…)

…And the results were encouraging!

I found I could wind up the dimmer to about 85% before things started complaining, and that was taking a mere 9.1 Amps at 12 Volts.  This works out at a snitch under 110 Watts.

Would it be enough to heat a stew or soup?

Well, to be honest, I can’t answer that because I didn’t have it on long enough, but when I put the cooker onto ‘warm’ (…i.e. ‘Keep Warm’…), even without my Heath-Robinson power control, that took only 4 Amps.

This tells me that it should be able to warm up a pot full of stew quite nicely.

By reducing the current to the cooker, it increases the battery life to about 5 1/2 hours.

Of course, this is if no-one is cycling and putting power back into the battery at the same time.

When I finally get this box and the slow cooker down to LEAF, you can bet your life there’ll be cyclists!

(Even if I have to drag them from the road nearby.)

…And back to the new box…

…I mentioned that it ‘just needed a FET’ to be complete.

Ha!  How wrong can one man be?  Yes, I changed the FET and made some other additions to the earthing circuit, but realised that the displays were nowhere near bright enough for outdoor use.  This has meant that I’ve had to build another, much smaller board only having 16 transistors and about 40 resistors on.  This board takes the +5 Volt output from the PIC and converts it into a +12 Volt signal coming directly from the battery.

This means there is now no ‘stress’ on the PIC, and I can adjust the brightness accordingly.  If it’s still too dim, then I’ll wind the current up some more.

Of course, this has brought further ‘challenges’.

The ‘Reset’ button, at the moment, merely stops the processor, then when the button is released, sets it going ‘from the top’ again.

As you hold the reset button down, one, or more, of the LED’s are on.

But, if I’m whacking too much current down the LED’s for too long a time, then these will blow.


This means I have to rewire -and reprogram- the reset button to be on another leg of the PIC.  When the PIC realises that this leg has gone low, then it will simply halt everything -including the display routines- then start ‘from the top’ again.

So, while the second box is not quite done, it’s certainly a couple of steps nearer.

Tomorrow, I plan to carry on, and don’t worry.  I have photos of the new board to show you.

(* In answer to the question posed in the title:  Because then it wouldn’t be fun.)

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