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Tuesday
Jun112013

Delays Can Be Cool...

You may remember that I had a fancy new coolant header tank made up to replace the plastic BMW part that I fitted during the original build:

It's a lovely bit of kit, but my first outing after fitting it threw up a slight flaw. It seems that the original BMW tank had several baffles built into it, especially around the low coolant level warning float switch. This prevented the coolant from sloshing around the switch, making it open and close and flash the warning lamp on the dashboard.

Well, the new tank doesn't have these, and with the coolant level at it's correct level it sloshes in the tank under normal driving to such a degree that the warning lamp is doing a good impression of the worst disco in the world, or a very irratic morse code signal... It's very distracting! 

Rather than have the tank cut apart, baffles inserted and rewelding it all, I decided to go down the electronic route again.

The level switch is normally closed when the coolant level is correct, and open when it falls enough for the float to drop. What I've knocked up is a delay circuit, that will only light the warning lamp if the switch has been open for a set length of time. The way I see it, it wouldn't matter if there was a delay of a minute or so during a sudden, catastrophic loss of coolant (such as a burst hose), as the clouds of steam would give it away...

And with a slow loss, there would be sufficient coolant in the jacket, radiator and lines to keep the engine from overheating in the small delay introduced before lighting the lamp.

Anyway, all the details on the new circuit (and how it works) can be found in the electronics section - specifically, here.

Here's the new circuit in the flesh - just on veroboard, as it's not very complicated and didn't really warrent a dedicated PCB:

And here's a couple of short boring video's of it in action - first in test mode:

And in the shortest built in 'working' mode:

 I'll install it and see how it goes - initially set to the minimum time delay. If that doesn't do the job, I'll extend the delay by moving the jumper over to the next delay, and so on.

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