Bongo Fury

The Maplins "water alarm" kit

http://www.maplin.co.uk/Module.aspx?ModuleNo=22564

is only £3.99, and the components can be re-arranged on the board to work as a low water level indicator. The kit is VERY simple to solder together, and I'd be happy to create a post detailing the mod to get it to work on the Bongo's.

If anyones interested, I'll buy another kit, and photo the assembly.

Sounds great -if it works, I'd be keen.

There have been cheap coolant alarms mentioned before (although not this cheap!)

http://www.igmaynard.co.uk/bongo/forum/ ... lant+alarm

That's the one, ScubaBongo, but, as bought, it buzzes when water is present. I've
simply re-biased the transistor, so it's off when water is present, and buzzes when the level drops.

I'm not claiming any great invention, and am happy to post a sheet on doing it.

Certainly keen if it works reliabley, but I'm slightly nervous, due to the post by Hadyn in the older 'Cheap Coolant Alarm' thread that I posted above.

I quote:

"...the low coolant alarm I represent has been developed over a 6/7 year period. The current it allows into your coolant is approx 45 micro amps (thats micro not milli). Anything much above this will cause problems with different metals in the system and a problem we call "probe filming" This will occur very soon after fitting the alarm and will give false alarms. The device above works as a simple low level switch which will cause a pump to switch on (this could indeed be used to switch a light/buzzer) However the current used could well be far to high to introduce into a vehicles cooling system.
This device is not designed as a coolant alarm and to use as one could be a big mistake."

I'm on the Mech side of the family myself, so this sort of elec-trickery confuses me. If the problem quoted above is not relevant to this circuit, then yes please, I'd love a fact sheet (and I'll be down Maplins as soon as I get round to recommisioning my coolant system!).

If for some reason there is a flaw in this cunning plan, I guess it could be easily rigged as cheap High-Coolant alarm without too much bother?

Are you connecting this direct to your vans 12v?

Many thanks

This (for me at least) is one of those tricky areas where I'm not confident that taking risks with a device that is ultimately intended to mitigate a risk, is worth the risk - if you get me.

The theory is that the Haydn alarm is a complete kit, ready to install and developed for and tested as fit for purpose. Although costing more than you might otherwise pay by employing some skillful DIY (say £40 more) this is small beer as a one-off payment for a device that - when it works - may save you hundreds of £s or -when you need it to work but it doesn't - may result in damage causing the same amount. Added to that, once you fit a device you naturally tend to relax on your normal checking routines. So you need it to be a dependable device.

I love experimenting - but only where the cost of failure is bearable.

Good luck though, whatever you opt to do (hey - you might develop a fit for purpose 1/2 priced alternative!)

The kit comes with a 9v PP3 housing, but it can take the vans 12v. Also a 12v led could be put across the buzzer mounting, either as well as, or instead of.

There's 11,000 ohms across the 13volt supply, so current is ???? 0.0011A? So it might be a bit high if your info is correct. I think that the resistors in the pack can be replaced with higher values, to cut the current further, I can have a play and see.

Appreciate the feedback,

SD

stilldesperate wrote:
. I think that the resistors in the pack can be replaced with higher values, to cut the current further, I can have a play and see.

Sounds like a way forward. I would offer my help, but I don't think it would be any use!

Nice project, hope it works out.

stilldesperate wrote:The kit comes with a 9v PP3 housing, but it can take the vans 12v. Also a 12v led could be put across the buzzer mounting, either as well as, or instead of.

There's 11,000 ohms across the 13volt supply, so current is ???? 0.0011A? So it might be a bit high if your info is correct. I think that the resistors in the pack can be replaced with higher values, to cut the current further, I can have a play and see.

Appreciate the feedback,

SD

Haven't checked out the Maplins alarm in any detail, and won't be doing so, as I've got a Haydn Mk 1 already. However, I assume that it works by passing a current through the coolant, and using this to detect loss of coolant when that circuit breaks. If the resistor you mention IS "across" the 13v supply (in parallel with the coolant circuit?), that will have no effect on the current through the coolant - only a series resistor would.

Stilldesperate, have you actually tried this circuit in your Bongo?

I can't see it working without considerable modification. I'm assuming that by 're-biasing' the transistor you mean the probes are now located at the lower half of the input potential divider?

Is the transistor a Darlington Pair (ooh-er, missus) as it appears in the circuit diagram provided by Scuba? In which case (if my memory doesn't fail me - and it well might) it'll need around 3V at the base to switch on the transistor - twice that of a single transistor? Depending on the 'resistance' of the coolant (and I've no idea what it is - but would guess around 500k+?!) this would then need the 'upper' resistor to be at least 1.5M for the base voltage to be below the triggering level with the probes in 'water'?

Perhaps the thing to do would be to set the triggering level to just above switching point using two high-value resistors (or a potentiometer), and then wire the coolant probes in parallel with the 'lower' resistor to then bring the input voltage to below triggering level when the probes are immersed . Hopefully the base voltage will go back up to re-trigger the transistor when the probes are 'dry'.

You clearly know what you are talking about - can you tell me if I'm making sense?!

Seems lovely and cheap but I will stick to the brilliant Haydn mk3 alarm, its the dogs bollocks for me.

I would be very concerned about too much current going through the coolant causing electrolysis type issues.

Very possibly, missfixit, although in the scenario mentioned by myself above - using large value resistors to set the base voltage to just above triggering level - it would only have around 8uA going through the solution - which is teeny, tiny.

However, like many electronic circuits, what works in theory just doesn't work in practice! This is why it's such an enjoyable - read 'bludy aggravating' - hobby.

If Stilldesp does manage to get it to work, it could well be a useful added 'reassurance' to some Bongo owners, those who simply weren't considering the 'professional' alternative due to it's cost (not that I think it's an unreasonable price - it strikes me as being fair enough).

I would imagine that those who can afford it, would still go for the 'tried and tested' system.

It's been a long time since I got my head around the calculations & theory involved, too many other things to fill my brain these days
Be interesting to see what comes of this one, always good to see people thinking outside the box & coming up with alternatives

Agree.

I am also a member of two kit-car forums ('cos I have two kit cars...), and the whole ethos of kit cars is coming up with home-made solutions...