Electrical query?

BobE

BobE

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I've a Bukh 24..
Found that the Temprature alarm light had failed (filament gone and also connecting wires to spade teminal)..
Now I find that the damn thing is wired in series with the acoustic buzzer so don't know if there was an overheat problem...
Had to buy a set of bulbs. (Not sold separately) Over £ 30 !!!
New bulbs show 25 to 27 ohms on my meter as against the two remaining old ones at 16 ohms.
So when one switches on the motor the red ( Charging) and yellow ( Oil pressure) come on and I can tell if the bulbs are OK....
But the temperature one never comes on because the temp sender doesn't "make to earth" until the temp limit is exceeded.. and if the bulb/lamp fails I'll never know!!!
So what if I simply join the two spades at the back of the lamp and if the temp gets high then at least the buzzer will sound even if the lamp has failed...
I could of course run a second wire direct from the sender to the buzzer...
Is there any point in the extra length of wire?
Do I need to put some sort of resistance in the direct line to get the lamp as well as the buzzer to work??
Any electrical gurus out there to advise please??

BTW Bukh suggest that one should check the thing annually by shorting out the sender with the engine running.

A Happy, if belated, New Year to you all..

Cheers Bob E...
 
I think that as long as you have the bulb(s) in the circuit that would be be enough resistance for the buzzer.

Does the buzzer come on with low oil pressure, ie when you just have the ignition on?

If so it would be good to rig it so that you get the buzzer whether you have Oil, charge or temp failure.
 
Yes the buzzer and the charge and low oil pressuer come on when the key is turned. Because of course there is no charge or oil pressure until the engine is started..
But the problem is that the low oil pressure and the overheating lamps are in series with the buzzer so when one switches on the overheat light will stay off 'cause the sender assumes that the temperature is OK..
So if the bulb fails one doesn't know that it's failed...
Only way of testing seems to be to run a wire to short the sender to neg earth...
Which I'm highly unlikely to ever do as a start up sequence..
???
Cheers Bob E..
 
Bob
I'm not familiar with the Bukh set up, but it seems very strange to have the lamp and buzzer in series. Are you sure this is the arrangement? Do you have a wiring diagram?
 
[ QUOTE ]
Looking at it, it does look as though the lamp and buzzer are in series ????

[/ QUOTE ] I am not going to download 15Mb of manual I dont need especially if it's that difficult to follow but from BobE's description it sounds as though it is designed so that any of the alarms sounds the same buzzer.

Witout knowing the details of the buzzer I would not consider shorting the terminals of the warning lamp, but fitting a resistor, with the same resistance as the bulb, would be an acceptable way forward.

An alternative would be to fit a test push button switch from the bulb to negative so that the bulb could be tested. That would retain the bulb so indicating the reason for the alarm.
 
The diagrams in the Bukh owners manual do not show the resistors and diodes in the distributor plate (centre top on the control panel).

Looking at the full diagram in the workshop manual (pages P46-47) it is clear that the buzzer will sound if any of the 3 fault conditions occurs, and is independent of the lamps, being wired in parallel with the lamps.

J
 
The buzzer will be in series with the lamp:
+V--Ign Sw--Buzzer--E--Lamp--Sensor--earth
The --E--is the split to the other --Lamp--Sensor--earths, so they will all sound the buzzer.

The thing to short to earth is the sensor, then the lamp and buzzer for that circuit should come on.

If the new lamps are nearly twice the resistance of the old ones, then I suspect they will be only half as bright, and in the worst case, won't allow enough current through the Buzzer to allow it to sound!
If shorting the sensor to earth doesn't sound the buzzer. Try interchanging the old lamps from one of the other circuits, then shorting the sensor to earth.
 
You could always wire in a push to make test switch to test the bulb. How you do this could be variable, but I think I would do it as part of the ignition, during the test period take off from one of the other two bulbs and feed the temp lamp +12v.

The type of switch I am thinking about would reset as soon as you stop pressing it, depending how dry the panel installation is, you could use something like...


splash-proof push to make.

I think my panels might be similar, you have brought up an interesting point..
 
[ QUOTE ]
You could always wire in a push to make test switch to test the bulb

[/ QUOTE ] I thought I'd already suggested that. Just needs a simple non latching push button. Good idea to get a waterproof one, or fit a water proof "boot".

The overheating warning light can then be tested at any time; when stating the engine or whenever the fancy takes you. (the buzzer will sound as well)

But I think you'll find, subject to reference to the wiring diagram, it will have to be wired from the negative side of the bulb to 12 v negative. In parallel with the sensor anyway.
 
Sorry Vic, I only read the first part of your post, I was skimming down and actually surprised no one had suggested a push test switch.

Must read more carefully, I usually hate it when people do this /forums/images/graemlins/frown.gif

[ QUOTE ]
But I think you'll find, subject to reference to the wiring diagram, it will have to be wired from the negative side of the bulb to 12 v negative. In parallel with the sensor anyway.

[/ QUOTE ]

No doubt you are right, but I was not writing or at least meaning what my sentence actually reads like, I, not knowing how the panel is wired was actually meaning take off from one of the other indicator to provide +12v to the temperature indicator, rather than as it reads, take off from the +12v side of the other bulb. I am so used to writing +/- that it is just natural to specify when talking of a power supply, +5v +9v etc, but a point well made as it could confuse.
 
Re: Electrical query? Update...

Yesterday ( Wed) pm.
I went to Maplins Christchurch and bought some resistors..
Then went to boat and rigged up, with those small croc leads, a 12 supply to one of the old ( 16 ohm) lamps. Then checked it worked.... OK... Then put a 10 ohm resistor across the lamp terminals... The lamp stayed off but the resistor went a lovely cherry red!!
So then tried a 20 ohm resistor... Lamp came on fine and resistor was certainly not hot to the touch...
Then had to go..
Next move is to see if resistor does the same with a 25 ohm lamp ( the new ones )and if that's ok (may have to get some more 13p a time resistors) I'll take the new lamp out of circuit and see if the buzzer works through the resistor.
I guess that I'll probably have to go up to, say 30 or 50 ohms, to get rid of the heat problem??
Anyway it keeps the old grey cells working during the off season!!

Thanks for all the advice....
I don't want to fit ancillary test switches, buttons, etc...
I just want to ensure that if, for some strange reason the lamp filament fails ( ?vibration?) I'll still have a buzzer to warn me of overheating..
Whenever I'm doing an oil change etc.. I'll be able to short out the temp sender to check lamp and buzzer function???

Cheers Bob E...
 
Nigel,
What happened was that I got nothing when I shorted the sensor so had to start logically checking through the overheat circuit..
When I got as far as the lamp panel had to dismantle the thing in the cold cockpit...then I found that the filament wasbroken and one leg from the little bulb in the holder was disconnected from the spade terminal...Of course by this time I had bits of components all over the place and the lamp itself had been cut apart with my scalpel!
I reckoned I could fix it all back with Araldite.. Then I realised that one of he two screws securing the lamp panel ( with the 3 lights) to the main panel had rusted the plastic mounting .. So went to see the nice Bukh guys in Poole.. They told me that spare lamps were £17 each!! But the were no longer available and I had to buy a new panel for £35 or thereabouts... What the hell life's toooo short and my pension's not with the Rock mob so I bought the assembly...
Your circuit explanation is as far as I can see exactly what I have...
Anyway previous update is posted before this..
Cheers Bob E...
 
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