Bavaria PB42 Circuit Board

nigelmercier

nigelmercier

RIP
Joined
20 Jun 2007
Messages
16,234
Location
Live in Kent, boat in Canary Islands
www.bavariayacht.info
I'm still trying to figure out the function of the PB42 PCB on my Bavaria 47, see here

Apart from the water tank sensors (which are my main concern) this PCB also has connections to the positive supply to the bilge pump, the shower pumps, and the fridge. What do these have in common that require routing via a separate board?

There is also a feed directly to the positive of both battery banks (marked "Measuring ..."), and there was originally a feed to an output of the charger marked "=". I guess these are all for the Battery OK lights on the Panel 20.
 
It looks like a couple of quad op amps driving the LED's, based on water resistance, we did a similar one in the 90's.

Can you gve us a photo, and a bit more detail of wires, i.e. TCM, TGxS etc. what the connectins are at the LEDs

I will try and work something out for you.

Brian
 
I've put all the info I have in this file, and deleted the image above. There are no LEDs, just a switch that selects Tank#1 or Tank#2 and displays the level on an analogue meter.

My plan is to replace the whole works with a digital display showing the number of litres and percentage for each tank. Not sure whether to use the sensors direct, or via PB42.
 
Nigel,

While Brian has his ponder....

There's a layer missing in the circuit board schematic, but regardless, I think the only 'functionality' built in to that boad is to convert the signal from 4(?) level probes into an output suitable for an analogue / digital meter. It seems to be used as a marshalling point for other things, but there isn't any circuitry associated with them. There are two separate tank level circuits, so if you're seeing the same problem on both, it's almost certainly a wiring fault around the tank 1 / tank 2 switch or the meter. This may take the form of a 'dry' joint on the circuit board connector feeding these items (X3)

I'd spend some time checking this wiring, and the switch itself, then pull the board and check for dodgy solder joints, and re-make any suspect ones.

It's difficult to describe what a suspect joint looks like, but you'd normally expect to see a smooth, shiny fillet of solder between the lead and the circuit board - anything else is suspect. Especially look for the solder 'shying away' from the lead or board; visible cracks in the circuit board tracks near connections (especially large, heavy connections); rings of flux around leads, or anything that looks grey and lumpy rather than smooth and shiny.

I would expect that the board would have been coated to seal it for this sort of application - if so, you may have to scrape this off the connections to check them properly. (then re-laquer!)

I think that the 2 chips on the board are the least of your worries. In my experience, LM324s are pretty robust, and anyway if the problem affects both tanks it would mean identical faults on both chips.

I would put money on it being a *physical* problem, rather than an electrical one - i.e. poor connection or short in the wiring, or dry joint on the PCB.

(I'm certain Brian has much more experience of this than me, so if he comes up with something different, please ignore the above /forums/images/graemlins/smile.gif )

Happy Christmas,

Andy

(Waiting for the little sods^H^H^H^H darlings to go to SLEEP!!! )
 
Circuit boards are a great invention for car manufacturers and apparently also for boat builders. They can be very cheaply mass produced and you just plug in pre made wiring looms. However that doesn't mean they are suitable for boat environment. As already said they are prone to hair cracks bad solder joints and corrosion.

If the board is reasonably big as in not crowded you can sometimes fix them by resoldering everything but be carefull. If it is cramped (miniaturised with Surface mount technology then start thinking about a replacement. good luck olewill
 
I think misterg gets the prize. I have a B44 with a similar system. The tank sensors are 4 metal rods of differing length which push down into the water. As the water level rises it creates a low resistance between the rods to a reference (ground?). The 2 IC's on PB42 convert the discrete levels represented by the measurements into an analogue voltage which is read by the meter. The meter is the same as that which is used to display the battery volts.

As to the jumping around of the readings, it could be normal. When the water is showing 1/2 full but has been used up to be near the threshold of the next measuring point (say 1/4 full), movement of the boat will cause the water to splash away from the sensor rods and the meter will jump between 1/2 and 1/4 until the boat is stable or the water is used further to mean it can't hit the 1/2 full rod. Same for each discrete measuring point. The beauty of the system is that it requires no moving parts in the tank and whilst is subject to "jumps" it is more stable than an analogue measuring system.

Any more accurate digital system will have to deal with the constant level changing and also know the way the tanks taper down the side of the hull. The level change by use is not at all linear.

As to the other wires, I agree that the PCB is used as an easy assembly point, particularly when bringing in ribbon cable to a connector rather than soldering each wire. The spade connectors other than the power for the tank metering system are really just a handy distribution board.
 
[ QUOTE ]
I have a B44 with a similar system. The tank sensors are 4 metal rods of differing length which push down into the water...

[/ QUOTE ]

Right, so the PB42 sums the values from these. In this case there would be no real point in removing the PB42 for my new system. However, it would be handy to have some data on the sensors - is there a manufacturer or model name?

So this leaves me with the mystery of the rest of the PB42 board, not shown in its schematic. Why do the 12V feeds to the other devices (things with motors?) pass via the board?
 
[ QUOTE ]
So this leaves me with the mystery of the rest of the PB42 board, not shown in its schematic. Why do the 12V feeds to the other devices (things with motors?) pass via the board?

[/ QUOTE ]

I think that the simple answer is "because it's handy".

Both the circuit board pattern and the wiring diagram have them as simple "in and outs" - i.e. physically mounted on the board, but not electrically connected to anything. I would guess that it's done this way so that the panel can be completely wired up and finished away from the boat (maybe by a specialist subcontractor). Thus when the panel is fitted to the boat, there's only a line of spade connectors to push on (quick, unskilled task), rather than having to route wires from the boat loom around the panel, terminate them and fasten them in neatly (slower, more skilled task).

The above is just a guess, but I don't think there is any electrical significance to them going through this board.

Andy
 
They are literally rods of metal about 2mm in diameter in a cluster about 15mm apart. They have no "smarts". One of them is the "common" point (the longest) whilst the others are each shorter by the equivalent of 1/4 of the volume of the tank. When there is no water between a given rod and the common rod the resistance will be high so the voltage at the pin of the IC will be high. When water is high enough to touch a rod at the same time as the common rod the resistance is lowered and the input to the IC is lowered. The IC converts these different inputs into an analogue voltage to drive the meter.
I can't think of any benefit of trying to use the same rod/sensor system if you want more accuracy. You will need more measuring points or a continuously variable sensor. There must be many such devices around for professional liquid measuring in manufacturing and probably even for specific marine use but you will need advice from someone involved in the business. The system on the Bav is simple, has no moving parts and in my experience is generally accurate enough when working correctly.

As to the other connections, I agree with the manufacturing convenience idea. I notice all the power cables going via PB42 are 6mm whilst others from the +ve distribution are only 1.5 or 2.5mm. This suggests that PB42 is to provide a more robust linkage point or an more convenient place to route the larger less flexible cables.
 
[ QUOTE ]
When water is high enough to touch a rod at the same time as the common rod the resistance is lowered ...

[/ QUOTE ]

Doesn't this cause electrolysis? Or does the current only flow when you check the level?

[ QUOTE ]
I notice all the power cables going via PB42 are 6mm ...

[/ QUOTE ]

Hadn't spotted this, good point.
 
As the current is tiny and between the same materials (stainless I think) I don't think electrolysis comes into it. As far as I can see, the measuring circuit is always active when the main power is on. It is only the meter which is switched in/out of circuit when you make the measurement.
 
You must log in or register to reply here.

Other threads that may be of interest

Baggywrinkle
Test run of the Lithium system that has been sitting in my cellar for most of this year.
Replies
5
Views
308
claymore
claymore

Share this page

Top