CBE PC110 control panel and water level indication.

[Brian Kirby]

I have a puzzle. :-D

 

Our van is all CBE electrics, and the above control panel was apparently supplied to Knaus as part of a CBE "kit" that includes waste water tank level "probes", and associated connecting wiring harnesses.

 

The fresh water tank level indication has always baffled me, in that a substantial amount (25-30 litres) of water has to be loaded before the PC110 readout registers water in the tank. Once water is registered (minimum 1/3 full: 100 litre tank) it performs relatively well.

 

However, over the past 18 months or so we have only done a handful of short trips. Under these circumstances the amount of water necessary to stop the panel "low water" indication endlessly flashing has resulted in pointless waste of water as, on return home, at least that quantity has to be dumped. So, I began to try to discover why the panel indication did not reflect what both the CBE and Knaus manuals suggested it should.

 

After a lot of checking, I discovered that the tank probe installed in the van is a CBE 505144, with 4 probe rods. I cannot find any details of this probe from the CBE website or elsewhere. Having examined it in situ the 4 rods comprise two of equal length approx. 32cm long, one very short rod, and a third of intermediate length. There is general guidance elsewhere that the long pair of rods should terminate about 4cm from the base of the tank. In this case they terminate approx. 12cm above the floor of the tank.

 

The tank itself is approx. 48cm deep from top to bottom, and the probe is set into a 4cm deep recess in its top, leaving 44cm between the recess and the tank base. So, were the longest rods 40cm long they would terminate approx. 4cm above the tank base, which corresponds with the above guidance. Water should be detected when the tank is about 10% full (say 8 – 10 litres) which would make more sense.

 

The best it seems I can achieve is to replace the 4 rod 505144 tank probe with a similar 4 rod probe but with longer rods. These are available, and can apparently be cut to length.

 

Does anyone know whether doing this might damage, or create an incompatibility with, the PC110 panel? I’m assuming that one of the two long rods carries a current that returns when in contact with water via the other long rod, and so on as the water level rises to reach the intermediate length rod and then finally the short rod registering on the PC110 control panel as 1/3 full, 2/3 full and, finally, 3/3 full.

 

This wouldn’t give an accurate representation of the amount of water present, but it would reduce the minimum amount necessary to register on the PC110 from 25-30 lither to 8 – 10 litres, and would also allow me to cut the intermediate rod to a length corresponding with 50 litres, or half full, which would be useful.

 

[Robinhood]

Brian,

 

having now caught up with this, I'll abandon PMs.

 

CBE electrics with this kind of probe need a probe which is "tailored" to the particular tank. This can be achieved either by buying different length probes (approximating to the tank dimensions if it's an "electronic" unit) and/or (depending on type) cutting down the length from an appropriately larger size.

 

If the appropriate probe and length is achieved (by the prescribed means) it won't make any difference to the functioning, other than the capacity measurement; such tailoring is part of the designed function.

 

I think you need to re-check the current probe, however. Though I can find reference to the part number you quote in conjunction with a PC110 panel, CBE themselves appear to sell PC110 kits with a 5-probe unit (SP5/40), and this looks sensible to me, as (only from reviewing web details, admittedly) your panel supports 4 measurement-levels ("reserve", "1/3", "2/3", "full"?. This would need 5 probes. (and you want the "reserve" to light at somewhat less than 30%)

 

As you say, there is advice that these (non-electronic) probes can be cut to length (which, with a limited number of lengths available for the 5-probe ones makes sense), in which case, an SP5/50 (available online) might suffice if the probes were cut to the appropriate length.

 

https://leisurelines.net/5-rod-cbe-level-probe-tanks-up-to-500mm-3328-p.asp

 

(Other sources are available) Confusingly, this is described as both 5-rod and four rod, but if your panel gives 4 steps of readings, I can't see how this can be done with only 4 rods. (SP5/40, SP5/50, and SP5/70 all seem to be available).

 

 

[Robinhood]

...well, further research indicates that there may be only 4 steps displayed ("reserve" and empty effectively being one measurement)..

 

Accordingly, though described in some adverts as a "5-probe" unit, the SP5/nn appears it may well be a "4-probe" one. (especially if you don't see "empty" and "reserve" as separate measurements).

 

If this is so, then (regardless of your measurements), it looks to me as if it is working as designed. The initial signal will be delivered at 1/3 full (approximately your 30 litres?), and it will show reserve/empty below this. It's confusing, however, given your measurements - is the tank depth consistent all-round, or has the length of the probes been set to reflect a step in the tank floor?

 

Patently, if this is the case, then longer probes will inhibit the warning, but the 1/3 reading will then be delivered for less than 1/3 content (the 1/2 reading can possibly be adjusted by setting it's length correctly).

 

CBE instructions are rather sparse, but if you go to:

 

https://www.cbe.it/newsite/wp-content/uploads/pdfs/000255_02_MT214.pdf

 

...it will download a PDF for a different, stand-alone, water display panel which uses the same SP5/nn sensor series. In that (CBE) document it confirms that the probes should be cut to size to match the tank capacity.

 

If you confirm you have an SP5/nn probe, then a cut-down longer replacement (sp5/50?) looks like at least a partial solution. (all the probes except the shortest can be cut to desired length).

 

 

 

[Keithl]

Brian,

 

The rods appear to be basic stainless steel rods and nothing complex so as an experiment could you try extending the two longest by 8 cm? Maybe push a length of copper pipe over them or twist copper wire around them or use some form of electrical connector? Out of curiosity what diameter are they?

If that works then either take the plunge and buy a new tank unit for £35 or try making the experiment permanent?

 

Keith.

[thebishbus]

If you just want extend the length of one rod Keith's idea is good . You could use a rustless coil spring that would slide up and down the rod with the overhang the length that you want.

Brian B.

[Tracker]

Our easy way to deal with unwanted lights was to cover them with opaque tape - it don't stop the light but it stops the annoyance it causes!

[Brian Kirby]

Robinhood - 2021-10-10 7:57 AM

1 ...well, further research indicates that there may be only 4 steps displayed ("reserve" and empty effectively being one measurement)..

2 Accordingly, though described in some adverts as a "5-probe" unit, the SP5/nn appears it may well be a "4-probe" one. (especially if you don't see "empty" and "reserve" as separate measurements).

3 If this is so, then (regardless of your measurements), it looks to me as if it is working as designed. The initial signal will be delivered at 1/3 full (approximately your 30 litres?), and it will show reserve/empty below this. It's confusing, however, given your measurements - is the tank depth consistent all-round, or has the length of the probes been set to reflect a step in the tank floor?

4 Patently, if this is the case, then longer probes will inhibit the warning, but the 1/3 reading will then be delivered for less than 1/3 content (the 1/2 reading can possibly be adjusted by setting it's length correctly).

CBE instructions are rather sparse, but if you go to:

https://www.cbe.it/newsite/wp-content/uploads/pdfs/000255_02_MT214.pdf

...it will download a PDF for a different, stand-alone, water display panel which uses the same SP5/nn sensor series. In that (CBE) document it confirms that the probes should be cut to size to match the tank capacity.

5 If you confirm you have an SP5/nn probe, then a cut-down longer replacement (sp5/50?) looks like at least a partial solution. (all the probes except the shortest can be cut to desired length).

First, thank you all for your comments/contributions. I've picked out this post by Bob to hang some further details onto.

 

1 I don't think that is how this panel was intended to function, but it is how it functions in practice. From the Knaus and CBE manuals the reserve function should be there. My own research corresponds with yours, that this would require 5 rods to be present, as in your preceding post. If the longest rods then extended to within 4cm of the base of the tank, only 8 - 10 litres of water would be required for the water level to contact them. Then, if the second longest rod was of the same length as the present longest (32cm) rods it would contact water at around 30 litres, the third longest rod would then contact water at around 60 litres, and the shortest rod, as at present, when the tank was full. This would give a 20 litre reserve, when the red "R" LEDs would illuminate, changing to the first group of green "1/3" LEDs at 30 litres, to the second group of green "2/3" LEDs at 60 litres, and finally to the "3/3" group at 100 litres.

 

However, the Knaus modified PC110-KN fitted is paired to a DS300-KN distribution box, and the CBE 505144 tank probe definitely has only 4 rods, as above, and connects to the DS300 via only 4 wires through a 4 pin plug and socket connector on the PC board, so there appears only capacity for a 4 rod probe. Notwithstanding, the CBE website is quite specific that the PC110 panel pairs with a SP5/40 tank probe having 5 rods, the longest of which are 40cm long. I initially thought someone had taken the wrong probe from a parts bin, and fitting a SP5/40 probe would probably restore normal service. I then noticed that the CBE manual for the PC110-KN states that the installation includes a "4-RODS TANK PROBE - it measures the content of the drink water tank, 4-levels visualization". This (and counting the number of and connecting wires/rods on the CBE 505144), coupled with the presence of only 4 contacts at the DS300, led me to conclude that this was a deliberate (somewhat inexplicable) downgrading of the PC110 functionality.

 

So I e-mailed CBE to see if I could get a manual for the PC110, as featured on their website, with the SP5/40 probe. After two abortive responses attaching versions for the PC110 with 4 rod probes, and ignoring my other questions regarding switching probes, it seemed I'd hit a brick wall. So, I concluded that the best alternative was to accept that 4 rods were all I could get, and focus on longer rods so that less water would be required to fool the PC110 into "thinking" it had 30 litres on board, when it had only 10!

 

There are a couple of further points. If the PC110 is switched on when there is no water in the tank the low water warning lights flashes continually and, if the panel is not then turned off within about 20 minutes, the panel locks up and becomes completely unresponsive including the on/off switch. Then, the only remedy is to pull the main 50 Amp fuse which isolates the whole installation from 12V power, wait a few seconds, and then re-insert the fuse.

 

Second, the connection socket on the DS300-KN PC board is paralleled by another, identical, socket which is merely indicated as "Not connected". It seems possible that the SP5/40 probe might be equipped with a 5 wire connector at the probe end, but that the connection to the DS300 uses two plugs into these two sockets (possibly wired 3 and 2, or whatever). I had hoped that a copy of the PC110 manual for the version with the SP5/40 probe, which I assume must have 5 connecting wires, might make clear how those 5 (assumed) wires would connect to the DS300. But the enquiries I have made so far first elicit a request for the relevant PC110 part number (shown on the back of the PC110) and, when I explain that I have no instructions for removing the panel but would like the manual for the version on the web, as above, I get a manual for a version with a 4 rod probe. I don't think CBE's "customer services" people have access to the technical department - or else they know the KN version of the panel is a goof, and don't want to concede their error!

 

But, longer probes would at least remove the risk of the panel locking out when the tank contains less than 30 litres.

 

Part of my reason for posting was to see whether anyone else has a PC110 panel on their van (Knaus or other), ideally with a 5 rod tank probe, that would allow me to find out how the 5 rod probe connects to the DS300. If both the parallel sockets are used for that purpose, I might even risk getting a SP5/40 probe, plus its bit of 5 wire harness, and seeing if it works.

 

2 There seems to be considerable confusion over the designation of the various probes, which I gather emanates from the main wholesaler, who attaches the wrong probe pictures to the CBE codes, and even describe probes as having different numbers of probes to those clearly visible in the pictures. So the retailers just copy over the wholesaler's pictures etc resulting in quite a bit of confusion for any prospective buyer - the more so as few retailers stock the items, only ordering from the wholesaler when a buyer orders from them. I haven't yet contacted the wholesaler, but I suspect they will simply blame CBE in the traditional way!

 

3 & 4 I agree.

 

5 I'm confident that the fitted probe is not an SP5, but if I could fit one, my measurements suggest the SP5/40 should be the right length for the tank.

 

Thanks again to all.