Reich Charisma tap not working

[swpostie]

This has got me stumped!

I have two taps in my caravan - one in the kitchen, one in the bathroom.

They are both Reich Charisma, operating the submersible pump via a microswitch in the tap head.

A few days ago the bathroom tap stopped working. I assumed the microswitch was broken as, if I opened the bathroom tap and operated the kitchen tap, water would flow.

So I fitted a new microswitch this morning and, before reassembling the tap, tried it. It didn't work!

I tried connecting the two wires together, bypassing the switch. Nothing.

I disconnected the microswitch and connected a meter to the supply wires: battery volts.

I connected the meter to both old and new microswitches: continuity or open circuit (for both) depending on the position of the switch.

So:

I know I have a supply to the switch.
I know I have an earth.
I know the switch works.
I know the pump works.

The only thing that I can think of is a possible short circuit on the earth side of the bathroom circuit but I can't think why there would suddenly be one or how I would go about finding it!

I would've thought on a vehicle like a caravan, with so much wood and plastic in its construction, "accidental" earths would be unlikely.

Anyway, this is as far as I've got and I would be grateful for any thoughts, ideas or advice!

 

[ProfJohnL]

My initial suspicion from your description suggest a wire fault but like you the symptoms and test results are not conclusive. If as you have postulated there is short to battery negative on the return wire, then when the switch is closed it should have blown the pump supply fuse!

Bear in mind that all the switches in all the taps should be wired in parallel, and the will normally switch the positive side, meaning that when the switch is closed ( ie taps open) 12V with respect to battery negative will appear on both wires to the switches.

Can i just clarify, when you say you have checked with a multimeter can you please be more specific about how you connected the meter.

When you checked the tap wires with the meter, Were any other taps on? If any other tap was ON, it would feed 12v positive to both wires.

Was the meters positive terminal to one wire and the negative terminal to the other wire? or was it the meters negative terminal to a negative wire in the caravan and the positive to each ot the tap wires in turn?

 

[swpostie]

Hi Prof - I was hoping you'd see my post!

With regard to connecting the meter: with the microswitch disconnected I connected a voltmeter to the bare ends of the supply wires. The pump was enabled on the switch panel but all taps were closed - meter read 12v.

I also connected the meter across the two wires on the new and old microswitch (not connected to loom) to test for continuity: both tested positive for continuity with switch closed (tap open) and open circuit with switch open (tap closed).

I've, since posting, established continuity between the -ve side of the microswitch and the +ve side of the pump (by connecting a jump lead to my newly soldered joint and my meter between the other end of the jump lead and the positive terminal of the pump). I made sure the tap was closed and, thus, the circuit open.

Thanks for your help.

 

[ProfJohnL]

Has the jump lead sorted the problem out? I do hope so, but it leaves the old wire as a bit of a mystery. Its grounded enough to cause a multimeter to show a full 12V but not enough current capacity to blow th efuse or run the pump????? Mystery :S

 

[swpostie]

No - the problem persists!

I perhaps didn't explain myself very well; I was merely using the jump lead to extend the lead from the multimeter so that I could confirm, specifically, that the connection between the microswitch and the pump was intact.

I also tried connecting the +ve side of the microswitch to the +ve side of the pump (using the jump lead) to see if the pump would run - it wouldn't.

 

[Damian]

A point you may have overlooked.
The tap ONLY has a positive connection, it has NO negative.
The microswitch is just a power interrupter

 

[swpostie]

Hi Damian,

Thinking of the circuit as a whole, surely the tap must have a positive and negative connection?

When I talk of the positive and negative sides of the microswitch, I'm referring to the side nearest the electrical supply as the positive and the other side as the negative.

Looking at the vague "typical" wiring diagram, amongst my caravan's paperwork, I'm assuming that power comes from the battery, to the switch panel, then to the microswitch, then to the pump, and then to earth.

So, while my "negative" side of the microswitch doesn't go directly to earth, it's heading that way!

After all, isn't any switch just a "power interrupter"?

 

[Damian]

Yes, you have the right idea for sure.
All the taps are linked on one side to each other supplying 12v to the microswitch.
The other side of each microswitch are connected to each other back to the pump.
So, every time you operate any tap it completes the positive supply to the pump.
The negative is usually very close to the pump.
So, from your description it would seem that you have a break in either the supply or return from that one tap.
If you have 12v at the microswitch then the break is in the return, but finding it will be difficult.

It is going to take a time with a continuity tester and extended leads to test each wire from each tap.

 

[ProfJohnL]

This is a tricky one,

Though with the information we now have I'm beginning to suspect a high resistance connection to the faulty tap. DC systems are notorious for allowing a poorly made connection to corrode. This increases the resistance of that connection which restricts the current that can pass. Such connections will often pass enough current to for a multimeter volts range, but fail to pass enough current to power the load item.

I suggest that as teh fault only occurs with on tap, then its sensible to start at the faulty tap and trace the microswitch wires back to their connection to that block. If the fault continues trace the wires from that block and so on.

If you find corrosion, of a wire that has gone brittle or the conductors have turned black, the wire needs to be replaced and the connection remade.

Theres no quick fix for this, its a just a logical progression back along the wires until the fault is found.

 

[swpostie]

Hmm, looks like I'm going to have to try and follow the wires back to a junction.

So far I know they go through the bathroom wall into the bottom of the wardrobe and then down through the floor.

Unfortunately it was too wet yesterday to have more than a cursory glance under the 'van so hopefully Sunday will be dry.

What fun!!

 

[swpostie]

Thanks, Prof, for bringing up the idea of a high resistance in the circuit - I had been so caught up with volt drops and continuity that I had overlooked this completely!

It makes perfect sense; if we consider Ohm's Law then if a resistance increases and the voltage remains the same then the current must decrease. So, as you said, I would still have a 12v supply and I would still have continuity.

But I might not have enough current to run the pump.

The wires from the tap run under the sink then (in a rubber sleeve) turn downhill and are cable-tied, with the water pipes, to the waste pipe. They follow this down and through the wall into the wardrobe.

Now, I often catch the wiring when getting anything out of the bathroom cupboard so it's quite likely that one of the wires (or both) may have become brittle.

I would imagine that the first cable tie will be a major stress point (if a wire gets an unexpected tug), but will also help to prevent any shocks from being transmitted further along the wiring.

So now I'm thinking that, before I crawl around underneath the 'van looking for a connection that hasn't been disturbed for years, that might have suddenly decided to become faulty, it might be worth my while just replacing the wiring from where it enters the bathroom.

So that's what I'll do - I'll be trying to solder with crossed fingers!

 

[bertieboy1]

swpostie,
Our first van had tap microswitches for controlling the pump.The first time a switch failed I replaced the faulty switch and fitted an interposing relay controlled by the microswitches with the relay contacts controlling the water pump,never had a problem after that.(the relay contacts having a better dc rating than the microswitches)
Going back to your problem,you confused the issue by referring to positive and negative wires at the microswitch.
The wire after it goes through the switch is still positive with respect to earth.I might be wrong here but a wire becomes negative after it passes through a device with a load resistance ie the side connected to earth or negative.
Check the continuity of the wire(s) that goes from the switches to the pump.
I know caravan wiring diagrams are produced by non electrical people and impossible to fault find with so good luck

 

[swpostie]

Hi Bertie,

Thanks for your input. With regard to your relay, am I right in thinking a relay is an electronic switch that allows a small current to control a larger current? If so then it sounds like an excellent idea to prolong the life of microswitches!

However, I've only had to change a couple (I think) in the last 9 years or so so I'm not going to go down that route - but, knowing that you've had such success with it, I shall certainly look into doing it if I find myself replacing microswitches more frequently, or they become difficult to come by.

Your comment about my use of positive and negative with regard to the switch was interesting, I hadn't thought of it like that before. If I understand you correctly, are you saying that the wire is only negative if it's going straight to earth, and still positive if it's going to another component (such as the pump)? If so, I can see the difference. I was using the terms to distinguish the side closest to the battery as opposed to the side closest to earth - perhaps "upstream" and "downstream" would have been more appropriate!

I have checked the continuity from the switch to the pump and it's fine, as is the supply at the switch. And that's what flummoxed me!

But the Prof made a very good point when he talked of resistance. I had overlooked it completely and I think he's on to something!

So, before I try to follow my wires, to their undisturbed junctions, I'm going to take the easy option and just renew the bathroom wiring - I found the old flex from a discarded iron in my toolbox yesterday and threw it in the bin, thinking "what am I keeping this for?", but I took it out today - it's just the right length and there's even a spare wire!

I'll give it a try and let you know if it works.

 

[bertieboy1]

Hi Swpostie,
I'll try to answer your questions as you put them -
1.A relay lets you switch a higher current when the rely contacts rating is greater than the switch controlling the relay.A relay is not an electronic device,it is simply a coil of wire wound round an iron core.When the coil is energised ie when you open your tap (the microswitch closes) and put a voltage on the coil the contacts of the relay are attracted by the coil and close to switch on the pump.
2.In electrical terms always state it as it is ."upstream" and "downstream" are used in electrical terms but not in this context plain language is always easier to understand.
3.There is no side closest to the battery as the battery has both positive and negative polarity (terminals).What I was trying to say is that a wire is positive as long as it is separated from earth (or negative) by some load this could be a relay coil or light bulb or pump motor etc.
4. High resistance has an effect on low current devices,a small resistance can stop a device operating,as the Prof says check all the connections for corrosion and clean if required this will reduce the resistance.
I would guess provided you haven't done anything like haul wires about the the wiring is ok and it's the connections you should be concentrating on.
Let us know if the problem gets solved

 

[ProfJohnL]

Hi Swpostie,
I'll try to answer your questions as you put them -
1.A relay lets you switch a higher current when the rely contacts rating is greater than the switch controlling the relay.A relay is not an electronic device,it is simply a coil of wire wound round an iron core.When the coil is energised ie when you open your tap (the microswitch closes) and put a voltage on the coil the contacts of the relay are attracted by the coil and close to switch on the pump.
2.In electrical terms always state it as it is ."upstream" and "downstream" are used in electrical terms but not in this context plain language is always easier to understand.
3.There is no side closest to the battery as the battery has both positive and negative polarity (terminals).What I was trying to say is that a wire is positive as long as it is separated from earth (or negative) by some load this could be a relay coil or light bulb or pump motor etc.
4. High resistance has an effect on low current devices,a small resistance can stop a device operating,as the Prof says check all the connections for corrosion and clean if required this will reduce the resistance.
I would guess provided you haven't done anything like haul wires about the the wiring is ok and it's the connections you should be concentrating on.
Let us know if the problem gets solved

Looks like I've got competition at last for extended descriptions

 

[swpostie]

Tap fixed!

What a relief!!

I renewed the bathroom wiring and the problem persisted.

I followed the wires through the floor and across the 'van and back in behind the fridge.

I took the fridge out and the kitchen sink out to find the wires actually came up behind the cooker!

I took the cooker out and it was clear the wires from the bathroom tap came across, underneath, the 'van and up behind the cooker to a junction.

Using an ohmmeter I found that one of the wires, between the junction and the bathroom tap, had a resistance of about 0.1 ohms, while the other had a resistance of around 4.5 megohms!!

Therefore, I replaced that wire.

And the other one for good measure!

Result - a working bathroom tap!

Many thanks for all input - a problem shared really is a problem halved.

 

[ProfJohnL]

Glad we were able to point you in the right direction - now which way is the pub?

 

[Hutch]

Oh really Prof, , Nice to see you have helped someone without confusining them .
Best regards
Hutch.