PCB's in Caravans

[JohnHannah4356]

I have just had what you might call an idle chat with a heating engineer who has been to service my neighbours' gas boiler (house that is ) He asked whether the van parked at the foot of the drive was mine. He went on to say that caravan PCB's especially that for a heat exchanger are affected by standing, unheated, thro winter and as a result are very expensive to replace. The remedy is to have a low heat source switched on permanently, I have never heard of this problem in 10 years of caravaning, anyone cast light on this.
John, Chesterfield, Derbyshire

 

[ProfJohnL]

Hello John,
Its not as black and white as the 'engineer' has made out. Most modern Printed Circuit Boards (PCB) are resin bonded glas fibre, and as such are prestty stable, also the individual components are usually hermetically sealed. Current European standards for caravan related equipement require circuit boards to be tested for correct operation over a wide range of temperatures. Usually the components that re most vulnerable are the mechanical switches and unsealed varaible resisters.

The biggest problems are usually related to humidity and condensation which can have short term and a longer term effects. Short term, condensation can bridge or partially short out the connections of some electronic components. provided the PCB has been designed in accordance with the EU regs, then whilst this may cause it malfunction, it should fail 'safe'. The condition usually disappears as the condesation dries out or eveporates.
The longer term problems are due to a combination of moisture, metals(component legs) and the residue salts from resins etc. These can set up corrosion which can degrade solder connections.
There are things that manufactiures do to help reduce these issues, thourough post assembly cleaning,and confromal coating to resist moisture penetration.
The bottom line is if the caravan is dry, then temperature is unlikely to affect the the circuit board, if the caravan has a damp problem then cold weather may affact the circuit board.

 

[Guest]

As it is my job to fix these 'caravan pcbs' then I can tell you for sure the engineer is mistaken, or to be fair. mis-reading what he's seen, least I've been guilty of jumping to the same conclusion.
With the first very cold snap early Feb 2010 and a couple of 'strange' electronic failures, I'd indeed lept too the cold being the cause, seemed reasonable as we had not experienced such cold since before these boards were designed. Maybe they simply could not stand such low temperatures?
This last and worse winter I thought must, if I was correct, result in similar faults reappearing, not a single one!

One mechanical problem that have become 'prevalent' this year is Carver Cascade gas valves sticking open, I have changed more valves this year than in the previous twelve years!. I've stripped a few and can find nothing that might cause it, I really don't know but extreme cold is one possible.
Another is Carver's mk2 Fanmaster electric elements, quite a few of these this year have snapped, the metal is brittle so you can snap it as easy as a stick of rock!? Again not sure, but I've a feeling this may have something to do with cold, ie, they are known to become damp inside and if this damp were to freeze enough, it could easily break the element. Mind you, I've more thoughts on this as snapping is, as I said, far from unknown.
In short then, I agree with John's conclusion and any such apparent pcb damage caused by 'cold' is a coincidence

 

[Past_it]

I do believe at times the caravan industry, or its suppliers, are going over the top with technology, in fact it seems it's technology for technologies sake, whether we need it or not.
Of course the other side of the coin is when it goes wrong ....sorry guv we can't get that spare part its been superseded you'll have to buy a new one !!!
The biggest danger to electronics is vibration, humidity and heat, not cold.

 

[SteveP]

I would probably point a finger at where the PCB's are sourced.
Chinese, cheap and cheerful!

 

[RogerL]

The biggest danger to electronics is vibration, humidity and heat, not cold.

Although vibration when cold can acceleration fatigue in soldered joints on PCBs - plenty of other evidence of caravans vibrating because the manufacturers don't routinely balance the wheels/tyres.

 

[Surfer]

The biggest problems are usually related to humidity and condensation which can have short term and a longer term effects. Short term, condensation can bridge or partially short out the connections of some electronic components. provided the PCB has been designed in accordance with the EU regs, then whilst this may cause it malfunction, it should fail 'safe'. The condition usually disappears as the condesation dries out or eveporates. The longer term problems are due to a combination of moisture, metals(component legs) and the residue salts from resins etc. These can set up corrosion which can degrade solder connections.

Spot on! The above is the reason why my mobility scooter woudl nto work when spring came. It had been stored in the garage for the winter and it seems condensation got to the PCB board and when switched on, took out the ICs on the board. End result a mobility scooter now sitting in the garage as repair costs are more than the scooter is worth.

 

[ProfJohnL]

The biggest danger to electronics is vibration, humidity and heat, not cold.

The OP is relating to storage conditions, not operating conditions, so being specific vibrations will not arise during storage, and As I explained previously humidity certainly can cause both short terms and long term problems, But not cold by its self. Most electronic components can survive STORAGE temperatures typically of -50C to 105C. Solder joints should remain sound within that range.

The killer for most electronic components is heat - technically its not the heat its self,but the inability for the component to disipate any heat generated by its operation. The circuit designer should ensure that each component ona PCB can radiate convect or conduct heat away from the component for all normal operating conditions. That is why some components have to be mounted on heat sinks.

 

[Damian]

Quote"The circuit designer should ensure that each component ona PCB can radiate convect or conduct heat away from the component for all normal operating conditions"

I am sure they do so, but then Truma strap the PCB to the outside of a tank full of hot water, in its own shrouded enclosure which retains heat around the board, ....................................

 

[RogerL]

but then Truma strap the PCB to the outside of a tank full of hot water, in its own shrouded enclosure which retains heat around the board, ....................................

I've seen worse - a number of car manufacturers bolt the ECU rigidly onto the engine !

 

[NickinFrance]

One issue not mentioned is Thermal Shock, if a device is switched on from cold, some components will heat quicker than others & often the mass of of the PCB, this can cause fracturing of soldered joints.

Many years ago I was the sales manager for a company that made power supplies & a major customer was an oil exploration company who wanted a large number of standard products modified for use on North Sea rigs.
These had triple dipped transformers, conformal coated pcbs' etc.
One day one of their (idiot) inspectors asked our chief engineer what would happen to one of our 500w Linear PSUs (that weighted about 50 kg) if it was dropped in the sea, without a pause he replied "it would f******g sink".
It cost the company a very good meal to keep the contract.

 

[Shirker]

I would probably point a finger at where the PCB's are sourced.
Chinese, cheap and cheerful!

Seems a bit Daily Mail to equate Chinese solely with cheap and cheerful. A lot of crap comes from China but also some really good high-end stuff. I wouldn't describe the electronic components of an iPhone or iPad as 'cheap and cheerful' even though it is sourced and made in China. You get what you pay for irrespective of geographical location.

 

[Guest]

Oh so true, when I went over there and not being able to sleep, I found myself sitting at the 1st class bar with the CEO of a massive company with five factories over there, this was 3am but still highly informative about how to do business with them.
Basically you give them a project and they will make it to any standard you wish, the real deciding factor comes down to the price you want to pay, not their abilities to produce any required standard.
They also don't like someone giving them a job and then leaving them to it, then to just sit at home waiting for a container to arrive, they do like full involvment from inception to delivery or they will milk it!... After all, their fully aware they are being screwed as whatever price they get is far less than it's 'retail value'The guy on the plane BTW was head of what might be thought of as the successor to Lucas and a few other big companies now under one umbrella, they make about 95% of all cars steering gear produced worldwide...so your cars steering is almost certainly MADE in CHINA!!

 

[ProfJohnL]

The Chinese connection reminds me of what I belive is true story:- a colleage of mine used to work for a multinational company that made components for teh car industry. The company were embarking on a new project, and the question of the place to manufacture came up. It was decided to try a Chinese supplier. The project specs and designs were sent of to the company , and after a few weeks the first samples arrived for checking and testing.
The goods inwards team recived the packages and noted that of the thousand samples, 997 were in one box and 3 in a seperate box. The paperwork stated supplied as per order 1000 units with 0.3% reject rate. All the parts except the 3 passed the good inwards inspection.
The project team were puzzled by this so the Chinese company were quized, They came back with the answer that the origional order asked for 0.3% reject they were puzzled by this request for faulty items but that was what the order wanted so thats what they made.
I seem to remember the multinationals order wording was actually ambiguous in translation to chinese so it produced this strange requirement.
The Chinese company added that they had to take three items from the batch and actually change them to make them faulty!

 

[Guest]

I could well believe it John, when someone went to China prior to me with one of the last production Cascades tucked under his arm, he told the factory to copy it exactly. This they did slavishly....including, to me, a glaring machining fault in the heat exchanger die, now evident in the casting!
The reason I went was to correct many problems, the first meeting was a bit tense, to say the least, he had already had a copy of my report and was not a happy chappie!!
Forearmed with my chat on the plane, I explained through the interpreter, I was sure he was more than capable and my sole purpose was to explain what he had to achieve, how he achieved same was then solely his concern.
He seemed to like that and grabbed the original sample to point at that big fault, he then had to tell the interpreter what was on his mind, however having seen what he was pointing at, a smile came across my face and as I was looking at him, he paused as he realising I was way ahead of him.
I leant over still smiling at him and said to the interpreter, 'how does he think I knew he was so good' and when she translated that....he burst out laughing, from that point, we got on like a house on fire!!