yes, its also nice for me to see what is happening in the model submariners community in the UK. I think the scenes are very similar as we share the same hobby and model submariners "are just made from the same wood" without regard where they come from.
Also the problems (many old men, only few young newcomers) seem to be quite similar...
I missed to mention that on that meeting we experienced a sudden explosion of a hydrogen/ oyxgen gas mixture inside a model submarine. That model, a Graupner "Shark", was running submerged when a certain sound of explosion could be heard. The model fell to the bottom immediately and had to be recovered. When back to the shore we could see that the big hatch had been lifted by the explosion and the locking straps of aluminium had been bended by the pressure so the hatch wasn't tight any more.
The model was equipped with nickel-metalhydrate cells which are normally declared as "gastight". I asked that modeller colleague how he used to charge the batteries and he confirmed to charge them with the hatch open! So hydrogen wasn't produced during the charge (due to overcharge). But that modeller mentioned that the battery had become weak before that explosion so I suppose that already one cell of the stack had been discharged completely and was charged in reverse polarity by the persisting load current. In this case the input of electrical energy cannot be stored by chemistry and results in electrolysis of the water portion of the electrolyte generating free hydrogen and oxygen.
And a concentration of 4 per cent hydrogen will be sufficient for an explosion if ignition is provided by sparke of motors or switches.
So we should learn not to discharge our batteries too deep just to avoid reverse polarity charge on cells and generation of gas.
photographs of the model after the explosion (the hull remained intact because the pressure was released very quickly by lifting off the large hatch)
Last edited by Hermann on Mon May 14, 2012 10:38 pm; edited 1 time in total (Reason for editing : correction of a typing mistake)