For a self-contained portable set we have already recom- mended the combination of dynamo and accumulators, whereby regular X-ray work may be done with only an occasional run of the dynamo. The driving power for the dynamo must be decided according to the special circumstances of each case.

The various methods possible are discussed on p. 45.

The dynamo should be shunt-wound, and should supply current of a higher voltage (4 or 5 volts more) than the total E.M.F. of the accumulator’s strongest discharge.

The charging switchboard should carry a voltmeter and ammeter, and the current should not be switched on to the accumulator till the voltmeter registers the proper voltage. Towards the end of charging the voltmeter will be observed to register much higher, with a corresponding drop in the register of the ammeter.

It is advisable to have an automatic switch inserted in the circuit between dynamo and accumulator, by which, if the dynamo should for any reason stop unexpectedly, the circuit would be at once broken. Otherwise, in such an event, the accumulator would rapidly discharge back through the dynamo, to the probable damage of both.

3. Charging from Public Supply Mains.—Where readily available, no one would seek other source than this for charging accumulators, but the current must be suitably regulated or modified before turning it on to the cells. Con- nection direct to the mains of a supply at any usual voltage would destroy the cells.

The methods of modification necessarily differ according as the supply is continuous or intermittent in character. (a) Continuous Current.—Where installed, continuous current from the main should be used for direct supply to. the X-ray installation, as described earlier, but for bedside work demanding portable apparatus accumulators will further be necessary.

No related posts.