P= I x V, so if the power demand is the same, wouldn’t a higher voltage with series batteries allow the same power at lower amperage?
Further complication is in something called Thevinen’s Theorem: the maximum power transfer theorem states that “ the maximum amount of power will be dissipated in the load resistance if it is equal in value to the Thevenin or Norton source resistance of the network supplying the power “.
In other words, the load resistance resulting in greatest power dissipation must be equal in value to the equivalent Thevenin source resistance, then RL = RS but if the load resistance is lower or higher in value than the Thevenin source resistance of the network, its dissipated power will be less than maximum.
Now we are considering the internal resistance of the batteries themselves. I can’t imagine the calculation! but the source resistance of the batteries calculates much differently when they are in Series compared to when they are in parallel. In Series, the resistance is simply additive, but in Parallel, it is an inverted summation.
Maybe that’s why the power panel looks so exotic.
Cheers.
There was another interesting feature of British WW1 sub electrical motors that allowed them to adjust power needs. They could operate the motors at “full-fields” or "half-fields”. But I can find no description of what this means exactly. I assumed that full-fields would mean all of the armature windings would be activated, thus increasing power, and half-fields would mean using only a portion of the windings somehow.
But then I’d read something like this;
As the boat rose [the skipper] reduced to full fields,
…which indicates that full-fields was “slow speed” mode. Very confusing. Is this terminology still used for some electric motors?
Yes it is. Field weakening can be used to achieve higher speeds but this is because of counter-emf developed in a DC motor. It involves controlling the field current (stationary field coils) not the armature (rotating). Motor current is always flowing thru all armature coils as long as it is energized. Such a technique would be used on a DC motor in propulsion service where depending on the load, field weakening could kick in at a certain motor amps to gain some revs.
Not just WW I, some early generation drill ships with SCR drives and DC propulsion shaft motors did use this when in transit.
So when the captain is calling for ‘full’ fields, or reduced fields—-this is presumably a rheostat or other variable resistor setup in series with the field coils, more resistance equals less field current which means less back emf and higher speed. Full presumably means take out all resistance - rheostat/resistance to zero (or min), max back emf, full torque available but reduced speed.
But it sounds like a nightmare for commands ‘when I say full I mean slow’—-later engineers probably said—look let’s just reverse the control labels, and call it ‘full ahead’ they don’t need to know what goes on beyond that.
That is why the order was "start with half the current.” Current and power increased from that point. As power increased so did current, power increased above the level of current that could be carried safely at the voltage of the batteries in parallel.
That was the whole point of going to series, higher power could be obtained without burning up the cables.
Thanks KPChief and Jamesbrown for making all this clear and adding the photo–here’s a quote from a book that describes exactly what you-all are taking about.
Stand by!’ shouted Raymond, and down came the periscope again. The motors eased down as the fields were increased by the torpedo ratings working at the motor-boards in the after compartment.
(From Under the Periscope: With the HMS I23 in the Great War by Mark Bennett. By the way, there were no I-class subs. in his book Bennett was careful to keep things anonymous, even to the class of subs he served on. )
That trove of photos from the Scotland People Trust is the only significant source of photos of the interior of an E-class sub. The photo you supplied shows the aft end of the engine space with the stern torpedo tube beyond it. The compartment was so cramped the engineers couldn’t stand. They sat on that stool with their legs down in a well, to one side of the propulsion motors that were under the deck shown.
