Tores mailbox VIIC and VIIC/41 operation and technical details

[Katuna]

Maybe I've been looking at this all wrong. Are the Automatic Battery Switches, located in the Galley and next to the Capt. bunk, simply a circuit breaker or is it the switch gear to shunt series/parallel? I'm looking at the schematic Don put up. I presume the switch he highlighted in blue is what is in the cabinet or is it everything to the right of the green line? I'm a bit thick headed most of the time so I'm a little slow to catch on. It was my belief that the gear to switch from series to parallel was in there but now looking at the schematic, I'm thinking that took place in the Main switchboard.

[Don Prince]

Hello Katuna,


The batteries are located below the deck as indicated in the u-historia.com drawing and the battery breakers are located as indicated above deck in the Officers' Wardroom and the galley. The circuit breakers just connect the batteries to the E-room.


The port switchboard circuit is drawn in the schematic on the left side of the green line, and the starboard switchboard is not draw in on the right side just to keep things simple, but it would be very similar. The battery parallel/serial switches are on both the port and starboard switchboards as drawn.


Regards,
Don_

[tore]

Katuna

The Automatic battery switch is a two pole simple automatic circuit switch between the batteries and the main switch boards. when switched on, the automatic battery switch in the galley is connected to the stb. main switchboard in the E-room, and the automatic battery switch next to the CO cabin is connected to the port main switch board in the E- room. The automatic batteryswitches are locally placed protecting circuit switches for the batteries. As battery parallel/ serie switching is a part of the the propulsion control, the switches are placed in the operation control part of the swichboard. 
Tore

[Katuna]

I've got it now. Somewhere I had read that the ABS cabinet held the series/parallel switchgear. This makes thing much more simple.


Once again, thanks.

[Don Prince]

Hello Katuna,

After reviewing my documentation... I realize I have posted and then deleted a post in an abundance of caution. However, I believe I have got it right this time.

The older "Lever Type Switchboard" U-Boat power distribution schematic shows battery room #2 powering the main port switchboard in the switchboard rack and auxiliary switchboard 1 and auxiliary switchboard 1a in the e-room/aft torpedo room. While battery Room #1 provides power to the main starboard switchboard on the switchboard rack, and to auxiliary switchboard 2 in the control room. This circuit drawing is the first attachment.

The newer "Rotary Type Switchboard" has the exact same functionality, except auxiliary switchboard 1a is powered by auxiliary switchboard 1 or auxiliary switchboard 2. This circuit drawing is the second attachment

Note both the automatic circuit breaker and the disconnecting fuse must be shut for battery room powering functionality.

My personal comments:

Both disconnecting fuses sample the voltage at the transfer switches to the auxiliary switchboards 1 and 2. If there is a short circuit, then through the transfer switches one disconnecting fuse will see B- while B+ is on the battery side. This short circuit will cause the disconnecting fuse to trip the circuit breaker for that battery room.

Does my explanation make any sense?

Regards,
Don_

[Don Prince]

Hello Mr. Tore and All,


If you think about it, the disconnecting fuse makes a lot of sense. Instead of having a huge circuit breaker that can handle and sense nearly 2,000 amps in order to trip may not be the most reliable disconnect. However, the sampling circuit with the disconnecting fuse would have very little current and is only looking for a differential in voltage (with a 6 second time delay) to trip its battery room circuit breaker.


Regards,
Don_

[Don Prince]

Hello Mr Tore,


This discussion brings up an interesting point...


If one battery room is out of service, I assume they could run both switchboards on one battery room (Just put the battery in parallel). However, there would be limitations when running both switchboard in this instance; the e-motors armatures must be in series to limit the current drain on the operational battery room. Otherwise, there would be twice the normal current drain on the one operational battery room if all of the armatures (4) were in parallel...


Does this make sense?


Regards,
Don_

[Raymic1]

Just following this with interest.
This may not be relevant but just reading in U Boat War by Buchhiem


"In order to increase pressure on the hydroplanes, the E-motors are switched to high speed.
At low speed, the batteries are switched to run together"

[Don Prince]

Hello Raymic1,


In this case:

1. High speed would be battery serial (220 VDC unregulated) and the e-motor armatures in parallel (least resistance and higher current flow).
2. Low speed would be battery parallel (110 VDC unregulated) and the e-motor armatures in series (greatest resistance and lower current flow).


The term "switched together" is not technical enough and must be defined? As together in battery in parallel, or as together in battery in series. It looks like he meant Parallel for low speed...


Regards,
Don_

[Katuna]

Then would the fuse and the circuit breaker both be in that ABS cabinet? Those are great schematics.

[Don Prince]

Hello Katuna,


Yes, I believe that the automatic circuit breaker and the disconnecting fuse are both in the same small cabinets in the Officers' Wardroom and the Galley. Unfortunately, I do not have any photos of them. If someone visits U-995 perhaps a photo could be captured of both installations...


The images below on the main switchboard switch for the Type IX U-Boat shows some smaller wiring besides the main buss bars for the heavy battery current. The documentation that I have for the Type VII C U-Boat (my translation) indicate that the wiring near the main switchboard switch is for the switchboard battery amp meter (with two switchable ranges) and a voltage meter.


Regards,
Don_

[Katuna]

I'm an AC voltage guy by trade so DC voltage often times frightens and confuses me. However, looking at the schematics, I would think that the DF leg is more of a control voltage. If there is an issue with the motor, such as a cooling problem or clutch issues and amperage is running high, then the DF would blow, disconnecting the main power (supplied from the CB) at the switchboard. If there is a direct short or grounded winding in the motor or supply power, the CB would trip. By definition a circuit breaker is an amperage device. If the DF directly affected the CB, then the CB would actually be a relay or magnetic contactor that is directly commanded by another source.


I'm unfamiliar with 1940's German/European schematics so I'm not totally sure of the symbol used for the CB in Don's schematic. It appears to me to be a switch but it has a couple extra bits to it. In the section below from Tore, it looks like either a manual disconnect or magnetic contactor with overloads located on the load side of that switch.


From a modeling standpoint, I guess this is all moot but it is fun to try and decipher how all this worked. Would sure love to see inside one of those cabinets. Don, your last picture is about what I was expecting the components to look like. 

[Don Prince]

Hello Katuna,
This is my translation of a document which I will email to Mr. Tore  for his comments...

Accumulator system
Page 10 and 11
Safety equipment.
1. To protect against overloading of the batteries, a battery self-closing switch is installed between the battery and the main circuit board with the following tripping option.
a) Over-current triggering adjustable for overcurrent from 3000 - 7500 A and for a delay time up to 10 sec, normal Set for 5000 A and 6 sec.
b) Short circuit triggering adjustable for 11000 - 22000 A, normally set for 13000 A, triggers without delay.
For further information see Description and Operating instructions, main switchgear and auxiliary switchboards.

[Katuna]

Ok, time for a new topic. Mr. Tore, I remember seeing a photo somewhere of the engines and on the "purge" valves (next to the injectors), they had small catch can, presumably tin cans from the galley. I would assume this would have been to catch any oil/fuel/water that would have been blown out while cleaning the cylinders out. Do you ever remember seeing anything like that? Thought that would be a nice detail to add to my engine.

[Don Prince]

Hello All,


I have modified my 16 July posting....


Don_