Sub speed during battery recharge

[Archive1]

I have noticed that during diesel surface runs with battery recharge the sub speed is no slower during the recharge period than afterward. I recall that in SH3/GWX during recharge the speed was compromised and returned only after full battery charge was finished. Maybe that was not the case with US subs. Anybody know the answer?

[Zero Niner]

IIRC the propulsion system in U-boats had the diesel engines directly linked to the prop shaft or to the generator. Depending on whether batteries needed recharging or not, the engine room crew would decouple one for the other.

For US boats, the engines were linked to the electric motors at all times. It is the motors that provided the torque to turn the prop shafts. So I suppose in a sense, the props would still be turning and whatever leftover juice diverted to recharge batteries. Whereas for U-boats you could either turn the props or recharge the batteries, but not both at the same time.

Another difference is that U-boats only had 2 engines, whereas US fleet boats were equipped with four. I'm assuming that not all engines would be required to provide the amount of electricity needed (via the motors) to propel the sub on the surface, except maybe at flank speed.

[Orion2012]

Originally Posted by Zero Niner

For US boats, the engines were linked to the electric motors at all times. It is the motors that provided the torque to turn the prop shafts. So I suppose in a sense, the props would still be turning and whatever leftover juice diverted to recharge batteries. Whereas for U-boats you could either turn the props or recharge the batteries, but not both at the same time.

By electric motors do you mean generators??

http://www.maritime.org/fleetsub/die...3.htm#fig13-01


In regards to no notible change in speed in game, are you setting the speed by ordering ahead standard, or by giving an order for ahead 8 kts. If doing so by Knots, it could be that the crew calculates the amount of additional force required to move the boat at the requested speed on just 2 motors. But when ordering ahead standard it dosen't.

[Zero Niner]

generator = machine that converts mechanical energy into electrical energy
(electric) motor = machine that converts electrical energy into mechanical energy

[Orion2012]

Originally Posted by Zero Niner

generator = machine that converts mechanical energy into electrical energy
(electric) motor = machine that converts electrical energy into mechanical energy

'

Thanks for clarifying that.

[Rockin Robbins]

Kraken has a top speed while charging of 17 knots at 1/4 charge, 20 at full charge. So with 1.5 and TMO there is a reduction in top speed while charging batteries.

[phil21]

AFAIK the propulsion system on US-Boats is diesel-electric. That means the four diesel-engines are connected to generators which produce power. Power is then diverted to either the electric motors which are connected to the shafts with the propellers or to the batteries or both. So the crew could run all the diesel-engines+generators with full power and use e.g. 50 % of that power for the electric motors and the rest for recharging batteries.
But if you order full ahead all the produced power by the generators is diverted to the motors and nothing is recharging the batteries...

This explains that US-Boats have nearly the same topspeed while charging.

If you want to recharge batteries use a low speed, the crew automaticly uses high power for the diesels/generators but low power for the motors/shafts. So you have much more power for the batteries.

[Rockin Robbins]

Right now I'm on the surface with 1/4 charge, being chased by one of those @#$$%^ subchasers, who's just out of range behind me. You'll pardon me if I keep the throttles WFO and don't worry too much about optimal battery charging speed.

[SteamWake]

I believe what is happening is that the engines throttles are set to match a speed.

Wether or not the load of a generator is in the loop.

Once the batts are topped off the throttle is reduced slightly maintaining the ordered speed.

Havent done any tests to confirm but I believe the fuel consumption is higher when charging batts.

Ive also notice that when flank is ordered if you switch off the battery charger you get another knot or two of top speed.

[SteamWake]

Originally Posted by Zero Niner

generator = machine that converts mechanical energy into electrical energy
(electric) motor = machine that converts electrical energy into mechanical energy

A generator is really not much more than an electric motor spinning on its own or being turned by some other source.

In fact there is problems with Large electric motors 60 hp or more spiking current into the circuit (sorta kinda backwards) when first cut off before the switch is fully open or VFD ramped down. Chokes are placed on the outputs specifically to deal with this situation. The inertia of the motor still spinning causes it to act as a generator.

Modern Diesel electric Locomotives use a thing called dynamic brakes. These dynamic brakes are basically the electric engines coupled to the drive wheels. The drive wheels spinning the motors and generating a electric current. This current is diverted into a series of resistive elements (heaters) and the waste heat is blown out into the air. The sum of the resistive elements can be altered placing a 'load' on the engine/generators changing how much inertia is required to keep them spinning. Saves on the real breaks and is quite energy efficent.

Again basicaly a motor spinning on its own becomes a generator.

[Archive1]

Not being a engineering technical sort I'm not sure I understand all of the above. But would it be fair to say that the sim as written is correct? That is, for US subs even while charging depleted batteries the speed does not decrease but remains essentially the same (although maybe consuming more fuel)?
Amazing how much you guys know.