Double Pole 24v Dc System

Hi to everybody,

I have a 25m ex German Navy motor boat with 24v double pole system. I spent hours searchign on internet for more details and schematics for such system but without proper result. Is there anyone that knows where I can find some literature on this issue or a wiring diagrams?

Thanks in advance!!

 

What is the difference between a regular 24 volt dc system and double pole?

 

Double pole dc systems are two wire insulated configurations meaning that no part of the circuit, in particular the negative, connected to any ground or equipment. The system is so called "floating".

Standard for small recreational boats is the two wire one pole grounded configuration, i.e "negative ground" polarized meaning that the negative of the battery is connected at ground potential usually engine block.

 

Its always a curse when the original wiring diagram for the yacht has been lost. Junction box location is particularly important.

There is nothing complicated about a 2 pole system and the Germans are noted for professional engineering so troubleshooting should be possible even without the diagrams..

Is there a manufacturing label on any of the electric box 's ? I might be possible to request the original drawings.

Nigel Calder , Boatowners Electrical Manual ,,is a good general book

 

It is no surprise to me that you cannot find the information on the net.
The boat was surely designed and built in pre-internet times, and whatever documentation exists will at least be classified as "secret" and stay that way for a whole century.
The wiring will be as complicated as possible with many redundant circuits that never saw a single volt unless the ship was severely hit.

My son once bought an ex-army Landrover with 24V floating wiring, once used as a communications vehicle. The amount of wiring, shielding and waterproof junctions was astonishing; we were able to remove more than 3/4 of all the wiring without impairing any function.

If you have any specific questions or language related problems, write me a PM.

 

I took the boat last year, and this will be second big refit. First one was done from 94'-98' when the original Torpedofangboot was converted into yacht. That time the original 24v system was refreshed but most of the original cabling and components including the breaker and switch panel remained.
Yes, it was done in german way, pretty tidy and not so hard to trace. On the other hand the system is not simple as basic design was done for the navy use and with limited number of devices connected. Then when all the new items were added during first refit and since it is centralized, it became complex with lot of long wires.
Now I want to make a new breaker and switch panel and to design the system as "distributed" following modern standards.
My problem is that I couldn't find details about floating dc systems in general. The standard negative ground systems are well explained and there are a lot of wiring diagrams on the net.
Also this is DIY project and since I am almost out of the budget I can't take a expert to make this job for me.
The question that bother me most is the following: If i have power cable 2 x 4 sq.mm wich is fused with 30A double pole dc automatic breaker that is feeding a blade fuse panel box that has negative bus bar (meaning that only the positive is protected by blade fuse and all the negative are connected to the bus bar). The blade fuse panel should supply power to devices that are rated 2A, 5A or so.

Is this fine?

 

Down stream from the two pole breaker the positive side is fused.

This is a two pole refrigeration diagram. Power enters from the left via a two pole 32 amp breaker switch.

Downstream negative is common and addition equipment such as relays, pumps, instruments are separately fused on the positive side.

Im not an electrical engineer, but I believe this is typical 2 pole installation

 

It depends on cable length and current drawn. A 4 mm2 cable has approx. 0.009 ohms resistance per meter, so at a 10 Amps load the drop is 0.09 V per meter.
The breaker also has a (device specific) voltage drop.

If somebody can explain to me what is the benefit of a fuse in the negative wiring, please step forward.
I would rather hard-wire the negative side; it lowers the resistance, increases reliability and fault finding is easier when you can be sure the minus is always connected.

 

Hi,
You can probably get everything and more about your boat. The good news is Germans NEVER EVER throw documents away and they are very good at administration. Most of the technical documents about boating are located at the military archives of the Bundesarchiv (national library). The bad news is you need to hire a specialized researcher, you cannot get in these archives yourself

Another nice thing is you probably can get the ships logs and building plans as well.

You can find researchers via the Bundesarchiv http://www.bundesarchiv.de/benutzung/sachbezug/militaer/index.html.en

I have an former eastern german patrol boat and found quite a bit of info this way.

 

Hoxha thanks for this information, I never thought about this possibility. It is interesting because I would like to get more info on the boat history not just on technical details. Which researcher did you use? I have a problem with the language since I don't speak German (yet)! I got most of the technical manuals with the boat but in german so I had to translate them to english or some to my language.
Which type is your boat? Just curious, mine is torpedofangboot built by Burmester.

 

I don't have the name from the researcher at hand. But I found him because the german national library has a listing on the site of all certified researchers. the site is in English.

mine is a Eastern German border patrol boat, a grenzboot. 10 meters. http://www.staatsgeheim.com/wp-content/uploads/databeeld21.jpg.pagespeed.ce.xfe27iyjmo.jpg

 

The point of a double pole system is to keep your supply clean and isolated. Example is for use supply to electronic or radio equipment, or if you have multiple battery banks that need separation ie emergency bank.

This does not make it simple but in some ways makes it easier to trace and understand. Unfortunately later someone that doesn't understand the system may make some poor modifications like taking a negative from a nearby circuit.

The primary breaker is most likely supply line protection and not for overload of device. The negative is fused in case of that cable insulation being damaged and supplying power to another circuit. It also helps with isolation when damaged.

Once the power arrives to the consumer device the wiring might be very much one pole with some individual circuit protection.

Sooner or later a negative will find it's way to the ships ground through some appliance or equipment casing. This is when it gets confusing as you can't understand why you get voltage difference to ground, but just remember it is not a load carrying ground (ie voltage will fall if load is applied). Try to prevent this happening if possible.

 

Trouble shooting a 2 pole is much easier and as you say earth faults mysteriously appear and must be dealt with. Fusing every negative after the breaker would be overkill. I very rarely see a fused negative downstream and when I do it makes sense . Electric motors in a system for instance. Alternators are both upstream and downstream so negative is fused. .

 

You would think so, but in fact it does exactly the opposite.
Especially for electronics (but for other loads as well) you want the supply to have the lowest possible impedance and highest reliability. That calls for solid copper conductors with as little junctions as possible.
The fact that even the best devices can fail and short out dictates the use of fuses in strategic places, but as each fuse has a much higher resistance than the circuits connected to it, their number should be kept to a minimum.

Fortunately most double pole circuit breakers ignore current flowing through the negative contact, but because there are spring loaded contacts involved there still is a reliability issue.