January 30, 2017

Stray magnetic fields undersirable in submarine lead-acid battery use.

Electrical currents in a submarine’s electrical equipment, especially in its batteries, can induce stray magnetic fields. Above are used batteries at main battery supplier to Collins submarines, PMB Defence. Each battery cell weighs about 3 tonnes, is about 1.5m high and a metre wide. The entire battery weight for a Collins is about 450 tons [150 cells] (Photo courtesy overclockers forum. Comment #9).
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In a Comment on 26/1/17 10:24 PM an Anonymous advised, along the lines:

Electrical currents in a submarine’s electrical equipment, especially in its batteries, can induce stray magnetic fields. Such distortions of the electro-magnetic field can lead to magnetic anomaly detection (MAD) of a submarine. MAD detectors may be frequently present in seabed arrays and on the tail booms of ASW patrol aircraft.

It is therefore important that diesel-electric submarine maintenance in port and during missions minimizes stray magnetic fields. This is partly achieved by arranging the contents of the submarine (especially batteries) for magnetic minimization. Another measure is degaussing a submarine’s iron, especially in its hull, before a mission.

A major way to minimize a stray magnetic field is be achieved by partial cancellation of magnetic field through “alternative arrangement of two battery modules with an opposite current loop. So, for the n-row by m-column array of battery modules, n and m are even numbers, and for the submarine with two battery sections, m is multiples of four.”

Existing lead-acid batteries may function by being closely packed in modules [1]. Such an arrangement doesn’t need pedestals (which can form a rigid structural base of a battery) and this minimizes stray magnetic fields. No pedestals also have the benefit of lowering the center of gravity. The lower the center the lower the chance of battery shaking, vibration and, in extremis, falling over.

Alternatively, lead-acid battery arrangements may use pedestals because this benefits battery installation and maintenance.

But discussion of precise battery arrangements is a highly confidential area for which there is little open source information. So one cannot be sure how diesel-electric submarine building and customer countries arrange their lead-acid batteries.

[1] see Page 11.2 (Figure 11.01 Battery compartment – typical arrangement) and Page 11.16 (Figure 11.06 Arrangement of cell group water cooling connections) of this Canadian Forces (CF) Oberon class (“O boat”) Training Notebook (Electrical). This Notebook would have been based on UK Royal Navy and Vickers original information. Notebook is decades old now and used to be classified “RESTRICTED” http://jproc.ca/rrp/rrp2/oberon_battery_and_electrical.pdf (about 10MB)



BACKGROUND

The Japanese Ministry of Defence Standard NDS F8016B concerns “General rules for design of equipment with small stray magnetic field”, 5.3”Arrangement of main batteries for submarine” which specifies that submarine is generally equipped with 240 directly connected cells as a group. 

Flowing from NDS F8016B Japanese lead-acid battery arrangements might adhere to the following rules:

i) width of each column of cell module should be the same.  (240 = 20 columns x 12 cell modules) was decided based on these rule. In this case columns of 20 satisfies rule. 

ii) numbers of each column are desirably multiples of four or must be at least an odd number (20 = 4 x 5) and number (12) of cell module in a column satisfies rule 

iii) desirable numbers of cell modules in a column are multiples of four. (12 = 4 x 3). Logically speaking, if the rules are satisfied, other arrangements such as three groups of 24 columns or four groups of 16 columns are possible.

iv) polarity cancellation of a pair of neighbouring columns should be conducted by cross connection of these columns, and so on.

6 comments:

Anonymous said...

Hi Pete

I estimated performance of LIB-submarine (LAB-submarine) as follows:

Nominal voltage per unit battery-module [1]: 36 (2)V.
Submerge period at 4kont/h [2, 3]: 7-9 (3-3.5) days
Acual submerge peiod at 4knot/h [4,5]: 6-8 (1-1.5)days
Output hold period for sbmaerge at 18knot/h: 3-4 (1) hours
Recharge time very short (long)
Charging frequency for 60days-surveillance 8-10 (40-60) times

[1] Values are based on various data for LIBs and LABs. LIB-modules (LAB-modoles) are connected in parallel (series) for generating voltage of nearly same maginitude
[2] Data of LABs are basted on reported simulation of varioue submarines.
[3] Data of LIBs are based on comparison with those of LABs.
[4] As complete discharge shortens life of battery, I assumne 90% (30%) of capacity is discharged in actual submerge by using LIBs (LABs)

Regards

Anonymous said...


Hi Pete

I compared LIB-submarine with LAB-AIP(fuel cell)-submarine.

Surveilance performance at low speed depends on surveillance period. For relatively short period such as 30 days, as underwater operation depends on AIP, LAB-AIP-submarine may show better performance than LIB-submarine. But, performance difference between LAB-AIP-and LIB-submarines is not bigger than that between LAB-AIP-and LAB-submarines.

For longer period such as 60 days, liquid oxydgen is consumed and half of this period is dominated by LAB. As a result LIB-submarine may show better performance than LAB-AIP-submarine.

As output of AIP is low, high speed performance is dominated by batteries (LIBs or LABs). LIBs-submarine shows much better performance.

Regards



Peter Coates said...

Hi Anonymous

Thanks for those LIB and LAB details.

I'll add them to comments at http://gentleseas.blogspot.com.au/2017/01/lithium-ion-battery-arrangements.html#comments and place them in an article soon.

Regards

Pete

Peter Coates said...


Hi Anonymous

Thanks for the data.

I have published your LIBs-LABs data, at 12/2/17 1:39 AM, as an article with a comparative Table on February 21, 2017.

I'll combine your advice at 12/2/17 3:10 PM with points at https://www.shephardmedia.com/news/defence-notes/japan-leads-way-li-ion-submarines/ in an article next week.

Regards

Pete

Anonymous said...


Hi Pete (12/2/17 1:39AM)

Before correction
Nominal voltage per unit battery-module [1]: 36 (2)V.

After correction
Nominal voltage per unit battery-module [1]: 108 (2)V.

Reason of correction: Improvement of circuit breaker.

Regards

Peter Coates said...

Thanks Anonymous

For 21/2/17 8:24 PM.

I really apprciate your help.

Regards

Pete