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R E S E A R C H A N D D E V E L O P M E N T B R A N C H

DEPARTMENT OF NATIONAL DEFENCE

CANADA

DEFENCE R ESEARCH ESTABLISHMEN T OTTAWATECHNICAL NOTE NO. 77-5

NICKEL/CADMIUM AIRCRAFT BATTERIES:MULTICHANNEL GASSING-RATE METER

K. Feldman ’ and R .L. Haines

Electrical Power Sources Divis ion

RECEIVED MARCH 1977PROJECT NO. PUBLISHED MARCH 197754-0 3-07 OTTAWA

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TABLE OF CONTENTS

Page

ABSTRACT/RESUME (1)

TABLE OF CONTENTS (ii)

INTRODUCTION 1

GENERAL DESIGN 2

DETAILED DESCRIPTION 2 V

A tt achment to Cells 2

Filter Chamber and Orifice 6

Manometers 9

Interconnections 12

The Structure

CALIBRATION 13

CLEANING 15

ACKNOWLEDGEMENTS 16

REFERENCES 17

APPENDIX I 18

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ABSTRACT

The instrument described is used to assess the state of health ofseparators in nickel/cadmium aircraft batteries and thus to permit removalfrom service of those cells which may be expected to fail catastrophicallyin the near future. Twenty channels are provided to permit simultaneousobservation of all cells in a complete battery . Each channel measures thei-ate of emission of gas from one cell during overcharge by means of the pressurebuild up in a chamber from which the gas escapes via a suitable orifice .Construction , calibration and cleaning are discussed .

RESUME

L’appareil désigné sert à évaluer l’état des séparateurs desaccumulateurs nickel/cadmium d’aéronef et sert de cette façon a ~liminer .Iesaccumulateurs susceptibles de provoquer ultérieurement une défaillance majeurede la batterie . Vingt canaux permettent d’observer simultanément tous lesaccumulateurs d’une batterie. Chaque canal perniet d’évaluer le dégagementgazeux d’un accumulateur lors d’une surcharge ~ ].‘aide de la pression forméedans une chambre de laquelle s ’échappe le gaz par un orifice approprié . Saconstruc tion, son étalonnage et son nettoyage sont discutés.

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INTRODUCTION

The separator material between the positive and negative p lates ofnickel/cadmium aircraft batteries performs several critical functions . Twoof these are of concern here . One function is to prevent oxygen , generateddur ing overcharge at the positive p late , from reaching the negative plate.The other function is to prevent migrating metal from forming short circuitingbridges between the plates .

Partial failure in either or both of these functions permitsundesirable reactions to occur . Ultimately catastrophic failure may follow .Failure conditions usually build up slowly and may therefore be detecteddur ing maintenance procedures before the danger point is reached . It hasbeen found that separator deterioration leading to both types of failure canbe detected in early stages by observing the gassing characteristics ofindividual cells during overcharge and on recharge after post—charge periodsof open circuit stand (1).

To facilitate making the above observations the multichannelgassing—ra te meter described in this paper was developed at the DefenceResearch Establishment Ottawa . It may be used to observe when each of thecells in a battery start to gas and subsequently to measure the rate ofgassing. In the latter use , the arrangement facilitates intercomparisonof the cells at a glance .

This paper gives the principles used and details of construction ofthe meter as built at DREO . It should be recognized that many of these detailsare somewhat arbitrary and are presented for illustrative purposes. Due tothe nature of the environment to be expected in nickel/cadmium battery shops ,mater ials used should be resistant to attack by potassium hydroxide , shouldnot be Inflamable , and should be reasonably robust.

A provisional parts list based on the laboratory model and givenfor preliminary planning purposes is given in Appendix I.

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GENERAL DESIGN

S ince the nickel/cadmium batter ies normally used in the CanadianF~ rces ’ aircraft contain 19 cells each , the gassing rate meter providesseparate channels for each , p lus one spare channel for a total of 20. Theindicators are manometers arranged adjacent to each other. This providesease in comparing the gassing rates of the various cells with each other ,and perhaps with a “standard ” wh ich may be connected to the 20th channel.A p hotograp h of the unit is shown in Figure 1.

Each channel is composed of cell attachment fittings , a filterchamber , an orifice , a manome ter , and interconnecting tubing . These detailsmay be seen in the photograph of a single channel assembly shown in Figure 2.In use , the cell attachments are substituted for the vent cap normallycovering the cell. Gas emitted by the cell passes through the tubing and isrel eased near the bottom of the glass bead filter. After passing upwardth rough the filter it escapes through the double orifice provided by the

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hypodermic needles which project through the rubber stopper at the top endof the tilter chamber. Because of the restricted orifice , gas pressurebui lds up in the chamber in d i rec t propor t ion to the rate of gas emiss ioniron the ~e 1 1. * Tubing connects the chamber to the manometer so that thelatter indicates the pressure in the chamber . A calibra tion scale relatesthe Pressure to the gassing rate of the cell. For convenience , the readingsare made using onl y one leg of the manometer .

D ETAILED DESCRIPTI ON

ATTAC}fl~ENT TO CELLS

A di igram of attachment fittings is shown in Figure 3. The fittingspr vide a gas tight ~ onniV ction between the cell and the tubing to the meter.

* See b r example , Chemical Engineers ’ Handbook , ed ited by Perry and Chilton,Puh i l 4 11& d by ~1 . r i ~ UI! I , ~th edition , pages 5—11

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V They are convenient to attach and remove with normal vent cap keys , andi nc lude safety ven t s to avoid excess ive pressure b u i l d up in the cell in theev e n t of an ac c i d e n t a l b l o c k a g e in t h e sy s t e m . They are made by mod i fy ingnorm a l ven t caps to accept “Na lgene Quick Di sconnec t s ” (Fi she r cataloguenumb er 15—3 15A) .

C o n s t r u c t i o n p rocedure is as f o l l o w s . Norma l cell vent caps aremodified by removing the vent p lugs . The r e s u l t i n g holes are then enlargedt o inch. The upper 3/4 of this hole is further enlarged to 11/32 inch .The smaller section of the connect—disconnect is inserted into the hole andis e p ox i t d i n t o p lace .*

The m a t i n g p a r t of t h e q u i c k — d i s c o n n e c t is mod i f i ed to provide theS U c t \ v a l v e desired f o r p r o t e c t i o n in case the gas escape path becomesbloc kc d . A ~ 5 3 d r i l l is used to make two holes th rough the connec to r bod yas slic~’n in F i g u r e 3. Any b u r r s ~round the holes are c a r e f u l l y removed .Then a rubber sleeve (3 /32 inch ~ al l , 11/ 16 OD Amber n a t u r a l rubber tubingabout 5/8 inch long) is slipped over the connector to cover the drilled holes.The holes arc positioned so they will not be blocked when the connectors areengaged , h ut w ill not he located too close to the edge of the rubber sleeve .

.\it~~r assembly, the above combination is tested (see Figure 4) tocns 1rt~ t h at no gas leakage t~~ke s p l a c e below a pressure of approx imate ly-~ ps i , h u t that the s a f e t y va lve r eleases be tween about 4 psi and 10 p s i .

FILTER CHAMBER AN!) O R I F I C E

t h u counp onents In the f ii t u r chamber are shown in F igure 5. Thechamber c o n s i s t s of a l u c i t e tube w i t h 1/16 inch wa l l th ickn ess and one inchou t e r — d i i ~~c t e r . I t is about e i gh t inches long . The ends are closed w i t h #4r ub b e r s t o p per s . The cy l inder is mounted ve rt ically and the bottom five ors ix i n c h e s are f i l l e d with three m i l l i m e t e r diameter glass beads to act as V

a r il ter .

The top stopper is penetrated by two hypoderm ic needles and twoluc it~- tubes. Holes for the lucite tubes can be made with cork borers. Oneof the tubes reaches to within about 1/2 inch of the bottom stopper and servesas the gas inl e t. The other tube reaches only a fraction of an inch belowthe top stopper and is connected to the manometer to permit measurement ofthe prt•ssur~• developed in the chamber. Roth tubes are made of 1/16 inchw a l l thickness L u c i t e and have 1/4 inch ou ter d iameters .

The hypodermic needles are i d e n t i f i e d as “ local anesthesia needles(45 L N R ) 22 gauge x 2 1/2 inches ’ . They serve as a double or i f ice through

* The use of epoxy in the connector is not e n t i r e l y s a t i s f a c t o r y sincei t does not bond to the d i s c o n n e c t s . However , the j o i n t is u s u a l l ygas proof it the p re s su re s encountered in t h i s a p p l i c a t i o n .

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U N C L A S S I F I E D 9

F which the f i l t e r e d gas escapes and therefore determine the s e n s i t i v i t y of thesys t em. A t u l l y charged cell , with p e r f e c t separa tor and be ing charged at20 amperes , produces gas at a r a t e s u f f i c i e n t to give pressure of approx—i m a t elv 0 .46 psi in the chamber .

The h y p o d e r m i c needles may be inser ted b y mere ly f o r c i n g themth rough the s t o p p e r . However , t h i s procedure r e q u i r e s grea t care to avoid

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b e n d i n g the n e e d l e s . A more s a t i s f a c t o r y method is to f i r s t inser t a morerobus t (17 gauge) needle in the o p p o s i t e d i r e c t i o n . The r equ i red needle is

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t h e n i n se r t ed i n t o the po in ted end of the large need le . The l a t t e r is w i t h — V

drawn , leaving the des i red need le in p lace .

I t was found tha t the h ypodermic needles were not exac t ly ident icalcaus ing v a r i a t i o n s in s e n s i t i v i t y f rom channe l to channel (some obviousvariations in needle length were observed) . P rocedures f o r min imiz ing thesevariations are given in the section on calibration .

MANOMETERS

The manometers are made of lucite tubes having 1/16 inch wallthickness and l/~ inch inner diameter (smaller diameter tubes give troubledue to capillary effects and bubble entrapment). Details of the shape anddimensions are given in Figure 6. The lucite tube may readily be hea ted andbent but precautions are necessary to prevent the heated tube from collapsingand to avoid development of strains in the bends. The latter may result incracks either soon after cooling or after intervals of up to several months.

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One convenient method to prevent collapse at the bend is to fillth e tube with table salt and stopper the ends , before heating and bending .Bends made by the following procedures were crack resistant: A jig consistingof a slotted 1/2 inch hoard with rounded corners in the slot and with short V

side guides as shown in Figure 7 is used to aid in making uniform bends. Thesalt filled tube of proper length is rotated over the jig by one person while

‘V another heats the tube at the desired location by use of a heat gun (such asis used for shrinking shrinkable sleeving). When the tube is heated suffi—ciently it softens to the point where it is unable to support the weight ofthe extended end. Heating is then discontinued and the tube is bent over theslot in the jig. It is held in position and allowed to cool slowly untilrigid. The bend is then annealed by insertion into boiling water for about5 minutes. To prevent any change in the bend during this treatment the U isclamped suitably. After the heating the tubes are allowed to cool slowly toroom temperature .

The length of the manome te r as shown in Figure 6 , when used w i t hthe fluid described helow and with the chamber orifice described above , is

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suitable for measuring gas flow rates expected when cells are charged atcurrents not exceeding ahout 35A .

The I luid used in the manometers is made up of one part water t o V

four parts of glvcl r in. This mixture was chosen because it is not i n f l a m m a b l e ,

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Marker: Hi g h Density Polyet h y lene Tubing, 5/ 16” OD,1/ 4 ” long, sp lit long itudinall y

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has the right viscosity for this application (i.e. it is neither too sluggishnor too “splashy”) and does not evaporate rapidly . In addit ion dyes are usedto colour the f lu id d i f f e r e n t colours , making adjacent groups of four thesame colour . This is done to aid the operator in correlating manometerreading wi th cell n umber. Small quant i t ies of gauge oil are added to thesurfac e of the main fluid in both legs of each manometer to still fur ther V

reduce the water evaporation . (Gauge oil is inflammable therefore only smallquantities of it are used). Specific gravity of the glycerine water mixtureis approximately 1.2.

The fluid may be made up as follows (quantities are suitable forone 20 channel u n i t );

Mix 200 ml of Glycerin with 50 ml of distilled water.Di vide this mixture into Uwo equa l portions . To oneof these add 0.5 ml of Shirriff orange food coloringor equivalent and stir until uniform color is obtainedthroughout the mixture. Similarly, add 0.5 ml ofSalada Green food coloring or equivalent to the secondportion.

Sliding markers are clipped on the manometers to permit rapidmark ing of readings , to permit observation of trends etc. The markers aremade by cu t t ing 1/4 inch lengths of 5/16 inch OD , 1/16 inch wall thickness ,high density polyethy lene tubing. Each is opened by a longitudinal cut .

S It is convenient to insert the fluid into the manometers by use ofa syringe with an attached length of tubing . The tubing is inserted to thebot tom of the manometer and is withdrawn as the f lu id is injected . Thisavoids the t rapping of bubbles and wet t ing the upper parts of the tubes.

INTERCONNECTIONS

Gas t i g h t connect ions between the cell attachmen t fitting and thef i l t e r chamber and between the manometer and the f i l t e r chamber are made bymeans of Tygon 1/4 inch ID , 3/8 inch OD tubing . A s l ight problem is encount—ered in tha t the manometer outside diameter is larger than the inside diameterof the tub ing . This is solved by hea t ing the end of the tubing for about aminute in boiling wa ter and stretching it slightly by inser ting long nosedpliers and open ing them sufficiently. The tubing may then be forced on themanometer tube and a good seal results. Connections to the small tubes inthe filter chamber are easily made but are frequently not gas tight. Theseconnections are therefore improved by ty ing lacing tape tightly around them .

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THE STRUCTURE

The structure carries all of the parts of the separator conditionmeter except the modified vent caps. It is made of lucite te give resistanceto attack by electrolyte and to render various parts of the system visiblefor easy inspection. The basic dimensions are shown in Figure 8.

The front part of the structure is provided with a recessed portionto permit the inser tion and removal of calibra tion char ts mounted on a suitablepanel. This facilitates use of appropriate calibrations for different charging

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rates as well as observation of the back leg of the manometer tubes ifnecessary .

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The back panel is made detachable to facilitate the removal ofindividual filter chambers should this become necessary , as , for example , toclean the filter beads (if the tub ing connecting the filter chamber to themanometer is long enough , the chamber may be lifted out without removing theback of the structure).

CALIBRATION

The term “calibration” is used here to imply two separate activities.One is the fine adjustment of sensitivity of the channels to get more or lessuniform response from channel to channel. The other is to produce one or morescales against which to read the manometers in terms of percentage of theoret—ical maximum gassing—rate .

Since the sensitivity is determined by the hypodermic needle V

orifice , if the needles were comp le tely uniform no differences should appearbetween channels. However , differences sufficiently large to attract attentionsometimes do occur . These differences may be minimized by taking advantageof the double needle arrangement . A constant gas rate source such as the

V reference gas cell* is operated to give a gassing rate in the vicinity of fullscale . This is connected to each channel in turn and the manometer height ismarked with the markers. Channels giving obviously low readings are checkedfor leakages at the various joints.

Af ter any leaking joints are repaired , these channels are testedagain and the manometer levels are marked . Obviously high channels , if any ,are then checked for needles with obstructions (wires for cleaning are norm—

S ally supp l ied with the needles).

* A cell similar to the nickel/cadmium vented cell except that all ofplates consist of sheets of stainless steel.

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If some channels now give higher and lower levels than the m a j o r i t y ,the deviations are minimized as follows. The gassing rate from the source isadjusted to about one—half its previous value. Needles in the offendingchannels are then blocked off , one at a time, and the resulting manometerreadings are noted and recorded if necessary . This makes it possible to listneedles which give high readings and needles which give low readings . Singleneedles are then switched between channels to alter the sensitivity in thedesired direction (for instance if it is found that one channel has twoneedles which both tend to give high readings , one of these is exchanged witha needle from a channel where both needles tended to give low readings).Occasionally a needle must be discarded and a new one used in its place .

Construction of a reading scale is fairly simple if the referencegas cell or other source of known gas flow is available. A suitable sheetof paper or other material (supported on cardboard etc. if necessary) isslipped into the recess behind the front legs of the manometers (see sectionon “The Structure”). One channel is connected to the gas flow source flowingat the rate selected as the 100% base (assumed to be 16 A in the unit describedhere). The manometer level attained is marked on the scale. The materialmay then be removed from the structure and a horizontal line is drawn through V V

the marked point. Since the needed scale is linear , other lines as desiredmay be computed and drawn.

CLEANING

Cleaning may occasionally become necessary. This applies particu—larly to the attachment fittings which may become blocked with carbonate orother materials. Such material is usually readily soluble in water so periodicrinsing in a container of water is normally sufficient . This may be donewithout detaching those components which are fastened to the tubing .

If a significant amount of liquid collects in the filter chamberthis should be emptied , and the beads should be washed in distilled waterand replaced . This may be done by first lifting each chamber out of itscompartment (removal of the back panel of the structure may be necessary orconvenient), and removing the bottom stopper. The beads may be caught in acontainer and washed . When the beads are relatively dry they may be pouredback into the chamber by tilting the bottom of the chamber upward and usinga suitable funnel. The bottom of the funnel stem should reach beyond theopening of the gas entry tube to avoid beads being trapped in the tube . To S

avoid the same problem with the tube leading to the manometer , a suitablewire may be inserted into this tube through the bottom of the chamber beforethe funnel is put in place. When the beads have been inserted and the funnelremoved , the cylinder may be held in a nearly horizontal position while thewire is slowly withdrawn and the stopper replaced .

An important cleaning task may arise if the hypodermic needlesbecome partly blocked . This causes the readings given during use of thechannel to be higher than normal and may be readily identified by interchang-ing channels on a given cell and comparing the readings (or by using a reference

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cell and a known charge current). The hypodermic needles are normallysupplied with cleaning wires which may be inserted several times to dislodgeblockages . It may also be advisable to periodically clean the needles byusing a syringe to force distilled water through them.

I

ACKNOWLEDGEMENTS

The contributions of Messrs P. Willis , R. Schupe , B. Valiquette ,and C. Brown in overcoming technical problems are gratefully acknowledged .

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REFERENCES

1. K. Feldman , R.L. Haines and R. Hayashi, Nickel/Cadmium Aircraft Batteries:Failure Prediction in Battery Shops by Gassing Rate Measurements, DREOTechnical Note No. 76—12. A brief version of this paper was also releasedas DREO Report No. 739 for presentation at the 27th Power Sources Sym—posium, Atlantic City , New Jersey, 21—24 June, 1976.

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APPENDIX I

PROVISIONAL PARTS LIST*

1. Nalgene Quick Disconnects (Fisher #15—3l5A) 20 only

2. Ni/Cd cell vent caps with rubber rings 20 only

3. Hypodermic Needles (45 LNR) 22 gauge x 2 1/2 inches 40 only

4. Class Beads, 3 mm diameter (Fisher #ll—312A) 3 1/2 lb.

5. Rubber Stoppers , #4 40 only

6. Glycerine 1 pint S

7. Lucite Tube, 1” O.D., 1/16” wall thickness 18 ft.

8. Lucite Tube, 1/4” O.D., l/16”wall thickness 24 ft.

9. Lucite Tube, 3/8” O.D., 1/16” wall thickness 60 ft.

10. Gauge Oil 1 oz.

11. Rubber Tubing, 11/16” 0.D., 3/32” wall thickness, AmberNatural Rubber 2 ft.

12. Tygon Tubing , 3/8” OD., 1/16” wall thickness, AmberNatural Rubber 80 ft.

13. Lucite Sheet , 1/2” thick Approx 2 ft x 4 ft

14. Lucite Sheet , 1/4” thick Approx 1 ft x 2 ft

15. Lucite Sheet , 1/8” thick Approx 1 ft x 2 ft

16. High Density Polyethylene tubing 5/16” O.D 1 ft.

17. Shlrrif Orange food color (available in food stores) 0.5 ml

18. Salada Green food color (available in food stores) 0.5 ml S

* This list is provided for preliminary planning purposes. It is based on alaboratory model and items 13 to 15 inclusive are approximate only . Details

relating to the construction of the laboratory model are presented forillustrative purposes.

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Defence Research Establishment Ottawa I—- UNCLASSIFIEDNational Defence Headquarters ~b GROUP

Ottawa K1A 0Z4 N/A3. DOCUMENT T ITLE

Nickel/Cadmium Aircraft Batteries: Multichannel Gassing—Rate

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ENT DATE - -- ‘-‘ ~~~~~~~~~ ‘~~‘ 7a T O T A L NO OF PAGES 7h NO . OF RE ES

//~ MAR i~~ 77 ~~~ ~~~~- 1~41~T 18

- PROJEI R GRIt~~I NO. 9a ORIGINATOR S DOCUMENT NUMBER(5I

54—03—07 -

DREO TECHNICAL NOTE NO. 77-5

8b CONTRA CT NO 9b. OTRER DOCUMENT NO.(SI (Ar t y other rumbe s that as beas s S gne d thSS documer rt (

10. DISTRIBUTION STATEMENT 1~~ R ~~ ~~~~~~~~~~ 7 ~~~— -:

UNLIMITED DISTRIBUTION ~~~~~~~~~~ -~~~~ S

11 SUPPLEMENTARY NOTES 12. SPONSORING A C T I V I T Y

t3 AB ST RA~~~~~

D~~ SE

The instrument described is used to assess the state of health ofseparators in nickel/cadmium aircraft batteries and thus to permit removalfrom service of those cells which may be expected to fail catastrophicallyin the near future. Twenty channels are provided to permit simultaneous , -

observation of all cells in a complete battery . Each channel measures therate of emission of gas from one cell during overcharge by means of thepressure build up in a chamber from which the gas escapes via a suitableorif ice. Construction, calibration and cleaning are discussed.

(UNCLASSIFIED) r L/

USIS 5”

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UNCLASSIFIED -~~~

S.surity C Ias, ,~ ,c a t S o n —

K EY WORDS

GASSING RATE METERMULTICHANNEL METER

NICKEL/CADMIUM BATTERIESSEPARATOR HEALTH

INSTRUCTI ONS

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