CA1230378A

CA1230378A - Device for indicating the fully charged state of a battery

Info

Publication number: CA1230378A
Application number: CA000479321A
Authority: CA
Inventors: Heinrich Rabenstein; Klaus Gummelt; Klaus Salamon; Jurgen Schulz
Original assignee: VARTA Batterie AG
Priority date: 1984-04-18
Filing date: 1985-04-17
Publication date: 1987-12-15
Also published as: NO161705B; DE3563798D1; NO161705C; FI79421B; NO851194L; FI851436L; DK165385A; EP0161398A1; US4642600A; ES286107U; DE3414664A1; ATE35739T1; DK165385D0; EP0161398B1; FI79421C; DK172487B1; ES286107Y; FI851436A0; JPS60235374A

Abstract

Abstract of the Disclosure The temperature rise associated with the catalytic recombination of battery gases at the end of the charging process is converted into an electrical signal suitable for checking and controlling charging in a temperature-sensitive component such as a commercially available NTC or PTC resistor coated with a PTFE-bound palladium-activated carbon mixture. An additional activated carbon layer protects the catalyst from poisoning by the stibine present in the battery gases.

Description

~3~37~ 21~94/387 The present invention pertains to a device for indicating the fully charged state of a battery, especially a lead-acid storage battery, by determining the temperature of a recombination catalyst. It is known that both excessively strong and excessively weak charging current levels are harmful to the life of a lead-acid storage battery. Generally, the charging of starter batteries and the like is controlled in accordance with voltage. However, voltage is not always a clear indication of the fully charged state because voltage is also influenced by other factors, such as by aging of the battery. However, a lead-acid storage battery is always certain to be fully charged when oxygen and hydrogen evolve from the positive and negative electrodes in a stoichiometric ratio. Since this event is immediately imminent when a rise in temperature occurs in a hydrogen- and oxygen-recombining catalytic device, such a temperature signal has been used to control the charging process. DE-OS No. 26 38 899 published on March 2, 1978 in the name of Norbert Fiedler, inventor teaches that a lead-acid storage bat-tery will generally lack approximately 10~ of the amount of current needed for full charging at the time when the evolution of gas begins. This current is supplied in the form of an aftercharging current, the duration and intensity of which are set in a preselectable ratio with respect to the parameters of the original charging current. The time of the switch-over from the main charging phase to the aftercharging phase is determined by detecting the ,~'' ~ ~ 7~ 21~94/3~7 temperature rise occuring in a recombination device, which serves as a regulating variable. To this end, DE-OS No. 30 20 606, published on December 4, 1980 in the name of Nissan Motor Co., Ltd. which pertains to a data collection device for an automobile, teaches that a temperature signal sent from a catalytic converter is capable o~ being fed into a control circuit along with a battery voltage signal to provide such regulation. The present invention has as i-ts primary object to provide a device which operates on -the principle of gas recombination, and which permits the heat of reaction induced by recombination to be detected promptly, without major measurement procedures, to convert the heat of reaction into a signal which can be received by a voltage regulator. Fundamentally, a number of electronic components can serve such a purpose. The following are mentioned as illustrative examples: temperature-sensitive diodes; transistors; thermistors or hot-carrier thermistors, i.e. semiconductors whose electrical resistance is dependent on temperature in such a way that their conductivity increases in a hot state and decreases in a cold state; the so-called PTC resistors, which operate in the opposite sense; thermo- couples based on poorly eondueting eopper-nickel alloys (eonstantan); or a platinum resistor, e.g. the "Platin 100" resistor, which has a defined resistance of 20 Ohms at 100 C~ However, the use of such thermoelectric "sensors" is often limited by a chemically aggressive environment. --2-- ~30~78 In practice it has heen fo-lnd that a hot-c~rrier thermistor, characteri%ed by increasing electron transmission with rising temperature, also known as an ~lTC conr3uctor (~ITC = Negative Temperature Coefficient), is particularly a-1vantageou.sly user3 according to the present invention. ~s an alternative, one m~y use a PTC resistor, which operates as an electrical resistor at elevater3 temperature, but which is capable of switching oEE the charGing current in accordance with the recombination reactlon used. It is particularly advantageous to initially heat such a PTC resistor, to ensure that the recombination catalyst alwa~s remains dry, and tnat the recombination catalyst operates without delay at the end of the charging cycle. These components are then coated with a catalytically active substance, in any oE a num~er of diEferent ways. ~owever, it must always be en.sured that at least the surface area oE the component which extends between the contacts be kept free fro~ metallic conductinrJ material in order to prevent the formation of a short clrcuit shunt. This is especially so in view o- the use oE a pallar3ium catalyst, as is preferred in accordance with the present invention. The risk of forming a short-circuit shunt will occur, for example, in the case of galvanic application of a precious metal, if the deposition is carried out under conr3itions which are favorable to a higl nucleation rate, i.e. high current density, high bath concentration, and high temperature. ~qasking oE the surface areas to be protected with a lacquer is reco~1mended in such case. ~ther processes Eor catal~st application are preferably preceded by coating oE the hot-carrier thermistor or PTC resistor with a nonconr3uctinrT plastic. 7~ 21894-387 It is also advantageous to cover the catalyst- containing layer with an antimony-adsorbing layer in order to prevent premature poisoning of the catalyst due to the adsorp- tion of antimony from the stibine which is inevitably present in the battery gases. Activated carbon serves as an especial- ly effective adsorbent. The activated carbon can also be the actual carrier for the precious metal catalyst, if desired. The additional layer of activated carbon also serves as a diffusion barrier, to prevent explosions (an ignition break- through barrier). Broadly, the present invention provides a devicefor indicating the fully charged state of a storage battery, especially a lead-acid storage battery, by determining the temperature of a recombination catalyst, comprising a temper- ature-sensitive electronic component whose surface is provided at least partially with catalyst ma^terial~ and is adapted for exposure to the battery gases. More particularly, according to one aspect the invention provides a device for indicating the fully charged state of a storage battery, especially a lead-acid storage battery, by de-termining the temperature of a recombination catalyst, comprising a temperature-sensitive electronic com- ponent from which extend electrical leads and ha~ing an outer surface which is provided at least partially with catalyst material and is adapted ~or exposure to the battery gases, wherein the catalyst material is covered with an antimony- adsorbing layer. According to another aspect, the invention provides a device for indicating the ~ully charged state of a storage battery, especially a lead-acid storage battery, by determining --4-- ~3~ 2189~-387 the temperature of a recombination catalyst, comprising a temperature-sensitive electronic component from which e~tend electrical leads and having an outer surface which is provided at least pariially with catalyst material and is adapted for exposure to the battery gases wherein the catalyst material is comprised of a mixture of carbon and palladium. Further detail regardlng a device according to the present invention may be had with reference to the detailed discussion provided below, with reference to the following illustrations, in which: Figure 1 is an enlarged perspective view, in partial section, of an NTC conductor prepared according to the present invention; and Figure 2 is a fragmented, perspective view of a vent plug with an NTC conductor passing through it. A commercially available design of the NTC conductor is that of a flat cylinder with a diameter of about 4 mm and a height of about 1.5 mm, having leads attached to top and bottom sides thereof. With reference to Figure 1, such a hot-carrier thermistor 1 is covered with a thin plastic or lacquer coating ~4a- ~so that the entire region around the lea~l-throuqi~ points ~ OL the leads ~ is left free from catalyst metal, in order to prevent short-cireuit bri~es from forming. In accordance with the present invention, the remainder 0~ ri!e hot-earrier ther~istor 1 earries a eatalyst layer 4 (preferably a carbon/palladium catalyst), which is in turn covered by an antimony-ad~sorhin~ activated earhon layer 5. Ilhen plaeed in operative assoeiation with the batt~ry, it is important for the temperatllre-sensitive eo~ponont aecording to the present invention to be plaeed soas to be prol~erlv aceessed by the gases evolved dllring battery charging, but so as to prevent the access of aeid mist. ~ILth reference to Figure 2, the hot-carrier thermistor l is, for examplo, preFerably positioned underneath one of the gas release plugs 5 of the battery, so that the leacls extend through holes provided in the release plug 6 as shown. The leads of the deviee are then couplo(l to an appropriate charging controller (not shown). NTC conduetors aceording to the present invention are ~l.so advantageously placed in the gas eollecting pipes associated with the cells oE some types of batteries. Catalyst coatings ~ accorr~ing to the present invention for the hot-earrier thermistor 1 will now be explained in ~urther detail, based upon two examples. E~ample 1 In a Lirst step, the hot-earrier thermistor was eoated with a thin insulatinc~ layer, by dipping into a s~yntlletie resin. ~lterllativelv, a PTF~ or PVC coatin~ call ~e applied in the form of a spray. --5-- ;378 In a second stc~, the coated hot-c.lrricr therrnis'or was then 3ipped into a paste, prepared by mixing 75 g activa~e~3 carbon ~ith 25 g PTFY in 1~0 mL ~2~ with 10 mL of a 5?6 P-lCl~ solution added. Contamination oE the area around tne contacts was avoided as previously described. ~ third step was to dip the hot-carrier therrnistor into a strongly reducing rnedium, e.g. a sodium borate solution. Palladium precipitates in this process in very finely dispersed forrn. If desired, it is possible to then dip t'ne prepared hot-carrier thermistor in an activated carbon paste which has been prepared, for exampl~, from 100 g activated carbon powder and 160 ~L of a 0.7% aqueous carboxymethyl cellulose (Tylose) solution. ~ he hot-carrier thermistor was ready for use after subsequent drying for 2 hours at 11~C. ~xample 2 The hot-carrier ther~istor of Exa~ple 1 was a~ain coated with a plastic layer. Separately prepared was a mixture of 100 g activated carbon, 135 ~L water, and 11 ~L of a 5% PdC12 solution, mixed with 10 ~L of a 30% sodiu~ hydroxide solution in which 0.5 g so-liu~ borate was dissolved, to reduce the PdC12. The hot-carrier thermistor was ilnmersed into this paste while leaving free the contact areas, such that the catalyst material was applied in an already activated state. Drying was carried out at lnnC. ~ ~ad~ ~ark 3~ The c~talyst-containing coatin~ material ~"as cem-nte~3 onto the plastic-coated hot-carrier thermistor in the forrn of a pi,ll . ~ ombining recombination an~ temperature indication in one small component has the advanta~e that the component can be manu~acture~ at lo~ cost, an-l requires very little s?ace in use. Equally important is the Eact that the response time of the device is very short due to t'ne lo~ heat capacity and the low heat transmission resistance between the recombination me~ber and t~e temperature-sensitive component.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS: 1. A device for indicating the fully charged state of a storage battery, especially a lead-acid storage battery, by determining the temper- ature of a recombination catalyst, comprising a temperature-sensitive electronic component from which extend electrical leads and having an outer surface which is provided at least partially with catalyst material and is adapted for exposure to the battery gases, wherein the catalyst material is covered with an antimony-adsorbing layer.
2. The device of claim 1, wherein the electronic component is a temperature-sensitive resistor.
3. The device of claim 1, wherein the catalyst is a mixture of carbon and palladium.
4. The device of claim 1, wherein the antimony-adsorbing layer is comprised of activated carbon.
5. The device of claim 1, wherein the electronic component is coated with a nonconducting material at least in the region of the electri- cal leads.
6. A device for indicating the fully charged state of a storage battery, especially a lead-acid storage battery, by determining the temper- ature of a recombination catalyst, comprising a temperature-sensitive elec- tronic component from which extend electrical leads and having an outer surface which is provided at least partially with catalyst material and is adapted for exposure to the battery gases wherein the catalyst material is comprised of a mixture of carbon and palladium.
7. The device of claim 6, wherein the electronic component is a temperature-sensitive resistor.