Battery Issues with PMAC ISA 0 pages

Application Note

PMAC boards utilize small lithium batteries to retain user programs and buffers in PMAC memory during periods when external power is not applied. The batteries come in two styles: a 2/3 A-size battery on older versions of the PMAC PC and PMAC VME, or a can-stack battery on all other versions of PMAC. This note covers several issues regarding the batteries that may be of concern to PMAC customers. >

Composition

The PMAC batteries contain a lithium metal anode and a carbon cathode which are separated by a non-
woven glass fiber separator. These are contained in a stainless steel casing with a thionyl chloride (SOCl2) electrolyte. There are no heavy metals used in the casing or active components: no mercury, no lead, and no cadmium. The average open-circuit voltage is 3.7V. The electrochemical reactions are: Anode: 4Li = 4Li+ + 4e Cathode: 2SOCl2 + 4e >
- = SO2 +4Cl >
- + S Net: 4Li + 2SOCl2 = 4LiCl + SO2 +S >

Safety

The chemistry used in lithium batteries has at least the theoretical potential of explosion under some circumstances. The battery manufacturers that Delta Tau uses for PMAC have taken great care that this will not happen. The batteries used in PMAC have Underwriters Laboratory (UL) certification. As the most prominent safety testing body in the United States, UL performs extensive testing of equipment under both normal and abusive conditions. For batteries, this includes prolonged short-circuit testing. The PMAC batteries survived the short-circuit test without failure җ test results indicate a 1A current draw and 25C temperature rise under these conditions, well within design specifications. >

Transportation

Some institutions place restrictions on the air transport of some large lithium batteries. The United States Department of Transportation (USDOT) exempts all lithium batteries that contain less than one-half gram of lithium from any restrictions. The batteries used in PMAC fall into this category, and so are exempt from any USDOT restrictions on air transport. Even so, these batteries have passed the testing procedure used to certify larger lithium batteries as safe for all types of air transport. These tests include low pressure testing to 15,000 m (50,000 ft) equivalent, shock, vibration, and temperature testing. >

Disposal

Some localities consider used lithium batteries from industrial use to be hazardous waste, and therefore illegal to dispose with normal refuse. Companies should check with local, state, and national disposal regulations for proper methods of disposal. Neither Delta Tau nor the battery manufacturer is aware of any lithium battery recycling programs. Delta Tau will accept used batteries from PMAC customers at no charge to the customer. Customers interested in doing this should contact the factory for a Return Material Authorization (RMA) number before sending the batteries. A company specializing in battery disposal is BDT Inc. of Clarence, New York. Their phone number is (716) 634-6794; their fax number is (716) 634-6749. >

Battery Life

The PMAC batteries have a capacity of 1 Ampere-hour (1 Ah). They are used to retain the contents of the three static RAM ICs on PMAC when 5V power is not present. There is no measurable current draw on the battery when 5V power is applied, so only PMAC off-time counts against battery life. The batteries have a conservatively rated shelf life of eight years, so they should not be counted on to provide power after this time, even if they have not been fully drained. >
Battery with PMAC ISA 1 size="-1">