Despite the numerous sonic and engineering advantages of Jeff Rowland Design Group’s DC Power Supply (DCPS), some concern has been stated regarding premature battery failure and acid spillage. This uncertainty is understandable considering previous experiences with, and the reputations of, others; but it is nonetheless unfounded with the DCPS.Rechargeable batteries can give many years of faithful service(1) - or they can fail in an annoyingly short time.

Battery manufacturers’ specification sheets predict hundreds, even thousands, of charge/discharge cycles and many years of service. Still, many people find six months or a dozen or so cycles in everything from children’s toys to cordless appliances to be more typical. Why is there such a discrepancy?In fact, secondary (rechargeable) batteries can indeed last a very long time if properly applied. Poor charge management(2) more than anything else is responsible for the difference between laboratory life and life in hands of the consumer. Many otherwise intelligent engineers do not appreciate the crucial importance of accommodating the needs of the battery. The few who do are often forced to submit to the pressure of the marketplace for smaller, lighter and cheaper products, without regard to service life.

The widespread use of Nickel-Cadmium (NiCad) chemistry is a good example of a charge management nightmare. NiCads are very particular about how they are used. Expensive custom microcomputer chips are even available that are programmed solely to predict just how much charge a NiCad wants or can stand at any given moment.
NiCad misuses are numerous: Charge or discharge too fast and they overheat and then vent or rupture. Discharge them too deeply and the weaker cells(3) of the battery suffer reversal(4). Partially charge and discharge them repeatedly and they "remember"(5) this service and do not deliver full voltage throughout their discharge. If mounted too close to a heat source such as the charger and they fail prematurely. (Heat in general is a major enemy.) Charge them for too long and the grow internal shorts and fail.

NiCads can be charged too slowly as well. The perfect trickle charge rate for a brand new NiCad will not keep up with its much higher self-discharge(7) rate when it is older. NiCads are particularly bad in this regard. Left untouched, the go flat in a few months when new and go flat in a few days near the end of their service life. Since they always seem to be-dead when needed the most, people tend to charge them continuously. This can destroy a NiCad in just a few months, yet some manufacturers even recommend or design in this kind of torture!

There are only a few applications where NiCads truly excel. For example, in a night watchman’s flashlight, Nickel-Cadmium can potentially deliver many more deep discharge/charge cycles than can competing chemistries. The watchman’s job provides the ideal charge management: The battery is mostly discharged through the watchman’s shift and gets just the right 12-16 hour C/10 (8) charge by the next day, with plenty of opportunity to fully charge; no time to overcharge; no time to go dead from self-discharge; gentle discharge; little opportunity for cell reversal or memory; and always ready when needed.In the face of such challenges, why should you believe that Jeff Rowland Design Group’s DC (Battery) Power Supply will provide a long and trouble-free life? As with all Jeff Rowland Design Group products, the answer is simple: The same skill and vigorous attention to detail that distinguish our amps and preamps has also gone into the charge management of the DCPS.Starting with the battery chemistry, a proven and much more manageable type called absorbed-electrolyte Sealed Lead Calcium (SLC) was chosen for the DCPS. Unlike NiCad, which gives no reliable indication of its charge needs, the terminal voltage of an SLC battery will rise significantly, repeatedly and dependably as full charge is approached. Better still, SLC "first cousin," the flood-electrolyte Lead-Acid (LA) battery, enjoys a reputation of lasting up to several years in the brutal environment of an automobile engine compartment. In the more civilized indoor world of a home audio system, SLC has the potential to last even longer than LA.

However, unlike a Lead-Acid car battery, SLC batteries simply cannot leak! In a car battery, the lead and lead-sulfite grid plates sit in a bath of sulfuric-acid electrolyte and no sealing scheme has thus far completely eliminated the possibility of leakage. With SLC there is no bath of acid to spill. A small amount of electrolyte is absorbed by the plates and separators-about as moist as a flashlight’s dry cells. Even if the SLC battery was cut open, no acid would pour out.Another advantage of the absorbed-electrolyte (sometimes called starved-electrolyte) technique is freedom from "sulfation." If a Lead-Acid car battery is run totally flat, its plates often become coated in a way that prevents the battery from ever accepting a charge again. This is not a risk with SLC batteries, since there is slightly less electrolyte present than is necessary to totally deplete the plates of lead-sulfate. From the plate’s point of view, the battery is never quite fully discharged.Cell reversal is as important a concern for SLC as it is with NiCad, but is much more manageable. SLC offers about 67% higher cell voltage at 2.0 volts per cell versus NiCad’s 1.2 volts. This means that an SLC battery’s voltage can drop substantially lower before the first cell reverses, making low-battery detection easier and more accurate. There are also 40% fewer cells to seal and interconnect for a given battery voltage.Utilizing a battery chemistry ideally suited to its task would not be of much benefit if it was abused by the charger. Jeff Rowland Design Group’s charge management method includes voltage regulation, current limiting and ripple filtration designed and built with the same care as if it was the amplifier’s main power supply.Voltage regulation ensures that the battery is maintained at precisely a full charge when the amplifier is in standby mode. Most common chargers are unregulated and tend to overcharge the battery when the line voltage is high and undercharge when it is low. Either case is ruinous to any battery chemistry.

Any time an SLC battery is below full charge, it will demand as much current as the charger can deliver. Since very high charge rates are inefficient and heat both the battery and charger, current limiting keeps the charge rate under control.
Ripple filtering is one of the most often overlooked elements of charger design. In either cyclic or trickle duty, filtering is relatively unimportant: The charger’s rectifier turns AC power from the mains and transformer into pulsating DC-60 pulses per second for a half-wave rectifier and 120 for a full wave. Each little surge of current through the charger’s rectifier simply adds to the battery’s charge. Float duty is quite another issue. Without filtering to smooth out the pulses, the battery goes through mini-charge/discharge cycles with each pulse and pause between the pulses. Although individually tiny, these cycles happen thousands of times an hour and cumulatively add up to a lot of wear on the battery.After taking care of all the elements of good charge management, battery life comes down to charge/discharge cycles and battery temperature. Sealed Lead Calcium batteries are normally good for better than 200 deep cycles (discharged fully and recharged). Even this large number is probably low for an SLC, since many more, shallower cycles represent typical ampIifier use, and the charger also contributes largely to the amplifier’s power needs. It would seem that half the depth of discharge would yield twice as many cycles; actually, it is even better than that. Cycle life improves exponentially as the depth of the cycle is reduced(9), so most DC supply owners will not "wear out" their batteries.Heat is a battery’s worst enemy. Sealed Lead Calcium batteries are well sealed, as it is not practical to employ a true hermetic (impenetrable) seal. This means that, over time, water molecules from the electrolyte slowly migrate through the battery’s case. After many years, failure occurs because of moisture loss. Failure is slightly quicker in ultra-low humidity environments, but it is temperature which exacts the greater toll. Every degree above the listening room’s ambient temperature quickens a battery’s eventual failure. Therefore, mounting a hot load such as the amplifier in the same box with the battery is highly undesirable. Normally this would also be the case for a heat source such as the charger, but the Jeff Rowland Design Group DCPS uses the same type of machined aluminum chassis as the amplifier. Given the relatively small amount of power dissipated by the charger and batteries, the temperature rise is similarly small. Keeping the DCPS and the amplifier away from heating ducts, direct sunlight and other heat sources will ensure a very long battery life.Since they have advantages, why are SLC batteries not more widely used? Quite simply, they cost a bit more and are slightly heavier than other batteries for a given storage capacity. We at Jeff Rowland Design Group believe that the potential for years of trouble-free service easily outweigh any aspects of their weight and cost.

(1) Battery life in this discussion refers to service life, which is a measure of how many cycles or years a secondary (rechargeable) battery lasts until it will no longer accept or hold a charge. This is distinct from capacity, which describes how much energy a battery holds.

(2) Charge management refers to how a secondary battery is charged and discharged. Much attention is paid to the charger and how it restores the battery’s charge; but we are really talking about an all-encompassing view of how the battery serves its product and also how it is treated.

(3) Actually, the word "battery" is often misused. A "D" cell is a single cell and, technically, not a battery. However, a flashlight can contain a battery of two or more cells. A nine-volt transistor radio battery is indeed a battery since it is made up of several cells connected together.

(4) Cell reversal happens when the weakest cells of a battery "go flat" first. The current flow from the stronger cells still travels in the same direction, but is now effectively backwards through the dead cells, charging them in reverse. When the battery is recharged, the reversal is usually corrected but the weak cells have become even weaker and will be more badly reversed in the next deep cycle.

(5) "Memory"-effects (more accurately called voltage depression) are much less a problem now. However, in spite of battery manufacturer claims to the contrary, this effect has merely been reduced, not entirely eliminated.

(6) There are three general categories of battery charging. In cyclic service the battery is alternately discharged (as with a night watchman’s flashlight battery). A cyclic charge rate can be fast or slow, but if the charging is primarily to keep the battery fresh in the face of its self-discharge, then it is called trickle charging. However, if the charger has to maintain the battery while a load is present on the battery at the same time, it is called float charging.

(7) Just sitting on a shelf, all batteries eventually go dead, some substantially faster than others. The shelf-life of Lithium primary (non-rechargeable) cells is so good that better than 90% of their energy is intact after ten years. But the newest entry in the rechargeable field, Nickel Metal Hydride, has a self-discharge rate so high that it loses up to half of its energy in just a month.

(8) Charge rates are often described as a ratio withe the ampere-hour capacity. In other words, C/10 would be a one amp charge rate for a ten amp-hour battery. Add a few extra hours for good measure and you have a proper overnight charge but far too much for a continuous trickle charge.

(9) Very approximately, cycle life increases by 10 raised to the power of one, minus the depth of discharge. For example, how many 25% discharge cycles can be provided by a battery rated for 200 deep cycles? 200 x 10E(1-0.25)= 1125.