Upon arriving in the field with a suite of astronomy gear that must be set up before nightfall, an astronomer has a lot of work to do, often in a short amount of time. The considerations discussed in this section are an essential part of how an astronomer gets the job done on time and how the job gets done correctly. These considerations apply to all the astronomer’s equipment, batteries included. And finally, as no battery lasts forever, we will close out this series of articles by discussing factors that can limit a battery’s useful life.
Before going into details, description of commonly encountered power solutions is in order. I use the term “solution” to avoid the names that commercial producers use for their battery equipment (like pack, tank, etc.), and because the specific power equipment that an astronomer selects specifically solves the astronomer’s power problem.
As discussed in Part 1, a complete power solution consists of battery itself, possibly a battery enclosure, possibly a monitoring device or devices, circuit protection for the outlet connections, the outlet connections and a battery charger. The battery is likely to be withing the enclosure, and all the other components are likely to affixed to the enclosure by means of a panel mount. The battery charger restores the battery’s charger, in a manner that preserves the battery’s useful life, and quickly enough that the battery is available the next time that it is needed.
As for the battery itself, all that was said about volts, amps, amp hours and charging in Parts 2 and 3 apply. A monitoring device is required to detect when the battery has reached is maximum safe discharge level so that the battery can be disconnected and not be damaged by being overly depleted. Sometimes a color-coded charger indicator serves this purpose. Circuit protection can be either a circuit breaker or a fuse that interrupts the circuit if a higher load than is anticipated is encountered, usually one for every outlet connector. The most common outlet connector accepts the cigarette lighter plug, but Anderson Powerpole connectors are becoming more common. The enclosure that contains the battery, and to which the other components are mounted, can take a wide variety of forms. Manufacturers’ enclosures are custom made. Trolling motor or other battery boxes are sometimes used by do-it-yourself (DIY) builders of power solutions.
There are four important considerations concerning battery use in the field: handling, setup, connecting, and use. The less time spent on placing the battery into service, the better, because there are so many other details to which the astronomer must attend before darkness arrives.
From a handling perspective, batteries are heavy and can be difficult to transport and handle in the field. Generally, the higher the capacity in amp hours, the heavier the battery. A carrying handle of some type is essential here, as it can allow many batteries to be carried with one hand, leaving the other hand open to carry some other gear. Commercially marketed solutions have handles or carrying straps. Most battery boxes that DIYers use have handles.
Having all of the components mounted on the enclosure helps not only by eliminating setup time, it also prevents polarity errors in connecting components and it prevents components from being forgotten or lost.
Getting polarity correct when connecting equipment is essential and should not be presumed to be as easy as it looks. If a connection can be made incorrectly, an astronomer in the field who is in a hurry can probably find a way to do it incorrectly. A red wire and a black wire, for instance, does not look the way one might expect when viewed under red lighting. The consequence of reversing polarity is the likelihood of damaging expensive equipment and ruining a night’s observing session.
During use, monitoring devices, at the very least a voltmeter is recommended. Most battery manufacturers will specify a minimum voltage to which a battery can be discharged to, and a voltmeter is required to monitor and avoid this situation. An ammeter can be helpful too, as it provides an indication of the rate that power is being used, which gives some estimation of long the battery will provide power before hitting the minimum safe voltage. Also, the astronomer will know if the load on the battery is heavier than it should be, in which case the anomaly can be corrected before the battery is prematurely exhausted.
And finally, a word about commercially available power solutions and one that is designed and assembled by the astronomer. Ultimately either type solution can provide the voltage and amp hours that are needed to get through a night of astronomy. And the principles of volts, amps, capacity and charging apply equally to both types as well, so choosing a solution that provides the needed capacity is critical in either case.
Where the two approaches differ most, however, is the DIY solution requires research to select components, and it could require some level of electrical skill and sense of adventure on the part of the astronomer. Other differences are that amp hour for amp hour, a solution that the astronomer builds will cost less than the commercially produced one. In the higher capacity solutions, the difference could be a couple of hundred dollars. Or alternatively, much more battery capacity can be obtained for the same amount money. And finally, with the DIY solution the type and quantity of connections desired by the astronomer can be built in to suit the astronomer’s needs.
Batteries do not last forever and have limited useful service lives that vary by battery type. What is more, there are factors that can shorten a battery’s expected service life. Over charging or over discharging a battery are chief among these factors. Keeping a battery on a maintenance charger can eliminate overcharging, and keep the battery properly charged for extended periods of time. Having a voltmeter as part of the power solution package permits the astronomer to monitor voltage and disconnect the battery before it becomes over depleted. And finally, being exposed to unmoderated high and low temperatures in a garage or outdoor shed can send a battery to an early demise.
Doug and Jim have both used commercially available power solutions but are transitioning to DIY solutions. Let us and others know about how you decided on your power solution by leaving comments below.
© 2021 Jim Johnson and Doug Biernacki