All the connections and switches are on the front/top panel.
I’ve been relying on the PSC Power Station battery for most of my power needs for about three years. At nearly $1000, it’s a moderately expensive solution but its versatility and reliability make it a purchase I’ve never regretted.
The heart of the unit is a 33 amp/hour sealed lead-acid battery but it’s the associated electronics and engineering that make it valuable. There are four XLR connectors to supply power and each of them can feed 6 volts, 12 volts or 18 volts depending on which pins the power cable accesses. The ability of the unit to accept charging while in use makes it particularly useful. In practice, one connects it to power whenever it’s available and relies on the battery when it’s not. The charger seamlessly accepts any power from 90 volts to 260 volts. One can feed it whatever power is available in the U.S., in Europe, wherever one finds oneself, and the charger automatically adapts.
Although it has never let me down, I wanted to ascertain how much run time I could count on in the field. As we move into progressively more power hungry equipment with DAT recorders replacing Nagras and frequency agile wireless replacing receivers that could run off 9-volt batteries, the issue of battery run time becomes more important. I set up a test to measure how much run time I could expect. A caveat: my test has some built-in inaccuracies that should be understood:
1. The unit I am testing has been in regular service for about three years. Presumably a brand new unit would have more capacity.
2. The equipment was running continuously. In actual operation gear works sporadically and there are often opportunities to conserve by temporarily shutting down components.
3. The recorder was on but not actually transporting tape. Consequently, its power consumption was a bit less than if it were recording.
After topping off the charge on my Power Station battery, I switched on the following components on my sound cart: Fostex PD4, Cooper 106 mixer and two Lectrosonics 205 frequency agile receivers. I connected a Neumann mike to the Cooper and set the gain so an audio signal would be fed continuously. I also connected lav mikes to the Lectrosonics transmitters and turned them on so the receivers would have continuous audio, reasoning that the power consumption of all components might be greater with an audio signal. I could have run additional radios or added a video monitor but my interest was in learning how much capacity I might reasonably expect not how quickly I could exhaust it by overtaxing.
I looked in every hour to check the status lights on the Power Station and battery supply as metered by the Fostex and the Cooper. For more than six hours of continuous running all indicators showed ample power. At the seventh hour the Fostex meter was down one bar and I began to check every 30 minutes. At nine hours the red warning light on the Power Station came on and I shut down the test and connected the charger. Although the Fostex and Cooper both continued to indicate ample power, the end was in sight and I didn’t want to imperil future use of the battery by over-depletion.
The carry handles are not too comfortable but, in practice, the unit isn't moved very often.
Status lights indicate connection to AC power for charging and, when the unit is switched on, battery condition and circuit fault.
Wiring and operational information is permanently diagrammed on the base.
The PD4 battery meter dropped one block after seven hours and then remained steady for two more hours.
(mouse over to see the drop)
While the Cooper battery meter was indicating a full tank until the end.
|
Time
|
Results
|
| 1:15 PM | Start Battery Test |
| 2:15 PM | Everything OK |
| 3:15 PM | Everything OK |
| 4:15 PM | Everything OK |
| 5:15 PM | Everything OK |
| 6:15 PM | Everything OK |
| 7:15 PM | Everything OK |
| 8:15 PM | One notch down on PD4 meter, otherwise OK |
| 8:45 PM* | Unchanged (Cooper meter still reading OK) |
| 9:15 PM | Unchanged (Cooper meter still reading OK) |
| 9:45 PM* | Unchanged (Cooper meter still reading OK) |
| 10:15 PM | Red light on Power Station (equipment meters still OK) |
Nine hours seems a reasonable performance considering the power needs of the operating components. How does this compare with expectations? If one knows the power needs of each component it is possible to calculate the total power draw and compare that with the rated capacity of the battery to determine run time.
Batteries are typically rated in "Amp/hours." A battery rated at 10 Amp/hours should be able to supply current to a device drawing 2 amps for 5 hours. In practice, actual performance is usually somewhat less. There are several reasons for lower expectations:
1. A battery is rarely charged to its absolute full capacity.
2. As batteries age, their capacity diminishes. (A phenomenon I have personally encountered on the tennis court)
3. Battery output is loosely related to ambient temperatures. Yield is higher in warm temperatures and markedly lower in cold.
The Fostex has variable power needs depending on what it is doing. According to Neil Stone Jr. (of Colossal Sound Services and The Sound Check) a Fostex typically needs about 1.5 amps although 3 amps are momentarily needed for power-up.
The Cooper is rated at 600 mA @ 18 volts. Since the Power Station battery is actually a 12-volt unit (although it can be configured to output 18 volts) we need to make a calculation of the effective draw from 12 volts. Allowing for some loss for the voltage conversion, the Cooper's draw @ 12 volts is about 1 amp.
The Lectrosonics 205 radio receivers are rated by the manufacturer at 260 mA each @12 volts. Operating together two units would need 520 mA or about half an amp.
Adding it up we have 1.5 amps, 1 amp and 0.5 amp for a total draw of about 3 amps. A 33 amp/hour battery should be able to provide 3 amps for 11 hours. My experience of nine hours run time is about 20% down from calculated expectations but within the range of normal.
A "stock" unit next to a modified battery. This is a routine modification for PSC.
Mouse over for a closer view.
In the spring of 2003 I had PSC install a new battery. I haven't run a new test since then but my sense of the matter is that the capacity is substantially greater. This is hard to substantiate because, in practice, the unit is usually connected to power when it's in use. In any event, it is never run flat. Still, there were signs that the original battery was probably becoming a little "tired" by the time I ran the test. The outboard dbx limiter tended to become buzzy when the cart operated for any extended period without being connected to AC and I would often disconnect it to conserve power. With the new battery, there seems to be more oomph and I can run for a considerable time, even with all accessories operating, without any trouble. If I were to repeat the test I expect I could add at least an hour, and probably two hours, to the stable run times.
While the unit was a PSC getting a new battery, I had a modification performed. The technicians added a 4-pin XLR power connection and a routing switch. This makes it possible to use an external battery for power and still take advantage of all the charging and voltage control circuits of the Power Station. Regrettably, only one battery is active at any time; one selects either the internal cell or the external cell and the selected battery supplies energy and receives charge. But it does provide considerable peace of mind on shows with extensive outdoor filming away from power. One could start the day with an external cell and use it until lunch, switching over to internal power for the afternoon. During the afternoon, the first battery is at base camp hooked up to a charger. It provides much of the functionality of the new PSC PowerMax. Of course, the Power Max has some advantages. It has six rather than four outputs. And it has the capability to accept more than one battery at a time. With the modified Power Station, you're always carrying that 30 lb. internal battery around, even when you're not using it. Still, a simple modification to an existing piece of gear is a lot less expensive than a whole new system and it provides considerable additional security and flexibility for minimal expense.