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Power Supply For Sound Recordists
12 Volt sealed lead acid battery/power supply setup. A 12 volt DC (direct current) system distributing power to your equipment, through a multi output device like the Rastorder PDU (Power Distribution Unit) makes a lot of sense. You can supply the 12V power from a battery, or even a 12V regulated PSU (Power Supply Unit) plugged into AC mains power (Alternating Current). The major advantage of using this distribution method is that no matter where you run out of power you can commandeer a12V battery from somewhere, albeit a crew car or a spare camera battery and input it into the PDU to continue the uninterrupted power supply to your equipment. A combination that works extremely well is a battery charger from Bee Technical http://www.beetechnical.com/ connected to a 12V sealed lead-acid battery of at least 33 amp hours, which in turn is connected to a Rastorder PDU. If mains power (90 to 264 Volts AC, depending on the model) is available you connect one mains lead to the charger. When you move you disconnect & re-deploy that mains lead. If its too much trouble or you are in the field you can leave it disconnected and your power comes from the battery.
They can be successfully used as a combination battery charger / Power Supply Unit if you are aware of certain issues. (1) Both these chargers must be connected to a good 12V lead-acid battery (above 8.5V) to work. When you turn the charger on it first of all, assumes its connected to a battery and tries to determine if the polarity in the connection is correct. It needs to see at least 8.5V from that battery to determine this. If polarity is correct it then opens a relay, supplying power. If there is no battery in the circuit it cannot perform this task, hence no power. To trick it into turning on you just need to connect it to a compatible battery till it performs this task and then you could take the battery away. (2) Both chargers have an auto-boost mode, which is factory set to a default 14.7 volts. If they are connected to a battery with a load on it (i.e. your equipment) they can mistake it for a flat or partially discharged battery and stay in the auto-boost mode, supplying 14.7V continuously. This is not particularly good for a sealed lead-acid battery as it will eventually be overcharged and damaged. This higher boost voltage may also be too high for some 12V equipment. One solution is to have the auto-boost disabled so the charger also acts as a de facto single stage 12V regulated PSU @ 13.8V. (3) When the charger is supplying power to the battery and hence along to the equipment via the PDU, the equipment will always get first bite at that power. Hence if your battery is fairly flat it wont charge very well if most of that power is being taken by the equipment. Also, the maximum amount of current that the charger is recommended to supply continuously, is about 75% of its rated output, so a BH-1208 (8 amps) can continuously supply 6 amps and a BH-1214 (14 Amps) can continuously supply 10.5 amps. They can actually supply full maximum power for a few hours at a time. (A current model Rastorder PDU is capable of handling 10 Amps). If this combination ends up not offering sufficient flexibility in power needs for your equipment, the next step is to buy a regulated PSU. You can run this around mains power availability, while your battery is being kept fully charged at all times with the separate charger, possibly with its boost mode re-connected.
More on lead acid batteries. As a rough rule of thumb, a fully charged 12V lead-acid battery will read about 12.9V. A half full 12V battery will read around about 12.5V A flat12V battery will read about 12V. A battery with a stable reading below 12V can be considered to have been abused! If you buy a new deep-cycling, lead-acid battery, as a preparatory measure, it can be cycled a few times to bring it up to its full capacity. This means you charge up your battery and run it down by powering your equipment without the charger plugged into mains. When your battery is flat you re-plug into the mains, restoring power to your equipment, you then leave the charger connected to the battery overnight without your equipment connected to completely recharge it. You can repeat this initial, preparatory deep-cycling for several days simply to bring it up to full capacity (obviously with mains available). Preferably the battery should always be kept fully charged, except when actually being used for work. Lead-acid batteries are not like Ni-Cads and do not develop a memory effect. After initially deep-cycling them a few times to increase their capacity NEVER deliberately flatten them - or leave them flat - before re-charging. This is not necessary and will only lessen their life. At the end of the day or session, leave the battery on charge. With a correct charger, a known good battery can even be left on charge indefinitely. All batteries have recommended boost and float mode voltages, normally 14.7V boost &13.8V float. Always check with your supplier if a new battery and your chargers voltage settings are compatible. Cheap battery chargers the danger. Sealed lead acid batteries are sealed; they usually have an overriding safety vent that is only one way out. When they do vent they generally lose gas (sometimes liquid) that is used in the chemical reaction process of storing electrical energy. You cant replace this gas and it depletes the batterys reserves, sometimes severely and sometimes immediately. Non sealed wet Acid batteries of the type we use in our automobiles usually have removable caps, which you can undo while charging, so they can vent any gases. With these however if you lose too much liquid in the form of gas, you can top the battery up with distilled water and usually carry on. The control of the chemical reaction taking place inside your lead acid battery with the connection of an electrical current from a battery charger is of critical importance when the battery is sealed. Especially if you have paid a lot of money for a good battery and you use it in a priority application. Maintaining a specified regulated voltage output from the charger means that the sealed lead acid battery cannot be overcharged and/or overheated, saving it from venting (or serious buckling or even explosion if the venting mechanism fails). Cheap battery chargers are nearly always unregulated. Having comprehensive filtration circuitry to convert the AC (alternating current direction) to a DC (single current direction) further maintains the constant voltage. Any residual AC ripple causes the voltage to fluctuate up & down; there goes that critical regulation again. Cheap battery chargers nearly always have inadequate filtration circuitry. Available batteries Panasonic 12V/33Ah SLA battery weighs 12kg, 196mm x 130mm x 155mm provides a large amount of power at a reasonable cost and is easy to physically move around. (fits in RastOrder battery box) Sonnenschein dryfit batteries, http://www.sonnenschein.org/ have many extra attributes; including deep cycle versions, permitted inclinations of up to180 degrees, the ability to sustain deep discharges without damage and are approved for transport by air as non-dangerous goods. Needless to say you will probably pay a little more for these features. They can be purchased in Australia from http://www.beetechnical.com/ DC to DC Converters. If you are having trouble keeping the power up to your Fostex recorder or Cooper mixer when your battery supply starts to run low then maybe you need a step up Dc to Dc converter, to convert your 12V to 15V. http://www.ete.co.nz/ has a great range, enclosed in their own housing with flying leads. AC to AC step up transformers. If you are planning a trip to the US and you want to take along your 240VAC sequential battery charger, then an AC to AC step up transformer from ETE Ltd will allow it to run on 110VAC. (no worries) www.ete.co.nz/Products/Transformers/isoNZinUSA.htm Cart lighting http://www.jaycar.com.au/ has flexible LED map reading light, (cat ST-3059) plugs into cigarette lighter socket & has on/off switch. Attach an under dash lighter socket to your cart & connect to your 12V DC power. Single (cat PS-2008) Double (cat PS-2009) They also have a range of12V DC Cold Cathode Fluorescent lighting kits in white & colours. 100mm length (cat SL-2870) 300mm length (cat SL-2890) Some more reading; Reprinted with kind permission, From: "Douglas Tourtelot" Newsgroup: rec.arts.movies.production.sound August 2007 Subject: Re: New Sound Cart, Power Supply Questions and More Okay, here it is in a nutshell; what I do, and it seems to be regarded as the most popular way to power carts these days (I did not say the only way!). I have (at least) two 36aH Glass Mat cells in cases. I use wheelchair battery boxes because they give enough protection without being heavy. Don't burden yourself with more weight than you can push, that being said by a man with a very heavy cart. ATA cases for your batteries? No! Pelican cases maybe. An 80aH battery would be unbearably heavy, and you need two, one charging on the truck or at base camp or where ever. Used to be that a 32aH would power me all day. Used to be that 12 D-cells would power me all day. Used to be Now, my 32aH battery gets me through kick-outs and moves from setup to setup. If you are going to have Mackies, and computers and DV824s, and video monitors, you will need to let the set lighting folks know early on that you will ALWAYS need AC. But so will Video village with their two monitors, and all the Steadicam batteries charging on the bottom of their cart. I run from the set AC to an AC strip. Then to the AC input on a 55aH 13.8 battery charger permanently set to "trickle charge." I use one made by Iota, you can get them on eBay for about $150 or so. Nice quiet fan on this one. Don't get a "three stage charger" since if it senses a low battery, (unless you disable the boost mode) it will put out 14.5VDC and blow up all your toys. Use one of those on the truck (another $150) to charge your spare battery. Did I say that you WILL need a spare? I come out of the Iota on 12ga. wire (don't use lamp cord but if you don't run tons of stuff, 14ga. will probably do it and is much easier to work with) through Neutrik Speakon two-pole connectors. AWG: American Wire Gage. A wire diameter specification. The smaller the AWG number, the larger the wire diameter. These are beefy and between the 12ga. and the Speakons, you won't loose a whole volt at the DC distro like you will with lesser gauge stuff. This plugs into the Speakon connector on my battery box. I use 12ga. there as well from the battery poles to two Speakons in parallel. Then, out of the Speakon on the battery to a Battery Buddy lo-DC shutoff switch (now no longer made and the replacement is called the "Battery Brain." Don't know anything other than it claims to do the same thing). This automatically shuts off the DC from the battery when the voltage goes to 10.4 volts which is the bottom end of a gel cell before permanent death. If you leave the Mackie on over the weekend, you come back on Monday and swap to the spare and put your now 10 volt battery on charge. Cool and you haven't killed it (how expensive would it be to kill a battery a week.) You WILL leave the cart powered from time to time. Now, off the Battery Buddy with two sets of, yep, 12ga. One set goes to my 300w pure sine-wave inverter that runs the 01V96 and the DV824. The inverter is sold by DonRowe.com and works great. Retrofitted with a Speakon and a silent fan. The other split (12ga.) goes to a custom-made DC distro panel with ten 4 pin XLR (yep, Speakon and 12ga. in the distro; very tough soldering job onto the small cups on the 4-pins but it can be done. Use bus-wire). From there to all the 12VDC stuff on the cart with 4-pin jumpers of various gauges, small for stuff like the Lecro T1, bigger for stuff like twin video monitors. Keeping your voltage up to the end of the line is important. This setup works perfectly as a UPS of course. Take away the AC. Doesn't matter. Your cart was running on the battery anyway. Plug the AC back in, and your battery starts to charge on the cart and with a 55A charger, it maintains a full charge if it's kept plugged in most of the day. The spare battery gets used for emergencies like leaving the cart powered over the weekend, or sometimes, to stretch my batteries into allowing a short setup away from AC. I have learned to power down non-necessary items on the cart, and in fact, the whole cart for longer down-times which makes this possible. It makes me jumpy to have to do this however. The only fuses are auto-reset 20A breakers in the batteries, and a good cube-type surge suppressor on the AC strip plug. Shorts are bad in general but the battery breakers seem to be all that is necessary in my experience. BTW, this setup is protected from 220VAC (you could read 240VAC here) **** -ups on set. I know. It has happened to me twice (on one show!!!) with the surge suppressor and the AC fuse on the Iota being the only casualties. There was a lot of very dramatic smoke from the surge suppressor and from me the second time it happened. Blew up everything on the video village cart twice. Consternation abounded! Jobs were lost. Whew, there you have it. BTW, this is an expensive undertaking, but anything less will do nothing well for a big cart but give you headaches, and this business gives those away for free. D. This information is courtesy of RastOrder P/L. RastOrder P/L accepts no responsibility for the application of this information. |
