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.The above illus-tration shows a simple tubing manifold system for feed lines and gas exitlines.On the next page is another view of the rack of stacks.In designing a power supply, consider the number of photovoltaic pan-els needed, as well as how many electrolyzers.Then, size the gas pro-cessing system and storage to provide the appropriate quantity and qual-242ity of gas for your fuel cells. Planar Fuel Cell StackRack of planar fuel cell stacks243 Planar Fuel Cell StackOutput configurationsYou can take power straight from the fuel cells; or use supercapicitors tocondition the output; or feed small rechargeable batteries if you have spe-cial applications that require them.For instance, if there are high amp draws from motor start ups, etc., puta supercapacitor in parallel connection with a 12 volt rechargeable battery,and use this to supply those intermittent load needs adequately.To use arechargeable battery alone, as mentioned, simply connect the output fromthe fuel cells to the battery and draw power from the battery.To use asupercapacitor and rechargeable battery, connect the battery and superca-pacitor in parallel, connect the fuel cell output to these, and draw yourpower from the supercapacitor and battery connected leads.With thesesystem additions you will need a diode so that reverse flow does not occurto the fuel cell stack, and fuse the circuit on both sides in case of shorts.Aswitch, either remote or direct, should be used to connect the power supplywith any lines or equipment being powered.If you have AC power require-ments you will need an inverter to convert DC to AC electricity.244 Planar Fuel Cell StackRunning the stacksIn operation, let the fuel cells run for a few minutes before connectingto a load.It would be a good idea to install a voltmeter and ammeter fromthe fuel cell to output line, and also at other junctions if so desired, so thatyou can monitor the system at various points.These systems can be total-ly automated, manually controlled, or both.Cold weather can wreak havoc with PEM fuel cell stacks for a variety ofreasons.It is important to set up the power supply so that it is as wellinsulated as possible.At the same time, proper air flow must be main-tained to feed the cells, and adequate ventilation provided to keep anyhydrogen gas from accumulating.Hydrogen gas monitors that are correctly calibrated on a proper sched-ule should be used in any power supply system to provide alarms for haz-ardous conditions.Automatic cut offs can be used in conjunction with analarm system to shut down the gas flow to the power supply.System maintenance and reliability are very important, so be sure toconsider this in every step of your design.Engineering a practical andsafe fuel cell power supply takes a bit of thought.It is best to start outsmall and build up slowly, so that your mistakes do not turn out to be cost-245ly or dangerous mistakes. Planar Fuel Cell StackOf course, you can purchase a stack and then build the rest of the sys-tem around that, or purchase other system components as well.Fuel Cells2000 has an excellent web site with a list of available fuel cell units withphotos, specifications, and prices (access URL via Resources page).Stacks can also be purchased on the surplus sales market.At the time of this writing, new 1KW stacks can be purchased for around$6000.00 to $8000.00.Used units of the same output may cost around$4000.00 to $6000.00 Most current stacks have an operating life of 1500to 2000 hours.More expensive units can go above the 2000 hour range.It may seem at first that building a power supply is more expensivethan buying one.However, the average life of these purchased units isonly 12 to 24 weeks of continuous duty, so replacement costs and serv-icing fees can make building your own seem more reasonable.If you dobuy a unit, find out how easy it will be to replace the parts and performother maintenance.Have fun, and always be safety conscious, so that you can have manymore days of experimenting and discovery.246 ResourcesSafety - MSDS and hydrogen safety guidelinesHydrogen ResourcesSupplier URLS (Click here for a more extensive list)McMaster-Carr Many, many useful itemsHMC Electronics Rosin, flux pens, solderE.Jordan Brookes Co., Inc. Tab and bus ribbonPlastecs Solar cells, tab ribbonAll Electronics Electronic and electrical suppliesSurplus Sales Of Nebraska Electronic and electrical suppliesElement 1 Power Systems MEAsOcean State Electronics Printed circuit board, ferric chlorideetchant, trays, tongs,Micro-Mark Hobby milling machines, routers, end mills, and lotsof other items useful for fuel cell building.Caswell Plating Electroplating and electroless plating supplies.Techniks Inc Press-N-Peel PCB Transfer Film247 Templates for the L79 Fuel Cell StackIf possible, set your printer options to print to the edge of the paper, or print thetemplates to a paper size such as 11 x 17 , if your printer has that capability.Because the electrodes and MEA assembly are 8 wide, some printers may not beable to print either the right or left edge for Templates 1, 2, 3, or 5.This will notmatter for printing to the transfer film for the electrode templates they have beenaligned so that all of the image needed for the transfer can be printed by any laserprinter on the 8.5 x 11 transfer film sheets.For the other templates, if an edgeline is missing, you may wish to take a ruler and mark it on the template at exact-ly 8 wide.Use the on-screen template page as a reference
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