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.This small power stack was designed to produce 6V at between 1 to 2amps under load.Much of the current output depends on the quality ofthe membranes used.If you purchase untested membranes from Element1, expect anywhere from.5 to 1 amp or more output.To test the short circuit current simply change the multimeter setting tothe current reading or use an ammeter and connect the probes to thesame terminals that used to get the voltage reading.Trouble shootingIf you do not get any readings, you have just entered fuel cell builder'shell.This is a place where your shoddy previous work (or somebodyelse s) comes back to haunt you, and you are forced to contemplate andwork to fix your mistakes.So, where could the problem be and what is the best way to trou-bleshoot your system? The first rule of troubleshooting is to prevent trou-ble in the first place as much possible.Do not rush while constructing thestack.Test, check and recheck as you go along, and do things right the237Planar Fuel Cell Stackfirst time so that you don t have to troubleshoot.Then, if there are stillproblems, you can be confident enough to rule out many possible causesof trouble, and zero in on the real cause and fix it.Make a troubleshooting check list to have in hand before testing the fuelcell stack, and follow the check list regimen always, because if you don t,it is very easy to get confused.In a system of this nature there can be many different problems.First,check for the obvious.Are the multimeter probes connected? Is the multi-meter working properly?Then, look at the system as a whole.A simple visual inspection of a sys-tem can sometimes show the problem immediately.Is everything connect-ed properly? Are there any gas leaks causing pressure failure or loss ofgas? Are valves connected properly, and turned on or off, at whatever set-ting they should be for the system to work?If you are sure the system is getting gas, then consider closing the valvein increments on the outlet of the fuel cell to see if that produces anyresponse on the multimeter.Do this until it is dead ended.After a shortperiod of time, if there is no meter response, open up the valve again andmove on to another test.238Planar Fuel Cell StackNext check the fuel cell stack itself, and whether or not there is gasleaking between the plates, etc.If there is a leak here, it must beresealed.Since this stack is connected electrically in series, if one of thePEMbranes is not working, it will shut down the whole stack.This is whyeach membrane should be tested prior to installation in the stack.However, there can also be damage to a PEMbrane during construction ofthe fuel cell.Another possibility is that the connections are not solderedwell and you will have to inspect the tabs to see if that is the case.Morethan likely there will be no problems.To test individual PEMbranes prior to assembling them in the final MEA,you can make a small test fixture.Construct a single slice fuel cell, suchas the easily constructed L78 detailed in Build Your Own Fuel Cells.Touse the L78 as a test cell, don't glue the Mylar® sheets together, justinsert the PEMbrane between the two Mylar® sheets along with the gas-kets and other layers of the fuel cell, and hold the layers together for thetest with insulated binder clips, or use screws as outlined in the text.Youcan of course, improvise on this as you wish.239Planar Fuel Cell StackDesigning fuel cell stacksThe L79 is a planar variation of some of the construction ideas involvedin the L78 stack, as presented in Build Your Own Fuel Cells, which alsohas printed circuit board for the electrode plates.While working with thismaterial, we realized that flow fields could be routed in the circuit board,so that the material could function for a dual purpose: as both a collectorplate, and a gas flow field.As you construct the L79, no doubt many new ideas and configurationswill come to mind.After completing this fuel cell stack, you should feelconfident enough to make modifications to improve the performance; andyou'll probably discover better or more inexpensive materials and methodsfor fuel cell construction.Once you understand the basics of fuel cell con-struction, it is easy to come up with many variations.Fuel cell power suppliesYou may wish to build a fuel cell stack power supply with greater volt-age and current output.A good start is to construct a 12 volt 10 ampere power supply, whichcan be constructed with either planar or block stacks, as discussed inBuild Your Own Fuel Cells.Whatever design you choose, this project will240Planar Fuel Cell Stackrequire 120 MEAs that will deliver around.5 volt and 2 amperes eachunder load.Shop around to get the best price for MEAs.There are URLs for sever-al suppliers that can be accessed via the Resources section of this book.In the process of talking with suppliers you will learn a lot about MEAs,which will help you decide which product is best for you.You can alsomake your own MEAs, and if this interests you, Build Your Own FuelCells has a detailed section about this subject.To construct the power supply based on the L79 planar stack will requireten stacks of twelve MEAs each, and will have an output of 6 volts at 2amperes per stack.Five series connected pairs of stacks produce 12 voltsat 2 amperes per pair.The five pairs are then connected in parallel for atotal output of 12 volts at 10 amperes for the power supply (see below).Wiring for 5pairs of seriesconnectedstacks, wiredtogether inparallel [ Pobierz caÅ‚ość w formacie PDF ]