Mod Your E-Flite ultra-Micro Battery Charger to handle up to 5 batteries @ once

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This modification is very easy to do if one has some very basic soldering skills and can drill a 1/8 inch hole. The modification will void your E-flite Chargers warranty so you may want to consider this before you start hacking away.

I came up with this mod after several people have asked if the Ultra-Micro battery adapter can work with the supplied E-Flite charger that comes with our beloved Vapor and Blade mcx aircraft. (and others) The problem is that our adapter was designed for the modeler that already had a charger and only wanted to lug around one nice charger to his favorite indoor flying site. Therefore the Ultra-Micro adapter features a common standard JST connector instead of the hard to find and "work with" connectors that match the battery. So in order to get the E-Flite charger to work with the adapter we simply drill a hole and solder a JST connector to the back of the connector that is recessed in the charger.

You will need:

• E-Flite 300 ma Charger
• JST Female connector with at least 3" leads (TME Part number XTR-JSTF)
• Ultra-Micro Battery Adapter (TME Part number XTR-MPB)
• A fine tip soldering iron and some electrical solder

You can click on the photos below to see a much larger image.

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• The first step is to turn the charger on its back.
• Then remove the battery cover and then remove all the batteries.
• Pry off the four rubber feet in the corners. You may need to use a small screw driver or hobby blade to pry them off. Put them in a safe place sticky side up in order to be able to re-use them.
• Now remove the four corner screws with a small Philips screwdriver.
• Carefully remove the bottom cover.There are wires connecting the bottom half to the top

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• Inside find the small board in front that supports the primary battery connector. It has a red and black wire going to it and sits in the front of the charger. The space above the circuit board (as shown in the picture) is where we will need to drill a small hole

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• Temporarily place the bottom cover and flip the unit right side up again
• Locate the spot below the connector on the front low enough so that we miss hitting the PC board. Be careful not to drill too deeply so as not to damage any wiring or circuitry
• Using a 1/8 inch drill bit, carefully drill the hole as shown.

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• Now carefully remove the bottom again and blow out any plastic debris from drilling.
• Insert the pre-tinned leads of the Female JST connector to through the hole from the front of the charger
• Carefully bend and solder the red wire of the JST connector to the pad on the circuit board with the red wire already on it
• Carefully bend and solder the black wire of the JST connector to the pad on the circuit board with the black wire already on it
• You may find it easier to remove the small little board from the unit and have someone hold it while you are soldering. (if you do, don't lose the screws!)
• When done check your work to make sure there are no solder bridges from the red leads to the black. You also may want to put a drop of glue on the inside where the JST wire goes through the hole to act as a strain relief for support. A hot flue gun will work well here as well as 5 minute epoxy or CA. Make sure it doesn't run out the hole in the front. Another method is to loop the leads into a not with about an inch of leads free BEFORE you solder them to the board

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OK, now we are almost done!

• Re-assemble the bottom housing to the top with the four screws, the four rubber pads, the batteries and the battery cover.
• Your unit is now ready to operate

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IMPORTANT make sure that all batteries to be charged are close to the same state.  Typically if you fly until cutoff or you time your flights you will not have a problem. Just make sure you don't have a full charged battery mixed up with your discharged pile other wise when you connect them in parallel the fully charged battery will dump its charge into all the discharged cells causing a rush of current that could damage the cells or pit the connector.

You now have a modified charger that still works as originally intended with one battery but it also  now has a JST connector for ewxpansion. Plugging in our Ultra-Micro Adapter into the JST allows you to charge up to 4 more batteries simultaniously. Simply connect from 1 to 5 batteries into all the connectors and your charger will begin automatically as usual. Since the charger is current limited it will not work any harder with 5 cells as is did with 1 so there is no fear of overloading your charger.

At this point it may sound like you are getting something for nothing. Of course that is never the case, but you will find the PRO's here outweigh the CON's.

The downside is that it will take longer for the charge LED to go out with more batteries on charge. As you approach 5 cells, your charger may take over 2 hours to charge. However you will have 5 times as many batteries than the original design which makes up for the added wait.

The upside is that instead of 300 ma going into just one cell, the current is divided into all the cells in proportion to their capacity. This shared (reduced) current will make your batteries last longer. For longest life we recommend you have at least 3 batteries charging at once which will bring down each cells charger current closer to 1C or less.


Enjoy your modified charger and remember that when you want to get a charger that will grow with your needs, the Xtrema Charger is the ultimate future proof charger on the market with 42 volt output and up to 8 AMPS of current and free updates for life. (Andi it will even charge a single Ultra-Micro battery as well 

Please add your comments or questions below!

Albert
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[Mcintosh1964]

Hello, The modification works great! I have 1 adapter connected to a ParkZone charger that came with my Champ. I have now collected over 30 of these 3.7 volt single cell batteries and would like to know if there is a connection limit to the adapters. If I understand the theory correctly the only thing that can happen when connecting let's say 4 adapters to one charger is that it may take 8 hours or more to charge all 16 batteries. Is there a downside to this? Can I assume that it would be so far below 1C that this can only be a plus for battery longevity? Is there a easy way for me to calculate the C-Rate?I have a few of the chargers that have come with my micro Helis and planes but only have one AC wall adapter. What I would like to do is have 5 adapters connected to one charger so as to charge 20 batteries at one time. This would give me hours of flying without having to worry about recharging batteries.
Thanks for any help and sugestions.