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RC Battery Pack Building and Re-Building

One of the major problems with most battery packs, no matter how good the battery cells are, the connections between the cells and from the pack itself usually suck big time. These crappy connections are typically little tin foil accordions paired with small gauge power wires, and stock Tamiya connectors which simply do not allow free flowing current between the cells and to your RC.

I have some decent packs, GP3300s, PowerMax Pros, Trinity, etc.., the power wires were thin and were initially replaced with Deans Wet Noodle 12 gauge wires and connections to the ESC were upgraded to Deans which was a huge improvement.  These slightly upgraded packs were great for the lower current requirements of the brushed motors I had been running. Deans and high current wires are a typical upgrade for almost any pack.  Once I moved to a brushless motor system however, all my packs seemed to really heat up and performance lacked in a very obvious way.  Although better than most, the PowerMaxs and even the Radio Shack GP3300s use a thicker foil accordion connections between the cells, they are still way too thin for the current hogging requirements of something like the Novak 4.5R brushless system.

The between cell connections simply could not allow enough current flow between the cells.  This issue is typically displayed in the form of a hot battery pack. Another indication was the fact that the ESC was pulling so much current that it would actually brown out the receiver (yeah a lot of current).  This issues was resolved with the addition of a simple 4700mF capacitor wired into the ESC's external battery pack slot (kind of a battery back up for the receiver).  Even with the fix, the system still lacked the power I knew it had. The problem was I either needed better higher quality battery packs or needed to rebuild the packs with better between cell connections (battery bars) so all that lovely current could flow when it was needed and not get bottlenecked at the connection points between the cells.  Instead of going out and buying new packs I decided to rebuild my old ones first and it worked beautifully.

What are better connections (i.e. battery bars) going to do for me? Basically the current will flow more easily from each cell to the next with the least amount of resistance.  Resistance causes the cells to overwork themselves and heat up, heat is bad for a battery. The hotter the pack is, the less runtime, current, and life it will give and have, and the hotter the cells get the more resistance. The cycle starts over with more heat and more resistance. You should see a pretty noticeable difference in peak power, overall runtime, all with much cooler running batteries once the battery pack is rebuilt with good quality battery bars such as Deans Probar 3s. 

Battery Pack Styles - There basically two types of battery packs, shotgun or stick packs which stack the batteries positive to negative like batteries in a flashlight or brick or side-by-side style packs which are just as they sound more on these styles in the articles below.

Buying new cells or rebuilding an existing pack and making a new pack? No problem, follow, the same process as described in the articles below.  I would go ahead and buy matched cells if possible. Matched cell packs are built with cells that discharge from a time and voltage perspective almost identically.  They typically will run longer with overall higher voltage than unmatched cells.  Over many uses matched cell will eventually become unmatched cells but will still perform better in the long run for you than un-matched cells.  If you are simply a basher (non-pro), I would recommend going with a high Mh cell like the Radio Shack GP330 or other quality 3300mh to 4200mh cells for longer runtime.

RC Battery Pack Building and Rebuilding Important Notes & Tips:

Before you start tearing open packs there are some things you should know and may need to buy. 

  • What type of configuration are your going to use, a standard stick pack or a side by side or some custom configuration of more than 6 cells?  Keep in mind that occasionally side-by-side packs are wider than stick packs.  A side by side pack will fit tightly in the Rustler and Stampede without problem, however I would recommend attaching the positive and negative leads to extra Deans Probars and bend them over the pack. This will give the battery an extra 1/8" to fit into the battery holder better.

  • Are you pretty good at soldering, soldering battery packs is a little tougher than soldering small gauge wires especially with an underpowered soldering iron.

  • Do you have at least a 75W soldering iron or more would be preferred with at least a 1/4" chisel tip?  A 30W hobby soldering iron is not gong to cut it.  I use a $30 stick style 80W Weller soldering iron with a huge 1/2" tip for battery building that tops out at 900 degrees.  This big iron is more for production work and I would really suggest nothing less to keep you from going insane.  The big thing here is the mass and heat of the chisel tip which allows a solder joint to happens almost instantly versus say a 50W soldering iron which may take 10-15 seconds or longer to solder the same joint.  More time means more heat stress on the cell itself.  That huge 80W Weller makes battery building a breeze and leads to much more professional results.

  • Standard electrical grade 60/40 solder is recommended however a good quality silver solder will be harder to solder but will improve pack performance slightly.

  • You will need 5-7 battery bars per 6 cell battery pack (7 battery bars are needed if you do not want the power leads to attach directly to the batteries - sometimes clearance dictates the extra bars).  Remember this is the critical connection between your cells, so buy at least Deans ProBar 3 battery bars.  I have seen some out there thicker and wider, but I will let you be the judge as to whether these are overkill versus an upgrade.

  • Do you have spare large gauge power wire for the rebuild (sometimes you find that your recycled power lead wires are too short).

  • You will need Deans or other low resistance power connectors if you don't already have them for both the male ESC and female Battery connections.

  • Big 2 1/2" battery pack shrink wrap - depending on your application.

  • IMPORTANT At least 2 cell shrink wraps for each naked un-shrink wrapped cell such as the ones in my PowerMax Pro stick packs. DO NOT ATTEMPT TO BUILD A PACK WITH NAKED CELLS YOU WILL BLOW ALL OF THEM - TWO LAYERs OF SHRINK WRAP MINIMUM.  So in my case I needed 12 cell shrink wraps for one 6 cell pack of naked cells.  Naked cells will not have any plastic coating and look silver, if in doubt, add a layer of cell shrink wrap.  Also a really great idea in the RC Car action article on having an extra layer on each cell in regard to gluing cells together.

  • Heat shrink should be done with a heat gun or hair dryer and not a torch as I found out.  It will simply melt apart with a torch.

  • Custom Logo'ed pack as show above, just glue a 1 5/8" wide logo of your choice onto each cell with simple craft glue before shrink wrapping each cell.

  • Some power lead sized shrink wrap tubing for the connection ends.

  • A Dean's speed jig for battery building is helpful, however an improvised cell vise using a ruler and some masking tape will also work well.  I used a strip of masking tape on both sides of the cells taped to a ruler to hold the cells together and straight while I was soldering the cells.  A battery jig is very helpful as an extra hand and worth the $10-$15.

  • Always start by rebuilding your most crappy performing pack first.  It will take you at least 2-3 packs to figure things out and get a professional looking pack.

  • Want out? You starting to think "Dude this is just too much work?"  Well it's actually pretty easy and simple which probably takes far longer to explain than actually building a pack, however there is a process to follow and about $7-$10 worth of materials to get your battery pack back in shape.  These guys, I have heard build good packs and may be an option if you either don't have the soldering skills yet or just at the point where it would be worth the money for someone else to do it.

There are the articles I would HIGHLY recommend you read them all before proceeding with tearing apart your battery packs.GP3300B.jpg (127738 bytes)

Good Luck!