Nov 2, 2014

A Fool-Proof Bullet System for Series Packs

Ever tried to run your 12S stick packs with bullets instead of using an EC5 Y-harness and accidentally plugged in the wrong two connectors? If so, then what followed was probably a violent explosion during which time you simultaneously burned your fingers, vaporized your bullet connectors, and soiled your pants. If you made the mistake of plugging the packs into your charger after a flight before disconnecting the series lead, then add “destroying a charger” to your list of things.

We’ve all made one of those mistakes if we’ve tried to use bullets before and afterwards, it was back to EC5’s, Dean’s, or another paired connector, which requires an ugly series Y-harness hanging off of the front of your ESC. Well, no more dangerous wiring for me! I came up with a fool-proof way to set up bullets on your series packs so that you’ll never misconnect something again!


It’s very simple, so let’s check it out. You’re going to need the following:

1. Two lipos that you wish to run in series.

In my example, I’ll be using two 6S 5000mAh packs in a stick-pack arrangment.

2. Two male-female sets of two different bullet types (Castle 5.5/6.5mm, RCPROPLUS, PRC’s, Scorpions, etc).

I’ve chosen to use RCPROPLUS Supra-X 6mm bullets (red for + and black for -) on the main leads and PRC6 6mm bullets (red for + and blue for -) on the series leads.

3. An extra length of wire and a crimp splice for extension of the rear pack negative lead.

This is only needed if you’re running a stick pack configuration. Side-by-side packs won’t typically require extensions.

4. Soldering setup and necessary skills to solder high-current bullets.

My trusty RadioShack butane mini-iron gets the job done with no issues at all!


Ok, so here’s the theory. First let’s assume that we’re going to use a stick configuration for this example. For my systems, I always use the positive lead on the front pack and the negative lead on the back pack as the two MAIN power leads. In other words, MAIN leads┬áconnect to the ESC, while SERIES leads connect between the two batteries to make them into a 12S stick. This leaves us with the front negative lead and the back positive lead as our SERIES leads. Label them with a piece of tape or a label maker so that you don’t get them confused.


For my MAIN leads, I use the RCPROPLUS Supra-X connectors because they have a very solid connection with a detent that snaps them together and a very rugged and easy-to-disconnect plastic housing. Also, I use the female gender for my pack MAIN leads and the male gender for my ESC MAIN leads.


For my SERIES leads, I use the PRC6 individual bullets in red and blue colors as they’re lower profile and fit easier into airframes that are narrow. Since these leads will connect together at the packs, you will need to run different genders. I have chosen to use female red PRC6’s on the positive SERIES lead from the back pack and male blue PRC6’s on the negative SERIES lead from the front pack.

Now, if you’re doing a stick also, go ahead and solder on your black negative wire extension using the crimp splice I mentioned above. Once you’ve done that, strip the leads of the pack one at a time and prepare them for soldering the bullets. Don’t ever strip positive and negative pack leads at the same time or else you will risk them making a connection and arcing or injuring you.

Ok, so now you’re done soldering…well, not yet! You’ve only done half of the job. ­čÖé The packs look great, but you still need to add the male MAIN connectors to the ESC and then build yourself some charge leads…

This is one point that people don’t like about this system, but I think it’s perfectly fine once you get used to it. Because each pack has a different combination of connectors, you need a specific charge lead connector combination for each one. Simple…four more bullets to solder and you’re done. Just make sure that you’ve matched the genders and colors with their respective opposites on the pack side. Just so we’re all on the same page, if you set yours up like I have with my system, then you’ll need a charge lead with a male red MAIN connector and a female blue SERIES connector and another charge lead with a male black MAIN connector and a male red SERIES connector.


Now you’re all set! Plug ’em in, get ’em charged, disconnect ’em and reconfigure to the series wiring, then plug into the ESC and go fly! ­čÖé You’ll never need to worry about blowing stuff up again!

– Justin