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Building Custom Battery Packs

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  • HOW TO: Building Custom Battery Packs

    I know a lot of you are now using lipo battery packs, but some are still using the old stuff.

    I hope this will help someone wanting to reconfigure a stick pack or build a custom pack. I haven’t noticed any threads on this topic so I hope this isn’t a repeat.

    Why Axial thinks we want to Velcro a stick pack to the top of a crawler…I don’t know why. So we need to order a split pack or go Lipo. The place for weight is the front axle, not the roof.

    Right after I ran my new AX10 around for a few minutes with a stick strapped to the top I knew I would need to make a change. I reconfigured a 1500 stick pack with six full size nicads into two three packs and mounted them on an aluminum plate that I made.

    Like this.

    This was much better and I would have kept it this way if I didn’t buy a HPI Bug body for the crawler. The batteries were too high and too far to the outside with the Bug body since it both curves down and inwards toward the front. I would have to mount the Bug body way too high. I wanted the Bug lower so the only option was to make another pack. (Or yes…buy a little 2/3A split pack or lipos, I wanted something now)

    I am NOT posting this as this pack design is a good one. I’m not sure about that yet, so far it’s is working fine. I tested the Bug body on it today and it does come close to hitting the battery pack, but since most of the front end movement is rotational the batteries clear the Bug body mounted lower. This is just to show how to build a custom pack.

    I needed smaller batteries but didn’t want to order a split pack of 2/3A’s. I went to Lowe’s and looked at battery packs for cordless tools. They had a Black and Decker pack that was shorter than all the rest. It was 12V and it was on sale for $21.00. Yes I could order a pack for a little more, but like I said…now is better. Then when I thought about it more, buy two packs for $42 and have 20 batteries, enough for three battery packs.

    I removed the batteries from the B&D battery pack and found they were 4/5 C 1200’s. Nice, they were all in cardboard so I wouldn't need to shrink wrap each battery and as a bonus the top and bottom of the pack had a nice hard silver insulation material that I could use to separate batteries and to form the new battery pack.

    I won't let this grow even longer with how I arrived at this pack design. The jury is still out on it.

    I decided on a strange arrangement of three batteries side by side and three in a triangle attached behind the three flat ones to be mounted on top of the steering servo.

    About now I thought about my camera.

    Here’s a picture to compare the size of the batteries from the stick pack (on left) with the 4/5C batteries from the B&D pack. Same diameter, but shorter.

    The three on the left in a triangle has been hot glued together, I have black tape holding the three on the right about to be hot glued with the four extra batteries in the middle.

    I just hot glue the batteries into the shape of the pack I want. A few things to keep in mind. Plan how you place the batteries so that you have an easy time making your connections. And most important make sure to double check that you don’t have anything shorting out and that the insulation (in this case it was a cardboard sleeve) is good on all the batteries.

    The hook up is simple but it can confuse you, at least it can me. I wanted the leads to exit the pack at the rear from the top two batteries. So I numbered the batteries to keep the confusion down. The battery that will have the RED positive lead is battery 1. Then to connect them all that you do is follow a + - + - + - + - + - + - . The battery with the BLACK negative lead is battery 6 in this case since I am using six batteries to build a 7.2V pack.

    I used a double thickness of that hard insulation from the B&D pack to separate the batteries where needed and to form the bottom of the pack so it sets nice and tight on the servo. I also used it at the exposed ends of the batteries.

    After the pack is formed make your connections by soldering tabs and wires to the batteries. Be sure to tin all your soldering spots and wires and to use a soldering iron that gets hot enough. You want to clean the spot where you wish to solder on the battery, I use a Dremel with a little grinding wheel to scuff it up a little. You don’t want to over heat the battery so you need an iron that gets hot enough so you can touch it to the battery, hit it with some solder quickly to distribute the heat to the battery better and leave a nice spot of solder behind. A soldering iron that isn’t hot enough will have you holding the iron on the battery too long.

    I forgot about the camera while doing all the above. Here’s what the pack looks like hot glued and all connected up and ready for a shrink wrapping.

    A shot of the bottom where it will ride the servo.

    A test fit in the crawler.

    Shrink wrapping an odd shape like this can be fun but it went well, only took three pieces to cover the whole pack. Plan your moves and remember…it shrinks. Black tape or duct tape works too.

    I only had blue shrink wrap so I mask off the wires and shot the pack with a few coats of Dupli-Color Truck Bed Liner, the stuff that comes in a spray can. Great stuff for this job.

    I remembered the camera again, it was nearing midnight and I was getting tired.

    Some shots of the completed pack.

    I removed the servo plate that I made and used the stock Axial one. I was able to use the battery straps from Axial to hold the pack.

    I see some blue, the wrap shrunk a little more after a good charging. I’ll touch that up.

    I like how it is all under the Bug body. And it follows the contour of the Bug hood.

    The pack is a little higher than I wanted. But it is on the front axle, it’s under the body and the body is mounted lower than I could have with the other bigger double stand up packs. Hopefully some of this might help someone build a custom pack. I would rather do things myself and I know I’m not alone here on this forum. Sorry I didn’t remember to take pictures of some of the steps. I'm new here and just wanted to share a little.
    Last edited by Rckcrwlr; 02-02-2010, 03:08 PM.

  • #2
    Re: Building Custom Battery Packs

    Great Build Instructions...maybe this will get a couple people out to try it themselves.

    Going to Sticky this one...

    Does the pack hit the body when the front axle is under load??? It looks close.

    Rckcrwlr's Feedback Thread


    • #3
      Re: HOW TO: Building Custom Battery Packs

      very nice!! THANKS


      • #4
        Re: HOW TO: Building Custom Battery Packs

        Thank you guys . Glad I could add something.

        I really didn't plan on doing a "how to", just thought that I should take a few pics as I was doing it. But I kept forgetting to take pictures.

        The post above is.... as said above, about some basics of building a battery packs. I started making them 15 years ago when I was building and running scale electric dragsters. The design of this battery pack is sort of a test. I ran it yesterday with good results, didn't hit the body at all.

        My crawler has very little sprung weight, most of the weight is in it's unsprung weight, the batteries, wheels, tires and axels. Becasue of this almost all of the suspension movement is actually rotational so both front shocks never both compress at the same time. Being new to crawlers I don't know if they are all that way or not. It's always one compressed while the other in extended. No problem with it so far.

        It's not as tight as the pics above make it look.


        • #5
          Re: HOW TO: Building Custom Battery Packs

          Great write up man, very informative. I just had to make a few packs for my on-road car & I have to make one tonight for a customer. I don't like doing it Keep having this dream about me ruining cells It only hapened once, but I don't wanna do it again.

          Oh and great find o them cells how do they work for ya.


          • #6
            Re: HOW TO: Building Custom Battery Packs

            Originally posted by Crawln Coles
            Keep having this dream about me ruining cells It only hapened once, but I don't wanna do it again.
            Get a good quality, adjustable iron and make sure you tin first...and you cannot go wrong...

            Rckcrwlr's Feedback Thread


            • #7
              I was wondering as to where to get cells for this kind of project never thought of lowes.
              Going to try to build something for my creeper to lower the center of gavity .