Building Custom Battery Packs

[LoveToROCK]

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.

[BigSki]

thanks for a great write up. It has given me some ideas on how to fit some 3300's around the front axle.

[Chris_The_Battery_Man]

Man I could go on for DAYS about building custom batteries. I remember the Time I made a pair of 5s4p lipos for a huge heli back before the balancing taps were around and before Thunder Power existed too I believe. I think I should post pix of some of the odd batteries I have made over the years in a different thread for a few chuckles

[SeanD]

Not trying to take ant business away from you, Chris_the_Battery_Man, () but the ability to make your own custom packs is a great skill to have in this hobby. I just whipped up a 2/3a 7 cell pack for my Wk last night and there's something satisfying to create a pack and see it make your rig come to life. Sorry to sound so philosophical - its almost the weekend and I can taste that first beer already

[Chris_The_Battery_Man]

Oh no worries. It's the true hobbiest at heart I try to build what I can because I truly love to build from scratch.

[kwkride]

I really like this write up! Thanks for the tips!

[LoveToROCK]

Originally Posted by Chris_The_Battery_Man

Oh no worries. It's the true hobbiest at heart I try to build what I can because I truly love to build from scratch.

I enjoy it also.

I have 14 more batteries but no shrink wrap the right size. Going to try a few different ideas with them. Painting the Bug body now.

[blacksmith]

Is your run time the same with smaller B&D batteries . I like setup on top the servo do you think it will work with the bigger batteries . I am worded about my run time . By the way I like the anvil in the background .

[LoveToROCK]

Run time is a little less but much longer than 2/3A packs.

No, the regular size sub C's wouldn't fit like that.

That's my 1/10 scale anvil. Also have a 1/4 scale and a full size one. How can you live without a good anvil?

[crantma]

Saw this after i built my first battery. It looks just like your first set, with batteries standing upright, but I mounted it straight to the axel. I just covered the batteries with black electric tape and seems to be o.k. .You are right There doesn't seem to be much on building batteries. Thanks

[partsjockey]

I'm a newb, my ax-10 hasn't even arrived yet, and info like this is what I'm after. Cash flow is low so Li po is no time soon, but I'd love to see more ideas, and how to's on building batteries.

[motorhead77]

im having trouble soldering mine together, i didnt know u had to tin the batt too. im using a macco gas soldering iron, do u think this will gat hot enough? and i also used electrical tape for insulation.

[mysharona]

Something you forgot to mention is that you need a REALLY hot soldering iron. The one I use goes up to around 900*, and I usually set it around 750-800. I use Radioshack 60/40 rosin core solder.