Building a racing battery pack

[Nader]

Most 160/175 racers run a total loss ignition system. The bike has no alternator, and the battery provides the juice for the coil/spark for the duration of the race. The battery must eventually be recharged, depending on its capacity.

Most people run the original sized lead-acid battery that can last all day between recharges. Alternatively, one can use a dry cell battery pack with a smaller capacity, and change it out for a fresh pack between each track session (I use 3 packs, and usually only need 2 for a day). The advantage is in the weight savings (and possibly reliability) of the small dry cell pack.

Using the average Ni-MH AA rechargeable battery (about 2500 mAh), I'll get about three 20 minute sessions before it runs out.

The following is a pictorial on how I soldered up a dry cell pack from loose batteries. I've used Ni-MH in AA sizes (10 cells soldered in series to make 12V) because it was cheap, and it's been reliable for me for the last 2 seasons. In this pictorial, I'm experimenting with Li-Ion because it's lighter, but potentially less durable and finicky to charge.

Oh, this arrangement needs a special digital charger for this setup, found at hobby shops for around $50.

Disclaimer: I'm just showing how I did my setup, and do not encourage anyone else to do the same. Soldering results in toxic fumes, don't breathe them. Solder the batteries wrong (completing a circuit), and you can cause an explosion. Overheating batteries during soldering will ruin them. Mischarging batteries will ruin, and possibly explode them. Racing motorcycles is potentially dangerous, too.

[Nader]

Here are the supplies. This a Deans female plug connector premade into a pigtail. They allow quick battery changes. The bike needs the positive end on the wire harness, seen on a later pic in this thread. I'm also using Deans battery bars to connect the cells.

[Nader]

Those cells are larger than AA. I lightly sanded the terminals so solder could stick better, glued the cells together with contact cement, then presoldered the terminals. Had to be quick so as not to allow the cells to get too hot during soldering. Heat kills batteries.

[Nader]

Here's how it looks after my sloppy soldering of the pigtail and battery bars between the terminals. The cells were arranged to be soldered in series, and am using only 4 cells since each is 3.7V. My other NiMH packs use 10 AA 1.2V cells.

[Nader]

Then it all gets encased in heatshrink tubing. I get the supersize tube from Frye's. Had to be careful not to overheat the batteries while heating the shrinkwrap.

[Nader]

And here is a murky picture of it installed on the bike. There's the male plug on the bike's wire harness, too.

The pack is small and light enough to secure with velcro and a backup strap. Like I said, I usually use Ni-MH, and others have used Li-Po. I don't know how this Li-ion pack with it's excessive voltage will pan out, which is why I only made one pack for now.

[smestas]

Nader,

Great information here. Thanks.

I have a question though. In your first post you wrote "10 cells" to make 12 volts but in your photos you show only 4 cells. Can you run on only the 4 or are there some other packs of cells used to run on?

Thanks.

[geordy]

First Nader was talking about using a pack made of 10 x 1.2 volt nickel-metal-hydride AA's. That's different from the pack that he has built and shown in the picture. That pack made of 4 x 3.7 volt protected lithium-ion cells.

[I_FLY_LOW]

you could also use a 3-4 cell li-poly pack, found at r/c hobby shops...
Get one with a high discharge rate, and capacity... their light, and last a long time on a charge...