I have completed the LiPo conversion to my mate's Fighter and must say that I am really pleased with the results. Many people love the Fighter for its weight and handling advantages but wish it had the speed and power of the Bomber. This conversion comes close to fore-filling these desires with out compromising the OEM feel of the bike.
So first thing was to decide on an appropriate voltage without going too over the top. I settled on 18s which is 75V hot off the charger. 6s LiPo's are the most economical LiPo package so it made sense to series connect 3 x 6s packs and then parallel 2 banks together to create an 18s 2p configuration.
Next exercise was to figure out exactly what I could squeeze into the Fighter battery compartment. The Fighter's battery compartment is not what you would consider cavernous and as such, correct battery selection was very important. I also wanted to keep the cell capacity as large as possible so as to the keep the actual number of cells fitted to a minimum. My Bomber has 15 packs in it which is a real spagetti of wiring to contend with. This setup is only 6 packs and makes for a much tidier installation.
Battery selection came down to two possibilities. Zippy 6S 8000mah 30c packs or Desire Power 6S 8300mah. The Desire Power packs are a great quality pack and have a little more capacity however, they are around 50% more expensive then the Zippys. As much as I would have liked the extra capacity, it just wasn't worth it for an extra 40W/hrs.
However, on a side note, if maximum capacity was your aim, you could actually squeeze in 8 of the Desire Packs. This would give you over 1500 W/hrs minus your 10 to 20% safety margin. Only problem is that you would either need to run 12s 4p or 24s 2p.
The Zippy's come with 5.5mm bullets which makes them nice and easy to plug together in series. Just be careful not to plug the last pair together (yes I did this once. = Big plasma ball, black hands, and seeing stars for a bit)
The packs were arranged with the bottom 2 packs with their narrow side down and a 3rd pack on top with its wide side down. This makes the stack 120mm high and just slides into the battery compartment with a mm or 2 to spare. The stack arrangement gives you room to fit the plugs and wiring without a struggle. The 8 pack setup that I mentioned above would be a nightmare to plug in.
It should be noted that the standard 70A Anderson's plug is used to match the existing plug. I wanted to make sure the stock battery setup was still fully compatible after the conversion.
So now to the bike modifications. When using LiPo's, much attention needs to be given to safe handling. I think it is of paramount importance that the battery pack can be isolated from the outside of bike quickly and easily. This means part of the battery wiring needs to exit and re enter the battery compartment. This is what I came up with.
Basically the internal main power cable from the controller to the battery is cut in about the middle and re routed through a 10mm hole (grommet protected) just infront of the seat post. This position gave me enough room to get a drill in and nicely hides the plug from view when tucked away. It should be noted that CoMo steel doesn't drill easily however, using lots of steps and lubrication, this can be achieved without too much trouble. The hardest part is coming to terms with drilling a 10mm hole in your brand new $7,000.00 bike.
Next job was to fit some good quality plugs to protruding wires. This isolation point also becomes the point where the bulk charger is plugged into.
I used EC5 plugs for this job. These are a really nice 5mm protected bullet plug that plug together firmly but still still disconnect without too much force needed.http://www.hobbyking.com/hobbyking/store/__9194__EC5_5mm_Connector_Pair_.html#
Batteries now slide in as 2 banks held together with velcro wraps. http://arkrc.com.au/products/SCLOCKSTRAPL-Scorpion-Lock-Strap-%28L%29.html
. These wraps are designed specially to hold big LiPo packs in model helicopters and have a high grip sticky surface. They really hold the packs firmly together so perfect for a bike application. Still enough room to plug the packs in without a struggle.
And the finish product ready to roll.
Now to some updated specs:
18s 2p 16ah Zippy LiPo pack
Voltage 75V hot off the charger
1100 W/hr max capacity.
900 W/ hr safe conservative usable capacity
Top speed 70 kph (Confirmed)
Max current: Set to 50A via the CA
Max kW: 3.7kW limited via the CA
Range should be close to a stock Fighter setup. Estimate 60km max but 40km under brisk riding conditions.
Bike weight: 32 kg.
Charging: 1200W Bulk charger. Estimate 1 1/2 hours charge time.
Finally charging needs to be covered. A bulk charger from BMS-Battery will be used.http://www.bmsbattery.com/alloy-shell/29-alloy-shell-1200w-lifepo4li-ionlead-acid-battery-ev-charger.html
I have selected a 1200W LiFePo4 charger re calibrated to 75V peak. Bulk charging LiPo's with a LiFePo4 charger is thread on its own so I wont go into it here except to say its a very effective method of charging high capacity high voltage LiPo's.
And the cost.
Packs are $94 USD per pack = $564.00
Misc Hardware = Approx $80.00
Bulk charger = $140.00
Shipping = $120.00
Total cost = $904.00
Also one of the handy things about this setup is that its now a piece of cake to carry a Aux battery on a seat post mounted rack. You could carry say 3 x 5000mah or ever 3 x 8000mah packs without overloading the rack. With the plug now external, its a 20 second job to plug in and you are ready to go again.