Considerations for a replacement Tidalforce battery

I'm very fortunate with my 4 Tidalforce bikes in that I have been able to locate and use relatively new or only slightly used Tidalforce hub batteries with my TF bikes! Of course, this will change as the current front batteries start dying or losing capacity. Hopefully, this won't be any time soon!

In thinking about upgrading or replacing the front hub battery, here are the key things I"m trying to keep in mind.

The battery needs to be able to handle the load the Tidalforce bike needs. If you have a 750 watt Tidalforce bike, then with a quick calculation, (750W/36V= 20.83Amps) you'll need a battery that can put out about 20 amps continuously. This is sometimes difficult to find since most battery manufacturers (especially the Chinese ones), don't really publicize the maximum discharge rate (known as the "C") of their batteries.

When looking at a battery, the "C" rate is equal to the capacity of the battery. If your battery is rated at 10Ah, then 1C would be 10A. So using this rule, you will need a 10Ah battery that can output 2C. If you have a 20Ah battery, then it must be able to output 1C, etc.

If you have a Tidalforce 1,000 watt motor, then you'll need a battery that can output 27.7 Amps maximum since that is what the motor will draw. (1,000W/36V=27.77A). If you have a 10Ah battery then you'll need one that can output 2.7C.

Also, the controller that is located in the Tidalforce motor housing is a current based controller and not a voltage based one.

If you're trying to maximize the speed of the bike, then you should use a battery that can be customized to be higher than the standard 36V nominal rating of most bike batteries. Remember that higher voltage means higher speed. Larry H. known as Deerfencer1 on the Tidalforce forum has proven this. He is able to get higher than average speeds with his X powered S-750 named "Uma" because his LiPO batteries don't sag very much from their nominal voltage because they have very high C ratings.

LiPO batteries designed primarily for RC flying and driving toys are designed to have very high C rates. Typically they can be 20C to 30C for an 7.4-18V battery. This translates into very high current output capabilities. An 18V battery putting out 30C equals 540A! Of course that battery won't last for very long, but it will definitely give you all it's got in a very short amount of time! Of course, I don't recommend you run the batteries down by drawing such high current from them!

However, if they can truly deliver these amazing currents, then they must have very low internal resistance which means that the batteries will not heat up much when used heavily. This is definitely not true of the NiMH batteries in Tidalforce front hubs! I've noticed huge amounts of sag from my 1000W S-750 X motored bike I call "Red." Voltage drops down to almost 30V when I ride my bike at wide-open-throttle or WOT. I was shocked to find this out recently.

So in order to keep the speed up and to utilize my X motor to it's fullest capabilities, I need to find out 1 critical thing.

What is the high voltage cutoff (HVC) of the Tidalforce motor.

I need to find this out by testing the controller with a variable power supply and find out the what the actual voltage the TF bike controller will not accept and just shut the controller down. If I have a variable power source that can vary in small increments from 36V up to around 50V, I should be able to find this out. This number may vary with each bike since it's an analog circuit and there are variances in the parts and in the wiring.

After discovering this number, I then need to design a low-sag battery that will come very close to this HVC so that I can maintain the highest speed.

The A123 20Ah prismatic cell may just be the perfect choice. It is made up of 3.65V maximum voltage cells and so can be customized to voltages in increments of 3.65V.

This means that a 36.5V battery would be made up of 10 of these cells.
An 11 cell pack would give 40.15V.
12 cells would give you 43.8V.
13 cells would give you 47.45V.

Along with the maximum charge voltage, the batteries can be charged with custom settings on the charger. The Hyperion EOS 1420i NET3 charger does this very well. It can be customized to charge to any voltage you select.

So after determining the HVC of the Tidalforce controller, we will design a battery to suit it to perfection!

More later,
Ambrose