Respect Your Regulator: Safely Charging Lithium Powersport Batteries

Written by Evan Grist. Posted in Tech-n-Tips

The particular charging requirements of these batteries is often not clearly stated by the manufacturer, and plenty of misinformation spread online doesn’t help either. Using the same voltage regulator that worked just fine with your old battery can potentially result in a dangerous lithium-ion battery failure including expanding cases, explosions, or fire. Let’s understand how to safely charge a lithium battery on your adventure bike!

Most powersports lithium-ion batteries are of a type called LiFePO4, or Lithium Iron Phosphate, which is ideal for these applications. By nature, they have a constant discharge rate, and can maintain their voltage under load, delivering full power until almost completely discharged. They are manufactured from multiple individual cells connected together, and these cells have a fairly narrow ideal voltage range.

Below their ideal voltage they cannot be charged efficiently, and above it they are susceptible to poor reliability at best, and physical damage at worst. Your bike’s voltage regulator is responsible for controlling this, and it’s called “average output voltage.” Lithium batteries will generally have some basic built-in circuitry to balance the cells, keeping their output evenly matched for best performance. This is why it is also a good idea to have a lithium or manufacturer-specific battery charger for at home-maintenance, since a powersports charging system cannot provide this functionality.For LiFePO4 cells to be charged most efficiently and last as long as possible, the battery voltage needs to be kept as stable as possible. By nature, a powersports charging system will have some variation in the battery voltage, but it is critical to use the correct voltage regulator to control this factor, called charging voltage ripple.

Normal Regulator Output

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The average output voltage is a key factor in safely and reliably charging lithium batteries. Most common powersports voltage regulators were designed for use with lead-acid and AGM batteries which have an ideal charging voltage of 14.6V. These types of batteries are very tolerant of even higher voltages and will not suffer any issues until sustained use well over 15V. In contrast, lithium batteries have a maximum voltage limit of 14.6V, above which damage can begin to occur. Due to this, a lithium battery-specific regulator should have a much lower charging voltage to protect the battery.

MOSFET Regulator Output

It’s a risky proposition to use a standard voltage regulator with a lithium battery, since the typical charging voltage is already at the maximum range, and any variances in components and construction can push that even higher. Again, fine for a lead-acid or AGM batteries, but why take the risk with your shiny new lithium-ion!? The RMSTATOR lithium battery regulator, for example, has a charging voltage specification ideal for battery protection, ensured and stabilized by using premium components and construction.

The other important part of lithium battery charging is the “voltage ripple,” or variation in the output voltage from a powersports regulator. Voltage ripple in your bike’s charging system output is unavoidable in the way these voltage regulators work, however it is critical to keep it to a minimum for efficient charging and reliability of lithium battery cells.

Normal Regulator Voltage Ripple

Excessive charging voltage ripple can cause the individual lithium cells to become unbalanced and inefficient, affecting their lifespan. Using premium electronic components can make a significant difference, which is often why cheap voltage regulators are much worse in this regard. OEM regulators could solve this component quality issue but are not designed with charging voltage ripple in mind. Poor quality components and construction can introduce noise into the output that is undetectable with a typical multimeter.

MOSFET Voltage Ripple

The best way to improve charging voltage ripple for lithium battery use is with a MOSFET type of voltage regulator, which uses fast and efficient transistors to perform voltage regulation functions. RMSTATOR’s renowned MOSFET regulation circuit is used exclusively in our lithium battery regulators. RMSTATOR’s regulator is designed for universal fitment. It is easy to install, and fits the original regulator mounting location for many adventure bikes. (For more information on MOSFET regulators, see my article “MOSFET MADNESS” in ADVMoto Jan/Feb 2017, No. 96).

___________________Evan Grist is an electrical engineer for RMSTATOR located in Fort Collins, CO, who’s been buying, selling, trading, wrenching on, and riding motorcycles for over 16 years. Evan specializes in powersports electronics, specifically charging and ignition system components. He enjoys street, dirt, and adventure riding, often doing all three in the Northern Colorado mountains on his KTM 950 Adventure. RMStator.com

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