8/25/2021
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Engine Charging Systems and Use with Lithium batteries

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Basics

Most charging system employed on engines for recharging the vehicle’s battery generate an alternating current (AC) with stationary coils of wire (stator), and rotating permanent magnets (see figure 1 below). The AC is then conditioned with a regulator-rectifier to create a DC current/voltage required for charging a battery (see figure 2 below).

Most modern charging systems actually create 3 phase AC power which is then rectified and regulated to create DC charging current / voltage (widespread use since the 1980s). The use of three phase AC creates a DC voltage with less ripple (see the Figure 3 below, green line is DC output).

Figure 3

The AC producing coils are always trying to put out the same amount of power at a given RPM, which creates a problem when the battery is fully charged. Much like a hose filling a pail of water, if something is drawing water from the pail at the same rate it is entering it will not over flow, but if the water keeps coming in with none being taken out, it will over fill.

The regulator rectifier prevents overfilling a battery by shunting the coils, thus limiting the system voltage to acceptable limits (generally 14.2 to 14.6V). See the clipped voltage output of a 3 phase system in Figure 4 below (green line).

The battery’s purpose in the system is the energy storage “bank”, a power source for starting and operating equipment when the engine is not running or at low RPM such as idle speed. Most systems do not charge the battery at idle for the output voltage is too low. This is particularly true for LiFePO4 lithium batteries with a resting voltage of 13.2V.

Motorcycle

A typical motorcycle charging system is shown in Figure 5 below.

Figure 5

Lithium Battery (LiFePO4) Charging Waveform Recommendation

The idea DC profile for charging a LiFePO4 battery is a AC ripple with a frequency > 5kHz and a AC ripple voltage magnitude < 10% (<1.5V). But in the real world, frequency > 500Hz and AC ripple voltage magnitude <1.5V is acceptable.

The voltage ripple amplitude within the cell decreases with increasing frequency for the cell does not have time to react to the change in charge current, due to short time period with higher frequencies.

At frequencies below 5 kHz and high amplitude ripple voltage, the resultant charging current ripple introduces heating in the cells due to the cell resistance (IR losses). Note the “and” in the previous statement, for this is the worst case situation when both are out of ideal ranges.

Of the two, low frequency and high ripple amplitude, an AC voltage ripple magnitude >1.4V causes more heating. Oxidization of the transitional metal can occur with high AC ripple voltage charging at higher currents (> 1C). The oxidation of LiFePO4 occurs at cathode and higher temperatures only speed up the oxidation. The free oxygen (as a result of the oxidation) is then free to react with addition lithium causing further increases to the temperature. If not caught quickly enough, this results in permanent cell damage, and if uncorrected, thermal runaway can result.

Are Vintage Single Phase (or Magneto type) Charging Systems Acceptable for Charging a Lithium Battery?

The quick answer is no, and here is why. Take for example, the Rotax 503 engine (Provision 4; with 4 main mounting bolts on the gearbox) designed with points ignition and pull-starting. It uses a single coil (named magneto for permanent magnet construction) within the stator for auxiliary lighting power and battery charging. Since it is a single coil, it will produce one AC waveform per revolution of the engine (see Figure 6 below for an installation example of this type coil)

The Rotax engine also has a regulator-rectifier has shown in Figure 7 below (part 866-080).

The regulated/ rectifier voltage output of this particular Rotax system is shown in Figure 8 below. Note, the DC output has a low frequency (two pulses per engine revolution, 33Hz at 2000RPM) and high amplitude ripple (full charging output 14.5V).

Figure 8

To compensate for the poor charging voltage Rotax recommended a large 16Ah lead acid battery to act as a buffer, and in some cases a capacitor to smooth the DC voltage. This DC charging voltage while not ideal for a large lead acid battery was acceptable.

This type charging voltage is not acceptable for a lithium battery for its large AC ripple at low frequency (< 5kHz and >1.4V) will damage the cells due to heating and plating (see the above section for lithium battery charging requirements).

Not all older Rotax engines charging systems are the same. The example given above is for a Rotax 503 (Provision 4). The Rotax 582 engine (per the Rotax manual) has a flywheel generator with 12 permanent magnets and 8 coils, so it’s charging voltage would be vastly better with higher frequency (> 200 Hz at 2,000RPM) and less ripple amplitude. A Rotax 503 Provision 8 (late model with 8 main bolts on the gearbox) is also said to have 12 magnets and 8 coils.

Are Automotive / Airplane Alternator Charging Systems Acceptable for Charging a Lithium Battery?

Yes they are. Modern alternator construction differs from the magneto type charging system presented above, for they are typically three phase with multiple magnetic poles so the output voltage is similar to that shown in Figure 3 and 4. The higher frequency AC is a result of having more magnetic poles (typical is >500Hz at 2,000 RPM) and the three phase coil arrangement with three phase rectification produces lower ripple voltage (typical is <1.5V).

An alternator uses battery/internal power to create a magnetic field (electro-magnet) within the rotor (rotating part) versus using a permanent magnet, and the voltage output level is regulated by varying the rotor’s magnetic field. This is a much more efficient method for excess charging voltage/current is not wasted in the form of heat. An alternator’s design offers an additional benefit in that the peak output current is self-limiting, for the maximum charging current is typically demanded when the battery is depleted and voltage is low. But when the battery voltage is low, the resulting magnetic field within the rotor will also be lower, and as such the alternator output will be lower. Figure 9 shows a typical alternator charging system. In addition, automatic over-voltage circuit protection is recommended for your charging system. This is an important backup safety feature to protect the aircraft electrical system from high voltage events (typically > 16V).

Are Automotive / Airplane DC Generator Charging Systems Acceptable for Charging a Lithium Battery?

In most all cases, Yes. Modern DC Generator construction differs from the alternator explanation above, for the output is DC by design (no rectifier circuit). Typically, the construction of a DC generator is the reverse of an alternator, where the coils are on the rotating part (armature) and the magnetic field is on the stationary part. The DC output is created directly by using a commutator to capture each coil’s voltage at the same polarity and amplitude. The voltage output level is regulated by varying the magnetic field. Generators do have a residual magnetism (like a permanent magnet), so they can output charge current even without a battery. Due to the residual magnetism and the regulator design, users should be aware that excessively high charge currents may be seen after engine startup and above rated speed when the battery is at a low state of charge (drained battery).

© 2016-2019 EarthX, Inc. Application Note AN-1601 Rev New

References:
Source 1: Rotax Repair Manual for engine type 532, 1994

AGM Motorcycle VS Lithium: Fact and Fiction

As bikers, we’re passionate folk. We love our rides and we love customizing them, maintaining them, or caring for them. Everyone’s passion occasionally results in a difference of opinion and one of the heated debates in the motorcycle world is batteries. One person will tell you this battery is best, another will tell you this one is, and yet another person will give you an entirely different answer as to which battery you should use for your bike.

One of the big debates is whether to use Lithium batteries or AGM batteries on your bike. What’s the difference and why does it matter? Let’s put these two against one another and lay out the myths then clear it up with some facts.

Lithium and AGM

Husqvarna 324l. If you’re new to a lifelong passion of bikes, we’ll clear up some terms first.

AGM – AGM stands for Absorbed Glass Mat. An AGM motorcycle battery has the positive and negative plates separated by an absorbent glass mat that absorbs and holds the battery’s acid and prevents it from flowing freely inside the battery. The plates are tightly compressed into each cell and held under pressure in a plastic case. Unlike traditional Flooded/Wet batteries, there’s no need to frequently monitor and inspect an AGM battery, and they aren’t damaged by severe vibrations caused by extremely bumpy roads or conditions. AGM stores its electrolyte in a dry, or suspended state, transferred between the glass mat to where the battery needs it.

Lithium – Lithium motorcycle batteries are typically Lithium IRON batteries (not Lithium ION batteries—the ones that have been known to explode or catch fire) and are lighter than lead-acid based batteries. Energy is stored in Lithium ions instead of Lithium metal.

Pros and Cons

On the surface, AGM batteries are often considered the best for your motorcycle because of low self-discharge rates, sturdy construction, less risk of lead sulfate crystal build up, ability to function in lower temps and doesn’t have the same possibility of failure when deep-cycled.

Battery

Lithium Motorcycle Battery Review

However, AGM batteries require a specialized charger and can be easily damaged by improper charging practices.

Lithium ION and Lithium IRON are commonly used to power consumer electronics. Containing inorganic phosphates, Lithium batteries are currently the safest, most fire-resistant rechargeable battery. Discharge remains consistent until a Lithium battery is almost completely empty. But since the tech for them is still new that means they are expensive to manufacture and expensive to purchase. Also, there’s very little to indicate that a lithium battery is reaching the end of its functional shelf-date. It simply stops working altogether once past due for replacement.

Battery Myths and Facts

Myth: Lithium Batteries will explode.
We’ve all heard the stories by now. A smartphone caught fire and exploded, a laptop smoking and in ruins. But note, these stories are always associated with small electronics. The Lithium batteries that go in your bike are constructed from a lithium-iron-phosphate blend that gives up little in power density for significant chemical stability that’s not found in traditional Lithium batteries used in small devices.
Myth: You can use a regular battery charger for your AGM.
No, you can’t. Many AGM battery chargers have microprocessors that will collect information from your battery and adjust the current and voltage, accordingly, safeguarding from charge flooding. Overcharging will kill your battery, whether it’s AGM or Lithium.
Myth: Lithium is unsuitable and won’t start my bike if it’s cold outside.
The truth is any battery in extremely cold temps will have difficulty starting in winter. Lead-acid, AGM, Lithium—all their performance will be affected by the cold.
Fact: Almost all Lithium battery failures occurred in batteries without the right Battery Management System.
A Battery Management System is a sophisticated charger with the built-in technology necessary to balance your discharge/recharge loads on a lithium motorcycle battery. A BMS will shift a battery down when accidental overcharge situations that lead to overheating or fires may occur. No matter what type of battery you use, always purchase a charger/BMS specifically indicated for use with your type of battery.
Fact: Lithium motorcycle batteries weigh significantly less than most lead-acid batteries.
This is completely true. On average a rider can get up to 70% in weight savings with a Lithium battery. If you’re racing your bike professionally or on the weekends, you want the weight savings. If you own a Big-Twin bagger, weight probably won’t mean as much.
Fact: AGM’s have a very low discharge rate.
You can store an AGM battery for extended periods. If not left in a completely discharged state for a large amount of time, they can quickly recharge to over 95% of their capacity.

What AGM and Lithium Motorcycle Batteries Share

  1. Both AGM and Lithium batteries are sensitive to overcharging, you really do need a BMS for monitoring voltage for either.
  2. Older and vintage bikes may experience problems. Healthy motorcycle charging systems put out roughly 14 volts at 2,000 rpm, and a Lithium battery, for example, needs between 13-14 volts to charge. If your bike produces less, the battery won’t charge. The average battery charger is designed for the 8-volt requirements of lead-acid batteries; they will not charge a Lithium battery.

Which has the highest capacity?

Average AGMs have 6 cells roughly 2 volts each, while lithium batteries have 4 cells at about 3 volts each. They’re both 12-volt batteries, but when you look closely at capacity, the number you really want is “amp-hours.” (AH)

AH, or ampere-hour is the amount of energy charged inside your battery that will allow one ampere of current to flow for one hour. It’s a unit of measurement for the rate of electron flow or current in an electrical conductor.

A lithium battery manufacturer usually derives their number from lead equivalency, called a PbEq and this number is what you need to pay attention to. A PbEq number of 20 for example, may only have up to six amp-hours of capacity, which turns out to be less than an AGM battery.

If you want to charge your cam, phone, GPS, Comm-System, and more, the number of PbEq’s will be important to avoid finding yourself stranded in the middle of nowhere with a dead Lithium battery.

Which is better: AGM or Lithium?

The definitive answer is complicated. Your budget and what you’re willing to spend on a battery will be the first thing to consider.

If money is an issue, AGM remains the most accessible to all budgets and that’s a pro if you just spent big on your dream ride and to properly gear up. To be honest, you should not buy a cheap battery for your bike no matter which you choose. The old saying of, “you get what you pay for,” often terribly comes true.

Lithium Motorcycle Battery Shorai

For the fastest charging and overall capacity in addition to lighter weight, and if the PbEq’s are correct and you’ve invested in the right Lithium battery charger, a Lithium battery is going to be your best bet. They tend to generally last longer, can be faster to charge, and have a longer lifespan—so long as you don’t cheap out on the charger.

Lithium Motorcycle Battery Dead

These days, Lithium Iron batteries for motorcycles are stable with excellent internal circuitry, and charging tech has followed that lead with excellent BMS.

How To Charge A Lithium Motorcycle Battery

Ultimately it depends on you, but we highly recommend checking out Lithium-Iron batteries and considering the switch.