The question of how many hours of continuous battery life is the most popular among electric motor owners, and it's a fundamental problem that every hydraulic motorist faces when planning a fishing trip or an electric ride. Unlike the ICE, where the range depends on the volume of the tank, it all comes down to the problem of the electric motor. battery-capacity And if you're not calculating correctly, you can end up in the middle of a body of water, and you can't get back to shore quickly.
But you can't give a definitive answer of "5 hours" or "10 hours" without specific numbers, and there are too many variables that affect the final result, from the water temperature and the oncoming wind strength to the wear of the battery itself and the speed of the propeller. Traction batteries They behave differently than starters and require a different approach to measuring their lifespan, and in this article, we'll explore the physics of the process, learn how to read the Paykert discharge tables, and learn how to actually extend the time of autonomous navigation.
Before we get to the complex formulas, we need to understand the basic relationship: the harder you push on the handle of gas, the faster the battery discharges, and this dependence is nonlinear. At maximum speed, the motor can suck out all the charge three times faster than when driving at minimum thrust, which is why experienced captains rarely use maximum power, preferring an economical mode for long-distance transitions.
Basic formula for calculating working time
For the initial estimate of operating time, many people use simple arithmetic, dividing the battery capacity in ampere hours by the current consumption of the motor. If you have a 100-Ah battery and the engine at first speed consumes 10 Amps, theoretically it should run for 10 hours. capacity It's always lower than the stated rate, especially at high discharge currents, and this phenomenon is described by Paykert's law, which says that as the discharge current increases, the useful capacity of the lead-acid battery drops.
Also, you can't drain the battery to zero. AGM and GEL batteries The critical threshold is a residual capacity of 20%, and for lithium (LiFePO4), a discharge of up to 5-10% of the nominal value is allowed, although the BMS (battery management system) can turn off the power earlier. If you ignore this fact and calculate the time before the voltage drops completely, you risk planting the battery deep, which will lead to its sulfation and irreversible loss of capacity.
Always reserve 20% of your estimated travel time to ensure you are back on base even when the wind or current is amplified.
And you also have to consider the voltage, because 12, 24 or 36 volt motors use different currents at the same power, and the higher the voltage, the lower the current in the circuit, which means less loss in the wires and higher. System-wide efficiencyTherefore, on large boats with powerful engines, using a bundle of two or three batteries (24V or 36V) not only increases power, but also prolongs the operating time compared to one 12-volt counterpart of the same capacity.
Factors Affecting Energy Consumption
The actual operating time is rarely the same as the manufacturer's data-sheet figures, and there are many external and internal factors that need to be considered when planning a route. screw-loadIf you're swimming against the current or against the strong wind, the motor has to consume more current to maintain the same speed, which drastically reduces the autonomy time.
The second important factor is ambient temperature: the chemical processes inside the battery slow down in the cold, and at 5°C, the capacity of the lead-acid battery can drop by 20-30% compared to the summer levels at 25°C. Lithium batteries They are less sensitive to cold in terms of energy output, but they can not be charged at negative temperatures without preheating.
The third factor is the state of the battery itself and the quality of the connections. Oxidized terminals, thin wires or an old battery with increased internal resistance will eat up some of the energy, turning it into heat. Regular checks of contacts and the use of cables of the correct cross-section is an easy way to improve the efficiency of the system.
⚠️ Attention: The use of car starter batteries for electric motors is only permissible in extreme cases; they are not designed for long-term discharge with low currents and can fail after 10-15 deep discharge cycles, unlike specialized traction models.
Comparison of battery types: AGM, GEL and LiFePO4
The choice of battery type dictates how many hours you can spend on water. Traditional lead-acid batteries (AGM and GEL) are the de facto standard because of the affordable price. But they have a significant disadvantage: when discharged with high currents, their capacity drops, and it is highly recommended to discharge them below 50%, which means that out of 100 Ah of battery you can actually use only 50 Ah, so as not to kill it in one season.
Lithium-iron-phosphate batteries (LiFePO4) They revolutionized the electric motor world, allowing 80-90% of their nominal capacity to be used without harming their life, and they keep the voltage stable until almost the end of the discharge, allowing the motor to run at full power even when the battery is almost dead, and the lead battery in a similar situation will lose voltage, and the motor will start to run sluggishly long before full discharge.
Below is a comparison table showing the difference in effective operating time for different types of 100Ah batteries at a 20 Amp load:
| Type of battery | Nominal capacity | Permissible discharge | Useful container | Working hours (theor.) |
|---|---|---|---|---|
| AGM / GEL | 100 AH | 50% | 50 AH | 2.5 hours |
| LiFePO4 (Lithium) | 100 AH | 10% | 90 AH | 4.5 hours |
| Starter (WET) | 100 AH | up to 70%* | 30 AH | 1.5 hours |
| LiFePO4 (with heating) | 100 AH | up to 10% (in the cold) | 85 AH | 4.2 hours |
And you can see from the table that a lithium battery actually gives you almost two times the time of travel compared to an AGM analog of the same capacity. possession Lithium is higher, although it pays off in 3-4 seasons of active operation due to more charge-discharge cycles.
Why does the battery starter run out faster?
Starter batteries have thin lead plates designed to give off a huge current in a few seconds (start the engine). During prolonged discharge with low current, the plates quickly deform and crumble, sharply reducing capacity.
The effect of speed and mode of operation on autonomy
Many owners mistakenly believe that current consumption increases linearly with motor speeds. In practice, it's more complicated. At minimum speeds (1-2 divisions on the motor scale), consumption can be as low as 3-5 Amps, which allows you to stretch the charge of a 100-amp battery for 15-20 hours. This is the ideal mode for trolling or quietly moving along a windless reservoir.
When switching to average speeds (3-4 divisions), consumption increases sharply to 15-25 Amps. Here the law of water resistance comes into force: to increase the speed of the boat by 2 times, the engine power (and consumption current) must be increased by 8 times. The optimal mode for maximum range is 30-40% of the maximum power of the engine.
☑️ Optimizing energy consumption
Maximum speed (full gas) is a power eater. In this mode, current can reach 40-50 Amps or higher. The battery in this mode is under stress, its voltage drops and the heating increases. Prolonged use of full gas not only puts the battery down quickly, but also reduces its total life. Use maximum power only for short-term maneuvers or planing (if the boat allows).
Practical tips for extending the battery
There are a number of proven methods to get the most out of the charge. First, keep track of the rotor. Any grass that winds, or line or blade damage increases resistance and causes the motor to consume more current to maintain speed. Regular cleaning propeller It is a free way to increase efficiency.
Second, distribute the load properly in the boat, and the stern or nose stern increases the contact area of the hull with water, which leads to increased resistance, try to keep the boat even, and bottom cleanness also matters: fouling with shells or algae can reduce speed and increase energy consumption by 10-15%.
⚠️ Attention: Don’t leave the motor running in the air (without water) even for a few seconds. Lack of water cooling can cause the windings to overheat and the motor to fail, which will be a much bigger problem than a dead battery.
Third, use the right wiring. If you notice that wires are warmed, then the cross section is not enough for current current. Thick cables reduce voltage loss and deliver more energy to the motor. For currents up to 30 Amps, a section of at least 6 mm2 (10 AWG) is recommended, and for currents above 50 Amps, 10 mm2 (8 AWG) and thicker.
A speed reduction of just 20% can increase battery life by almost two times, thanks to exponential increases in water resistance.
How to extend the life of a traction battery
Battery life is one thing, battery life is another. In order for a battery to last for years, it needs to be properly charged and stored. Lead acid batteries (AGM/GEL) can't be stored in a discharged state. If you're finished with a season, be sure to fully charge the battery and put it on the battery. conservatory Or recharge once a month.
Lithium batteries are more unpretentious, but they also have their own specifications: their BMS (controller) can go into deep sleep during long-term storage if the voltage drops below a certain threshold. Lithium is optimal for storage at a charge of 60-70%, especially if you plan a long break in operation, which reduces the degradation of cell chemistry.
Use only high-quality chargers with a multi-stage charge algorithm. Cheap rectifiers can under-do or overflow the battery, which has a critical effect on its life. A good charger will determine the saturation phase and enter the maintenance mode, which is especially important for the battery. GEL batteriessensitive to recharging.
Can I use a car battery for a outboard motor?
You can technically start the motor, but you don't recommend it on a regular basis. Starter batteries are designed for short high-current pulses, not for long-term energy output. Deep discharge will quickly disable such batteries. Use only Deep Cycle batteries.
How do you know if the battery is completely drained?
For a 12-volt system, a voltage drop of up to 10.5-11 volts is critical. However, modern motors have built-in charge indicators or audible alarms, and it is best to focus on the built-in voltmeter of the motor or set a separate capacitance indicator.
Does cold water affect the electric motor?
Water itself has little effect on the motor, but cold air and water cool the battery, reducing its rechargeable capacity. In addition, cold water is usually denser, which can slightly increase the resistance to the boat, but the main blow is taken by the chemistry of the battery.
Do I need to recharge the battery after every fishing trip?
Yes, lead-acid batteries are preferably recharged immediately after use to avoid sulphation of the plates. Lithium batteries are more tolerant of storage in a partially discharged state, but a full charge before the next trip will ensure maximum operating time.
When buying a new battery, pay attention to the date of its production. Lead batteries lose capacity even when stored, so the "fresh" battery will last longer.