The transition to electric propulsion in water tourism and fishing has ceased to be an experiment of enthusiasts, becoming a reliable standard for small boats. Boat electric motors They allow silent movement, no vibrations, and no exhaust gases, which are critical for fishing disguise and passenger comfort, but the efficiency of the entire system depends on the right engine-traction battery bundle.
Many beginners make the mistake of buying a powerful motor but saving on a power source, which leads to rapid battery degradation and disappointment as a result. Traction batteries A significant difference from car starter batteries is the ability to deliver power in low currents over a long period of time, and understanding the physics of the discharge and charging process will allow you to avoid buying incompatible equipment and save significant money in the long run.
In this article, we will analyze the technical nuances of the selection of components, consider modern technologies for energy storage and give practical recommendations for operation. trolling motor will work out the stated time without losing power throughout the season.
Principles of operation and types of boat electric motors
The basis of any electric motor is its ability to convert electrical energy into mechanical rotation of a propeller with high efficiency. Modern models are divided by type of control into motors with a manual tiller and foot-controlThe choice of control type affects not only comfort, but also the power consumption of the system, since electronic control units can consume energy even in standby mode.
The key is the thrust, measured in pounds (lbs), which is not equivalent to the maximum speed of a boat, but indicates the force required to overcome the resistance of water. It is important to understand that increasing thrust requires a proportional increase in current, which directly affects the discharge. batteryFor light PVC inflatable boats, 30-40 lbs is usually enough, whereas for metal dural boats with two passengers, 50-60 lbs are already required.
Special attention should be paid to the cooling system. Most modern motors are water-cooled, which increases their efficiency, but requires careful attention to the depth of the dip of the lower unit. Insufficient rotor entraction can lead to cavitation and a sharp drop in efficiency, increasing current consumption by 20-30% without increasing speed. This is a common mistake that is made when installing the motor on the transom.
⚠️ Attention: Never run the motor out of water, even for a few seconds. Lack of water cooling can instantly damage the osteoils and windings, which is not a guarantee.
Selection of voltage on-board network: 12, 24 or 36 volts
The voltage of the onboard network is the foundation on which the entire power supply system of the boat is built. 12-volt The systems are easy to maintain and are suitable for small power up to 1 hp (about 500-600 watts). However, as the power increases, the current in the circuit becomes too large, which requires the use of huge wires and leads to energy loss for heating.
Transition to 24-volt or 36-volt This system allows you to reduce the current by half or three times at the same power of the motor, this allows you to use smaller cables, reduces the heating of connections and increases battery life. For motors with a capacity of more than 1.5 hp, the use of voltage above 12 V becomes almost a prerequisite for efficient operation.
The realization of high voltage is achieved by successively connecting several batteries or using specialized batteries with the right number of cells. When serially connecting, the capacity (Ah) of the system is not added up, and the voltage increases, so all batteries in a bunch should be absolutely the same in age, model and degree of wear.
Can batteries from different brands be mixed?
It is strongly recommended not to connect batteries from different manufacturers, different capacities or with different mileage in series, this will lead to a skewed voltage when one battery discharges before another, which will cause a deep discharge and failure of the entire chain.
Comparison of battery technologies: AGM, GEL and LiFePO4
The market offers three main types of traction batteries, and the choice between them determines the budget and specifications of your kit. lead-acid batteries (WET, AGM, GEL) are cheap and time-tested, but have limitations in depth and weight.LiFePO4) batteries are a modern alternative with radically different specifications.
AGM (Absorbent Glass Mat) technology allows batteries to be completely sealed and maintenance-free, which is ideal for boats. They withstand more charge-discharge cycles than conventional liquid batteries, but still it is not recommended to discharge them by more than 50% to save life.GEL) batteries are even more resistant to deep discharges but are very sensitive to charging modes.
Lithium batteries LiFePO4 They allow you to use up to 80-90% of the capacity without harm to chemistry, weigh 2-3 times less than their counterparts and have a built-in BMS protection system. Despite the high initial cost, their resource in charge cycles (2000-5000 versus 300-500 for lead) makes them economically viable in the long term.
| Parameter | AGM / GEL | LiFePO4 (Lithium) | Starter (WET) |
|---|---|---|---|
| Depth of discharge (DoD) | 50% | up to 80-90% | less than 20% |
| Weight (with equal capacity) | Severe (100%) | Light (~35%) | Medium. |
| Duration of service (cycles) | 300-500 | 2000-5000 | 50-100 |
| Sensitivity to cold | High. | Requires protection when charged | High. |
When buying a lithium battery for a boat, be sure to make sure that the built-in BMS has charge protection at negative temperatures, otherwise the battery can be irreversibly damaged.
Calculation of capacity and time of autonomous operation
The art of balancing weight, cost and desired travel time is the right capacitance calculation. The current consumption of an electric motor is nonlinear: at low speeds it is minimal, but when you go into plane or move against wind and flow, the current can increase by 3-4 times, so you need to calculate the system by average and maximum consumption.
The formula for calculating the working time is simple: Time (h) = Capacity (Ah) × Depth coefficient / Current consumption (A)For example, a 100 Ah battery at a discharge of up to 50% will give 50 Ah of power. If the motor at medium speed consumes 20 Amps, then the stroke time is 2.5 hours. However, you should consider that with the discharge the voltage drops, and to maintain power the motor can consume more current.
It is also necessary to take into account the loss in the wires and efficiency of the controller, it is recommended to lay a reserve of capacity of 20-30% above the calculated values, this compensates for the aging of the battery and unforeseen conditions, such as strong headwinds or currents, which will force you to work the engine at higher revs.
☑️ Calculation of the food system
Rules of operation and maintenance of batteries
The durability of the battery depends not so much on the quality of manufacture as on the operating conditions. For lead-acid batteries, deep discharge and, more importantly, discharge storage is destructive. The sulfation of the plates begins immediately after discharge, so charging It should be done immediately after returning from the water.
Temperature is also critical: high temperatures accelerate chemical reactions and self-discharge, shortening battery life; low temperatures reduce the capacity to be delivered; and charging a lead battery in the cold can cause irreversible electrolyte damage; lithium batteries, in turn, require special attention when charging below 0°C.
Regular diagnosis of the condition includes checking the rest voltage and electrolyte density (for service models). Storage) significantly extends the life of the battery by keeping it in optimal condition during the off-season.
⚠️ Attention: Do not use conventional car chargers to charge traction gel or AGM batteries. High currents and the lack of proper saturation phase can "boil" the electrolyte and destroy the battery structure.
Electrical wiring installation and safety
The quality of the connections in the motor circuit directly affects safety and efficiency. The use of insufficient cross-section wires leads to a drop in voltage in the battery to the motor, which manifests itself in the loss of power and strong heating of the cables. For currents above 40A, it is recommended to use copper wires with a cross-section of at least 16 mm2 (AWG 6), and for powerful systems - 25 mm2 and above.
All connections must be protected from moisture and oxidation. In salt water or just high humidity on a body of water, open contacts quickly corrode, increasing resistance. Be sure to use adhesive thermal shrinkage and special sea terminals. Installation of a main fuse or automatic switch on a plus wire in the vicinity of the battery is a mandatory requirement of fire safety.
The battery itself needs attention, too, and the battery must be locked in a sealed box that prevents water from reaching the terminals and protects against mechanical damage during rolling, and the box also functions to collect possible electrolytes in case of depressurization of the housing (relevant for liquid and AGM batteries).
A properly matched cable cross section and reliable contact insulation are more important than the brand of the battery itself, and poor contact will negate the benefits of any battery, even the most expensive.
How to store a boat battery in winter?
For winter storage, the battery must be fully charged and disconnected from any consumer, including the alarm system or trim system. Lead batteries are best stored at temperatures from +5 to +15 ° C, periodically (every 1-2 months) checking the voltage and recharging if necessary. Lithium batteries can be stored at lower temperatures, but also in a charged state (about 60-70%).
Can I use a car battery for an electric motor?
Theoretically, it is possible, but it is highly recommended that starter batteries (SLI) are designed to give off huge current for a short time (start the engine), and not for long-term operation. Deep discharge, inevitable when the engine is running, will quickly disable such a battery (in 10-20 cycles), while the traction battery will last for years.
Why does the engine lose power at the end of the day?
This is a classic sign of battery discharge. As the discharge goes, the voltage drops at the terminals. Since the power is equal to the product of voltage per current (P=U*I), when the voltage decreases, the motor cannot give out full power, and the boat speed drops, and the cause can also be overheated motor or poor contacts.