This is a post somewhat out of the ordinary. If you have no interest in boats, then read no further 😉
I have a boat, an Adec 530, equipped with an old Volvo Penta MB10A (15 HP) from 1976. The motor runs fairly well; it is not consuming a lot of gas and there is really no big fault with it, except that it occasionally leaks cooling water. It has the characteristic sound a two-cylinder inboard boat engine. But I do not expect this engine to run forever, without having to spend a lot of money on a slowly diminishing supply of parts. Also, I am not fond of the the gasoline fumes which are emitted from the engine. The idea of having a clean, near-silently running engine has is alluring.
So, I started to to look at various options. Obviously, electric drive is the conclusion most people would arrive at. The biggest problem with electric drive is the reach of the boat. We need to store energy. The amount of energy contained in one litre of gas and diesel is about 10 kWh. It is a very efficient way to storing energy. The efficiency of a gas motor is ideally 30 %, while on a diesel engine it can be as high as 50 %.
Today, a lot of electric cars are equipped with lithium-ion batteries and an electric motor for propulsion. While the lithium-ion is a good technology, it is not very safe. There are several incidents where people have gotten injured from exploding electronical devices such as phones. This is not something I would like to happen, especially not when you are on a boat.
Acid batteries are also an option, but those are heavy and are sensitive to deep discharge. For instance, a battery of with a charge capacity of 100 Ah should ideally not be discharged below 50 Ah. There are acid-battery technology such as AGM, which address this problem by using thicker lead electrodes and storing the electrolyte (sulfuric acid) embedded in fiberglass mats. However, these batteries are quite expensive and weight about the same as normal acid-based batteries. These are indeed a competetive option. There are other types of acid-based batteries as well, but AGM seems to be the best option.
Lastly, we have LiFePO4 batteries, a more recent type of lithium-based batteries. This, reportedly much safer technology in comparison to regular lithium-ion technology, is the most expensive option. However, the life expectancy of a LiFePO4 cell is much longer than the alternatives, making it less expensive than the above in the long run.
For the engine, I took some inspiration from electric cars. While 230 VAC electric motors are cheap, you need to convert the stored energy into alternating current and raise the voltage. This is not necessarily bad, but it increases the complexity of the solution and there will be a loss of energy in the conversion. Therefore, I decided that a 48 VDC engine would be a suitable option.
There are a few types of electric motors for DC. Brushed motors are cheap but the brushes have a limited life and that would require continuous maintenance, which I like to avoid. Brushless motors (based on Hall effect), have for a long time been expensive, but in recent years they have gotten much cheaper.
The effect required to match the current engine would be around 10 kW. However, I decided to go with a slightly weaker engine. The HPM-5000 from Golden Motor delivers 5 kW of continuous power, which is with my estimates enough for a small boat as mine.
The following is an initial schematic for how the engine and powerbank will be connected:
During this weekend I will hopefully order the parts.
Edit: I have ordered the motor and controller now, which hopefully arives next week.
Edit2: Messy desk