Alternator Failures

[SOLAR SUPPORT]

You can sometimes unwittingly force the alternator used in your boats to operate above their capacity. For example, it is very common to increase the available battery capacity. As the battery capacity increases, the operating time required to fill them with the same alternator will increase and you will need to operate your alternator for a longer period of time at a capacity that converges to the power limits.

If the ambient air temperature is above 25C° and the engine compartment is not well ventilated, the alternator will overheat at full load. The insulation of the copper windings inside can burn at 100°C and above. Under these conditions, you must protect the alternator from burning.

Some examples of alternator overheat protection measures:
1-Addition of thermostat controlled fan. It works when the alternator overheats. It turns off when the alternator temperature drops to normal.
2-To keep the engine speed as high as possible in order to increase the cooling capacity of the alternator fan during charging.
3-To cut off the alternator charge in a safe way when the above measures are not sufficient. It allows the alternator to cool down itself quickly.

Another event that threatens alternator is the sudden disconnection from the battery while operating under high charging load. In the meantime, since the strong magnetic field formed in the stator windings of the alternator cannot find a place to discharge, it creates a very high voltage current in the alternator. High voltage permanently damages the alternator and/or sensitive electronic devices that are open at that time. This event may occur as a result of the user accidentally closing the battery switch while the alternator is running.

Another scenario is that the Lithium battery, which is trying to protect itself against high voltage charging, shuts down uncontrollably to protect itself during alternator charging.

Under this topic, it is aimed to exchange information about alternator operation, load-temperature measurements, thermal control circuits against overheating, external regulators, alternator operations, alternator controls required for Safe Lithium battery charging.

Please share your past alternator failures on board and tell others why they happened.

[PaulCrawhorn]

Victron video

https://youtu.be/jgoIocPgOug

[SOLAR SUPPORT]

Mitsubishi 115A Alternator under load

Ambient temp: 30 C°
Engine Rpm: 1500
Alternator charge current : 75A
Temperature reading: C°

https://youtube.com/shorts/YsLCaQtuzis

[abroadreachtrvl]

Never had a failure.

Letrika alternator 120amp with a Balmar 618 regulator.

Runs about 86c while pushing out 95-100 amps at fast idle 1400 engine rpm.

Balmar is set to derate at 105c

This is charging a 300ah bank.

[SOLAR SUPPORT]

A Successful Alternator Operation.

Boat owners usually want to increase the energy storage capacity of their batteries with insufficient capacity, if the necessary space is available when the batteries whose service life has expired need to be renewed.

Classic car alternators have efficiency at a level that does not cause problems under suitable conditions for the car's not very large batteries and vehicle consumption requirements. These alternators are prone to overheating in narrow compartments with insufficient ventilation and insulation in boats, and at increasing temperatures with engine heat.

The working conditions of the alternator, which is installed at the factory, become heavier at this point. Because the working time and charging current required to charge the growing capacity batteries are higher than before and those are forcing the operating limits of the alternator.

My Mitsubishi 115A alternator was assembled at my Volvo Penta engine's factory. I need to charge my batteries, which I upgraded from 180 Ah LA to 380 Ah AGM, when they are at 50% SOC level. But the alternator was overheating at 25°C ambient temperature. I realized this after measuring 130 C° with a laser heat meter. Overheating first causes the insulation of the alternator's windings to burn, and the alternator windings start to burn by short-circuiting.

An alternator can cause conditions on the boat that could cause a fire. While this is the case, let's see that the vast majority of alternators do not have a self-control to protect against overheating that will destroy them. However, an overheated alternator could protect itself against burning by reducing the energy it produces. The thing I wouldn't want most on my boat is an alternator that could cause a fire.

In order to control the risks I mentioned , I had two options. I had to buy a specialy manufactured alternator which has an external regulator or modify my existing alternator. I had to disassemble and reassemble my alternator because the cost was much lower.

For the rotor excitation, I disconnected and isolated one of the existing electrical transmission brushes from the regulator. After soldering the two cables to the cuts, I connected these cable ends to the normally closed 70 C° Thermostat that I mounted outside of the alternator. Trials yielded positive results.

[SOLAR SUPPORT]

When the alternator is operated at around 60~70% of its label capacity for more than 10~15 minutes, it will overheat depending on the ambient temperature. The longer the alternator runs under load at these levels, the more likely it will heat up and burn, just like the forgotten pan on the stove. I keep the engine room door open to reduce the temperature in the engine compartment and therefore provide a cooler operating environment for the alternator. I plan to install a vent on this door near the cooling fan inlet. The operating tests of the thermostats, which are used to cool the alternator and to temporarily interrupt the charging for this purpose, were successful. Click for the video link.

https://youtube.com/shorts/1TS_VMBs9Qk?

The cooling fan starts working around 70°C. If this cooling is not sufficient to lower the alternator temperature, battery charging is temporarily stopped until the alternator returns to its normal temperature.