Rather than bump this thread - https://forum.allaboutcircuits.com/...-alternator-with-electric-motor.137737/page-2

My question is this, I am looking to buy a cruising boat and want to go electric and am trying to understand the use of an alternator in an electric motor set up.
The point of an alternator in a vehicle is to charge the starter motor however once this is done it makes sense to send that extra energy somewhere.
Also a point that was not made in the above thread, Tesla cars do this so if you do not run your Tesla you will get a flat starter battery even if you leave it on charge. There is a very funny YouTube video of James May having to dismantle his Tesla because of this issue.

 

If you 'want to go electric' why do you need an alternator? What would drive the alternator?
Welcome to AAC!

 

My question is this, I am looking to buy a cruising boat and want to go electric and am trying to understand the use of an alternator in an electric motor set up.
The point of an alternator in a vehicle is to charge the starter motor however once this is done it makes sense to send that extra energy somewhere.

Alternators are are driven by IC engines to charge the battery (not the starter motor), and there is no "excess energy" as the alternator regulator adjusts the output voltage to generate only the power needed by the vehicle and to charge the battery.

If you are thinking of using an electric motor powered from the battery to drive an alternator to charge the battery, that's a perpetual motion idea that will not work, as the overall efficiency of such a setup is likely about 50%.

The only use for an alternator on an all electric boat would be if it's part of a gas IC engine-generator as an emergency backup to replenish the batteries (which may be a good idea on a boat).

 

Rather than bump this thread - https://forum.allaboutcircuits.com/...-alternator-with-electric-motor.137737/page-2

Also a point that was not made in the above thread, Tesla cars do this so if you do not run your Tesla you will get a flat starter battery even if you leave it on charge.

The 12V battery in a Tesla -- not really a "starter", but the car won't go anywhere if it's flat, because it powers the accessories and computers -- is a different situation. These are charged from the main HV (375-400V) battery using a DC-DC converter, not an alternator.

 

Had one of those eureka moments after I posted this. Which is basically what everyone has said. Putting an alternator in would just add an energy drain to the engine so would be pointless annoyingly.

The 12V battery in a Tesla -- not really a "starter", but the car won't go anywhere if it's flat, because it powers the accessories and computers -- is a different situation. These are charged from the main HV (375-400V) battery using a DC-DC converter, not an alternator.

As per the James May video, it does work like an alternator in that it only works when the engine is on however yeah that was part of my eureka moment in that it is not there for starting and more like the coin battery on a motherboard to keep everything working even when you drain the other batteries.

 

Rather than bump this thread - https://forum.allaboutcircuits.com/...-alternator-with-electric-motor.137737/page-2

My question is this, I am looking to buy a cruising boat and want to go electric and am trying to understand the use of an alternator in an electric motor set up.
The point of an alternator in a vehicle is to charge the starter motor however once this is done it makes sense to send that extra energy somewhere.
Also a point that was not made in the above thread, Tesla cars do this so if you do not run your Tesla you will get a flat starter battery even if you leave it on charge. There is a very funny YouTube video of James May having to dismantle his Tesla because of this issue.

Hi,

You can use an alternator to charge a battery but the alternator has to have a rotating mechanical input to generate power to charge a battery. That can be an electric motor, but the electric motor would then have to have a separate input power.

I actually did this a very long time ago. Mount an electric motor with a pully to an alternator with its own pully and a V belt. The input was 120vac for the motor which was a 120vac motor, and the output from the alternator was used to charge a 12v automobile battery. It was essentially a car battery charger.
Sometime later I simplified it to a light bulb in series with a diode and the 120vac line. The charge current was not especially high, but it did charge the battery over time.

Did the same with a motor and air conditioner compressor from an old Cadillac automobile. It was used as an air compressor to run various air tools like a paint sprayer.

The trick with these mods is to get the right rotation (pulley) ratio from the motor to the rotational device, and make sure the mounting is strong enough to support the forces involved.