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Powering a 8KW motor from a generator


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Hello,

 

Rather than replacing my engine I was thinking about fitting a 8KW Lynch electric motor, the voltage can be set from 12-72V. I want to be able to power the motor directly from the generator, is there a way to calculate what power output I would need on the generator and what kind of ac to dc converter I would need?

 

Happy new year

Mitch

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I wouldn't go for basing the full current requirements direct from a generator, but have a batteries in the DC link, this will allow for short term peak currents. Running the motor at 72 v will keep the current down for the DC motor controller, and assuming around 200amps shouldn't be stupidly expensive.

Starting current typically eight times current at rated output.

That's for an AC induction motor, a DC motor starting current is up to the controller and available current

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There are a number of light aircraft that are powered by batteries and an electric motor, they get an hour of flight per charge. You could well get a similar system running from solar, but with a bigger battery could have several hours per day of no fuel boating.

Running an engine to drive a generator to drive a motor to drive a propeller sounds like a lot of low efficiency conversions to waste a lot of fuel

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Most electrical propulsion installation use 48-volts

 

If 48-volts is selected then flat out around 170 amps will be used

 

Typical installation the battery bank is around 500 / 700 amp hours capacity combined with a DC generator which as a minimum will have an output of 150 amps

 

For this installation will be on the low side

 

Keith

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Take a look at car hybrid systems. Remember that your electric propulsion motor won't be running at full chat all the the time, so a set of batteries to take up the slack and fill in when power requirements are highest will be by far the most practical and economic solution.

 

A relatively small and commonly available 240v AC generator driving a smart mains charger should be fine once the average power requirements are catered for in terms of battery bank size and charge capability. A bonus is that batteries can also get charged when shore power is available, with no additional equipment expense.

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What is the point of fitting an electric motor if it's going to be run from a noisy diesel?

 

I've seen a couple of boats on the Thames which had hydraulic drives powered by big diesel generators. While they were much quieter than a marine diesel engine I couldn't really see the point either. As a basic rule of physics every time you convert one form of energy to another there are losses due to heat, friction, etc, so it just seems inefficient to me. There are plenty of ways to reduce engine noise if that's the aim - but modern diesels with appropriate exhaust systems are fairly quiet to begin with.

 

Running a hydraulic drive from a generator is one thing, and I don't know much about running a big electric motor from a generator, but if I had to choose one I'd go for the former - hydraulic just seems more reliable to me.

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Take a look at car hybrid systems. Remember that your electric propulsion motor won't be running at full chat all the the time, so a set of batteries to take up the slack and fill in when power requirements are highest will be by far the most practical and economic solution.

 

A relatively small and commonly available 240v AC generator driving a smart mains charger should be fine once the average power requirements are catered for in terms of battery bank size and charge capability. A bonus is that batteries can also get charged when shore power is available, with no additional equipment expense.

If you go back to the OP's original question, he want's to run the motor directly from a generator not via a battery.

Edited by Flyboy
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Hello,

Rather than replacing my engine I was thinking about fitting a 8KW Lynch electric motor, the voltage can be set from 12-72V. I want to be able to power the motor directly from the generator, is there a way to calculate what power output I would need on the generator and what kind of ac to dc converter I would need?

Happy new year

Mitch

Just one 8kw motor? I don't think that will be near enough power for a decent size narrowboat. It will move it of course, but you'll have very little power available.

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Surely, Lynch could advise? I'm sure a soft-start would be possible in which case you would not need an engine of much more than 8kW. You'd probably not want to run an engine at its MCR all day. An 8kW motor is going to limit the top speed a bit.

 

Has anyone rented the all-electric boats on the Mon & Brec?

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