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Old 29-12-2015, 09:52   #196
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Re: Tug of War - Electric vs Diesel

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Elco states that the efficiency of their motors is 85% to 92%. As I understand it the loss is primarily due to heat creation. If a diesel looses 35% of it's power to heat & an electric motor loses 15% there's a 20-27% increase in efficiency with electric. This means you need a lot less electric hp to equal diesel hp.

Based upon Don's numbers which appear to be correct I typically use only 9 hp to run at 80% of hull speed on a 30' waterline length (6 tons). This is further supported by the fact that several Scout owners have replaced their 43hp Volvos with 30 hp Betas & report good results. Maybe the EP-2000, rated at 14.1 KW (19hp) max & 8.5 KW (11.4 hp) continuous would work.
You are confusing the efficiency at converting the power source into usable propulsion with the available HP. Both engines put out the rated shaft HP but for the same available amount of fuel, the electric motor will go much further.

The problem is even with electric motors being wildly more efficient at converting electricity into propulsion, the battery volume equivalent to a gallon of diesel holds such a tiny amount of energy, that a gallon of diesel will take you several times the distance as an equivalent volume of battery.
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Old 29-12-2015, 09:52   #197
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Re: Tug of War - Electric vs Diesel

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As I stated assuming both motors are rated in shaft HP (ie:crankshaft), the usable HP is the same as standard auxiliary devices such as the water pump and standard size alternator are already accounted for.

It's only if you start adding after market accessories that it makes a difference. Of course if you are comparing a diesel with a mechanical fridge compressor you have to add in an alternate way to power the fridge. With modern solar systems, these devices are becoming less common as there isn't the need.
OK. When you referred to shaft horsepower, since we are talking boats I assumed you meant "propeller shaft", not "crankshaft" since shaft HP (meaning propeller shaft) is a common term in marine applications.

Now that we've cleared that up I think we are saying the same thing.
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Old 29-12-2015, 10:03   #198
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Re: Tug of War - Electric vs Diesel

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It's been said before - but deserves repeating: don't size an auxiliary engine on a sailboat based on what you "typically use". It needs to be sized to provide sufficient power to get you safely through adverse situations such as fighting strong currents, headwinds and rough seas.


If you will never have to make headway against an adverse current and your marina is current free, always calm and never has 15 kt winds blowing you out of your slip then go ahead and install the very smallest engine or motor that will give you headway. Otherwise it may be prudent to have a little extra power available for those Oh Sh(ucks) moments.
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Old 29-12-2015, 10:11   #199
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Re: Tug of War - Electric vs Diesel

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I'm no expert but I think the voltage of the batteries has to equal the voltage of the motor. Of course different batteries provide more or less amps but if you have a 24 volt motor you would need two 12 volt batteries. The EP-4000 is a 108 volt motor so it needs 9 12 volt batteries to create that voltage.
Scout,

From reading this and a few of your other posts I think you are missing one piece of the puzzle.

To run an electric motor (or any other electric device for that matter) yes you certainly need the correct voltage but you also need the amps. Motors are rated by their power in Watts or kiloWatts. Watts are volts X amps. So you could have lots and lots of volts but if you have a tiny battery that can only supply a few amps you are missing half of the equation.

You can have a battery rated at 12V but if that battery is a flashlight size battery it doesn't matter how many volts it makes if you hook it up to a really big electric motor, say one in a freight train. Even if you had a 1000 Volt flashlight battery you aren't going to move that train.
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Old 29-12-2015, 10:29   #200
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Re: Tug of War - Electric vs Diesel

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OK. When you referred to shaft horsepower, since we are talking boats I assumed you meant "propeller shaft", not "crankshaft" since shaft HP (meaning propeller shaft) is a common term in marine applications.

Now that we've cleared that up I think we are saying the same thing.
Crankshaft or propeller shaft, I've never head of an engine manufacturer claiming the power used to run the water pump or other standard devices as part of the HP rating which was the primary point I was making.

Of course assuming both diesel and electric motors are rated the same way, it won't make much difference crankshaft or prop shaft HP. You might get some minor efficiency differences with a different transmission but certainly not enough to get the same performance with an electric motor of half the HP as some are claiming.
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Old 29-12-2015, 10:35   #201
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Re: Tug of War - Electric vs Diesel

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Scout,

From reading this and a few of your other posts I think you are missing one piece of the puzzle.

To run an electric motor (or any other electric device for that matter) yes you certainly need the correct voltage but you also need the amps. Motors are rated by their power in Watts or kiloWatts. Watts are volts X amps. So you could have lots and lots of volts but if you have a tiny battery that can only supply a few amps you are missing half of the equation.

You can have a battery rated at 12V but if that battery is a flashlight size battery it doesn't matter how many volts it makes if you hook it up to a really big electric motor, say one in a freight train. Even if you had a 1000 Volt flashlight battery you aren't going to move that train.

No! Power <> Energy!

That 12 or 1000 Volt flashlight sized battery would be capable of producing the same power (Amps or Watts) as a huge battery bank of the same voltage (if you disregard factors such as internal resistance ).

The problem is that it can only do it for a tiny fraction of a second before its stored energy is depleted.

It's the lack of Amp hours or kWh (energy) stored in the battery that is the problem , not the number of Amps or Watts (power) that it can produce.
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Old 29-12-2015, 10:38   #202
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Re: Tug of War - Electric vs Diesel

[QUOTE=Scout 30;2000160 Amps is just short for amp hours.[/QUOTE]

NO IT"S NOT!!!!!

Amps v Amp hours v Amps/Hr
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Old 29-12-2015, 10:40   #203
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Re: Tug of War - Electric vs Diesel

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Scout,

From reading this and a few of your other posts I think you are missing one piece of the puzzle.

To run an electric motor (or any other electric device for that matter) yes you certainly need the correct voltage but you also need the amps. Motors are rated by their power in Watts or kiloWatts. Watts are volts X amps. So you could have lots and lots of volts but if you have a tiny battery that can only supply a few amps you are missing half of the equation.

You can have a battery rated at 12V but if that battery is a flashlight size battery it doesn't matter how many volts it makes if you hook it up to a really big electric motor, say one in a freight train. Even if you had a 1000 Volt flashlight battery you aren't going to move that train.
Good point, flashlight batteries are probably not the way to go. Seriously though, I'm not trying to design a system here. Elco has already done that. I'm just saying what their system consists of & what they report for performance. If the consensus is that they are lying about the estimated performance possible I have a hard time believing that. That would not be a great business model.

Electric Engines 101 | Inboard Boat Motors | Elco Motors
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Old 29-12-2015, 10:47   #204
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Re: Tug of War - Electric vs Diesel

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Point taken. I'll use AH from now on.
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Old 29-12-2015, 11:02   #205
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Re: Tug of War - Electric vs Diesel

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While I am clearly not an electrical expert you clearly are what is your take on Elco's EP-4000 numbers? I know there are a lot of variables but generally speaking do they make sense to you based on 9 12v 198-255 AH batteries?

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Old 29-12-2015, 12:02   #206
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Re: Tug of War - Electric vs Diesel

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While I am clearly not an electrical expert you clearly are what is your take on Elco's EP-4000 numbers? I know there are a lot of variables but generally speaking do they make sense to you based on 9 12v 198-255 AH batteries?

Elco Motor EP-4000
I'm no electrical expert either - I just play one on the internet
Looking at their figures:
The numbers suggest a speed of 5 knots. They don't state how many kWh of battery storage they are basing the numbers on but we can work that out. Their 50 gal for 76 hours for diesel implies they are working on 10 HP based on standard consumption figures. That is about 7.5kW.
They claim about 5.3 hours on battery so that means about 40kWh of energy used. Avoiding running the batteries below 50%, that means you need 80kWh of storage.


Your 9 x 12 V x 255Ah batteries give you 27.5 kWh so you need 3 times that many. So you are looking at fitting 27 such batteries somewhere to meet their figures.

They also quote an 8.5kW genset. After that first 5 hours, you are going to be using all of the realistically available power from it to power the engine - there will be nothing left to recharge the batteries.

So 25 miles or so in calm condition on batteries, after which you are going to be running on diesel until you can stop somewhere and recharge.
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Old 29-12-2015, 12:52   #207
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Re: Tug of War - Electric vs Diesel

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I'm no electrical expert either - I just play one on the internet
Looking at their figures:
The numbers suggest a speed of 5 knots. They don't state how many kWh of battery storage they are basing the numbers on but we can work that out. Their 50 gal for 76 hours for diesel implies they are working on 10 HP based on standard consumption figures. That is about 7.5kW.
They claim about 5.3 hours on battery so that means about 40kWh of energy used. Avoiding running the batteries below 50%, that means you need 80kWh of storage.


Your 9 x 12 V x 255Ah batteries give you 27.5 kWh so you need 3 times that many. So you are looking at fitting 27 such batteries somewhere to meet their figures.

They also quote an 8.5kW genset. After that first 5 hours, you are going to be using all of the realistically available power from it to power the engine - there will be nothing left to recharge the batteries.

So 25 miles or so in calm condition on batteries, after which you are going to be running on diesel until you can stop somewhere and recharge.
I believe they are basing their numbers on 9 batteries & the biggest AH batteries they sell are 255 AH so it looks like the 5 hour range on batteries alone is unrealistic. In the hybrid mode they are running the generator from the start, not starting it when the batteries are down to 50% so they are including both the batteries & the generator when estimating hybrid range. However, it's really not clear what generator at what speed gives them what range. Worst case it appears they are saying you would need a 12 KW generator at 60% speed to get a 76 hour range. At the end of the 76 hours I assume that means that the batteries would be at 50%.

I wonder if someone from Elco would want to chime in on this thread. I'll try contacting them. I think it would be to their benefit to let us know what kind of numbers they've actually achieved with repowers.
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Old 29-12-2015, 13:04   #208
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Re: Tug of War - Electric vs Diesel

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Old 29-12-2015, 13:11   #209
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Re: Tug of War - Electric vs Diesel

I shot Elco an email & asked them to join in this thread. We'll see what happens.
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Old 29-12-2015, 14:20   #210
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Re: Tug of War - Electric vs Diesel

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Elco states that the efficiency of their motors is 85% to 92%. As I understand it the loss is primarily due to heat creation. If a diesel looses 35% of it's power to heat & an electric motor loses 15% there's a 20-27% increase in efficiency with electric. This means you need a lot less electric hp to equal diesel hp.

Based upon Don's numbers which appear to be correct I typically use only 9 hp to run at 80% of hull speed on a 30' waterline length (6 tons). This is further supported by the fact that several Scout owners have replaced their 43hp Volvos with 30 hp Betas & report good results. Maybe the EP-2000, rated at 14.1 KW (19hp) max & 8.5 KW (11.4 hp) continuous would work.
So, once you start to run an electric motor off a diesel genset, you get both the 35% losses of the diesel and the additional 8-15% losses of the electric motor, PLUS heat losses in the generator itself, and other losses in batteries and speed controllers etc...
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