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Old 08-28-2014, 02:43 PM   #81
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Re :Battery powered propulsion

Just to put battery vs diesel into perspective the familiar single wet cell deep cycle GP 27 battery holds about 1500 watts or 1.5 KWh when new and fully charged. It can produce 1.5 KW energy for one hour, then it is dead. At high discharge rates energy delivery is less than that and shown on the data sheets linked below but ignored for clarity.

http://www.trojanbattery.com/pdf/TRJN0111_ProdSpecGuide.pdf



Looking at engine makers spec sheets you will often see both a hp and KW power rating. 946 watts equates to 1 hp. The Hp and KW ratings have no time limit as long as fuel is available.



If a boat needs 25 HP to move it satisfactorily we need about 23.6 KW (25*946=)continuously.



Rounding everything off to simple numbers that 23KW power, or 25 HP, equates to 15 of the previously mentioned GP 27 batteries full energy content. (full discharge) ( 23/1.5=).



15 batteries may not seem excessive until you realize that the batteries will use up their 23 KW in one hour while the diesel will produce 23 KW until it runs out of fuel.



Batteries are indeed getting better but they would have to get better by 500% to power that same boat 5 hours. Liquid fuels have high energy content per gallon or cu ft. Tough to beat with a stored energy system like a battery.
And that is why Lead is Dead.

I use LiFePO4 and would never even try electric propulsion with lead acid batteries. My early proof of concept is an electric kayak that with just 64 lbs of lithium gives me 80 nm range.

The above mentioned Motorcat 30, while not as efficient as my kayak, would consume less than 300 Whr per mile at 5 kt. Thus a 36 kWhr lithium bank good to 80% DOD would give a range of 100 miles. That is only 750 lbs of LiFePO4 cells.
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Old 08-28-2014, 03:26 PM   #82
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Thanks SKi, brain fart there.

It should be 12 Batteries not 15, sorry but I could not edit the post to correct it
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Old 08-28-2014, 03:29 PM   #83
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So bob how much more power is in the equivalent of a gp27 with Li technology??

I don't think you would use 25 HP on your kayak


2X??
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Old 08-28-2014, 03:41 PM   #84
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This is an edit of the previous post to correct the 746 watts per hp error.


Re :Battery powered propulsion

Just to put battery vs diesel into perspective the familiar single wet cell deep cycle GP 27 battery holds about 1500 watts or 1.5 KWh when new and fully charged. It can produce 1.5 KW energy for one hour, then it is dead. At high discharge rates energy delivery is less than that and shown on the data sheets linked below but ignored for clarity.

http://www.trojanbattery.com/pdf/TRJN0111_ProdSpecGuide.pdf



Looking at engine makers spec sheets you will often see both a hp and KW power rating. 746 watts equates to 1 hp. The Hp and KW ratings have no time limit as long as fuel is available.



If a boat needs 25 HP to move it satisfactorily we need about 18.9 KW (25*746=)continuously.



Rounding everything off to simple numbers that 18KW power, or 25 HP, equates to 12 of the previously mentioned GP 27 batteries full energy content. (full discharge) ( 12/1.5=).



12 batteries may not seem excessive until you realize that the batteries will use up their 18 KW in one hour while the diesel will produce 18 KW until it runs out of fuel.



Batteries are indeed getting better but they would have to get better by 500% to power that same boat 5 hours. Liquid fuels have high energy content per gallon or cu ft. Tough to beat with a stored energy system like a battery.
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Old 08-28-2014, 03:49 PM   #85
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So bob how much more power is in the equivalent of a gp27 with Li technology??


2X??
Like night and day for many reasons. A group 27 high end is 105 ahr on the easy 20 hour rate and weighs 57 lbs.

My 100 ahr LiFePO4 cells is derived from a brutal 1 hour rate and weighs 31 lbs.

If the group 27 got its ahr rating from a 1 hour test (pulling 100 amps for 1 hour instead of 5 amps for 20 hours) it would be empty in 20 minutes due to Peukert effect and deliver 32 ahr.

Now move on to usable ahr, lead 50% DOD, LiFePO4 80% DOD. If the load is 100 amps, you have 10 minutes of run time on the lead acid whereas you would have 48 minutes run time on the battery that weighs 1/2 as much.

Cycle life, 400 cycles group 27, 2000 cycles LiFePO4.

Voltage sag, a lot at high current draw for LA, nil for lithium.

Charge acceptance, for the same reason you don't have voltage sag, you get outstanding charge acceptance with LiFePO4.

There is more, but you get the idea.
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Old 08-28-2014, 04:01 PM   #86
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I guess I missed it but how many KW rating in a 27 size equivalent?
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Old 08-28-2014, 04:07 PM   #87
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Quote:
Originally Posted by bayview View Post
I guess I missed it but how many KW rating in a 27 size equivalent?
100ah, discharge in 1hr, that's 100a. Assuming 12v, that's 1.2kW for an hour.
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Old 08-28-2014, 04:16 PM   #88
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I guess I missed it but how many KW rating in a 27 size equivalent?
A kWhr rating isn't quite comparing apples to apples when concerning the size of the load.

A LA group 27 would be at the 20 hour rate 1260 Whr with a 5 amp load.

At 50% DOD (recommended for LA for good cycle life) gives a usable 630 Whr.

I have a couple of 100 ahr LiFePO4 that are a bit smaller than a group 27 and 1/2 the weight.


One of these is 1300 Whr with a 100 amp load, and higher with the common 5 amp load. Usable at 80% DOD is 1040 Whr.

The main thing to remember is this, at a 100 amp load....

The LA group 27 has 192 usable Whr

The LiFePO4 has 1040 usable Whr.
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Old 08-28-2014, 04:24 PM   #89
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I should have mentioned that the ideal cats for this application are no different than most cats, that being "weight sensitive". A big bank of conventional batteries would quickly eat up your bridge-deck clearance and performance efficiency.....all the more reason to utilize the lightest possible storage.
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Old 08-28-2014, 04:51 PM   #90
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I should have mentioned that the ideal cats for this application are no different than most cats, that being "weight sensitive". A big bank of conventional batteries would quickly eat up your bridge-deck clearance and performance efficiency.....all the more reason to utilize the lightest possible storage.
Your right, have to watch the weight. While 750 lbs of lithium batteries sounds like a lot of weight, consider the other areas weight is saved with that size propulsion/house bank. No AC gen set needed, just a inverter. Since the bank is also the house bank, save 320 lbs over the common (4) 6 volt golf cart batteries. Weight savings of (2) Torqeedo 4.0 vs (2) 60 hp outboards is another 300+ lbs, so it is a wash on weight. Of course if you did it with lead acid batteries, the cat would be a slug.
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Old 08-28-2014, 05:05 PM   #91
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Bob: I chose the makers 1.5 kW spec to keep it a simple caparison to fuel. your batts also seem to be about 1kw so there is no fundamental difference in the distance that the example boat could run. Throwing around various discharge rates and acceptance rates doesn't refute the point that batteries are not a reasonable replacement for fuel in boats.
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Old 08-28-2014, 05:13 PM   #92
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The other thing I got to wondering about is the fire danger of big parallel battery banks. Are there lots of breakers between batteries?

One failed in short battery would cause all the rest to dump current at a very fast rate. We see this happen with just a few in parallel causing some excitement but 12 or 24 or more on parallel could get very exciting with several hundred amps from many batteries available
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Old 08-28-2014, 05:43 PM   #93
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That is why I'm using LiFePO4 chemistry. It doesn't have the energy density of other lithium cells but they are safer than all the others including lead acid.

I never parallel for capacity (even when I was putting together off grid LA banks), but chose cell capacity for the job in a single series string.

LiFePO4 cells are 3.25 volts and come in 20, 40, 60, 90, 100, 160, 180, 200, 300, 400, 700, and 1000 ahr sizes.
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Old 08-28-2014, 05:59 PM   #94
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Bob: I chose the makers 1.5 kW spec to keep it a simple caparison to fuel. your batts also seem to be about 1kw so there is no fundamental difference in the distance that the example boat could run. Throwing around various discharge rates and acceptance rates doesn't refute the point that batteries are not a reasonable replacement for fuel in boats.
I'm not throwing rates for the fun of it. Usable energy storage is what is being discussed for propulsion and the question was asked is how a group 27 stacks up to a LiFePO4.

On a 100 amp load (typical in electric propulsion)
The LA group 27 has 192 usable Whr so range on a single 12 volt battery assuming 300 Whr per mile, is 0.64 miles

The LiFePO4 has 1040 usable Whr at 1/2 the weight, and range on a single 12 volt pack is 3.5 miles.

A rather large difference don't you think?

Read up on Peukert Effect.
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Old 08-29-2014, 01:15 AM   #95
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I am familiar with reduction depending on rate it is shown in the Trojan data. As I said I was trying to demonstrate the inadequate energy density of batteries for propulsion of boats. Using worst case Lead discharge rates for your comparison merely says that your batteries are better. So what, they are still not going to power a troller.
How many GP 27 Li equivalents would be needed to produce 25 hp for 1 hour?
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Old 08-29-2014, 01:27 AM   #96
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I am familiar with reduction depending on rate it is shown in the Trojan data. As I said I was trying to demonstrate the inadequate energy density of batteries for propulsion of boats. Using worst case Lead discharge rates for your comparison merely says that your batteries are better. So what, they are still not going to power a troller.
How many GP 27 Li equivalents would be needed to produce 25 hp for 1 hour?
You just need to pick the right boat and you won't need 25 hp. The designers of the Motorcat 30 have done some tests with electric propulsion and achieved 5 kt on just 1500 watts. That is 300 Whr per mile.

Do the math, 750 lbs of LiFePO4 cells is 36,400 Whr X .8 (80% DOD) = 29,120 usable Whr / 300 = 97 mile range.
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Old 08-29-2014, 09:27 AM   #97
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Like night and day for many reasons. A group 27 high end is 105 ahr on the easy 20 hour rate and weighs 57 lbs.

My 100 ahr LiFePO4 cells is derived from a brutal 1 hour rate and weighs 31 lbs.

If the group 27 got its ahr rating from a 1 hour test (pulling 100 amps for 1 hour instead of 5 amps for 20 hours) it would be empty in 20 minutes due to Peukert effect and deliver 32 ahr.

Now move on to usable ahr, lead 50% DOD, LiFePO4 80% DOD. If the load is 100 amps, you have 10 minutes of run time on the lead acid whereas you would have 48 minutes run time on the battery that weighs 1/2 as much.

Cycle life, 400 cycles group 27, 2000 cycles LiFePO4.

Voltage sag, a lot at high current draw for LA, nil for lithium.

Is there some way to know LiFePO4 Ah at a comparable 20-hour rate? Would it be 2000 Ah (from the math)?

What are costs like? Initial acquisition, arm and a leg and your firstborn? Several boat bucks? Or...?

Switching one bank at a time would mean needing a separate charger for the different chemistry, yes?

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Old 08-29-2014, 10:24 AM   #98
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5 kts on 1500watts is5 knots on 2 hp. Does anyone believe that? Maybe with a canoe but who cares about canoes.

Americans aren't familiar with kW ratings for engines so the discussion becomes foggy where as we all know hp.

Just remember 746 watts or .746 kW equals one hp. (Thanks Ski)
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Old 08-29-2014, 12:10 PM   #99
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5 kts on 1500watts is5 knots on 2 hp. Does anyone believe that? Maybe with a canoe but who cares about canoes.

Americans aren't familiar with kW ratings for engines so the discussion becomes foggy where as we all know hp.

Just remember 746 watts or .746 kW equals one hp. (Thanks Ski)
It has got to the point that your not seeking information but rather arguing every point.

I've known 746 watts equals 1 hp for about 50 years.

I also know in a water medium it takes close to a 8 fold increase in power to double your speed.

Since boat builders do not give drag coefficients for their hulls, you have to compute from the vessel's top speed and hp required down to hp needed for the slower cruise speeds.

The Motorcat 30 runs 25 kt on 120 hp. Do the math!!!!

So it comes as no surprise the Motorcat designer was able to achieve 5 kt on a 1500 watt Minn-kota.
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Old 08-29-2014, 12:19 PM   #100
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I believe I am sticking to the point of battery propulsion of the type of boats discussed herenot constantly throwing out diversions and saying do the math. Be nice if you would show the math you promote so we can all learn something.
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