Dan,
I'm sorry, my assumption was for 12V batteries. The bad news is that that each 6V 260Ah battery has only 1560Wh, so you can cut all of my results in half. And with smaller batteries, Peukerts has a bigger impact on delivered energy. Here's my last two tables adjusted for the 6V batteries.
6 * 260Ah @ 6V = 260Ah @ 36V = 9.4kWh
9.4Kwh * 50% depth of discharge = 4.7kWh
110A @ 36V = 3960W. 4700Wh/3960W = 1.18 hours
With Peukert Effect for FLA = 0.7 hours @ 5kts (full thottle)
40A @ 36V = 1440W. 4700Wh/1440W = 3.26 hours
With Peukert Effect for FLA = 2.47 hours @ 3kts
8 * 260Ah @ 6V = 260Ah @ 48V = 12.5kWh
12.5Kwh * 50% depth of discharge = 6250Wh
85A @ 48V = 4080W. 6250Wh/4080W = 1.53 hours
With Peukert Effect for FLA = 0.96 hours @ 5kts (full thottle)
30A @ 48V = 1440W. 6250Wh/1440W = 4.34 hours
With Peukert Effect for FLA = 3.52 hours @ 3kts
Eric
--- In electricboats@yahoogroups.com, Daniel Michaels <nov32394@...> wrote:
>
> Thanks Eric,
>
> First I am using 6 6v batteries for the 36 vlt system and 8 6v batteries for the 48 if that does anything for your figures. I will work a little more with your figures for more understanding. Even using your figures 1.5 hrs at full throttle is more than enough for my application. 5 hrs is way over kill. If one cannot get out of the marina in less time than that he's in the wrong marina.
>
> This system is already being used in yachts so I know it works http://www.electricyacht.com/ They are using a belt drive with a 3 bladed prop. I took the numbers right out of the Atomic 4 book.
>
> Dan
>
> --- On Thu, 8/5/10, Eric <ewdysar@...> wrote:
>
> From: Eric <ewdysar@...>
> Subject: [Electric Boats] Re: Hello
> To: electricboats@yahoogroups.com
> Date: Thursday, August 5, 2010, 3:16 AM
>
>
> Dan,
>
> You've made a common mistake by thinking in amp hours while mixing different voltages. When your're dealing with battery capacities, you need to work in one voltage or switch to watt hours....
>
> This is why it's better to go with the 1kW/ton conversion. Your boat should be fine with a 4kW motor if you install the right propellor. You should find that your boat will power at 3kts around 1500W at reach about 5kts near your 4kW rating. Your new ranges would be as follows:
>
> 6 * 260Ah @ 12v (2P3S) = 520Ah @ 36V = 18.7kWh
> 18.7Kwh * 50% depth of discharge = 9.4kWh
> 110A @ 36V = 3960W. 9400Wh/3960W = 2.37 hours
> With Peukert Effect for FLA = 1.65 hours @ 5kts (full thottle)
> 40A @ 36V = 1440W. 9400Wh/3960W = 6.5 hours
> With Peukert Effect for FLA = 5.83 hours @ 3kts
>
> 8 * 260Ah @ 12v (2P4S) = 520Ah @ 48V = 25kWh
> 25Kwh * 50% depth of discharge = 12.5kWh
> 85A @ 48V = 4080W. 12,500Wh/4080W = 3.06 hours
> With Peukert Effect for FLA = 2.28 hours @ 5kts (full thottle)
> 30A @ 48V = 1440W. 12,500Wh/4080W = 8.68 hours
> With Peukert Effect for FLA = 8.37 hours @ 3kts
>
> You can see that your range doubles by getting the load down from 100A to 30-40A. These range numbers are conservative, but I wouldn't expect anything dramatically different. Gearing is an effective way to get the motor speed matched to the desired prop speed. Many 4-5kW motors generate peak power at 3000-3600 RPM. Running them significantly slower can lead to overheating and lower power outputs. Finding a motor that was designed to produce peak output at low RPM will allow you to run without gear or belt reduction.
>
> Let me know if you need more information.
>
> Fair winds,
> Eric
> Marina del Rey, CA
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