T-Pain Is On A Boat: Re: [Electric Boats] Re: Hello

Thursday, August 5, 2010

Re: [Electric Boats] Re: Hello

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@yahoo.com> wrote:

From: Eric <ewdysar@yahoo.com>
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.

> 36v at 140 amps run wide open
> 6 * 260 Ah batteries / 50% = 780 usable Ah. 780 / 140 amps = 5.5 hrs.

Your 12V 260Ah batteries = 3120Wh. Three in series are 36V 260Ah or 9360Wh. Six in a 2 parallel, 3 Series (2P3S) configuration equals 36V 520Ah or 18,720Wh. 50% depth of discharge puts you back to 260Ah or 9360Wh. Your load of 140A @ 36V is only 1.85 hours. You haven't stated what battery types, but at a high amperage load like this, Peukert's Effect will come into play. If these batteries are flooded (FLA) then your effective capacity will be closer to 1.2 hours. Here's the same info in a table form

6 * 260Ah @ 12v (2P3S) = 520Ah @ 36V = 18.7kWh
18.7Kwh * 50% depth of discharge = 9.4kWh
140A @ 36V = 5040W. 9400Wh/5040W = 1.85 hours
With Peukert Effect for FLA = 1.2 hours @ full thottle

> 48v at 180 amps 8 * 260 Ah batteries / 50% = 1040 usable Ah. 1040 / 90
> (180/2) amps = 11.5 hrs

8 * 260Ah @ 12v (2P4S) = 520Ah @ 48V = 25kWh
25Kwh * 50% depth of discharge = 12.5kWh
180A @ 48V = 8640W. 12,500Wh/8640W = 1.45 hours
With Peukert Effect for FLA = 0.9 hours @ full thottle

I'm not sure why you halved the load for your 48V calculation, but at 90A @ 48V your motor is only putting out 4320W or less than 6hp. Gearing won't change that, it only swaps speed for torque, the power stays the same.

The performance chart from Universal Motor Division that I've seen for Atomic 4 engine shows that an A4 produces 9hp at the crankshaft at 1500RPM. If you don't change the propellor, you will need 9hp at 1500rpm to get the same performance. 9hp = 6750W, it doesn't matter if it's from gas, diesel or electric. If we figure 80% efficiency for your motor and controller (check the performance chart of the motor that you are considering), then 6750W output needs 8400W of input from the batteries. That is very close to the 48V figure that you used. But Atomic 4 drivelines and props were notoriously inefficient to allow for the 1:1 drive and high RPM requirements.

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

--- In electricboats@yahoogroups.com, Daniel Michaels <nov32394@...> wrote:
>
>
> 36v at 140 amps run wide open
> 6 * 260 Ah batteries / 50% = 780 usable Ah. 780 / 140 amps = 5.5 hrs.
> run at half throttle or less and you will go much farther same as if you
> throttled back on the Atomic 4.
>
>
>
> 48v at 180 amps 8 * 260 Ah batteries / 50% = 1040 usable Ah. 1040 / 90
> (180/2) amps = 11.5 hrs throttle back even more and even I need some
> sleep.
>
>
>
> Is any of my math correct. I gave it my best shot.
>
>
>
> Dan
>