Hi Dave,
I have some figures based on my boat, which is a ex-racing trimaran and so has a long narrow centre hull, which when motoring is really all thats in the water. The outer hulls occasionally kiss the water so don't contribute to drag much at all when motoring. So she's well suited to be driven at low power. At 500 watts I can get around 2 knots on average, but I've seen 3 knots on occasion - perhaps there was a little current in my favour. you can see a graph of performance at
http://currentsunshine.com/?m=200908
The genset I have is a Honda 1000 which produces a maximum continuous output of 900 watts. I've tried it on a 15A charger but it shuts down immediately on overcurrent. And I figure thats because we need to use the actual voltage that the charger operates at, rather than its nominal 48 volts. Its probably set around 57 volts or thereabouts (or 4 x 14.25 in your case), and as well we need to allow something for losses, lets say 20%. Then the figures look like this:
57 x 15 x 1.2 = 1026 watts.
At this power its no surprise that the little Honda couldn't run it. I'm now using a 10 amp charger and the Honda 1000 handles it fine. The charge rate is over 500 watts, and so I should be able to manage 2 knots without drawing anything from the battery bank. As yet I haven't had the opportunity to do such a test. I'd like to do that soon - I have in mind to adjust the throttle so that the draw from the motor exactly matches the charger input and watch and see what speed is realistic.
The nice thing is that if there is wind I can sail, and so the circumstance where I would be wanting to use this method would be no wind, so its likely I could limp home.
Cheers
Chris
On 04/03/2010, at 3:03 PM, Dave Hackett wrote:
I've seen some post on this group that they can run their Honda 2000 generator plugged into their shore power plug and use their battery charger to "limp" home. I'm wondering about the numbers.
If I have a quad battery charger (eg Pro Charge) rated at 15 amps per battery (x4 = 48v), the full draw on the generator would only be (4 * 15A * 12V) = 720 watts. I just can't imagine getting even 2 knots at this power level. Am I missing something or do the chargers produce more then 15A when the draw out the other end is greater then 15A? Would this potentially burn out the battery charger?
DaveH
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