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Old 09-05-2014, 01:54   #16
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Re: LiFePO4 For Propulsion: Bottom Balancing, Cabling?, Mastech Power Supply as Charg

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Originally Posted by westwinds View Post
If you still have a running diesel engine, I would plot the engine RPM against speed through water. (no wind or current, speed run in both directions and take an average speed) Then find the propeller curve for the boat engine and look at the horsepower vs. RPM and finally plot the horsepower vs. speed. You could of course do the same thing with a table. What you will find is that the curve is not linear. If you double the horsepower you do not come close at all to doubling the speed. So, at lower speeds, you get much better range. At a power draw of 10.5 KWH, your range will be approximately 10 miles. Someone may want to check my numbers. I assumed hull speed and 80% efficiency. With the above table or graph, you might determine that you want a smaller electric motor for a much better range. Another option is to put a speed controller on the motor for your present design and develop the above graph for different power settings and speed. You could also make a graph of range and speed using the amp-hours available with the batteries you have selected. My last thought is you may want a generator to extend your range, probably of smaller horsepower than the electric motor where the batteries supply extra power for short periods with the extra thrust is needed.

The above calculations assume no wind and current. A calculation using GPS speed and power setting for actual conditions at the actual time of the sail would be a better idea, but for design purposes, the above graphs would be a good idea.
Thanks very much for taking the time to share all the info, and I'm sorry I didn't post that I'm beyond the point of calculating all of this. I chose to go with an engineered system that is basically a "plug and play" setup. Except for wiring the back-plane circuit board, the motor is in, aligned to the shaft, and the controller with most of the hardware is already installed. I'm just now getting to wiring up the battery pack and such... Yes, you are correct about much of this. I plan on a cruising speed under motor alone of around 3 1/2 to maybe 4 knots -- depending. This worked out to nearly 20 miles (on paper) with my original 160AH LiFePO4 pack, but when I went to buy my 16 160AH battery cells (from an EV car manufacturer going out of business), I made the mistake of asking how much it would cost to get 32 cells and double my "pleasure". So he gave me a slightly better deal, and for the price of $110 bucks each, I took the plunge for 32 new prismatic cells. Although that is quite a deal, it was later that I realized my 'battery greed' created the problem of not being able to fit the entire pack into the boat without separating the battery into two halves, or...running two separate 16s packs. Now that I have confirmed from several sources that this is not that big of a deal, I'm getting ready to wire them up in a 2p16s configuration (after I fabricate some containment boxes/end plates). Anyway, I appreciate you taking the time to run all this by me, and I have to ask, are you using motor propulsion on your sailboat also? Because if you're not, you've certainly done part of your homework. Thanks again!
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Old 09-05-2014, 09:20   #17
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Re: LiFePO4 For Propulsion: Bottom Balancing, Cabling?, Mastech Power Supply as Charg

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Bob,
What is your overall opinion of the quality of these units? The KP-K 2000 watt charger looks like an amazing deal, especially since it can be set to a custom setting depending on what your particular LiFePO4 cells need.
Thanks very much for pointing me in this direction. I've sent them an email with a few questions...before I pull the trigger on one.
They work as advertised. To keep the weight and materials down they used a thermo switched fan that kicks on after about 5 minutes of full output and will stay on until current taper.

Note the factory setting for LiFrPO4 58.4 volts (3.65 VPC), so you might want to top balance your bank.

I've got about 400 charge cycles from 80% DOD on this charger, not a hiccup.

Shipping was a bit slow.

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Old 09-05-2014, 13:37   #18
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Re: LiFePO4 For Propulsion: Bottom Balancing, Cabling?, Mastech Power Supply as Charg

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Originally Posted by Wireless1 View Post
Thanks very much for taking the time to share all the info, and I'm sorry I didn't post that I'm beyond the point of calculating all of this. I chose to go with an engineered system that is basically a "plug and play" setup. Except for wiring the back-plane circuit board, the motor is in, aligned to the shaft, and the controller with most of the hardware is already installed. I'm just now getting to wiring up the battery pack and such... Yes, you are correct about much of this. I plan on a cruising speed under motor alone of around 3 1/2 to maybe 4 knots -- depending. This worked out to nearly 20 miles (on paper) with my original 160AH LiFePO4 pack, but when I went to buy my 16 160AH battery cells (from an EV car manufacturer going out of business), I made the mistake of asking how much it would cost to get 32 cells and double my "pleasure". So he gave me a slightly better deal, and for the price of $110 bucks each, I took the plunge for 32 new prismatic cells. Although that is quite a deal, it was later that I realized my 'battery greed' created the problem of not being able to fit the entire pack into the boat without separating the battery into two halves, or...running two separate 16s packs. Now that I have confirmed from several sources that this is not that big of a deal, I'm getting ready to wire them up in a 2p16s configuration (after I fabricate some containment boxes/end plates). Anyway, I appreciate you taking the time to run all this by me, and I have to ask, are you using motor propulsion on your sailboat also? Because if you're not, you've certainly done part of your homework. Thanks again!
No electric power on mine, which is small enough to use a paddle for short distances! The reason I could carry on the way I did is horsepower is the same whether it comes from batteries or diesel. Do you have a power controller so you can go to a slower speed to get further range?
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Old 19-05-2014, 00:31   #19
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Re: LiFePO4 For Propulsion: Bottom Balancing, Cabling?, Mastech Power Supply as Charg

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Originally Posted by westwinds View Post
No electric power on mine, which is small enough to use a paddle for short distances! The reason I could carry on the way I did is horsepower is the same whether it comes from batteries or diesel. Do you have a power controller so you can go to a slower speed to get further range?
Yes, I have a Sevcon Gen4 controller and a hall effect forward/reverse throttle setup. The Sevcon also has regen available if I get the boat sailing fast enough, but I'm not counting on much of that.
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