In my cat setup, I finally achieved 4.7 mph at about 550#, 4.2 mph at about 750#, with a single modified T-34 motorguide operating at about 12V, 30 amps measured.
I am busy now refurbishing the hulls and building a deck to accomodate a second motor.
I was considering trying a 16V, 5-cell 40 amp-hr LIFEPO4 battery as a reserve or "turbo" alternative) to one or two lead acid batteries.
Does anyone know if the T-34's (powered through vari-max heads for a 45# thrust motors) will fail under this load, given the limited running time available from the battery?
Is this the following correct?
V=IR
12 = 30R,
therefore, R = 12/30
since R (of the motor) doesn't change with V of the new LiFePO4 battery,
16 = I x 12/30
I = 40 amps.
If this is right, with two motors running wide open, a 40 amp-hour battery should be past dead after 30 minutes running time. Correct?
If the motors survive, can the 16V LiFePO4 battery be recharged from a "12V" solar panel rated at 18-20 Vmp and operated on a timer?
John Casperson
--- In electricboats@yahoogroups.com, "dennis wolfe" <dwolfe@...> wrote:
>
> John, Your battery voltage drops as the battery discharges. As the volts go down the motor speed decreases, the boat slows and requires less power - thus the watts go down. You really want to monitor both volts and amps to test something like prop efficiency. This effect is very pronounced with a tired battery. I also found the cheesy auto parts store connectors I first used caused a lot of loss - the gold plated bullet connectors worked better.
>
> Here is a pretty slick fuse idea, goes right on the battery terminal.
> http://www.westmarine.com/webapp/wcs/stores/servlet/producte/10001/-1/10001/299119/377%20710%201629/0/Breakers%20And%20Circuit%20Prot/Primary%20Search/mode%20matchallpartial/0/0?N=377%20710%201629&Ne=0&Ntt=Breakers%20And%20Circuit%20Prot&Ntx=mode%20matchallpartial&page=CategoryDisplayLevel1&isLTokenURL=true&storeNum=5002&subdeptNum=9&classNum=295
> ----- Original Message -----
> From: john_casperson
> To: electricboats@yahoogroups.com
> Sent: Monday, January 25, 2010 11:37 AM
> Subject: [Electric Boats] Re: kill switch
>
>
>
> Thanks, Denny.
>
> I've never had to wire anything where I didn't have instructions.
>
> I was thinking about putting 100 amp resettables near each battery (+) terminal, the battery hot wires then leading to a 4 position (off, 1, 2, all) battery switch. A pair of hot wires (each protected by a 50 amp resettable) would lead from the battery switch, one to each of the controllers. I'll take a look inside the controllers to see if there is a light duty wire I can interrupt with a $10 kill switch.
>
> I think I'll try making my fairing from plastic decking boards cut on a bandsaw.
>
> I bought 4 APC props (10x6, 10x7, cw and cc) to test on a 30 pound thrust motor pushing the cat hulls but had not got around to it.
> At the weight I was testing (about 650 pounds) each 50 pounds of weight took about .1mph off top speed. My recollection is that you had achieved 5.0 mph with a 300 pound canoe, and I was already achieving 4.3 mph with some setups, which is about what I would predict from your numbers. I was concerned that the big props have to be run deeper to avoid cavitation, and this may cause me problems running up on the beach or operating in shallow water.
>
> My motors draw progressively less watts the longer (say, 15 minutes) that I run them, so it is difficult to say what is a faster setup unless I use a freshly charged hot battery, or normalize for watt draw. I don't know whether this is caused by motor, battery or leads. Everything I was using (ultimately) was new. If you figure it out, let me know.
>
> John Casperson
>
> --- In
>
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