# Solar/Electric boat race questions



## matjomo (Apr 11, 2011)

I am participating in a solar powered boat race in June in Iowa. I am a part of a senior design team from the University of Central Florida and we had our first test run this weekend.

My questions deal with getting more speed from our motor because the tests were somewhat slow. We are running a competition max 36 volt battery array but the circuit is allowed to step up to a max of 52 volts. We ran it through a rudimentary light switch.

We bought an alltrax speed controller but did not connect it because we do not yet have the throttle. 

my question is this: 1. Will the alltrax controller step up voltage and regulate current draw ( ie draw the current we tell it to from the batteries)?
2. If not, how do we make our AGNI motor run faster.

Thanks a lot,

If you have any follow up questions feel free to post them.

Matt


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## matjomo (Apr 11, 2011)

so i found out that the controller doesnt do any of that stuff. Does anyone have any ideas on how i can step up the voltage from 36 V to 52 Volts?

Also, the motor runs at a max current of 400 Amps, which gives the maximum power. Any ideas on how to regulate the amp draw?

sorry for all the electrical questions.. I am a mechanical engineer...


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## Tesseract (Sep 27, 2008)

Alltrax makes perfectly fine controllers in this power range - maybe even the best - so I'd stick with the one you bought and kick up the speed with a mechanical transmission such as a timing belt and pulley system or gears. Dunno how much power you need to transmit, but timing belt systems are amazingly efficient and can handle surprising amounts of power for both size and cost. Alternatively, use a larger diameter/steeper pitch prop that will run most efficiently at a lower speed and higher torque.

I mean, it would seem to me that hull drag and prop thrust would be the two most important criteria for winning a solar powered boat race, and both are squarely in your area o' expertise, ME.


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## Evilsizer (Jan 25, 2010)

have you thought about using super-caps? set them up in series to make up the difference in voltage. then have a button you can press for a "boost" feature. the thing then would be you need to determine how long you want that higher voltage/boost to run, ie 10sec or higher. you would then need to figure how much more energy you need on the super-cap side to do this. it would then take some time to recharge the super caps once all used up. that IMO would be the point to use a DC-DC step-up converter or two to speed up the charge rate of the super-cap bank. be stealthy, have a secret weapon. heheheh

another question that IMO should have been asked is which angi motor?


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## major (Apr 4, 2008)

matjomo said:


> so i found out that the controller doesnt do any of that stuff. Does anyone have any ideas on how i can step up the voltage from 36 V to 52 Volts?


Hi mat,

When talking about DC, you need a boost converter to step up voltage. In the power range you seek, you will not find anything available and an application specific design would likely be beyond your project. If the rules constrain you to 36V battery, get a motor suitable for 36V. To me, it is a lot easier to change a motor winding than to boost the DC voltage applied to it, but then I'm a motor guy 



> Also, the motor runs at a max current of 400 Amps, which gives the maximum power. Any ideas on how to regulate the amp draw?


Sure.....Regulate the "amp draw" by controlling the applied motor voltage (which a motor controller does) or by controlling the load, like changing the speed reduction ratio or prop pitch.

The Agni motor has a very stiff RPM curve w/r/t load for a given voltage. So if you experience less than expected RPM, chances are your battery (or connecting circuit) sag is killing you. Measure the voltage at the motor terminals under load. If that is near 36V (within a couple of V), then you have chosen the wrong motor or as Tess suggests, need to alter the prop characteristics (or hull).

Regards,

major


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## GerhardRP (Nov 17, 2009)

matjomo said:


> I am participating in a solar powered boat race in June in Iowa. I am a part of a senior design team from the University of Central Florida and we had our first test run this weekend.
> 
> My questions deal with getting more speed from our motor because the tests were somewhat slow. We are running a competition max 36 volt battery array but the circuit is allowed to step up to a max of 52 volts. We ran it through a rudimentary light switch.
> Matt


Can you give us more details about the boat and other constraints in the race rules. Also, is the objective time or distance?
Gerhard
Edit: found the website:
http://www.solarsplash.com/index.php
Since you are limited to lead acid, you should look for batteries with the best Peukert coefficient. For the endurance run keep your battery current at exactly the two hour rate.
Gerhard


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