Solarboat

Discussion in 'The Projects Forum' started by tomakos, May 1, 2009.

Feb 18, 2009
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Dear people,

I'm working for a project to make an electronic circuits for the electronic system for a solarboat. We want to make the effectivity of the circuit as high as possible. Because we are going to do races with it.

Now we want to make it like this:

We have a lipo battery of 44.4V and 20Ah (we're using a PCM to charge and discharge), solarcells at 44.4V and around 30A, and a PM motor. (motor circuits is not included in this circuit I'm making).

The circuit should measure and adept the voltage of the battery and the solar cells constantly . the circuit should take in mind what weather it is and what the distance it is untill the finish line of the race.

Now we want to do it like this:

We want the motor to be supplied by the accu and the solar cells together (to get as close as possible to the nominal workpoint of the motor). Therefore we need to regulate the supplied current of the battery to make it last whole the race. this shoudl be done to connect a potentio meter at the gat of a transistor which at his turn is connected to the battery.

further we want to use switches to use different circuits as the weather changes (one for full sun and no clouds and one for clouds)
by example when it's cloudy we use the battery and the solarcells together to the motor input but when the sun suddenly breaks through there's going to be a power peak which the circuit should moderate the lead the extra power to charge the battery with or mabye a few condensators.

Now I know my english isn't that good so if there are any questions just ask.
But as you understand i like to have some tips/maybe better ways to do this or just to get started.

2. Bernard Expert

Aug 7, 2008
5,226
600
Fools rush in where only angles fear to tread, & I'm no angel, but here goes: Wow, big boat[boat or bot?]; solar panel about 8 feet by 36 feet?
Questions: 1. Length of race in meters or feet?
2. Average speed of boat?
3. Maximum and average current drain of motor at what operating voltage?
4.How is boat's direction controlled
Some things you might need: Efficient speed controller[PWM]; Efficient buck-boost battery charger; Coulometer to follow battery condition; current monitors for battery,motor, & solar panel
To me PCM is pulse code modulation. What is an accu? accumulator or battery?

3. PRS Well-Known Member

Aug 24, 2008
989
36
Seems to me you just wire in your solar cells to charge the batteries and then use the batteries for power. If the sunlight gets brighter they will charge faster, if it gets dimmer they will charge more slowly and there's nothing you can do about that. In cars and trucks the batteries are in parallel with the alternator.

I'm trying to understand your problem. Are you saying that in bright sunlight you want to run just off the solar panel? What's the difference between using the solar panel to charge your battery and running directly off the solar panel? The way I see it you get the same result. I mean it's six one way and half a dozen the other.

4. Bernard Expert

Aug 7, 2008
5,226
600
Suggest that you learn as much as you can about Li Po batteries before using; try Googling Li Po battery charging , what an eye full.

5. PRS Well-Known Member

Aug 24, 2008
989
36
I think I see your point now. You want a high tec logic circuit to make your boat go as far as it can using solar power and drain the battery on a 'smart' basis such that it runs out of charge as you cross the finish line?

This approach would be an advantage over the plain old battery-charging technique because?

Feb 18, 2009
13
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the lenght of the race is in meters.

average speed is wanted around 17-20 km/h

we are using a 1.1 kW at 48V PM motor

direction is going to be controlled by a proppellor.

with accu I mean battery (in our language we call it accu or battery thats why my mistake).

I think it is an advantage because it is easier to end the race with a empty battery and thus every available energy we got was used.

I think of you use the solar cells to charge to battery and use the battery to drive the motor, that you'll get the problem that at the end of the race their will be still some energy in the battery and is thus energy which is not used and is lost.

Every bit more power we can get, we need to get to improve the effectiveness.

7. PRS Well-Known Member

Aug 24, 2008
989
36
I think I have the idea now.

It just occured to me that with a 'smart' boat, you'll be wanting to monitor the speed. Coincidentally, you can determine the battery state by the speed of the motor.

As for sunlight, you can use a photoresistor or diode. The variation of current or voltage can be amplified if needed, then used to drive an ADC (analog to digital contverter). This information can be used to tell your controller to disconnect the battery (via electronic switch and relay). With the battery disconnected you'll be running strictly on solar power.

8. Bernard Expert

Aug 7, 2008
5,226
600
Using pure speculation to see difference[ before tomakos last post]; Motor 2kW @ 36V, solar ave 20A, course 10 nautical mi., first est on time 2 hr.
Using battery50A, and solar, 20A, speed 8.4 knots, ran for .4 hr,remainder on solar only, speed 4.5 knots, finishing with total time of 1.875 hr.
Proratting battery over 4 time periods of about 30 min ea gave a total time of 1.78 hr. Closer than than I expected.
Thanks for update, but how many meters? Since useing both accum and solar, motor speed will not give battery condition. Try Googling boat, speed vs power ,several interestin sites.

9. Bernard Expert

Aug 7, 2008
5,226
600
Lost attachment, must be n new month.

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Feb 18, 2009
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I cant tell the exact distance we have to cover but i know if you sail with a speed of about 18km/h you will need 12hours to finish whole the race. but the race is seperated in 6different days so 1day you will sail about 2hours.

the battery voltage is limited (of you use lipo's) to 44.4V nominal. and the capacaty of the battery is limited for 20Ah.

11. PRS Well-Known Member

Aug 24, 2008
989
36
I rethought the issue and I think that you are confusing the issue of getting from point A to point B with the least amount of power is not the same as getting from point A to point B the fastest. You say it's a race. Very well, then. Put your solar panels in parallel with your battery and supply your motor from the combination. You save nothing and you gain nothing by refusing to charge your battery.

12. Bernard Expert

Aug 7, 2008
5,226
600
WE'll get it straight eventually; my take is that the boat runs for two hours, greatest distance is winner for thet heat, but averaged over six runs, so winner is greasest total distance traveled. With 48 V motor, it will never reach full output with either 44v sources or combined. Maybe use full solar in series with a battery-buck ckt., so that battery supplies the difference to maintain 48 V combined. Need a graph of solar V vs load, for several sun conditions. Wish it was 36 V motor.

13. thingmaker3 Retired Moderator

May 16, 2005
5,073
8
Actually, a charge controller is absolutley required in this application. ALWAYS use a charge controller with LiPo batteries!! With no charge controller, those 30A from the PV will destroy the battery. With a polymer battery, this destruction includes fire.

Fortunately, Tomakos plans to use a PCM charge controller. These are specifically designed for Li-polymer batteries.

Feb 18, 2009
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I've never used LiPo batteries before but I've done a lot of research about those batteries.
But am I correct to say that a pcm is enough to guarantee the safety? Because I've read too that the PCM doesn't control the balancing of the cell. Or am I mistaken here?

Btw I'm also using MPPT for the solar cells

Last edited: May 6, 2009
15. Bernard Expert

Aug 7, 2008
5,226
600
Do you have the battery , if so is there a tap on each individual cell ? How many people will comprise the underway crew, choose light ones, weight is your enemy. Did you see the solar boat races on the net, looks like " cats"or pontoon boats are the thing.

16. thingmaker3 Retired Moderator

May 16, 2005
5,073
8
The PCMs I am familiar with do control balancing. I am not familiar with all of them, of course. Which model will you be using?

Are you using a charge controller separate from the PCM, or does your PCM incorporate MPPT?

Feb 18, 2009
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I've only done the research, we are with a team of 4people who work at the technical things and a few other people who does the management.

btw we also have a site: www.artesissolarboat.be the site is just a week online so there's not much on it (and there is still only a dutch version) but more details and a english version are coming up.

Feb 18, 2009
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I've done some thinking and i came to this:

I'm going to make a circuit where the solarpanel is connected to a mppt which at his turn is connected to the motor and the battery.

Normally it is fully at the motor (unless its power goes over the nominal voltage of the motor and than the extra energy is redirected to the battery) and whenever there is a sudden peak of energy (suddenly more sun) this extra energy is redirected to the battery or capacitors.

you guys think this is a good solution or not?

19. PRS Well-Known Member

Aug 24, 2008
989
36
I was not really informed about this new type of battery LiPo. I read up on it and here's my thought. Its real advantage is in its ability to provide a high current to a load. Use a store-bought charger because it has the automatic smart charging requirements needed. Let it be powered by 120 volts AC. Now use an inverter to power the LiPo charger, this inverter being supplied by a 12 volt lead storage battery (use 2 or more RV batteries in parallel) which is connected conventionally to the solar panels. As for running directly off solar energy, let this be the means of last resort and just switch it in or out.

20. PRS Well-Known Member

Aug 24, 2008
989
36
Another thought. You are using a battery that has the advantage of being light weight (and so used in scale models) for a full scale project? In that case just go with lead acid batteries.