Solar Car - Charging Method

[devonsc]

Hi,

I'm confused regarding the connection of thies three portions, the solar panel, the battery and the motor. Do you guys mind explaining briefly how does the connection been done?

Meaning, does a solar car uses the solar panel to directly run the motor, however, if the solar panel couldn't produce sufficient output to run the motor, the source to run the motor will automatically being tap from the battery? Is this right?

OR

The solar panel is being connected in such a way where it constantly charging the battery used in the solar car and the power needed to run the motor is always being tap from the battery. In other words, there isn't any direct connection between the solar panel and the motor.

Advice needed....Thanks in advance

 

[shutter_man]

Hi

Though I did not build a solar-car.... I had my share of building a device that used battery for the extra boost...

Whell - Always used the battery for the supply. It is the one and constant point that power is always available.
Furthur - I would use a DC/DC with high efficiency (and current limit) to supply the battery the exact and correct voltage to recharge it. The main system will than be able to use the relative contsant battery suppluy, and it doesn't matter whose supply what.
Though - in the above case - the solar pannel would be used first, as the charging is in higher volateg than the battery - you'd need to really "drain" the DC/DC output to get to the battery voltage levels.

Another thought: If I wanted the fastest "race" car - (no care for long life of devices) - I would change it the other way arround.


Shutter_man

 

[pisoiu]

When you start moving your car, the ammount of energy required is enormous, there you will have the biggest energy peak consumed. Even if I did not built such a car, I think no solar panel is capable to do this. Personally I would not like to wait for a sunrise in order to start my journey... Energy must be stored somehow, and maybe the accumulators are not the only way. Take a look at www.epcos.com , they produce some very nice capacitors (5 kilofarads @ 2.5V). With such toys, which obviously must be charged from the solar panel, you can meet the energy demands for the moment when the car starts. Another way to charge those caps is to recover the energy from the braking system. It is better to convert it and put it into the caps than to waste it through heat disipation.

/pisoiu

 

[devonsc]

By the way, one question, the solar panel used in the solar car is only meant to charge the battery. Am I right?

Does it mean that it can be connected in this way? As shown: It looks "funny" to me

 

[devonsc]

Hi, shutter_man and pisoiu,

I'm actually building this battery charger unit to be fitted in the "middle" of the connection between the solar panel and the motor. I've been trying to read up certain website regarding Maximum Power Point Tracker but it seems that I couldn’t come into conclusion regarding the major differences between a MPPT and a normal battery charger.

Do you mind to briefly explain the difference between the MPPT and the battery charger? Am I right to say that, one of the major differences would be the ability for the MPPT to track and make certain adjustments to deliver a maximum power to the battery?

However, I'm building this battery charger unit, where I will boost the voltage level of the solar panel to an appropriate level for charging of the battery. This statement: "I will control the duty ratio of DC/DC converter to boost up the output voltage of the solar panel to an APPROPRIATE LEVEL". So, can I consider my battery charger a MPPT? However, I will not be able to deliver a maximum power to the load most of the time. In my situation, as a battery charger, I thought my main concern would be stepping the voltage level up to an appropriate level for charging to occur? Thus, how do I maintain or control to obtain a maximum power point from my charger?

By the way, I don't understand how do we connect the battery-motor-solar panel together. As in, if I simply connect them in series, does it mean that the output from the solar panel will first flow into the battery. But, if I turn the motor on, the motor will first "automatically" or "smartly" draw the current from the solar panel. If it is insufficient, then the remaining will come from the battery. Meaning, the possibility of having the motor undergo a charging process is impossible when I turn the motor on? Am I right to say this?

Thanks in advance.

 

[shutter_man]

Hi Devonsc

First - Battery charging (presumably Led Battery as they can supply immense currents and still retain normal operating - but - they are heavy... ) can be accomplish in two distinct ways: Current charging and voltage charging. Current charging of a led battery - is very tricky - as one "disregards" the voltage to the battery and limits only the current into it (using this method U can charge Led battery fairly quickly - but it is risky). The other way is top charge it with voltage limitation - that is - to "disregard" the current into the battery and set the voltage to battery as specified by the battery manufacturer.
UNFORTUNATLY - you must combine these methods to achieve optimum charging and long life to the battery. Further more - the need to use the charging while the engine is running immediately require a current limitation at the charger output.
I do not recognize the MPPT specifications - so I red some (**broken link removed**) and it seems that the MPPT is the "smart" use of a varying output source into a required fix input point. Further - If you'll read - Solar panels require an additional "power bath" an auxiliary power dissipation device to achieve long life.

Regarding Pisoiu remark on capacitors - ABSOLUTLY correct! The battery is current limited - and external capacitor for surge current is essential.

So - what does the DCDC do? Using a wide dynamic range of input voltage to generate the exact specified voltage for the battery (for example 13.6v) also - using a smart DCDC will enable you to limit the maximum output current from it (to limit yourself to a maximum safe charging of the batteries - and maximum drain current from the Solar.

The overall performance will have the following behavior: First the initial high current will drain the capacitor (as you'll need a LOW ESR capacitors to enable the high currents), second – the medium acceleration – will require more current than t he Solar panels with the DCDC can supply – so the current limit will kick in – and the voltage will fall from say the 13.6v to that of the Battery (~12v) and the engine will drain the battery. Fix speed driving – will require the minimum current – less than that of the Sol.Pan. and the voltage will rise again to 13.6v – and the current will split between the Engine and the battery charging.

Please be advise – there are charger "out there" – very smart ones – that can do a lot of what you need – charge the batteries, supply the engine, and keep the batteries alive with "pulse charging" or with "trickle" charging. Define the correct use your system over life span.

Hope it is a better description what U need.

Shutter_man

 

[yakroo]

I want use solar connect inverter?

 

[devonsc]

Hi yahroo,

Maybe you can elaborate what do you have in mind in detailed? That will help others to help you better.

 

[nvnam]

please give me your mail