boost converter design help

[AzimOthman]

hey guys...

i need help in designing a DC-DC boost converter to convert 12v supply from solar panel into 24v to power a dc motor for a solar car project..

i dont really know where to start really...

some specs:

input voltage: 12V
output volatge: 24V
output current: around 30A


thanks in advance for your help guys!

[amspire]

Is this booster also controlling the motor speed. If so are you going to control speed by varying the motor voltage, or by using PWM (pulse width modulated) 24V to the motor?

If the booster is just providing a constant 24V to be followed by a PWM motor speed controller, then is there going to be a 24V battery that this converter is also charging?

If there is no battery, is 30A the absolute peak current, even when the motor is starting, or can the peak current be much higher?

Richard

[AzimOthman]

nope.. this booster is only to provide 24v to the motor...

the PWM speed control is separate... no connection with this booster...

this booster is also not used for charging...


soo its sole purpose is just to provide 24v to the motor..


about the current.. i think thats the peak current..

[amspire]

So if the 12v is solar power, over what voltage range do you need to operate? It is usual to load the solar cells to the Volatage/Current point at which they are putting out maximum power. Is that something you need, and if so, do you have data from the solar cell suppliers?

If there is no battery, that means that if the motor is not using full power, any excess energy will just be lost. Is that right?

Or do solar cars tend to use maximum motor power nearly all the time?

We might need to know the frequency of the motor PWM, and if regenerative breaking is also going to be an issue.

Richard

[AzimOthman]

thats the problem also.. i dont have the solar panels datasheet..

but yes.. thats what i need.. the solar cells need to put out maximum power.. lets just assume we are only operating at 12V..

the motor PWM frequency is 2kHz from what i got from my friend...

[Simon]

if you have 30A worth of panelS then why not put them in series and get 24V direct ?

[sonicj]

if you have 30A worth of panelS then why not put them in series and get 24V direct ?

agreed. build your pv for the target voltage and skip the conversion.
-sj

[amspire]

if you have 30A worth of panelS then why not put them in series and get 24V direct ?

agreed. build your pv for the target voltage and skip the conversion.
-sj

Something has to regulate the load on the solar cells. Admittedly it could be the driver watching meters. What I just don't get is the fact there is no battery. It means if the car is forced to stop under a railway bridge, it won't start again. If there is a battery, then what we are talking about is a battery charger.

If batteries are not allowed, can an ultra cap be used?

Richard.

[Simon]

well starting from 24V would simplify matters as this could easily hit about 40V with no load, but easier to do an MPPT downstep regulation than a boost

[Zero999]

if you have 30A worth of panelS then why not put them in series and get 24V direct ?

You'd of course need more than 60A@12V to get 30A@12V.

My guess is he's either not thought this through or ignorant about the laws of physics and the cost and space requirements for a 720W solar panel.

There's obviously no other solution than to use a battery. If 720W is only the peak power requirement then it's totally silly to generate it continuously and not use it. It will work out much cheaper to buy 240W worth of solar panels and use them to charge a battery to supply the peak demand.

[A Hellene]

You might need to search for the term "Maximum Power Point Tracking," which is about high efficiency DC-DC converters designed to present an optimal electrical load to solar panel arrays under any given environmental conditions, in order to obtain every bit of the generated power.


-George

[amspire]

There are a  lot of 24V solar battery chargers commercially available. You can get something for $40 to $120 that can handle more then 30A.

I suspect that most of the 24V battery chargers are probably designed for a nominal 24V solar panel, but trying to understand the Chinese specs is a bit hard.

So the only reason I can think of not adding a battery is that this car is just not allowed to have a battery. Even a tiny 3AH 12V gel cel makes much more sense then no battery.

Also you would think that changing the 12V solar panel to 24V is just a matter of wiring.  24V would mean quarter the weight in copper wire required.

Richard

[IanB]

This is presumably some kind of special vehicle, for example a racing or competition vehicle that will run over a designed course in sunny conditions. I can see that working if you connect the solar cells directly to the motors. A battery would be extra weight to slow you down.

[amspire]

This is presumably some kind of special vehicle, for example a racing or competition vehicle that will run over a designed course in sunny conditions. I can see that working if you connect the solar cells directly to the motors. A battery would be extra weight to slow you down.

The benefits of a small battery would exceed any weight costs, unless this is a race at a constant speed around a track with no shadows.

But it does sound like it is all about the rules, so we can only wait for more information. For example, running the solar panels at 12v is nuts for efficiency, but it may be one of the rules.

Richard.