amitraj

Hello,

This is my first post over here.

I have an 85W (12V) solar panel to which an 84 W (7A) DC motor is connected. The armature resistance is arround 0.76 ohms. Hence the starting current for this DC Motor is 16A (i.e. (12V - 0V)/0.75ohms).

Could anybody guide me about building a current booster for this motor?

The limitation is I can not add another panel to this system. It will increase the cost heavily.

Please let me know if any additional information is desired.

Warm regards,
Amitraj

dknguyen

Use a capacitor to supply the peak current during the transient period. That's what they;re used for even on motor drivers with mains or battery sources. But make note about whether the wattage (and hence current rating) of your solar panels are for peak conditiosn and so your motor may still not operate unless in direct, full sunlight.

It seems like a fairly heavy continuous load to run off of solar panels though...

amitraj

Hello dknguyen,

Thanks for replying. I will check out that.

Amitraj

bryan1

Hiya Amitraj,
A good unit to use to drive pumps, motors etc directly off a solar panel is a device called a maxi-maximizer. I did notice in a renew magazine they sell a kit for them or you could try and find the schematic on the net.

Here is link to the mini-maximiser and by simply upgrading some of the parts should give you the required current draw.
http://www.voltscommissar.net/minimax/minimax.htm

Cheers Bryan

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amitraj

Hello,

Bryan - thanks for this effort!

I am not sure if this maxi-minimiser is available in India (of course I can import that).

I will too check out.

Thank you.

Amitraj

bryan1

Just build it yourself using verboard. Page 2 of that website gives you all the details. To beef it up for more amps put some bigger fets and caps on and a few other tweaks

Cheers Bryan

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amitraj

Bryan,

Thanks for the motivation!

I am working on the same now. Soon, I may come up with related questions!

Thanks a lot once again!

Amitraj

Oznog

I'm not sure that Maximizer makes any sense at all. PWM'ing the stalled motor will only lower the current which will not assist in starting it AFAIK.

Starting the motor with a capacitor may require a very large capacitor. It is difficult to say what is required since it depends on the inertia of the rotor and many other factors. Let's say it's very fast and requires 16 amps for only 0.2 sec, and the solar panel produces 7 amps out of that so we only need 9 amps from the cap. But if the capacitor voltage drops below 8v before 0.2 sec then the motor will not start.

I get 0.45 Farads for that hypothetical spec. There are stereo system "boost" capacitors readily available in that range in the US, but elsewhere finding that much capacitance in this range may be difficult.

It would make more sense to install a battery on your solar panel. Not only does this solve your starting problem but you can better utilize your panel. For example there are going to be many hours where the panel produces electricity but it is too little current to run the pump so it is useless. If you charge a battery for 1 hour in weak sun you can run the pump off the battery+panel for 30 min you get output you otherwise could not use.

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mneary

It won't work? Why not? Maybe you forgot that brushed DC motors have inductance. The MOSFET turns on, momentarily providing a large current to the motor. The catch diode carries this large current after the MOSFET turns off. Then the MOSFET turns back on, boosting the current again.

It's really a simple switching regulator, with feedback tailored to the purpose. Maybe you should re-read the article.

Hero999

I agree, I don't see how PMing a motor can help start a motor, if anything, it'll only make it worse.

For the capacitor idea to work, you need to give the capacitor time to charge before the motor is switched on.

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rjvh

as oznog said get a battery and you problem is solved and your system is overall better

Robert-Jan

amitraj

Hello all,

Thanks for the reply.

After studying the Maximiser, I also come to a doubt whether this spiking approach will suffice the motor requirements or not (interms of starting current and corresponding time).

With respect to the battery... thing is my whole concern is about a cheap solar powered pump. Not only cheap but easy to maintain. I am trying to support a small Drip Irrigation system with this assembly. In Indian scenario, farmers will not be happy with system where in they have to maintain a battery.. reason being they are used to traditional AC system, secondly the extreme poverty.

I think I need to lower down the pump specifications (in terms of input watts), so that without increasing the panel and without having a battery I can go on.

Any suggestions/objections?

Warm regards,
Amitraj

bryan1

That maximiser circuit is sold over here in Oz as a kit and it's been around for donkeys ages AND WORKS. although I haven't made on as yet as I haven't had the need I do know many people who use it on a daily basis including several people who I put them onto it. The circuit is designed for the public domain by a guy from selectronic ( the mob who make sinewave inverters). As Amitraj has stated his need is for drip irrigation and this circuit would be perfect for the application.

Below is the link to buy the mini-maximiser kit from ATA.
http://shop.ata.org.au/cart.php?targ...ategory_id=251

Cheers Bryan

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amitraj

Dear Bryan,

I am anyway building the maximiser circuit. That is the only hope I have!

Thanks
Amitraj

mneary

Failing to understand a circuit is no reason to declare that it won't work.

@armitrage: Build it - - you will likely be pleased.