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Thread starter #1
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

Well-Known Member
#2
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...
 
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bryan1

Well-Known Member
#4
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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Thread starter #5
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

Well-Known Member
#6
amitraj said:
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
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
 
Thread starter #7
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

Active Member
#8
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.
 
#9
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.
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.
 
#10
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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Thread starter #12
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

Well-Known Member
#13
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?target=product&product_id=16327&category_id=251

Cheers Bryan
 
#15
Failing to understand a circuit is no reason to declare that it won't work.

@armitrage: Build it - - you will likely be pleased.
 
Thread starter #17
Reg: Question in Maximiser

Hello Bryan,

In the maximiser ckt. the 0.1 microF capacitir (which is connected to the FET) is also connected to both the terminals of 1.5K!

There could be something wrong in my statement or could be in the image. Could you go theugh it and confirm where exactly the Cpacitor terminal is connected?

Warm regards,
Amitraj
 
Thread starter #18
Reg: Probable Error in the maximiser

Hello All,

I have come up with "probable" corrections in the ckt. Diagram given for the maximiser at : http://www.voltscommissar.net/minimax/minimax.htm

1.
Acc/to the diagram the 2K trimpot is connected to the junction where 3K3, 6.2V Zener, 100K, 100pF and Pin 2 of LM311N come together.

In this case the 3K3 and 6.2V Zener junction should be separated. That means there should be a jumper which will connect Pin2, 100K and 100pF to 2K trimpot and will cutoff 3K3 and 6.2V connection. (I hope this makes clear what I want to say!!) Otherwise, pins 2 and 3 of LM311N will be shorted.

2.
Same applies to o.1microF and 1.5K connect. If 0.1 :mu: F is also connected to Pin7 of LM311N then 1.5K gets shorted.
Please let me know if I have gone wrong somewhere. Or I am getting overconfident about this.

Warm regards,
Amitraj
 
Thread starter #19
Reg: Probable Error in the maximiser

3
Pin 8 and 7 are shorted through 100pF and 100K.

jumpers are required at both the junction point. i. "100pf and pin 8" & "100K & pin 8"

Please correct if anything faulty here.
 

bryan1

Well-Known Member
#20
Hiya amitraj,
Below i've ammended the schematic to show you where some lines cross they aren't connected. It is an error on schematic as usually a small raduis is put onthe line to show no connection.

revised max circuit.jpg

Cheers Bryan
 

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