I need a solar tracker for my Plantoid project. It will rotate a turntable with my potted plant on it, to follow the sun. Details of my project is on my web site at:
http://dh-sims-site.com/plantoid_project.htm
I implemented a simple circuit which I found on the web:

It works fine with a DC motor and without load on it but it doesn't move the turntable when loaded. I tested many motors with different power and voltages with no luck. I know that the transistors are rated for 1,5amps which is well enough for my motors. Any help will be appreciated. I am an experienced hobbyist only... thanks in advance...

 

you are overloading the motor or the turn table with the weight of the potted plant.

you need a higher torque motor or a slower, geared down, motor.

 

Motor rotates the turntable and the plant when voltage is applied directly, but when I connect the circuit it doesn't rotate. seems like it doesn't supply enough power...

 

Well the table following the sun would be enough for me...

You need a motorized gear reduction from an old drill or something. Maybe a cheap cordless screwdriver. I have one that runs on 2 AA batteries and has plenty of torque. Cost about $14 at WallyMart. I've seen regular battery ones for less too.

 

That is a poor excuse for a circuit. The 358 opamps can only source a few mA, which is not sufficient base drive for the NPNs (with any real motor).

Read post #9 in this thread.

 

More information on motor & solar panel might be helpfull. If motor runs when V is applied directly, then adding a " Solar Gleaner" might solve your problem. Explanation available on request.

 

thank you all for your responses...
@Bernard... what is a "solar gleaner" and where shall I add this circuit?... sorry if I am asking stupid questions, I am not very experienced about this... I am not using a solar panel in this setup, I am trying to follow the sun with balancing LDRs and will rotate a potted plant on top of a turntable which is sourced from an old LP player...

 

That is a poor excuse for a circuit. The 358 opamps can only source a few mA, which is not sufficient base drive for the NPNs (with any real motor).

Read post #9 in this thread.

@MikeML... thanx for the reminder, I read that forum post. I have already tested that Led based Greenwatts circuit but it didn't satisfy me... the one I posted above works better. Its only problem is it doesn't supply enough power to motor and heats up. If I replace the motor with a bigger one I will have worse probs. Is there a way to replace bd139 and bd140 in H-bridge with a more powerful darlington pair? or replace the op-amp with a more powerful one?

 

That is a poor excuse for a circuit. The 358 opamps can only source a few mA, which is not sufficient base drive for the NPNs (with any real motor).

Read post #9 in this thread.

Agreed, and comparators would be better than an opamp too, especially once the circuti has been improved to add some hsyteresis so the motors don't stop/start constantly (or grind away at stall).

 

For darlington transistors: NPN, 5A, TIP 121, NTE 261; PNP, 5A, TIP 127, NTE 262.
The " solar gleaner", based on the Mini-Maximiser, or Solar-bot allows a weak power source to supply a burst of power. An example: My bench power supply, 12V @ 4A could not start a 15W, 12 DC motor because high starting current tripped supply, but with gleaner in series, motor starts right up. It just charges a large capacitor, then dumps it across the load

 

@Bernard... Thx for the info... I once constructed that Mini Maximizer but never get it to work properly because I couldnt find D2 and used an equivalent instead... z3 is missing because I use it with 12v... If its this one:

Any further info with schematic and parts will be great about your gleaner... I want to try that together...
As of darlington pairs for my sun tracker, I will give a try with TIP121-TIP127 pairs..
Thx again for the help...

 

The schematic is there, parts might be different depending on source power & load. C 1 attempts to charge to power source OC, open circuit, V. R 1 selects the trip point; for solar panel,SP,or unregulated power supply, might set peak charge to 1/2 way between load operating V & OC V; for regulated supply set to within 1/2 to 1 V of output. R 1, any value between 10k & 1 meg. ZD 1, V ref about 1/2 load V, LM 336Z25 for 2.5V, zenor of choice, or forward biased LED will also work? Comparator, any similar or LM311 for single. R 3 & R 4 select hysteresis to select restart V. If power source can supply running current, then the P FET never turns off. Some possible P FET choices:
FDS9435A, 5 A, surface mount
IRF4905, 74 A, .02 Rds, 50 V
RFP30P, 30 A, .065 Rds, 60 V
When C 1 first starts charging, U 1, comparator, output, pin 1, will be high, cutting off P FET, because U 1-3,+, will always be higher than pin 2,-, because it is effectivley directly tied to C 1, D 1 rev biased.
As V on C 1 climbs, ZD 1 clamps pin 3 to ref. V; now when pin 2,reaches the ref V, U 1-1 goes low, turning on P FET, discharging C 1 into load.
C 1 should have enough capacity when charged, to run the load for a fraction of a sec or longer. With hard starting motor, 12 V 15 W , 22,000 μ F, at 18 V solar, runs motor about one sec.

 

@Bernard... well I mentioned earlier that I am not expert, just hobbyist... your explanation is far too complex for me... some parts I dont know what they are and the schematic is not easy for me to conceptualize... I am used to simpler schematics (I use Fritzing to make my hobby circuits)... sorry but can you supply a better schematic and parts list... more explanatory for a noob...
And thx for the suggestion about using TIP transistors... I replaced the H-bridge with them and the tracker circuit is now working better... It can rotate the turntable with load on it in both directions... only one of the PNPs gets hot and I placed a heatsink on it... problem solved... thx again...

 

What are you using for a power supply?
Any specs on motor?

 

What are you using for a power supply?
Any specs on motor?

I am using a converted ATX power supply which I made... I can use all kinds of voltages with it... I had the best results with using +5v -5v config... Indeed I want to use a single +12v supply (ATX case too big for the robot)... I tested many DC motors which are at hand, not geared, turntable belt driven... Actually I have an Arduino controlling the Plantoid Robot but did not want to spend IO pins for the sun tracking... Thats why I am trying to build a dedicated circuit for the purpose...

 

Adding a solar gleaner, probably would have little effect on your ckt.as there is effeciivley already such a ckt installed with the intermittant cycling of the motor, & power supply output filter cap. Adding more external capacity might help, but most likley problem is the 1.5 +- V drop thru H bridge, and power supply V droop under load.
If still interested in gleaner, I'll try again.

 

Adding a solar gleaner, probably would have little effect on your ckt.as there is effeciivley already such a ckt installed with the intermittant cycling of the motor, & power supply output filter cap. Adding more external capacity might help, but most likley problem is the 1.5 +- V drop thru H bridge, and power supply V droop under load.
If still interested in gleaner, I'll try again.

Indeed I dont want to add ur gleaner to this project... its working fine now (almost)... I need it for another solar robot project... to drive the motors directly with solar PV panel...

 

I made last adjustments and actual sun test today... TIP pairs are working great... no heating bacause system is on at short intervals... tested with +12v too and it works but +5v -5v config is better working as far as I can see... thx for the support...
@Bernard... I am waiting your help with the gleaner... I will integrate it to my solar rover and solar plane to drive the motor directly from PV panel... currently solar panels dont even start the motor if no battery is on the system... I am using solar panels to charge the battery during cruise and extend the mission...

 

Would be helpfull to know solar panel , SP, open circuit voltage, OC,& short circuit current, SC.
Motor, loaded operating V & current, alse guess at starting current, or DC resistance of motor.
' Suggest that you start a new thread, might have more helpers.

 

Would be helpfull to know solar panel , SP, open circuit voltage, OC,& short circuit current, SC.
Motor, loaded operating V & current, alse guess at starting current, or DC resistance of motor.
' Suggest that you start a new thread, might have more helpers.

OK... I will start a new thread for this. will try to supply all the data you are asking, but there are 2 projects associated (a plane with 1 motor having wing solar panels and 1 rover with 2 motors and smaller panels)... also have various battery, motor, supercap options on hand...