Low cost repair of Dolphin

by Hans MEKEL
(Toulouse France)

Hello. I am a Dutch electronics engineer, and live in the south of France. I have a Dolphin which worked well during eight years, but when I put it in the water this spring, it did what most of you describe, it stopped after one minute. As I analysed a bit what happened with other Dolphins, it must be a mechanical problem. I took it apart and changed a couple of ballbearings, but still it stopped after one minute. Then I decided to "fool" the microprocessor, by changing the value of the resistors which measure the current in the two motors. Those are the 1 Watt resistors next to the mosfets, the biggest on the PCB. I don't know the numbers of them. They are aproxx. 1 Ohm, and I soldered a 10 Ohms 1/4 Watt resistor parallel to them, to give them the value 0,9 Ohms. Now the microprocessor "sees" a lower current than before. Only 10% less, but that's enough to make it work properly again. During the conception of the PCB, they calculated the measurement to narrow, maybe as a programmed obsolescence. I hope that you can repair your Dolphin, with these very low costs (2 times 1 cent) and only an hour of work. Greetings Hans.

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Aug 18, 2017
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starstarstarstarstar 		Dolphin stops at 31 seconds
by: Hans

Hello Rick C.
My name is Hans and I wrote two years ago how I repaired my robot. It's been ten years now that I bought it and it still works fine after I maintained it two years ago. I changed most of the ballbearings, specially those of the motors. Yours shows the same behaviour as mine did before repairing it. So according to me, it must be a mechanical problem. Too much friction (mechanical losses), which causes too much current in the motors, and the system shuts down. If you read my comments which I wrote two years ago, you know what to do. To prevent from shutting down too soon, if after some years the friction rises again, I soldered a 1 Ohm resistance parallel to the shunt which measured the current in the motor.

Hope you succeed.

Hans.
Aug 17, 2017
Rating
starstarstarstarstar 		Shuts off after 31 seconds
by: Rick C

My dolphin shuts off after 31 seconds of run time. I have cleared the impeller and cleaned all hair and debris from the movements. It still shuts down after 31 seconds. I then took the unit and let it run while I was holding it in the pool and not allowing the unit to have a resistance from the drive. It ran as long as I held it. When I let it go to the bottom it then shut down after 31 seconds.
I have found that I can run the tracks tight or loose based on how far I stretch them between the movements. My next step is too take all the movements apart and ensure they are clean and all the bearings move freely. I will post after I do this. Does anyone have any advice?
Aug 13, 2015
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starstarstarstarstar 		Resistor Value is 18 Ohms
by: Dan

Hans,
I took apart my new motor unit and the burnt resistor is Brown, Gray, Black, Gold, Brown = 18 ohms 1% tolerance 1/4 watt.
Puzzle solved!
Aug 11, 2015
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starstarstarstarstar 		Circuit Board Resistor Value
by: Dan

Hans,
Thank you for the updated information.
I sure would like to repair the circuit board with the correct resistance. It would be great if Maytronics offered replacement control boards.
Dan
Aug 11, 2015
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starstarstarstarstar 		Resistor value
by: Hans

Hello anonymous,
I wrote before that the value of the shunt resistors are approximately 1 Ohm, but I was wrong. They must be around 0,1 Ohm, otherwise there cannot flow 7 amps through the motors. But then as I soldered a 10 Ohm resistor parrallel to them,which is only 1 %, it cannot be the fact that I added a resistor that changed the measurement, as it is in the same range as the precision. So probably it was the fact that I changed the ballbearings that repaired the robot. Mine is still working fine. Maybe there's a flag in the software, that's lifted after a couple of error detections, and which is dropped after a couple of on/off cycles without errors. I used this once in a system I developped.

I hope I didn't lead anyone in the false direction.

The fact that the resistor burned means that there was too much current flowing due to a blockage, probably a bad ballbearing. But still the current limits are very small, and soldering a resistor of approximately 1 Ohm parallel to them will prevent from failing with the slightest mechanical resistance.

Maybe someone else can tell you the exact value of the shunt resistors, as I'm not ready to open it to measure them.

Hans.
Aug 10, 2015
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starstarstarstarstar 		Resistance value of burned resistor
by: Anonymous

Hans, my control board has a burned resistor probably due to the motors having higher resistance due to the unit being about five years old. I have tested the motors and they are working fine.
Can you tell what the value of the original resistor was before you added the others in parallel?
Thank you!
May 15, 2015
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starstarstarstarstar
by: ADMIN

Thank you fort the terrific information!

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