Model Boat Mayhem - Forum

Technical, Techniques, Hints, and Tips => The "Black Arts!" ( Electrics & Electronics ) => Topic started by: AlanP on October 20, 2008, 09:07:13 PM

Title: Water pump
Post by: AlanP on October 20, 2008, 09:07:13 PM
I have just finished installing all the gear in my boat, it is fitted with a water pump for the fire hydrants, it's of unknown origin but seems to work OK on 6 volts.
My problem is that when the pump is activated all the other servos chatter, I am presuming that it is interference from it's motor. Could one of you enlightened souls tell me what I require to stop this please.

Cheers Alan
Title: Re: Water pump
Post by: Sandy Calder on October 20, 2008, 10:03:47 PM
Hi Alan.
These pumps will give off interference but it is easy to fix.A car windscreen pump does likewise.
If you are able to negative-earth one terminal,as in a car, you only need a single suppression capacitor and a diode.
That should stop the interference but you can fit a choke on the supply line if not.

What do you supply the receiver with? If it is a bec speed control, is the main supply 6 volt and does it share that with the pump?
Do you share your 6 volt pump supply with anything else?
Regards
Sandy Calder
Title: Re: Water pump
Post by: AlanP on October 20, 2008, 10:20:48 PM
Hi Sandy, the receiver is supplied from a 6v gell cell via the bec on a speed contoler. The pump has it's own 6v gell cell that it shares with a few lights.

I was hoping that I could just put a capacitor across the terminals of the pump but wasn't sure about the size

Alan
Title: Re: Water pump
Post by: Sandy Calder on October 20, 2008, 11:09:40 PM
Hi Alan.
The capacitor is the bare minimum and size does not matter.A 10nF ceramic disc will do.
Is that the same switch arrangement?
The diode will probably make a difference too and only costs a couple of pence.A 1n5817 -1n5819 or a 1N5400 series diode is enough.

A six volt battery will not supply enough voltage to the bec input and will give similar results very quickly.That is why I asked.
Regards
Sandy Calder
Title: Re: Water pump
Post by: AlanP on October 20, 2008, 11:23:42 PM
Hi Sandy
I could couple the batteries up to give me 12v and run everything of that. (would that help) I think I might have some diode's about somewhere, will have a look tomorrow, I presume it does not matter which way round the diode goes.

The switch arrangement for the pump is just a servo working a micro switch.

Regards Alan
Title: Re: Water pump
Post by: Sandy Calder on October 20, 2008, 11:36:42 PM
You would be adding an additional path for the interference back to the receiver.
The cathode (stripe) should be to the positive.

If you have interference problems you wou would probably be better off with a receiver battery.No?
Going up to 12 will cause the bec to become warm which may be a consideration.
Title: Re: Water pump
Post by: AlanP on October 20, 2008, 11:42:27 PM
Thanks for your help sandy, I will try a separate battery for the receiver and see what I have in the way of capacitors and diode's tomorrow and go from there.
I will post results on this thread tomorrow night

Thanks again
Alan
Title: Re: Water pump
Post by: Sandy Calder on October 20, 2008, 11:47:58 PM
Did you notice the earth connection too?
That will cut out common mode interference.That is a story and a half.
Regards,
Sandy Calder
Title: Re: Water pump
Post by: malcolmfrary on October 21, 2008, 09:42:51 AM
Compared to the other bits n pieces, the pump motor will be taking A LOT of current.  This could be affecting the line voltage, and this in turn will create  untold confusion in the servo electronics, which rely implicitly on stable voltage.  They can handle a reasonable range of voltages, but whatever it is, it must be stable.
The capacitor and chokes will do no harm, but can't cure the varying voltage problem.
Title: Re: Water pump
Post by: Sandy Calder on October 21, 2008, 12:16:01 PM
Compared to the other bits n pieces, the pump motor will be taking A LOT of current.  This could be affecting the line voltage, and this in turn will create  untold confusion in the servo electronics, which rely implicitly on stable voltage.  They can handle a reasonable range of voltages, but whatever it is, it must be stable.
The capacitor and chokes will do no harm, but can't cure the varying voltage problem.
The same goes for running bec off a 6volt gel cell.The voltage input falls belw the 5.something required to keep a stable 5 volts to the receiver.
That was my first thought but Alan pointed out the pump had its own supply and so interference is the cause of the behaviour.

If one terminal can be connected to the pump case and grounded then common mode interference goes away.If the capacitor and inductor are fitted per diagram then single ended interference goes away.
Regards
Sandy Calder
Title: Re: Water pump
Post by: AlanP on October 21, 2008, 08:22:35 PM
Well I racked around this afternoon but could only find two diode's marked 1N4001 didn't know if one of these would do so I put them aside and had another rake around, found a capacitor marked 473Z, fitted it and it seems to have done the trick.  :-))

Think I will still earth the pump case to the main motor case and then to the prop tube, also fit the correct diode when I can get one, seems OK on the bench but could be another matter on the lake.

Thanks for all the help

Alan