Motor spark suppression

[mickyb]

Hi Lads

A question for the electronic wizzards amongst us.....

I have a pair of Multiplex permax motors with a leaflet explaining the need to fit a 10 - 47nf capacitor across the terminals, a leaflet that comes with a pair of Mabuchi 400 series motors suggests the connexion of a 0.02mf capacitor but I have no such leaflet with the Jamaras.

Has anyone fitted spark suppression capacitors across their Jamaras ....if so, what value did you use please?

I see the crap weather is back......it's pouring with rain and the local council is spreading salt...to think I voted for the pillocks.....

have a good evening folks........Mike

[NigelDerEnglander]

Hi Mike,

I'm not quite sure if you know what you're asking? Whether there's a leaflet there or not, all brushed electric motors should have at least one suppression capacitor, preferably three. One across the two motor terminals, and one from each motor terminal to the motor case.

If it's value you're asking about then 0.02mF = 20nF so that is consistent with both leaflets.

As they say, any value in that range is fine, even a bit less or more - but _NOT_ electrolytic/tantalum capacitors which are polarised.
I just use whichever ones in approximately that range that I have lying around.

Yep, the early spring lasted 2 days and its now back to wet and windy weather!
Still, a good evening to be in and working on tanks!

Oh, my Jamara motors that I got a year ago came with a leaflet saying about the capacitors. In fact I'm fairly sure they came with the capacitors too...

Regards,

Nige

[mickyb]

Hi Nige

thanks for the reply.

All the leaflets say that there are 2 suppressors installed inside the can, but that they recomend the connexion of a third across the two terminals....mainly for suppression of signal interference rather that spark quench across brush/commutator assembly I expect.

I noted that all manufacturers were suggesting different values...... today I bought a pile of 0.02 mf capacitors from Maplin for my 400 type motors....then I noiticed that there was no leaflet with the Jamaras. There is quite a difference between the current rating of the Permax 4.5amp / Jamara 5.8amp  at 7.2 volts but they have only    5 volts expected from the El-mod unit, so my ignorance of calculating the required capacitor value shows.

My real concern is this:

I always isolate the RC power from the motor power in my models by using different batteries for each.......but.....
The el-mod setup for "prop" installation has a power feed from the data bus cable to the RC reciever. As the motor power feed is also from the same 7.2v battery, I was concerend that any interference from the motors would effect the el-mod and also the reciever unit. I expect el-mod protects itself but the battery supply is probably common and open to interference from the motors.

I hope that I have explained myself well........ this is not how you would normally install RC in a boat or plane is it?

There are many motors in the Tiger, each one is a source of interference, but the drive motors are the big concern to me......

Mike

[tiger205]

hi mike
          i have jamara motors, the 480hs bb type, i got mine off of nigel, and yes they did come fitted with suppressors as nigel thought, because the motors were a tight fit between the boxe's i broke some of the suppressors, so what i did was to take some off of the standard hl motors, 6 in all, and replaced the one's on the jamara motors, i did check with nigel afterwards if i had done things ok, and he said thats fine, like nigel said its best to have 3 on each motor, so thats what i got on mine.

          Tony

[mickyb]

Hi Tony, Yup the Jamaras have two fitted inside the cans, unlike the HL's which have them all on the outside. I just wanted to be sure that the capacitors I had were of a high enough value. Seems they will be ok at 0.02mf.

I got the el-mod back from germany today so I hope to fit it all in this week....cant wait to get it running.

Seeyah    Mike

[wibblywobbly]

Best of luck Mike. I have 100nf and 20nf suppressors sitting here waiting for the return of my boards.

Rob G

[NigelDerEnglander]

Hi folks,

The problem of electrical suppression - Electrical Magnetic Compatibility EMC - is a big subject nowadays. My colleagues spend days in EMC chambers (sealed electrical boxes big enough to take cars) making sure that our kit doesn't create undue electrical/magnetic interference.
I'm afraid it's a black art. Sometimes you need capacitors, sometimes inductors, proper earthing, Faraday shielding, earth loop prevention, ferrite beads, sometimes a complete redesign.

For us (tankers), the big problem is that any spark - generated by skipping of the brushes on the motor commutator - is effectively a wideband electrical noise generator. Thus some of it will be at the 27MHz frequencies that we generally use for RC. As it is in such close proximity to the aerial and receiver even the tiniest amount has a disproportionately large effect.

Ideally as well as the capacitors across the brushes, we should also have inductances in series with the power cables to the motors.

And yes, all the motors on the tanks should be suppressed with 3 capacitors. Whenever I take mine apart, I replace the single one that HL have used with at least 3. And sometimes I have wound an inductance in-line too.

To be really safe we should put the receiver and control boards in sealed metal boxes and add ferrite beads to all inter-board connections, but that is going a bit too far for a bit of el cheapo Chinese tat, I'm afraid!

To be honest, I added extra caps to try and stop the RX13 board crashing and failing with the BB gun firing continuously, but none of these things solved it, so to be honest, if you're using the tank in your garden, it's fine, and it's not affecting your TV or radio reception then don't worry about it.

I would however worry about it if I was flying a large, heavy, radio control plane on a flying field adjacent to an infant school in an area with a lot of known-violent parents....


Nige