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[Daryl]

Can anyone tell me what these are. They are connected to the motors of a Robbe Dusseldorf fireboat, I am restoring. I assume they are some sort of speed controller but how they work I havn't a clue. The simple solution is to bin them but I am curious as to how they work.

Thanks
Daryl

[HS93 (RIP)]

They are filters, a bit over the top . In the way they have been fitted I would have thought they would cause more problems than they would fix .  this type of thing is used on the feed TO a radio normally its just a ferrite ring with a couple of caps across them .I would bin them , but thats just my thought   Peter

[Peterm]

I found similar things on a 1983 `Happy Hunter` which I restored for someone.   They were in the motor supply circuit.   I ripped them out and rewired the system completely.

[Daryl]

Filters, umm that would explain why there arn't any on the motors, and you can just see inthe picture there is a lead soldered to the motor can. Looks like I'll have to pop into town and get a ESC or two.

Thanks for the help.

Daryl

[Doc]

Yep, 'filters'.  There are several ways for filtering electronics and some filters do 'other' types of filtering.  Using coils in filtering DC, or pulsing DC, is one way of stopping voltage 'spikes' from reaching the motors.  Sort of smooths out the pulses, if that makes sense.  Not exactly something I'd worry a great deal about, but it doesn't really  hurt anything.  I don't think I'd trash them completely, just in case.  Never know when you might need something like that.  (I don't throw away bent nails either, so take that for what it's worth.)
 - 'Doc

[ukengineman]

I would get rid of them. They could cause a lot of problems with modern high frequency switching ESC's
Alan

[wombat]

Looking at them, I would be inclined to leave them in personally.

Looking at the configuration, they appear to be common mode chokes designed to take out the common mode electrical spikes produced by the motor  (or possibly the ESC) which would then be converted inot differential mode spikes by any difference between the ground and supply line impedance

Tim the Wombat

[Telstar]

Hi  I have a early Futaba speed control ( about the beginning of the M series radios) it came with a suppression filter attached, looks just like the one in your photo, (after you take the cover off)
still works, but so does the Digimax system
Have a good Xmas tom

[BobF]

Ripmax currently, no pun intended, supply them fitted in their ready to run Interceptor, just fitted before the motor connection on both wires.

bob

[Daryl]

Thanks guys for all the great information, very much appreciated. I didn't know Ripmax still fitted them. Thanks Tim your explanation agrees with what little I know about common mode chokes, we have them at work but only used seldom. I think I'll leave them in and see what happens when I connect a ESC up to it. The person who had the boat last must have used it flat out as there is no speed contoller in the set up.

Many thanks for all your help

Merry christmas and a happy new year to you all.

Daryl

[Daryl]

Bumped into our head Techo boffin whilst making myself a cup of tea at work. I mentioned the chokes and what I intended to couple to them. He agreed broadly with Doc after some techno babble, after some reflection son and I have decided to operate on the boat and remove them and re-wire it completly. That should while away the time over christmas.

Thanks everyone for their help the information has been very useful.

Merry christmas to all
Daryl

[Tug-Kenny RIP]

I'm going to try these filters on my boat. It might help with the odd spikes that I'm getting. these are causing the ESC's to momentarily cut out.

I have watched the  D-C  to the motors on the oscilloscope, and the signal shows a  square wave  mark/spacie ratio  which deceases with throttle rising. There is also a half size   sine wave   which comes in periodicall and drifts up through the wave form.
Looks absolutely fascinating on the screen, but I have no idea what it's doing. I will photo the screen picture and submit it for you to browse.



Cheers...Ken

[OMK]

I'm with Doc and Wombat on this one.
But it's confusing why just one toroid is seen there. Since there are two equal windings on the same toroid, then would it now become a 1:1 transformer, as opposed to a choke? I'm confused. Why would this be? Would it have made more sense to make those windings on separate toroids... one in the pos. rail and one in the neg.? Because if it IS a transformer, would any unwanted voltages spikes on, say, the positive rail be transfered to the negative?

Tug-Ken:
I'm intrigued about that 'half-sized' sinusoidal. Whatever is causing it, it sure sounds like it ought not to be there. Any chance we could have a look at the aforementioned screen-shot?
BTW, I'm in the market for a new/used 'scope. I've been looking at the Textronix series.
Or would you have any recommendations?

[Doc]

PMK,
One thing, that coil should be in-line with the applied voltage, not from (+) to (-).  Coils stop AC (not really, but it slows it way down and only allows a very small part of it to get past it.  Coils conduct DC just like a straight piece of wire.  Another little 'goody' is that the frequency of the applied AC determines how big the coil has to be to be of any use.  The lower the frequency, the larger the coil.  Then, depending on how much current is going through the coil will determine how large the wire is.  If a capacitor is placed in front of the coil, it funnels most/some of the AC to 'ground' before it can get to the coil.  That's good.  Then, if you put a capacitor on the back side of the coil (going from + to - like the one in front), even more of the AC is funneled (shunted) to ground.  That's even more gooder.  That capacitor + coil circuit is called a 'filter' and used quite a bit in changing AC to DC behind a rectifier.
 - 'Doc

PS - Some technical terms it's interesting to know.
capacitor = 'cow-pastures'
coils = 'coals'
Enough heat in either one makes for some stinking smoke.

[Daryl]

A transformer would make sense as a 12v pump is fitted and the motors are 6v, I'll connect it up to a meter and see what appears the other end. Still convinced that I'll remove them. There are a few wires I havn't worked out what they are yet so there could have been two batteries.

Well its not a transformer but our head techo boffin has seen this set-up before, I'll remove them and fit capacitors as normal. Which should be more efficient.

Thanks for everyones help.
Daryl

[Doc]

If your "techo boffin" thinks that about a transformer in DC circuits, I think he'd better lay off the 'tea' for a while.  Changing voltages in a DC circuit can't be done with a transformer.  At least not the DC circuits in model boats/planes/cars, or full sized boats/planes/cars.
 - 'Doc

[HS93 (RIP)]

Tug ....Keny  what are yo feeding the motors with a speed ctr a dc supply?? if its a pwm speed ctr it will give a false reading ..99%of set up only req a few capps to sort things out  and not a filter.Peter

[Daryl]

Hi Doc, thats exactly what our guy said. I think he knows what he is talking about as I work for one of the worlds leading broadcast electronic equipment manufacturers and he designs the stuff we sell. His son is into R/C planes. I think they'd be better of off ripped out and capacitors substituted.

Daryl

[wombat]

I'm with Doc and Wombat on this one.
But it's confusing why just one toroid is seen there. Since there are two equal windings on the same toroid, then would it now become a 1:1 transformer, as opposed to a choke? I'm confused. Why would this be? Would it have made more sense to make those windings on separate toroids... one in the pos. rail and one in the neg.? Because if it IS a transformer, would any unwanted voltages spikes on, say, the positive rail be transfered to the negative?

Hi PMK,

Won't work if it is on a separate toroid - What it does is if you have a common mode signal applied to the motor (i.e. the same current flowing in the same direction in positive and negative, the flux induced by the negative winding cancels the current on the positive line and the flux induced by the positive winding cancels the current on the negative line - if you work the sums out (do not try this without a very stiff drink - a very large very stiff drink) effectively it means the impedance to differential currents is 0 (i.e current flowing in opposite direction on positive and negative) but the impedance to common mode currents (flowing the same way on positive and negative) is infinite. (OK in the real world a lot less.)


Hi Ken,

I would be interested to see this sine-wave. At a guess it is some interaction between inductance on the circuit and one of the capacitors. Depending on the frequency, you can make a guess at where it is coming from. For example if it is synced to the rising and falling edges of the PWM signal I would say it was the inductance of the motor ringing with the capacitance of the supression capacitors.

Tim the Wombat

[Tug-Kenny RIP]

Hi Tim

That's exactly what it is.   I haven't had chance to set it up yet, but will do as there is a lot of  interest.  I'll try the camera on the scope screen and publish it as soon as I can.

The sine wave comes from the leading edge of the the wave from the ESC. It then decrease in size for several cycles, and does not re-appear until about 30 cycles further on. It then shows again and moves down the length of the screen slowly and dissappears of the edge. I liken it to a 'ping' of the surpression cap. The recommended one is wired across the motor windings.



Cheers...Ken

[portside II]

P.M.K A MERRY XMAS TO YOU AND WHERE DID YOU PULL THAT CRACKER THAT KEEPS FLASHING UP ON YOUR PIC 

[OMK]

If a capacitor is placed in front of the coil, it funnels most/some of the AC to 'ground' before it can get to the coil.  That's good.  Then, if you put a capacitor on the back side of the coil (going from + to - like the one in front), even more of the AC is funneled (shunted) to ground.

I'm hearing you, Doc. From what I could glean from the image I get the idea it's like this (see att.). Two windings on a single toroid.
But bear in mind I used the term 'transformer' loosely (we're talking DC). Inductance, wire gauge, etc. is fascinating stuff. And the day when I discover how to shove DC up a trnsfrm and get loads of DC out... Thing is, I was wondering what would happen when a spike hits, say, the pos. rail. By virtue of the induced back EMF into the neg. coil when said voltage spike dies - (because BOTH windings are on the same toroid) - then surely the unwanted spike landing on the OTHER rail means double trouble?

By the by...
Doc is a neat handle. What's the story? Doc Halliday, perchance?


Daryl:
It's just a matter of time 'afore you hear the words thread and hijack. Yeah - I know, I know. Sorry, amigo.

Wombat:
Ah, right! I'm hearing you, too. So you call it common-mode signal. But I'm still confused. You say the induced flux cancels the (reciprocating) currents. Agreed... to an extent. But wouldn't you say that winding the coil in each rail on a separate toroid would totally illiminate unwanted induced flux?
I'm still running on an L plate, don't forget.
BTW, you say Ken-T's unwanted sinewave is probably due to the inductance ringing with the suppression caps'. But what caps?... the one's, presumably, on his motor?... ESC?... Where?

Yep - I've got that stiff drink in me paw.
Hit me....

[OMK]

P.M.K A MERRY XMAS TO YOU AND WHERE DID YOU PULL THAT CRACKER THAT KEEPS FLASHING UP ON YOUR PIC 

Taunton town. The same night I posted  http://www.modelboatmayhem.co.uk/forum/index.php?topic=2118.msg20681#msg20681

She told me her name was Early Christmas Present.

[portside II]

had a look at the earlier post's and given the option of your xmas cracker and Bob's pair of transistors i know which i would prefer to cuddle up to at night,
All the best bud

[Daryl]

Fasinating discussion keep the items coming I am enjoying reading them.

 As regards the negative spike, I have noticed but it is faint in the photo a capacitor linking both inputs and outputs. perhaps this would cancel out any emf, I havn't the chance to ask our techno boffin, he's on holiday hic hic hic if you know what I mean.

Daryl