Inside picture of a V-BOX II

[Llew]

Well Likvid, the rectifier is almost certainly D11 (to the right of the transformer secondary winding socket.)

The problem with putting a resistor in circuit will lead to lower voltages to the rest of the circuit though, and might cause problems with the supply to the ic(s).

Still, if it's been done, fair enough. It would normally be placed in one of the secondary supply's red wires.

Llew

 

[johnsattuk]

Can anyone good in electronics help?

I want to slow down the motor and after reading on the net you should place a resistor before the bridge rectifier, can anyone show where?

Most of us complain about motors being slow

Are you trying to quieten the motor or increase the accuracy or ??

 

[Llew]

I would've placed a resistor in the 36V line - but it would have to be a big one physically to dissipate the heat...

Llew

 

[johnsattuk]

Fair bit of room in the box, could perhaps mount one off the board.

The yellow disc by the bridge seems to be a PTC resistor, probably for current limiting, could perhaps replace this with a resistor or even a Zenner diode.

 

[Likvid]

Are you trying to quieten the motor or increase the accuracy or ??

Both.

The noise is really annoying me and my neighbors now when the warm sunny weather is here and they are out on their balconies.

Not fun when the motor is louder than when they talk to each others.

It's really really annoying and i don't want to be called the nutcase by all people where i live either.

 

[Likvid]

Fair bit of room in the box, could perhaps mount one off the board.

The yellow disc by the bridge seems to be a PTC resistor, probably for current limiting, could perhaps replace this with a resistor or even a Zenner diode.

Ok there are two red and one black wire coming out from the transformer.

Can i cut the red wires and place a resistor on both? would that be good?

 

[Likvid]

I would've placed a resistor in the 36V line - but it would have to be a big one physically to dissipate the heat...

Llew

I have read on newsgroups that placing the resistor after the rectifier like you suggest is no good thing as it will mess up the accuracy of the pulse count, eg too much overshoot will be the result.

From the newsgroup:

I do not argue for NOT inserting a resistance in series with the motor.
Quite contrary, inserting a resistance slows the motor down, but should
not be inserted in a way so the circuitry does not work properly. The
whole meaning with the positioner shorting the motor is to stop the
motor quicker, so it does not overshoot.

So, all in all, slowing down the motor is fine, and keeping the quick
stop function is also a good idea. To insert the resistor in the
motorleads in such a way the shorting does not work properly, tends to
slow down the motor AND in the same time tends to increase the
overshoot.

You might get marginally less overshoot, but with the same resistor
placed differently you will get no overshoot att all, at the same cost.

The way is to insert the resistance in series with the powerlead from
the transformer to the rectifier. That way the motor moves slower, and
when relays fall, the motor is shorted and stops quicker. If the
resistor is in series with the motor leads outside the receiver, the
circuitry can not short the motor (the resistor is in the way), and
hence it slows down slower and vershoots more.

Easy to try for yourself, just insert the resistor one way first and
measure, and then the other way. There is a big difference, especially
when using larger resistors with small motors, typically 33 ohms with a
Landis&Gyr (Arcivator) actuator on small dishes.

 

[johnsattuk]

I have read on newsgroups that placing the resistor after the rectifier like you suggest is no good thing as it will mess up the accuracy of the pulse count, eg too much overshoot will be the result.

The PTC is after the bridge and feeds only the relay contacts for the motor. Replacing the PTC with a resistor or a zenner would not affect the rest of the circuit.

Perhaps the ideal solution would be a resistor in series with the PTC, this would retain the current limiting in the case of a fault, slightly more tricky to implement.

You could mount a variable resistor in the box and could then alter speed/noise to suit quantity and quality or size of the neighbours.

Placing a resistor in the motor leads will increase overshoot.

 

[Llew]

Yes Likvid, I can see his reasoning - the faster the relays drop out, the faster the motor stops. But I still maintain that dropping the voltage to the whole circuit rather than just to the motor can't be a good idea. I mean you're dropping the supply voltage to the rest of the circuit by maybe half?

But then I don't have a v-box, so I can't really guess here.

Doesn't matter which red lead you place it in, one or both. With both, you can half the wattage size of each resistor.

Llew

 

[johnsattuk]

The PTC is after the bridge and feeds only the relay contacts for the motor. Replacing the PTC with a resistor or a zenner would not affect the rest of the circuit.

Perhaps the ideal solution would be a resistor in series with the PTC, this would retain the current limiting in the case of a fault, slightly more tricky to implement.

You could mount a variable resistor in the box and could then alter speed/noise to suit quantity and quality or size of the neighbours.

Placing a resistor in the motor leads will increase overshoot.

Iv'e been thinking

Perhaps the ideal solution would be a voltage regulator which generally have built in current limiting as well.

Motor speed control by a resistor is never a very good solution, the voltage to the motor will vary considerably with load, particularly at start, and the load on a dish motor does vary a lot, depending on whether climbing or descending the arc, wind load etc.

A fixed value one would be very easy to fit in place of the PTC, it would only need one hole drilling in the board, the neg. track is there on the underside, in the right place. Just need to decide what voltage you need from the range available.

A better solution would be to fit a variable regulator.A small potentiometer would fit nicely on the back panel, under the mains input lead. This would allow adjustment to suit the requirements of any setup.

There are some V.reg. on ebay at the moment 1.5v - 33v 3amp rating for 50p which is probably cheaper than a high wattage resistor solution for the budget minded enthusiast.

I did a check on my Vbox driving my 1224, was taking betwwen 500ma & 650ma at 36v, depending on position.

 

[Llew]

A nice idea there OG. We need to be careful though with something like that in the motor drive circuit. Although the regulator is S/C protected, back EMF from the motor can cause problems unless diode protection is added between the input and output of the regulator. And transient suppression diodes on each leg of the drive lines if they are not already provided.

Llew

 

[iwol]

so has anybody managed it and how

 

[johnsattuk]

so has anybody managed it and how

Have started, got all the bits and pieces together, but a bit busy lumberjacking at the moment. Will try to get at it soon

 

[Likvid]

Have started, got all the bits and pieces together, but a bit busy lumberjacking at the moment. Will try to get at it soon

Great, maybe i could buy the kit from you later on then?

 

[johnsattuk]

Have started, got all the bits and pieces together, but a bit busy lumberjacking at the moment. Will try to get at it soon

Assembled the bits, a bit hastily but trying to keep up

Pics:- Unmodded board, track cut and tinned, SMD diode and standoff soldered in pos., regulator h/sink and required components mounted in position. The adj. pot is on the end of the loose wires at the moment while I play.

 

[johnsattuk]

After playing a little

testing with 100deg swing 35W - 65E

@40v - 35 sec noise as expected
@30v - 48 sec noise slightly lower freq. but not much change in vol
@20v - 80 sec noise a bit less than 30v, more of a hum
@18v - 90 sec fairly quiet hum

noise is difficult to quantify accurately, above is how I perceived it, may try with a meter if I get time.

18v seems to be about the limit with my 1224 and 120cm Fibo dish, any less and it would stall. May stand less with other setups.

I have underestimated the size of the heatsink required, it is OK on the higher voltages, and skipping from sat to sat, but testing on 100deg swing at short intervals and low volts o/heats the reg.

 

[Llew]

From where is the noise originating OG?

Llew

 

[johnsattuk]

From where is the noise originating OG?

Llew

Small high speed motor, multi stage gear reduction, fastened to a large loudspeaker cone.

 

[Llew]

AH, sorry 2

Thought you meant something in the vbox

Nice mod BTW

 

[morphsta]

Sorry to resurrect an old thread, but I am having a similar problem here with my old superjack vbox.

With regard to the modification you recommend, I don't know how to make the choke properly. My electronics shop sells a number of RF chokes, but I don't know which would suit the mod best (I'm no electronics / RF expert!)

The specs range from 2.2uH / 0.25 ohm / 1000mA through to 1mH 14 ohm / 130mA (i.e. 2.2uH, 4.7uH, 10uH, 22uH, 47,uH 100uH, 470uH and 1mH). Could you recommend the right one to get?

Can anyone enlighten me on the right one to go for that will suitably emulate the "10 turn choke"!

Thanks,

Morfsta