Easiest way to control current

MisterBill2

Joined Jan 23, 2018
4,055
There are two totally separate things here. The rate of the swing is determined by the mass and the length of the pendulum. The strength of the swing is set by the magnetic drive force delivered by the electromagnet when it is triggered to send a pulse. A resistor to lower the drive magnet current will reduce that, while leaving the rest of the electronics with the full voltage so that they can function correctly.
Using a series resistor for the whole driver package is not working for you because you have way too much resistance and it is not possible to adjust it adequately. If you are unable to locate a low value variable resistor it may work to get some ten ohm 2 Watt resistors, and start with one of them in series with the battery connection. It will not take a lot to reduce the swing.
 

shortbus

Joined Sep 30, 2009
7,088
A resistor to lower the drive magnet current will reduce that, while leaving the rest of the electronics with the full voltage so that they can function correctly.
The tape over the electromagnets core (which is the MANUFACTURES direction for doing this) is the way to go.
 

WBahn

Joined Mar 31, 2012
24,854
I agree with you shortbus but I don't think anybody's listening.:rolleyes:
SG
It's only the TS that doesn't appear to be listening. Several different people have recommended following the manufacturer's instructions. We can't force the TS to do it.
 

Danko

Joined Nov 22, 2017
826
Seems it is solution:
upload_2019-2-28_15-41-18.png
EDIT:
About power of pot 510 Ohm:
Capacity of one D battery or two in parallel C batteries is 16000 mAh.
Usually clock mechanisms designed for one year continuous work from battery.
Average battery current I_a = 16000 mAh / (365 days * 24 hours) = 1.83 mA.
With 36" pendulum it will 2 * 20 ms current pulses in one second.
Pulse current equals (1000 ms / 40 ms) * 1.83 mA = 46 mA.
Coil resistance is 1500 mV / 46 mA = 32.6 Ohm.
Maximum peak power, dissipates by pot will when resistance of pot equals 32.6 Ohm,
so P_pot_peak = 0.75 V * (46 mA / 2) = 17.25 mW,
Maximum average power P_pot_a = 17.25 mW / (1000ms / 40 ms) = 0.69 mW.

Perhaps 100...150 Ohm pot resistance (not 510 Ohm) will enough for TS purpose.
 
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shortbus

Joined Sep 30, 2009
7,088
It's only the TS that doesn't appear to be listening. Several different people have recommended following the manufacturer's instructions. We can't force the TS to do it.
I have it on good authority that some one should look for the companies data sheet. Some one much smarter than me suggested doing that, but didn't follow through.
 

WBahn

Joined Mar 31, 2012
24,854
I have it on good authority that some one should look for the companies data sheet. Some one much smarter than me suggested doing that, but didn't follow through.
There wasn't anything for the person that suggested that the TS look for the company's data sheet to follow through on. The TS either did or did not take the suggestion. Their choice. Someone else posted the instructions from the manufacturer on how to do this (and I have it on good authority that this person apparently isn't even very smart). The TS either did or did not take that advice. Their choice. It doesn't sound like nobody is listening -- it sounds like just the TS isn't listening.
 

MisterBill2

Joined Jan 23, 2018
4,055
The difference is that reducing the magnet current will extend the battery life, while putting tape over the pole piece will possibly reduce the swing, but have no effect on battery life. In addition, the main goal of the manufacturer is ONLY profit, and if folks who have no ability to solder or un-solder correctly damage the unit and demand repairs or replacement that cuts in to profits. Thus the tape trick is the only one suggested because of those who are incapable of anything more complex. And I have sen the soldering attempts of some of those who are unable to solder. Sad indeed they are.
 

Tonyr1084

Joined Sep 24, 2015
3,676
Exactly what I suggested in post #13. However, my concern is how much current the pot can handle. Since I don't know how much current is passing through that coil, nor do I know how much the pot intended for use can handle, I can't be sure if this solution would work. My approach would have been to test various resistances using actual resistors, not pots. Potentially a 1 or 2 watt resistor. But again, I don't know without hard numbers. Voltage and resistance of the coil must be known before a feasible solution can be reached. We can assume a single cell battery such as a C or D cell battery, therefore max voltage may be 1.56 volts (new). Don't recall if someone listed the coil resistance, I'll review all the posts from the TS to see if that was stated. If I find such I'll edit this post.

[edit] Didn't find the coil resistance but in #1 & #3 the TS said the system runs on two C cell batteries in parallel. Doesn't seem consistent with the photographs I've seen, but at least if we assume 1.56 volts, we're still lacking the coil resistance. And in #1 there's mention of a chip on the board. In the photographs (post #40) I don't see a chip. Are we talking about the same thing?
 
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MisterBill2

Joined Jan 23, 2018
4,055
Once again, reducing the current in the coil is a better choice than just increasing the air gap. Of course the tape spacer method is simpler, it was created by a lawyer to minimize any possible responsibility for damage done by those who are clueless as far as soldering goes.
And the fact that the application uses two batteries in parallel indicates that the current pulse is not small.
Has anybody ever read the instructions and safety warnings on something as safe as a DVD player? Or as dangerous as a lawnmower? Most warnings seem to be aimed at unknowing folks.. So obviously they are not aiming for the technically competent, who can understand the circuit..
 

Danko

Joined Nov 22, 2017
826
But reducing the current also reduces the feedback, so there is then the risk that the oscillation will stop.
Because current in collector coil limited by coil or coil+pot resistance
and base coil is shorted by B-E transition, these coils represent
current transformer with constant (I_collector / I_base) ratio.
So condition for transistor saturation remains with any value of collector current.
EDIT:
TS's device simulation.
Collector current oscillation:
upload_2019-3-1_5-13-2.png
 
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MisterBill2

Joined Jan 23, 2018
4,055
The base coil serves to bias the transistor into conduction, the collector coil generates a magnetic field that pushes the pendulum away This is not a transfomer, it is a motor.
 
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