tom80smith Posted December 1, 2013 Share Posted December 1, 2013 Hi, I have built up the DC controller shown here, http://www.instructables.com/id/Simple-controllers-for-DC-motors-inc-PWM-inertia/?ALLSTEPS the main circuit with PWM additional circuit work fine, a little noisy but great control. My problem is when I wire in the inertia and braking circuit in step 5 the potentiometer is rendered next to useless, it will not adjust the speed with the inertia in and with it out I suspect that only the ajustment at the top end is having some effect, (the LED brightness changes), but it will not slow the loco speed down leaving me with just forward, stop and backwards control. I have built the circuit up on some simulation software, and the oscilloscope shows the duty cycle being dropped when the buttons are pressed but it is having no effect on the actual output voltage, this is how I have connected everything up... I thought that maybe the diodes in the inertia section feeding into control voltage are having some effect so I removed them and still have no control, any thoughts, ideas would be greatly appreciated, Tom. Link to post Share on other sites More sharing options...
34theletterbetweenB&D Posted December 1, 2013 Share Posted December 1, 2013 Without looking at the circuit diagram, I would take a wild guess that you simply have a component not in circuit so that the charge on the capacitor that should slowly build or decay and thus vary the output is actually stying near constant; usually our old friend the dry joint... Link to post Share on other sites More sharing options...
Suzie Posted December 2, 2013 Share Posted December 2, 2013 I am not too sure what D3 is doing so I would be inclined to leave that one out and wire directly to pin 5. As far as the controls are concerned, the potentiometer sets the speed like a throttle, and when you throttle back the train will coast until you apply the brake with S2 (gentle brake) or S3 (emergency brake). Starting off slowly with low levels of R1 should work OK and you should be able to ramp up the speed slowly. Measure the voltage on C1 with a high impedance meter to see that the inertia part is working OK. Link to post Share on other sites More sharing options...
tom80smith Posted December 2, 2013 Author Share Posted December 2, 2013 Thanks for the replies, but, with or without D3 there is a constant voltage when the inertia circuit is switched in, on the simulation software D3 seems to prevent the inertia circuit having an effect on the 'normal' controller circuit when switched out. Suzie, I think that there is a fault in my inertia part of the circuit as I am getting zero volts across C1 regardless of where the pot is set, just to confirm would you be using a seperate pot for the resistor r1 in the inertia circuit digram or keeping vr1 (in the inital circuit diagram) as the only pot, I only have vr1 and have omitted r1 from the original circuit, thanks again for the input I think I am connecting something up wrong as the rest of the circuit works great. Link to post Share on other sites More sharing options...
Suzie Posted December 2, 2013 Share Posted December 2, 2013 You need to lose VR1. R1 becomes your speed regulator. If you have no R1 there will be nothing to provide a voltage to charge the capacitor. Link to post Share on other sites More sharing options...
tom80smith Posted December 2, 2013 Author Share Posted December 2, 2013 O.k so the pot vr1 from the original circuit goes, r1 becomes the new speed regulator but is r1 not a 10k potentiometer? Link to post Share on other sites More sharing options...
Suzie Posted December 2, 2013 Share Posted December 2, 2013 It is amazing that you have been able to make anything from such a mess of disjointed circuits, but yes - R1 in the step 5 part of the circuit is a 10K pot - not to be confused with R1 in the step 4 part of the circuit. Note that the R2 and C1 in the step 4 circuit are not the same R2 and C1 as in the step 5 circuit. You will end up with two R1s, two R2s and two C1s with no VR1 Link to post Share on other sites More sharing options...
tom80smith Posted December 2, 2013 Author Share Posted December 2, 2013 Thanks for this I'm going to have re jig tomorrow, so basically the inertia circuit becomes the start of the main circuit, with the 555 timer circuit being added inbetween, without vr1, feeding TR1's base. Just on the step 5 (inertia circuit) what is the 40% setting on the pot? Link to post Share on other sites More sharing options...
Suzie Posted December 2, 2013 Share Posted December 2, 2013 That sounds about right. The 40% reference has baffled me I am afraid! Link to post Share on other sites More sharing options...
tom80smith Posted December 2, 2013 Author Share Posted December 2, 2013 Thanks again for the info Link to post Share on other sites More sharing options...
hnorwood Posted December 17, 2013 Share Posted December 17, 2013 Just found this thread. If I recall correctly, pin 5 in the 555 is directly connected to the internal resistor divider that determines the 2/3V and 1/3V levels. These resistances may affect the "inertia" timing if the diode is left out. In fact you'd be better off buffering the voltage fed into pin 5. (In the 7555 which is a more up-to-date version, the internal resisitors are 100k each.) (I take issue with the author of the piece where he says frequencies over 1kHz gave problems; my PWM controllers work at 20kHz without problems) Link to post Share on other sites More sharing options...
RMweb Gold SHMD Posted December 17, 2013 RMweb Gold Share Posted December 17, 2013 Yes, Higher PWM frequencies should have no effect I have ran loco's on "home brewed" PWM controllers where I could change from 4.9kHz to 19.6kHz whilst the loco was in mid journey. No effect was observable in the loco's speed (or distance travelled). However, on an earlier circuit, the "H-Bridge" driver IC was not symmetrical, in the high-low side as apposed to the left-right sides of things. This meant that at higher frequencies the loco would drive better in the outward direction but would stop sooner, at crawl speeds, in the return direction. (I soon ditched that IC!) Getting to the 7555, I seem to remember that it was CMOS based and thus had very high input impedances. (This means that it didn't affect - pull up or drag down - the circuit it was connected to. (Nowadays I would just use a microcontroller!) Kev. Link to post Share on other sites More sharing options...
Suzie Posted December 17, 2013 Share Posted December 17, 2013 Some motors (like Lima for example) have much lower torque at high frequencies, so while they might be OK once moving, you might have a bit of trouble starting them on a heavy train - that is if they don't burn out before running fast enough to cool off. While all might look OK, there might be a lot more heat being generated that does not show up straight away. Link to post Share on other sites More sharing options...
hnorwood Posted December 18, 2013 Share Posted December 18, 2013 I found the data sheet for the original 555 - as I thought the internal resistor divide is made up of three 5k resistors. You'd need a low impedance divider to drive that effectively. I can't see how adding the "intertia" bits to pin 5 of a standard 555 will work - perhaps he used the 7555. Link to post Share on other sites More sharing options...
tom80smith Posted December 18, 2013 Author Share Posted December 18, 2013 I may try the 7555 in place of the 555, but the circuit was semi dismantled due to testing and experimenting, after which I began a new thread seeking info on another type of controller, thanks for all the input though as I would like to get it up and fully operational at some point as I have spent hard earned money on it; a good learning curve though. Link to post Share on other sites More sharing options...
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