RMweb Premium 7013 Posted December 1, 2011 RMweb Premium Share Posted December 1, 2011 I have a new Bachmann 3F run in on DC, runs beautifully smooth, I have just inserted a Bachmann 21 pin decoder and progrmmed it. The only setting I changed was the speed steps from 28 to 128. However the loco starts too quickly then takes off like scalded cat and slows down again the repeats its erratic (no not erotic) dance. I have little experience with 21pin decoders (hence me trying to insert it upside down for 10mins!) but reading the site I see that CVs 54 and 55 should be alterd to tame the beastie. I read through all the CVs; 54 is set at 32 and 55 set at 24 I am happy to alter the CVs if these are the ones to do, but I am not sure if I should alter the values up or down? and should a for instance rise of 10 in 54 be followed by a rise of 10 in 55? and would it be better to start with single increments or say 5 at a time? I would be grateful for help form anyone who can advise me, ideally anyone who has chipped the new 3F, but TBH any help will be appreciated Link to post Share on other sites More sharing options...
RMweb Gold Dagworth Posted December 1, 2011 RMweb Gold Share Posted December 1, 2011 The only setting I changed was the speed steps from 28 to 128 The CV setting in CV29 for 28 or 128 speed steps is the same. Andi Link to post Share on other sites More sharing options...
brossard Posted December 1, 2011 Share Posted December 1, 2011 CVs 54 and 55 are for Back EMF I think. I think the BEMF may be defaulted too high. High BEMF is usually required for the older motors. First off, remove the capacitors on the motor. Try the loco again. I believe the Bachmann decoder is really ESU so based on those instructions, reduce the values of CV 54 in increments of 5 initially. Reduce CV 55 if you don't get much joy. The manual should provide some guidance as to what you need to do. Repeat until the loco behaves itself. John Link to post Share on other sites More sharing options...
Tim V Posted December 1, 2011 Share Posted December 1, 2011 reduce CV2 to near zero - that's the start speed. Link to post Share on other sites More sharing options...
RMweb Premium 7013 Posted December 1, 2011 Author RMweb Premium Share Posted December 1, 2011 Thanks chaps I will give the settings a go when I climb back into the attic tomorrow. Of course having the decoder plug in the tender I forgot about the capacitors. Link to post Share on other sites More sharing options...
smokebox Posted December 1, 2011 Share Posted December 1, 2011 From what I can gather by my own (very limited) experience of these decoders, CV54 affects the jerkiness when starting and CV 55 affects stopping. Adjust CVs one at a time until so that you can see what effect each adjustment is having. If all else fails, back emf can be turned off by setting CV49 to 0. There is a list of suggested CV values for a selection of Bachmann models on the Bachmann site Link to post Share on other sites More sharing options...
Orange Alco Posted December 1, 2011 Share Posted December 1, 2011 Their DCC Onboard steam locos generally have values for CV54 in the area of 12 and CV55 in the the area of 62, assuming the same motor is used in the 3F Link to post Share on other sites More sharing options...
RMweb Premium 7013 Posted December 1, 2011 Author RMweb Premium Share Posted December 1, 2011 Went to the attic had a play around with the CVs which certainly helped, however removing the three capacitors from the motor had a dramatic effect, my little 3F runs splendidly now and really looks the part. Thankyou all for all your suggestions, just goes to show why this site is the best, and in the bargain I have learned a little more about DCC! Of course there is always a downside, I have just seen my photo on the side! Link to post Share on other sites More sharing options...
brossard Posted December 1, 2011 Share Posted December 1, 2011 Great news. Probably the caps were most to blame. I haven't got 'round to chipping mine yet but on DC out of the box it performs brilliantly. John Link to post Share on other sites More sharing options...
RMweb Premium 7013 Posted December 1, 2011 Author RMweb Premium Share Posted December 1, 2011 Cheers John, I ran mine in (DC) down at my club today, but now with alterations on DCC it runs even smoother, and slow speed with a load on it was superb even on my track which is in need of a clean. Link to post Share on other sites More sharing options...
shibushe Posted December 2, 2011 Share Posted December 2, 2011 Yes, It nearly always the capacitors. I was however told that removing them infringes the rules of electrical conformaty. So you are likely to have a man with a clip board and a beard wishing to access your railway. All I can say is. "JUST YOU TRY MATE" Link to post Share on other sites More sharing options...
Lochinvar Posted December 3, 2011 Share Posted December 3, 2011 What's the theory behind the removal of the capacitors? And,with some similar running problems being experienced following the fitting of a decoder ('though not on a 3F), where can I find them,and how do I remove them? DR Link to post Share on other sites More sharing options...
craigwelsh Posted December 3, 2011 Share Posted December 3, 2011 Yes, It nearly always the capacitors. I was however told that removing them infringes the rules of electrical conformaty. So you are likely to have a man with a clip board and a beard wishing to access your railway. All I can say is. "JUST YOU TRY MATE" No issues with removing them unless you take the chip out and run them pure DC later. With the chip in the suppression requirements of the capacitor are dealt with by the chip anyway. Link to post Share on other sites More sharing options...
shibushe Posted December 3, 2011 Share Posted December 3, 2011 It was explained to me some time ago by TCS ( Train Control Systems ) When I had trouble with erratic running. The capacitor acts like a switch against the decoder. I always remove them from the start that way if there are problems then I know its not the capacitor. Link to post Share on other sites More sharing options...
Nigelcliffe Posted December 3, 2011 Share Posted December 3, 2011 What's the theory behind the removal of the capacitors? And,with some similar running problems being experienced following the fitting of a decoder ('though not on a 3F), where can I find them,and how do I remove them? DR Theory - the decoder uses pulse width modulation, and its control circuit tries to measure the back-emf from the motor during the gaps in the pulses. This allows the chip to adjust its output to suit how the motor is responding. The capacitor acts as a small store of electricity (to stop high frequency radio noise being sent back onto the track), so the voltage and current coming back from the motor will be modified by the capacitor. The net effect is that the chip cannot accurately sense the back-emf, so the control is poorer. ( The chip will be doing this work at high frequencies, eg 20kHz, some are higher). Capacitors, little round or blobby things, often yellow/orange, but can be any shape and any colour. They will be wired across the brushes (not necessarily close to the motor, they could be on a circuit board in the loco). Be careful on identifying when removing, there can be "good" capacitors in locos stop flickering of lights and other purposes. The RF noise issues are somewhat overplayed - they may be required so the manufacturers technically comply with a regulation, but in practise make no real difference. With kit-built analogue locos, nobdy I know will ever fit any suppression components. I've never heard of a detector van coming round to complain about it. A badly maintained motor scooter from the pizza delivery company, or someone using a set of ethernet-over-mains bricks will be sticking out vastly more RF interference. - Nigel Link to post Share on other sites More sharing options...
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