capacitor assistance

[Dagworth]

I do wonder if it would be better to put in the rectifier as per my circuit, and then an H bridge of thyristors to drive the output to the motor, with the gates of the thyristors fed from the pick up side of the rectifier? I'll draw it up at home, I'm writing this in the middle of a concert, Slade about to appear on stage!

 

 

Andi

[jdp298]

Well you're not far off describing what's there now. There's a rectifier function with the first 4 diodes. The essential extra element seems to be allowing the route back into the capacitor with another pair of thyristors. For sure there's a more elegant way of drawing it, but as CS Lewis once said, I apologise for the length of this letter, I have not had the time to make it short.

 

I've also been musing on what kind of diodes to use and have decided I'd probably go with nice clunky rectifier ones rather than schottky or even a MOSFET H-bridge. Yes there's a voltage drop across them, but that's fine if a pair of caps will only rate up to 11v (2 x 5.5).

[Stringfingerling]

I've read this thread with interest and would like to make these observations:

 

 

The people who advocate sorting out the chassis and track etc, and doing without any extra electronics must surely be aware that even the very best loco builders in small scales occasionally have problems with pickup, particularly under exhibition conditions.  I remember watching Tim Watson of the MRC having to pushing a loco on Chiltern Green.  Yes, that was years ago, but in 2mm scale, he is surely one of the best.  At other exhibitions I've  seen countless instances of the dreaded finger from the sky being used to rescue a stranded loco.

 

I've built chassis myself with all wheel pickup, compensation etc, but just once in a while dirty track wins.

 

 

If a clever electrical boffin who understands the problem comes up with a ready made, affordable, small lump of wizardry to put into locos, I feel sure that many expert builders would be only too happy to install it, even though they would still take care over track laying and chassis design.  For people who are less expert I think this would really help. This is where a belt and braces approach is a good thing; the more the electricity supply is backed  up, the more you can stop worrying about it and enjoy running your trains.

[Sebedee]

I too am following this post, and I am actively looking at collecting the components to give it a go.

 

The reasons that I have been looking at trying to get an Electronic Flywheel to work is directed firstly at the cost of Motors in O'gauge these days. The suppliers want to charge us £25 odd quid for a double ended motor that can supply enough power and take a flywheel, when some high quality, and highly suitable, single ended Mabuchi's can be found for around £5 each. This makes a terrific difference to the cost of an O'gauge diesel with twin motor bogies.

 

Secondly, there has always been a problem with twin worm drive loco's in that they have the capacity to eat their brass gear wheels. This is not just due to the low ratios used to try to get an irrelevant maximum speed from the loco (with the commensurate increase in friction between the worm and the Gear, as the torque required to just move the loco has been doubled, or the fight that occurs between the two bogies all the time, as one bogey will always want to go a fraction quicker than the other, but it's also due to the added stresses and strains on the gears caused by sudden losses of power stopping the motors, and therefore damaging the gear wheels as the worm stops rotating and the gearwheel is now locked in a battle to the death with a worm that will not move. You would probably only be able to see the damage under a microscope, but it's there and the dents in the gear wheel will increase wear at that spot when the power is reconnected. Do not underestimate the effect of 4 kilograms of rolling stock travelling at a scale 40 mph (40 cm / s - &etc.) upon a worm drive that has lost all it's electric impetus.

 

This version of a UPS has some very interesting features which I believe will be of interest to many other railway modellers. 

 

By using a latching relay you are reducing the wastage of volts through the diodes and transistors of other circuits, shame about the rectifier.

 

By using a battery as the power source you can change the Amp-age available for different scales, in N gauge I do not know what you would use, but in O'gauge we could even use one of the micro Lead Acid batteries being used as backup batteries to alarm systems - just remove the sheet lead from your loco and put one of these in !

 

By keeping the motors rotating we are reducing the wear and tear on the worm drives of our loco's, as we remove the hammer action on the gear wheel caused by a loss of power.

 

And that sum's up what I've always wanted from an 'Electronic Flywheel'. Something which just keeps the motor rotating. In O'gauge we don't need to worry about the loco keeping moving over the dirt, the weight of a passenger train alone will get the loco past the dirt, but I've always thought that if we can keep the motors turning then we should be able to reduce the damage to the mechanisms when the power does drop off, for whatever reason.

 

I'll let you know how I get on. It'll take a month or 2, but I'm building my next chassis at the moment and I'm looking for a nice little Lead Acid battery to put into it, and I don't think a TIP41C is 'excessive', I think 3A is 'required' !

[Stringfingerling]

I'm not contributing to the discussion or arguments, but I am asking for courtesy....    Bits of this thread remind me of a hilarious thread on a DIY site where two expert builders were discussing a technical point, initially politely, then abrasively, finally in terms of "F" this or "F" that, which was much like an argument between inarticulate schoolboys.   

 

If you know someone is wrong in their reasoning, surely the best way forwards is to explain very clearly, why you believe them to be mistaken, not to start name calling?

[Dagworth]

I'm not contributing to the discussion or arguments, but I am asking for courtesy....    Bits of this thread remind me of a hilarious thread on a DIY site where two expert builders were discussing a technical point, initially politely, then abrasively, finally in terms of "F" this or "F" that, which was much like an argument between inarticulate schoolboys.   

 

If you know someone is wrong in their reasoning, surely the best way forwards is to explain very clearly, why you believe them to be mistaken, not to start name calling?

I think you'll find that's what I did, and the other chap I believe is no longer here.

 

Andi

[Stringfingerling]

OK, thanks for that.

 

Rob

[raymw]

Hi,

Interesting, but I'm thinking it's getting to be almost as easy to use a uP with an ad input, driving a couple of mosfets, possibly cheaper, too. Wrt batteries, I am not sure at the current situation with capacitors, but to get across an inch or so of dirt, then that may be an alternative to primary cells. If not, some of the rc rechargeables may give a smaller size with more power.

 

I found Sebedees comments interesting, I had not thought about the strain on the drive mechanism. However, I'll be going dcc, and will be using controllers based on Paul's work, here - http://www.dccdiy.org.uk/motor.html, which are fine for O gauge (but you'd need sm components for N ). The advantage of the diy type, it would be relatively easy to build into the controller software  some code to prevent the sudden stalling of the motor (but it would still need a bu battery/cap for the dirty track scenario) . It was a few years ago I was messing with this (it's my pcb on that page).

 

Sorry if It's gone off topic, but having fitted  these controllers to a couple of Lima locos (O gauge), it made them into something a bit more worthy than the junk heap (apart from the general poor appearance of the things). O gauge dcc runs at 22V, and being basically hf, (well it's hf compared to dc) tends to keep the rails cleaner, or at least it jumps a bit better across the gaps . Anyway, I don't think you can easily fit a mechanical flywheel to the Lima cans, so it has to be some electronic gizmo.

 

Thanks for persevering with this project, Andi.

 

Best wishes,

 

Ray

[Suzie]

The DIY decoder is 13mm wide as described on the website, which leaves a lot of room for batteries even in a 00 scale Lima loco. I have one of them in a Lima Deltic with a 4700uF capacitor and there is loads of room still.

 

With a bit of jiggling you could probably get it down to 10mm wide which might be possible to squeeze in to a support vehicle coupled to an N gauge loco. Surface mount would be a lot better, and quite feasible nowadays if you want a few for a large collection.

[jprampolla]

I have read somewhere that small caps can help an analogue 12v. fed loco or power bogie to get across a bad pick up spot. Almost an electrical flywheel. Is this true? and if so what values please?

 

I use this 3300 mfd, 16V bi-polar capacitor  http://www.digikey.com/product-detail/en/ECE-A1CN332U/P1173-ND/227614

 

Size / Dimension 0.709" Dia (18.00mm) Height - Seated (Max) 1.398" (35.50mm)

 

with this FK-130SH motor http://www.mabuchi-motor.co.jp/cgi-bin/catalog/e_catalog.cgi?CAT_ID=fk_130rhsh

 

 

and I get about 3 inches of coasting after power is cut, as compared to none without it.  It is for an O gauge handcar (like the one in my avatar), but I believe the motor is similar to what could be found in many OO or HO scale locomotives.  I use it in parallel with the motor, just that simple. 

  

Hope this helps!

 

Take care, Joe.

[jprampolla]

This may be a longshot, but I didn't have room inside either, so I painted the cap to look like a barrel or keg, and have it on the outside.

                         

Perhaps there is a way to partially have the cap protrude through the shell of the loco, and the part that sticks out could be made to look like a tank, toolbox, or copula.    The benefit of the cap, for me, was remarkable.  I was able to go over insulated rails, uneven track, and gaps, without even a hiccup, at slower speeds.

 

Take care, Joe

[Satan's Goldfish]

Best read I've had in ages, don't know how I missed this one!

 

That's a brilliant circuit Dagworth, I'm adding it to my 'to do' list as I have a lot of old lima locos and an even bigger box of 9v batteries! Wrt the idea of using thyristors, I've always found when my circuit diagrams start looking like that for something that should be 'simple' then I've made an error somewhere, I've not run through it in my head yet but then I'm generally more inclined to use relays for reversing polarity as Dagworth has done.

 

I may have missed it, but out of interest Dagworth exactly which relay did you end up using and what was it's operational voltage range?

 

(From the start in my head this was going to work pending component values and with the components removed as brilliantly described by Suzie earlier on. All fantastically balanced out by some shocking electronic 'theory' which has had me in hysterics from others. Cheers all!)