[modeleng] Re: Electric engines and batteries

John,

No offence taken!

Some of my replies are written at work, so I am briefer than I might 
normally be.

I suggested bedsprings because in my time as an apprentice at 
Westinghouse Brake and Signal Co Ltd,. I spent a few months with 
Westinghouse Davenset Rectifiers helping with the design of thyristor 
controlled plating equipment (quite novel in 1979).  These units could 
deliver up to 3000A dc at 8v.

We used something that looked like a 3' sprung bed base as the load.  It 
was good in the winter as it would heat the workshop most effectively!

Coming back to Topsy, with regard to a flywheel, when I am rolling (i.e. 
the 12v to 24v switch) the current will be relatively low and I will 
have 2 or three coaches (and if they are fully loaded) then over a ton 
being pulled - that's a fair chunk of momentum!

Cheers

Peter

John Pagett wrote:
> Peter,
> 
> Firstly, I didn't know when I replied how happy you were dealing with 
> electricity, so if there was any "teaching to suck eggs", I apologise. My 
> background is electronics, but has spread a bit over the years.
> I suspect, though I'm happy to be proven wrong, that the KISS principle 
> won't give you the flexibility that you are after.
> 
> I like the idea of glowing bedsprings. I did wonder about tungsten lamps, 
> but the temperature co-efficient of resistance goes the wrong way. What 
> about stainless rod? I haven't done any sums but the resistivity is pretty 
> high and you only need a fraction of an ohm.
> 
> Alternatively, reduce the effect of the lurch by fitting a huge flywheel!
> Regards,
> 
> JohnP
> 
> ----- Original Message ----- 
> From: <psbr20252@xxxxxxxxxxxxxxxx>
> To: <modeleng@xxxxxxxxxxxxx>
> Sent: Wednesday, May 30, 2007 1:53 PM
> Subject: [modeleng] Re: Electric engines and batteries
> 
> 
> Hello John,
> 
> I wasn't clear at all in the previous message=2E
> 
> The motor is series wound, I already have a contactor (from its original
> application) to give the switching for forward reverse=2E
> 
> I did think about being clever and using a series/paralell arrangement of
> batteries, but gave that up on the basis of the KISS principle=2E  In a
> perfect world it would have been nice to have 4 x 6v batteries, but at
> =A3100/pair I was stretched to buy 2!
> 
> As a railway signalling engineer by background (and a safety engineer now)=
> 
> I planned to use auxilliary relays that were interlocked to remove any
> chance of shorts=2E  I never intended to use a switch with 90A contacts! e=
> ven
> assuming I could find one :-)
> 
> I think that all I can do is try the 6, 12, 24 option and see what happens=
> =2E
> If it is too much of a lurch, then if I can find some bedsprings I can use=
> 
> them as low value resistors and provide a step between 12v and 24v=2E =20
> 
> I could also try the 6, 18, 24 option=2E  My concern is to reduce the lurc=
> h
> at the start, I suspect that when it is rolling it may not be too bad=2E=2E=
> =2E=2E=2E
> (famous last words!)
> 
> Cheers
> 
> Peter
> 
> 
> 
> 
> 
> 
> 
> 
> 
> Original Message:
> -----------------
> From: John Pagett john=5Fpagett@blueyonder=2Eco=2Euk
> Date: Wed, 30 May 2007 13:34:15 +0100
> To: modeleng@freelists=2Eorg
> Subject: [modeleng] Re: Electric engines and batteries
> 
> 
> Peter,
> 
> Do you know anything about the motor windings=3F Is the field seperate or =
> is=20
> it series wound, for example=3F
> 
> To a rough approximation, unless it's series wound, the speed of a DC moto=
> r=20
> will be proportional to applied voltage=2E I think you'd need a 6V tapping=
> 
> for=20
> shunting and buffing up to stock, but a 2:1 change in speed as you go from=
> =20
> 12V to 24V might be too much=2E
> 
> There are other ways to arrange the switching of the batteries, but you=20=
> 
> would need to use (at least) a two pole switch which was break before make=
> ,=20
> but you could then get 6,12,18 and 24V=2E
> 
> I think I'd be inclined to use some big contactors, rather than 90A 
> wires=20=
> 
> going up to a switch=2E That might help with the sequencing too, using=20
> auxiliary contacts to prevent two from being energised at the same time,
> but=20
> it's your call=2E
> 
> If you do use a simple single pole switch, beware the posibility of
> shorting=20
> out a battery as you change from one tapping to the next (you could use 
> a=20=
> 
> large diode to help here)
> 
> JohnP
> ----- Original Message -----=20
> From: <psbr20252@blueyonder=2Eco=2Euk>
> To: <modeleng@freelists=2Eorg>
> Sent: Wednesday, May 30, 2007 10:59 AM
> Subject: [modeleng] Electric engines and batteries
> 
> 
> Topsy is a home brew 0-4-2 (I suppose strictly a B-1) narrow gauge outline=
> =3D
> 
> shunting locomotive=3D2E  It has followed my traditional method of design,=
>  t=3D
> hat
> is one of over-engineering!  It has a 2=3D2E2kW (24v 90A) forklift motor f=
> or=3D
> 
> its main drive, powered by 2 x 12v batteries=3D2E  The original controller=
>  w=3D
> as
> from 4QD, but following a disaster on my first running day (where Topsy
> gave the impression of not being able to pull the skin off a rice pudding)=
> =3D
> ,
> I had to have a rethink on the electric drive!
> 
> I think I have covered this before, but to refresh your memories!=3D20
> 
> I have been performing some experiments -
> 
> Firstly I had to determine whether or not it was the motor (secondhand fro=
> =3D
> m
> a scrapyard) or the controller (brand new from 4QD) that was at fault=3D2E=
> 
> 
> Simple solution, bypass the controller and attach 24v to the motor!  Topsy=
> =3D
> 
> needed a load so I coupled her up to Stumpy and three coaches with two
> passengers=3D2E  Stumpy uses an Eaton drive, so I engaged the dump valve=3D=
> 2E =3D
>  With
> 24v applied, Topsy struggled=3D2E  She made some progress, but came to a s=
> to=3D
> p
> on the slight gradient approaching the station=3D2E  So it looked like it =
> co=3D
> uld
> be the motor=3D2E  I then uncoupled Stumpy and pushed him away, well I tri=
> ed=3D
> ,
> it was very heavy and I found that the dump valve hadn't fully engaged, so=
> =3D
> 
> Topsy had been dragging Stumpy down the track=3D2E  With the dump valve fu=
> ll=3D
> y
> engaged Topsy made light work of a circuit=3D2E  So it was the controller,=
>  n=3D
> ot
> the motor=3D2E
> 
> I tried to speak to 4QD, all I kept on getting told was not to use
> secondhand motors and to use their "motor current" calculator=3D2E  I gave=
>  u=3D
> p=3D2E=3D20
> I then phoned Brian at Parkside=3D2E  Very much more helpful, he guessed t=
> ha=3D
> t
> the 90A was a running current and that at start up we were look at 3 times=
> =3D
> 
> that, so approaching 270A - 300A (no wonder the 120A 4QD controller curren=
> =3D
> t
> limited)=3D2E  Unfortunately he couldn't help=3D2E  So, Topsy was stabled =
> for =3D
> a
> while whilst I considered my options=3D2E
> 
> The options changed when two things happened, firstly we went to
> Lincolnshire to collect an 8 week old Clumber Spaniel puppy (Fergus) and I=
> =3D
> 
> took the opportunity of collecting 2 of Mike Palmers 6v batteries (recentl=
> =3D
> y
> offered at Station Road Steam) - who was only about 10 miles away!
> 
> So, now the burning question=3D2E  I have two 6v batteries and one 12v bat=
> te=3D
> ry=3D2E
> In series they give me 24v, but I have three potential tappings and it is
> this crude method of control I plan to use (I did look at carbon pile, but=
> =3D
> 
> I couldn't get the carbon washers)=3D2E
> 
> So, do I tap it as:
> 
> (a) 6v, 12v, 24v; or
> (b) 6v, 18v, 24v; or
> (c) 12v, 18v, 24v=3D3F
> 
> My first thought is (a) as it will give a smoother start, but are there an=
> =3D
> y
> other ideas=3D2E=3D2E=3D2E=3D2E=3D2E=3D2E
> 
> Cheers
> 
> Peter
> 
> 
> 
> 
> =3D20
> 
> 
> 
> 
> =3D20
> 
> 
> 
>   =3D20
> 
> 
> 
> =3D20
> 
> 
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