[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




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