[modeleng] Re: Electric engines and batteries

Peter,

Do you know anything about the motor windings? Is the field seperate or is 
it series wound, for example?

To a rough approximation, unless it's series wound, the speed of a DC motor 
will be proportional to applied voltage. I think you'd need a 6V tapping for 
shunting and buffing up to stock, but a 2:1 change in speed as you go from 
12V to 24V might be too much.

There are other ways to arrange the switching of the batteries, but you 
would need to use (at least) a two pole switch which was break before make, 
but you could then get 6,12,18 and 24V.

I think I'd be inclined to use some big contactors, rather than 90A wires 
going up to a switch. That might help with the sequencing too, using 
auxiliary contacts to prevent two from being energised at the same time, but 
it's your call.

If you do use a simple single pole switch, beware the posibility of shorting 
out a battery as you change from one tapping to the next (you could use a 
large diode to help here)

JohnP
----- Original Message ----- 
From: <psbr20252@xxxxxxxxxxxxxxxx>
To: <modeleng@xxxxxxxxxxxxx>
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=

shunting locomotive=2E  It has followed my traditional method of design, t=
hat
is one of over-engineering!  It has a 2=2E2kW (24v 90A) forklift motor for=

its main drive, powered by 2 x 12v batteries=2E  The original controller w=
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)=
,
I had to have a rethink on the electric drive!

I think I have covered this before, but to refresh your memories!=20

I have been performing some experiments -

Firstly I had to determine whether or not it was the motor (secondhand fro=
m
a scrapyard) or the controller (brand new from 4QD) that was at fault=2E

Simple solution, bypass the controller and attach 24v to the motor!  Topsy=

needed a load so I coupled her up to Stumpy and three coaches with two
passengers=2E  Stumpy uses an Eaton drive, so I engaged the dump valve=2E =
 With
24v applied, Topsy struggled=2E  She made some progress, but came to a sto=
p
on the slight gradient approaching the station=2E  So it looked like it co=
uld
be the motor=2E  I then uncoupled Stumpy and pushed him away, well I tried=
,
it was very heavy and I found that the dump valve hadn't fully engaged, so=

Topsy had been dragging Stumpy down the track=2E  With the dump valve full=
y
engaged Topsy made light work of a circuit=2E  So it was the controller, n=
ot
the motor=2E

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=2E  I gave u=
p=2E=20
I then phoned Brian at Parkside=2E  Very much more helpful, he guessed tha=
t
the 90A was a running current and that at start up we were look at 3 times=

that, so approaching 270A - 300A (no wonder the 120A 4QD controller curren=
t
limited)=2E  Unfortunately he couldn't help=2E  So, Topsy was stabled for =
a
while whilst I considered my options=2E

The options changed when two things happened, firstly we went to
Lincolnshire to collect an 8 week old Clumber Spaniel puppy (Fergus) and I=

took the opportunity of collecting 2 of Mike Palmers 6v batteries (recentl=
y
offered at Station Road Steam) - who was only about 10 miles away!

So, now the burning question=2E  I have two 6v batteries and one 12v batte=
ry=2E
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=

I couldn't get the carbon washers)=2E

So, do I tap it as:

(a) 6v, 12v, 24v; or
(b) 6v, 18v, 24v; or
(c) 12v, 18v, 24v=3F

My first thought is (a) as it will give a smoother start, but are there an=
y
other ideas=2E=2E=2E=2E=2E=2E

Cheers

Peter




=20




=20



  =20



=20


--------------------------------------------------------------------
mail2web=2Ecom =96 Enhanced email for the mobile individual based on Micro=
soft=AE
Exchange - http://link=2Email2web=2Ecom/Personal/EnhancedEmail


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