On Tue, 29 Jun 1999, Roger Elliott wrote:
> My girlfriend's TR-250 has a Lucas ammeter as the original Smith's
> shorted out. I pointed out to here that it reads backwards, The needle
> swings indicate discharge while it is charging and to charge when it is
> discharging.
It may be the original Lucas ammeter. My (TR4) gauges are all Jaeger,
except the ammeter, which is Lucas. It's supposed to be like that.
> We tried just swapping the leads on the back of the ammeter - it didn't
> change anything. This surprised me as I thought the meter basically
> read the direction of current. any suggestions on what to do to make it
> read correctly?
Paint + and - on the glass bezel, so it reads what you want. Most of the
gauges in these cars are only graphical representations of what's really
happening, and are not really that accurate. So long as you know what's
going on is best.
However, if you have accessories hooked right up to the solenoid (like my
amplifier is), thus bypassing the ammeter, then you will register a charge
when the accesory is on- as current is flowing out via the solenoid and in
via the ammeter! So even tho you are putting greater load on the system,
the ammeter displays a charge (only valid when the motor is running & the
alternator/generator is charging the battery)
When driving your ammeter should be dead-on center. It shuld only deflect
when you turn an accesory on or off; the exception being on initial
startup- you should register a charge while driving around right after
starting as the car recharges the battery.
> Also, I was messing with my 72 Ford pickup - replacing dash lights. I
> noticed that the ammeter doesn't have heavy wires going to it, which I
> thought was a requirement of ammeters. It just uses the same printed
> circuitry as the rest of the panel. Is it really something else that
> shows whether the battery is charging of discharging/ if so what?
You can bypass most of the current going through an ammeter by using a
shunt- basically a 'short circuit' that lets lots of current 'around' the
ammeter. I suspect that somewhere (like attached to some nice heavy
wires) in the Ford circuitry, there's the two attachment points for the
ammeter set on either side of a big bar of something (steel, copper,
whatever)- and the ammeter is calibrated to register on milliamps.
It's a good idea to use a shunt if you uprate your generator- ie,
replacing a ~20A generator with a ~55A alternator will cause your ammeter
to go wacko on hard charging / discharging- placing a shunt across the
terminals will reduce the amount of deflection that the ammeter will show.
The List Archives contain a thread regarding the use of a shunt on
ammeters. Give it a try (www.listquest.com) and see if you can find
anything.
-Malcolm
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