Charging indicator LED?

[Greybeard]

Hello electronics expert,
I'm thinking that I should be able to use a bi-colour LED to illuminate my ammeter. The LED would glow red when the battery is discharging and green when charging.
I'm thinking this might be a very simple circuit. What do you think?

Thanks

Neil Ives UK

[Motoanimal]

Neil,

There would probably be no circuit required at all because LED's only light when current flows through them in one direction. When a battery charges, current flows one way and when it discharges, current flows the other, so they could be connected in parallel just reversing one of them and then connect them across the ammeter shunt terminals, or if that doesn?t produce enough voltage wind a few coils of wire and connect it in series with the ammeter and put the LED?s  across that.  Some protection from overvoltage should maybe be considered, but a series resistor for each LED should suffice?

Phil

[Triton Thrasher]

Neil,

There would probably be no circuit required at all because LED's only light when current flows through them in one direction. When a battery charges, current flows one way and when it discharges, current flows the other, so they could be connected in parallel just reversing one of them and then connect them across the ammeter shunt terminals, or if that doesn?t produce enough voltage wind a few coils of wire and connect it in series with the ammeter and put the LED?s  across that.  Some protection from overvoltage should maybe be considered, but a series resistor for each LED should suffice?

Phil

You can't put resistances in series with the ammeter.

[Motoanimal]

Triton Thrasher,

I'm sorry, but I have to diasagree, of course you can, provided it is low resistance. After all, that is what the shunt of the ammeter is, i.e. a low value resistor with a meter across it to measure the voltage dropped!

Lets assume that the dynamo has the capability to produce 8 amps of output at full tilt (Probably a little optimistic for an A10, but bear with me!) Most commercially available LED?s operate at 3V(ish)

Using good old Ohms law V/I=R where
V= Volts
I = Current in Amps
R = resistance in Ohms

3/8 = 0.375 of an Ohm. Like I said, a few turns of wire, hardly a ?resistor? I?m sure you will agree? If you are particularly worried about dissipating this much energy , a simple solid state circuit could be constructed. Give me a little time and I'll come up with something...

Phil

[Greybeard]

Before we get too technical; can I simply connect a two colo(u)r LED across the ammeter to achieve the desired aim?

Neil Ives UK

[Motoanimal]

Before we get too technical; can I simply connect a two colo(u)r LED across the ammeter to achieve the desired aim?

Neil Ives UK

No.
That's the simple answer mate! There won't be enough voltage dropped to give the 2 -3 Volts required to light them. You would need a circuit like the one below, that I just scribbled down, but before you go off and build it, I have to say that I have done absolutely no calculations and I would need to experiment with values and test it before I could state categorically that it would work OK. There would probably need to be some overvoltage protection for the solid state components too, in the shape of a Zener diode or similar. These kind of circuits seldom end up as simple as they first seem!
Phil

[chaterlea25]

Hi Moto, Neil and All,
Motorcycle Ammeters are NOT shunt Ammeters as described
They are whole current meters, there are only a couple of turns of heavy copper wire inside
when current flows one way the magnetic field created moves the little steel piece one way (attached to spindle and needle) then opposit current reverses the magnetic field and  the needle assembly moves in the opposite direction,
I have a circuit somewhere that uses opamp chips to light individual LEDS the indicates voltage
depending on the range its built to it can have red leds for 9,10,11v and green for 12,13,14

HTH
John

[Motoanimal]

Hi Moto, Neil and All,
Motorcycle Ammeters are NOT shunt Ammeters as described
They are whole current meters, there are only a couple of turns of heavy copper wire inside
when current flows one way the magnetic field created moves the little steel piece one way (attached to spindle and needle) then opposit current reverses the magnetic field and  the needle assembly moves in the opposite direction,
HTH

So a couple of turns of heavy copper wire are?.... a resistor and an inductor, we are all really describing the same thing and what I have said still stands regardless of the construction of the ammeter itself.
Phil

[metalflake11]

Very interesting idea!........... This item may be of interest to you? I may fit one myself. Note that they do one to fit in a 8 millemeter hole that has an in-line circuit board. E-Bay item number 150479033981. Cheers!

[chaterlea25]

Moto
"I'm sorry, but I have to diasagree, of course you can, provided it is low resistance. After all, that is what the shunt of the ammeter is, i.e. a low value resistor with a meter across it to measure the voltage dropped!"

The motor cycle ammeter does NOt work on voltage drop!! simply the magnetic effect of a a copper coil

A shunt ammeter does, it measures the voltage drop across a low resistance (Shunt) using a millivolt meter
A different principle entirely 

John

[Motoanimal]

A shunt ammeter does, it measures the voltage drop across a low resistance (Shunt) using a millivolt meter

John

Agreed, but as mentioned before, the mechanics of the ammeter are completely immaterial (unless you are trying to score points off me) so could you please tell me how it affects everything else I wrote ????

Phil

[LJ.]

Neil... what you want is something like this... http://youtu.be/_5Xp__fiY6g ... The multi coloured monitor LED is just above the ammeter you can see it change colour as engine is revved and then a load applied. The blue LED on the left is a high beam indicator and the red on the right indicates the brake light.

Thanks Metalflake for the link to cheaper battery status monitors!

I have them fitted on all my bikes and find them quite useful. Today I took the A10 out and for the first short distance there was no charge but green light soon lit up a further few miles down the road, I guess the dynamo may have lost its magnetism due to standing unused for a while.

[chaterlea25]

Moto,
Going back up to your suggested 0.375 ohm resister, this would drop 2.25 volts across it
at 6 amps  (60 watt dynamo 12 v system etc )
Have you a source of 10 v headlight bulbs ? 


Good night
John

[metalflake11]

No worries LJ! With regards to the brake light indicator, is it wired in to the switch or a fibre optic wire from the back light? I have done the fibre optic thing on my '78 Bonnie and it works a treat. At night I know for certain I have a back light and stop light, and in the day it is still bright enough to tell me if the brake light is on too.

[Motoanimal]

John,
The last time I examined an A10 wiring diagram the lights were powered from the battery? not the charging circuit! The standad A10 is 6 volts.

Is this a 5 minuite argument or the full half hour  

Good night
Phil