Use a bi-color LED as an ammeter?

I read in sci.electronics.design that snipped-for-privacy@yahoo.com wrote (in ) about 'Use a bi- color LED as an ammeter?', on Thu, 30 Dec 2004:

You could, but the problem is that you need around 2 V (minimum) voltage drop across the wire carrying the charge/discharge current. That is far too high; you battery won't charge properly from the alternator and the starter won't work at all, probably.

pattern.

My flute teacher (when I was a kid) told me his job was to look at reconnaisance photos duing the second war - don't remember which type of colour-blindness he had but they got him to do that for the same reason.

so

What you really need is an ammeter that under no current flow indicates '12 oclock' and for discharge the needle swings to the left, should the conditions produce a charge to the battery the needle swings to the right. I reckon this could really catch on if someone chooses to make such devices. Even the colour blind could interpret that.

-- Regards ..... Rheilly Phoull

Its been done. I have one on my truck and I can't figure out why auto mfgs stopped incorporating them into dashboards.

I an see why someone might want to save some real restate on a motorcycle instrument cluster by going with an LED.

Crappy design. Mine is a milliammeter across a shunt in the battery line, with 1/4 amp fuses in the meter circuit and a fusible link off the battery.

My '65 Comet had a 10AWG to the dash and thru the loop on the back of the gauge. I didn't like the wimpy deflection, so I passed it thru once more

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devices.

Because they started way too many fires with full charging current flowing thru them.

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Well...that would be the safe way to do it, but manufacturers sure did it the "crappy" way for a good many years. :-/ I wonder why.

Even if they do it this way (my Landcruiser does), think about where the main battery lead goes next. To a fuse block under the dashboard. The exposure to damage isn't going to be increased much more by passing it through a high current ammeter located in the same vicinity.

The important safety feature in any of these designs is a fusible link just off the battery.

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But in a vehicle that doesn't do this, the main battery lead goes to the rear of the fuse block, outside the passenger compartment. Out there where you can't even get your hands on it, all covered in tape and rubbery sealant goop so it can't wiggle, flop, or fray. ;-) I still believe that the full-current-thru-the-meter style is just asking for trouble.

Of course, as long as it hasn't already done its job and been removed from the system for being a nuisance. ;-) I only wish I had pictures of all the "clever" wiring I've seen in cars.