How does an alternator work

[Batista230]

This might seam daft and bizarre
But I want to wire up a light or buzzer to tell me when the alternator has stopped putting current out
This is to be used for my charging system so I know when the alternators has finished charging the batteries up and I can switch my engine off
Yes I know the alternator will always be kicking out 14 ish volts when working properly
But even if the alternator is working under full load or idling its always shows 14V
I believe that the regulator deters whether or not a current is to be given off
Is there somewhere in the regulator that gives off a current (to wire to my sensor) when the alternator is under load or idling

Thanks
Batista230

 

[MikeHalloran]

You need a better voltmeter.

Beyond that, you didn't give us a clue about what size/year/make of engine or vehicle is under discussion here, so we don't know whether your alternator has an internal or external regulator, or how many wires connect to the regulator, so we couldn't me much more helpful than to suggest fitting an ammeter and/or a current sensor in the battery charging wire. With an appropriate sensor and some downstream sparky stuff, the sky's the limit in terms of how you want to be signaled.

How large and how elastic is your budget?

Why don't you automate the stopping, and starting, of the engine, so you don't have to be there at all?



Mike Halloran
Pembroke Pines, FL, USA

 

[pontiacjack]

Building a circuit to trigger a device (lamp, whatever) at a specific DC current thresshold is straightforward for an electronics guy. Break the alternator-to-battery conductor and insert a high-wattage/small-impedance (say 0.01 ohm) resistor (calculate wattage based on maximum charging current, plus a safety factor- 20% or so). Employ a high-gain (u = 1,000-2,000) voltage op-amp to drive the lamp, with the amp input across the resistor, and variable input-offset resistor divider to be able to adjust the thresshold. Construction is easiest with an IC, but unless you can find a nominal-12V chip, you'd also need a DC-to-DC converteer chip (12v-to-5v) and be stuck with using a 5v lamp. The last time I built one (application is a long story- optional reading below!) I used whatever discreet components I had around- NPN transistors, hand-wound wire resistor, etc. Zero cost and it's been working fine for a few years now.

Current-sensor application: My '55 Plymouth is all original except the added 12v cassette player which gets power from a 12v battery in the trunk (in true cheapskate fashion, a "junk" battery that would no longer start a car). A 6v-pos-gnd to- 12v-neg-gnd DC-to-DC converter (off the IGN circuit of the Plymouth's ignition switch) enables 12v battery charging when the car is running. The current sensor is in the charging line to the "trunk battery" and helps me monitor the "junkiness" of the battery.

 

[Batista230]

Current sensor
Would this do the Job?

http://www.ebay.co.uk/itm/20A-Range..._Measurement_Equipment_ET&hash=item2a28ad08d9

I am also looking for a meter that tells me how much current or capacity in amps a battery has
Have seen them before somewhere; do you know what they are called and who sells them

Thanks
Batista230

 

[pontiacjack]

That current sensor module might work for you, depending on what the 20 ampere rating means- if it may self-destruct at 20+ amps, no it won't work for your automotive charging circuit.

It sounds like you're looking for a load tester. My 500 amp one from Harbour Freight serves me well.

 

[BigClive]

Isn't using a hydrometer a standard method to test for the state of charge of a battery?

 

[moon161]

Use the charging current to energize a relay that keeps the ignition circuit closed. When the charging current falls off, the relay opens and cuts the ignition.

 

[Compositepro]

A dashboard voltmeter and ammeter used to be pretty common instruments in cars. They will tell you just about everything you need to know about the health of your alternator and battery. You do need to have a little more knowledge to interpret the readings than "is the idiot light on or not?". You can get these meters prepackaged at an auto parts store.

 

[DRWeig]

Good thought, Compositepro.

Here's a fine selection:

http://www.jcwhitney.com/ammeter-and-voltmeter-gauges/c27290j1s17.jcwx

No, I don't work for JC Whitney. I have, however, spent many thousands there over the years.

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[TheBlacksmith]

I though J. C, Whitney had gone out of business. I guess I finally "outmoved" them and they no longer know where to send my 397 catalogs a year. I once took a short term student loan in college to buy some fog lights from them.

 

[Batista230]

good idea
An amp meter will tell me if the alternator is putting any charge out or not and hence if the battery is taking a charge or not

But I though a hydrometer was for testing for the density of water or in this application water to acid ratio
How would it tell me if the battery had no charge in it?

Thanks
Batista230

 

[pmrobert]

Please, a *little* search engine exertion cannot hurt you.....
[link ]

http://bit.ly/V1jKCV

[/url]