ammeter shows increase in current with increased revs Why?

If that's the charge current going into the battery and it continues at that level you either have a flat battery, a seriously defective battery, an astronomically large battery or a defective regulator.

What's the voltage reading ?

Cure will depend on which of the above is the cause.

Charge the battery

replace the battery

fit a reasonably sized battery

or

get the alternator looked at.


A voltage reading will aid the diagnosis
 
Thank you VicS. The ammeter itself is new; the battery seems to carry a hefty charge and cranks the motor without any hesitation. The alternator is probably as old as the motor so may be passed its best. On which terminals do I check the voltage....... the battery's?
 
From the battery will do.
The alternator output teminal would be better but safer to avoid belts and pulleys.
 
At tick over the alternator is just energised.
The voltage it produces will be a little greater (around half a volts) than the battery voltage (measured before the engine is started).
As you up the revs, the alternator spins faster, its output voltage increases.
This larger voltage (just over 14 volts) allows more current to be pumped into the battery.
As the battery charges it's voltage increases causing the current supplied by the alternator to reduce.
 
Sounds about the same as mine. Alternator voltage output is speed dependent and is very low (12 volt or less) at tick-over. This is why the warning light on a car is often on at this point. When the engine speed rises, the voltage rises enough to put current into the battery and is then under control of the regulator.

I do not know which engine you have, but mine idles at 800 rpm and gives about 1 - 3 amps at this poimt. At 2000 rpm I get 30 amps for 1 hour or until the battery voltage stabilises at whatever voltage the Sterling regulator decides means full charge. It then reverts to a trickle charge which is usually about 5 amps (because it is making good the charge being drawn by the fridge.
 
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At tickover (400 revs) the ammeter shows +2 to +5 amps. At 1000 revs the ammeter shows +25 (about maximum) Is there a problem here?

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At the moment from the information you have given, no you do not have a problem.

At tick-over you will have very little output , as the alternator revs increase then your output amps will increases. Which is what you are seeing on your ammeter.

Once you have checked your voltage you may have a problem, but I would not pay a sparky till you have found a fault.

Brian
 
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Think I'll find an auto sparks

[/ QUOTE ] Don't do that untill you have checked the volts.

If you get a reading below say 13.something then you are looking at a situation where the battery is not fully charged and the alternator is working its nuts off to charge it. When it does, if all is well, the amps wiil drop back and the volts will stabilise at somewhere around the 14 mark, +/- say upto 0.4 volts

If its reading up around the 15volts mark or higher with 25 amps on the ammeter then definitely check the alternator.

All assumes no fancy gizmos boosting the alternator.
 
Not a problem. the alternator may not be getting "up to speed" at diesel idling revs due to (maybe) too big a pulley, or not original equipment. If you run at (say) 1200 revs for a while you will see the current gradually drop and the battery voltage (if you have a meter) rise. This is normal process of charging. Do you have to rev the engine to put out the 'ign' light when starting?
 
I'm glad someone has said this ... I read the OP and thought that maybe all was OK - as charge rate increases with engine speed till it reaches a plateau and then stops rising even with increased speed. But I started to think that maybe I missed something when I read first replies !

I wanted to ask OP : Ok so you have high ampage when engine speed is increased ... are you measuring amps shortly after starting engine or apreciable period after ? Reason I ask is that initially the alternator will be banging back charge to replace starting use .. and it may take an hour before charge rate drops back to maintenance levels ... so it's worth checking amps much later once alternator has replenished battery.

Also take note that if you start on one battery ... leave on that and charge up ... then switch to both or other battery - you WILL get a high amp charge rate immediately after switching over regardless of second battery condition as it balances out and drops back to needed charge level.

So really you need to check amps quite a while after charging has been in op.
 
The alternatopr isn't a trickle charger. It is supposed to be capable of charging a battery at up to 60 amps or whatever its rating is, so as to recharge the battery as quickly as possible. If you hand-crank an engine with a flat battery it may indeed take a high current to recharge (A 50 amp-hour battery would take 2 hours to recharge at your observed 25 amp currant).

The crucial thing is that the alternator's regulator is working - ie it progressively reducing the charging rate as the battery nears full charge. When fully charged the alternator should be giving only a trickle, regardless of revs.
 
connect a voltmeter to the battery, if the reading goes above 14.4v (after a while at 1000 revs) its the regulator.
the old lucas acr systems with seperate regulator/rectifier are prone to this. (diagram below)

11acalternatordiagram.jpg
 
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The alternatopr isn't a trickle charger. It is supposed to be capable of charging a battery at up to 60 amps or whatever its rating is, so as to recharge the battery as quickly as possible. If you hand-crank an engine with a flat battery it may indeed take a high current to recharge (A 50 amp-hour battery would take 2 hours to recharge at your observed 25 amp currant).

The crucial thing is that the alternator's regulator is working - ie it progressively reducing the charging rate as the battery nears full charge. When fully charged the alternator should be giving only a trickle, regardless of revs.

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Huh Hum ... I never said an alternator is a trickle charger - where do you get that from ? An alternator has a regulator to alter cahrge rate based on sensing and required level of charge.

60A is a higher than normal rated alternator than a lot of standard boat jobs have ... by the way !
 
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Huh Hum ... I never said an alternator is a trickle charger -

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I didn't say you did. I don't think anyone did. I was just observing that an alternator is supposed to be capable of charging at any required rate from a trickle up to its maximum rating. So an observed 25 amps might indicate it is simply doing its job, or it might mean the regulator has failed.

It's like a loo cistern refilling. It goes full bore until it nears the top, then gets slower and slower, and finally stops when the cistern is full.
 
But the alternator has no control on amperage.

It only controls volts.

The current is set by what the battery will take. Once the alternator starts to regulate voltage, so the charge amps fall due to the increase in battery internal resistance.

Brian
 
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But the alternator has no control on amperage.

It only controls volts.

The current is set by what the battery will take. Once the alternator starts to regulate voltage, so the charge amps fall due to the increase in battery internal resistance.

Brian

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Not entirely true.
A standard car alternator a) has a maximum current that can be drawn from it at any given RPM before the volts drop off.
This current can be quite low at tickover, particularly in older alternator designs.
b) senses its output voltage upstream of its output diodes. This gives it some 'internal resistance' or V-I slope, because the output diodes have some V-I slope.
There is also physical resistance in the cabling etc.

I don't think the OP has a problem unless his ammeter keeps showing 25A for several hours motoring.
A battery voltmeter is a useful tool as others have said.
Cheers,
Chris
 
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