Ammeter

[oldmod1968]

Hi, just fitted an ammeter (30amp) with an alternator . Its slows a very very small positive charge The battery condition shows 14V when running) . However if I switch the lights on the ameter hardly moves. I was expecting a large discharge. Could I have wired it in wrong?

Thanks

[bmcecosse]

Sounds absolutely correct to me !

[mike.perry]

Leave the headlights on for 15 mins then run the engine, if your battery is in good condition.

[Sandun]

Agree with bmcecosse - 14 v is correct - 1st measure volt of battery from digital multimeter, 2nd Go a round by your car , then check battery what happen - charge or not -good luck

[Alec]

Hello Oldmod,

depending on the size of your alternator you 0 to 30 amp ammeter may be too small, assuming all the load is going through it as it should, worth checking?

Alec

[bmcecosse]

It's never likely to charge the battery by more than 30 amps....... it will be fine.

[Alec]

.Hello BMCE,

That would be fine if that's all the load the ammeter carries but it does more than just that. I would agree that most of the time it will be fine but still worth checking.

Alec

[bmcecosse]

The ammeter doesn't carry any more load - it simply reads the too/from the battery. The power from the alternator that is going directly into the car systems doesn't pass through the ammeter. I've never seen more than about 10 amps charge going into the battery - and that for a short period only, immediately after starting from cold.

[Alec]

Hello BMCE,

if the ammeter is connected conventionally most circuits are fed through it although different manufacturers have variations. It does depend on how Oldmod's meter is connected? Basically better to be safe than sorry.

Alec

[bmcecosse]

Ammeter is ALWAYS connected in the battery lead. How else would it be connected?????????????

[Alec]

Hello BMCE,

yes of course, but it is what is also connected to the battery side of the ammeter, so feeding additional loads. Just have a look at some diagrams of cars fitted with ammeters as standard.

Alec

[bmcecosse]

Well - they are wrongly connected then! I've never seen such a thing...........except amateur home installs where anything is possible of course..........

[kennatt]

does this help http://www.enemyracing.com/ammeter.html or this http://www.houlihane.co.uk/amps.htm

[IslipMinor]

With an alternator and the engine running at 2,000rpm or more you should not get much movement on an ammeter - the alternator control circuit compensates very quickly for load changes. As has been said, the ammeter sees all the load going into and out of the battery, other than the starter motor, of course.

The maximum discharge depends entirely on what electrical load you have fitted, and then only when the engine is not running. The maximum charge depends on the alternator size you have, and I would always fit an ammeter with a range reasonably close to the alternator output. What size alternator do you have?

I have a 55A alternator, and commonly see an instant charge of 30-40A for a few seconds after starting. The charge reduces very quickly to a couple of amps after a short while. We have had 3 different alternators over the 40+ years we have had the Minor and all showed similar characteristics.

I have tried to load up a photo showing a 40A instant charge, but keep getting an error!

[bmcecosse]

Your battery must be well down Richard to need a charge of that amount..... do you have something draining it when not running? 10 amp charge would be unusual for me - and it's far from a new battery!

[Alec]

Hello BMCE,

"Well - they are wrongly connected then! I've never seen such a thing...........except amateur home installs where anything is possible of course.........."

I'm referring to manufacture's installations, wrongly connected?

And again as the subject of this post is a non standard installation, I stand by my suggestion to check out the ammeter is not under rated, a simple precaution as normally alternator ammeters are of a larger capacity.

Alec

[IslipMinor]

Roy, there is nothing connected 'permanently', so no drain, and as I said it has been typical of all the alternators in cars I have had that also have an ammeter (either original or retrofit) - the alternators have all been Lucas, so cannot comment on other makes.

It doesn't seem to matter whether the car is in its normal, quite warm 'attached' garage, or in a friend's rather cold one most of this winter, as my son's MGB was in ours for restoration! The current setup on the Minor is no different to to previous ones, it takes a few seconds of high charge (20-40A), tapering down over a few minutes later to a low charge (2-5A) and after a long trip down to zero - it's what I have come to see as absolutely normal behaviour.

[autolycus]

Isn't the obvious way to see whether an ammeter is inadequately rated for its application simply to watch the needle? If you never wallop the end stop with it, it's OK.

ISTR a previous similar discussion about wiring ammeters where someone (perhaps Alec) argued that the ammeter should be wired somewhere odd. When it turned into a "yes it is"; "no it isn't", argument, I gave up.

I've never had an ammeter on an alternator-equipped car, but I reckon you're at least as likely to see an overload discharge as charge.

Kevin

[bmcecosse]

Yet to see the wiring diagram of a car with the ammeter not connected directly in the battery feed.......

[Alec]

Hello BMCE,

"Yet to see the wiring diagram of a car with the ammeter not connected directly in the battery feed......."

Where did that come from, certainly not me, all I said was that other circuits are connected to the ammeter, (saves cable for the installation) so it is not just battery charge that is being carried by the meter.
Although I don't, a great many people consider that an ammeter should not be used with an alternator as they consider it a hazard, but as with any installation it is necessary to ensure an adequate rating.

Alec