Club Triumph

I have just replaced the dynamo on Tr4a with an alternator. The only concern I have is the ammeter now reads a fairly constant 8 to 9 amps into the battery. With the dynamo it would be all over the place depending on load but cruising along would be near zero. It has been tested on a run of about an hour, nothing hot to the touch or other obvious problems. Should I be concerned? The battery is in good condition. Where are all the amps going?

This is interesting on the autosparks website under 'wiring for alternator'....

https://webcache.googleusercontent.com/search?q=cache:LEue5mxKYkYJ:https://www.autosparks.co.uk/1059-triumph-tr4a-wiring-harness-set.html+&cd=8&hl=en&ct=clnk&gl=es

Slightly surprised they are claiming the ammeter resistance is an issue because it should be next to nothing.

I think with the original regulator there were separate outputs to the vehicle electrics and battery charging supply which worked at different voltages. The ammeter was integral to the correct operation of the charging circuit but of course is now subject to different electrical conditions so reads wrong and may have a voltage effect especially at higher current flows (V=IR)...

I need to check there isn't any load on the battery side of the ammeter however, I suspect I won't be able to find 10 amps worth.
The ammeter is an inline device, a higher charging voltage may deliver a higher current but not continuously. It should level off and return to zero when the battery is back to full charge.

I assume there is a volt drop across the ammeter proportional to the currect flow so when charging a discharged battery the higher voltage output from the regulator compensates for this so with an alternator in theory the battery might not recharge up so quickly. However I cant explain why it should now be showing that current reading..... 

My Vitesse's ammeter does that because the needle isn't correctly centred. The giveaway is that it still shows a few amps going into the battery when everything's off.

yes but presumably it was indicating ok before the dyno/alternator swop.....

However it appears that some of these cars have a fused power supply directly from the battery to the horn and over the years owners have used this to also supply fans and other items. Ok this wont have changed with the new alternator but perhaps now the load can be supplied at lower revs where as before the old dynamo couldnt and it came directly from the battery. Obviously with the dynamo the battery must have been discharging until the revs came up enough to charge it and this would have shown on the ammeter but only intermittently while now with an alternator its showing all the time?

With the dynamo, no lights, heater fan or load other than running the engine the ammeter would settle near zero once the drain of starting had been put back into the battery. With the alternator there is a constant 8 to 10 amps going into the battery (charging). The ammeter is connected directly to the battery so current must be following into the battery. The only other connection on the battery side is the solonoid for the starter motor. The starter motor works fine. Across the battery terminals there is 14 volts with the engine running and about 12.5 volts without the engine running.

According to the drawings on this site the ammeter should connect to the starter solenoid battery side terminal.

Its not possible that theres a problem with the ignition switch and the starter motor is running all the time is it? Although why it should do it now and not before the conversion I dont know..... 

http://www.advanceautowire.com/tr24a.pdf

The wiring is correct and as you describe. The other side is connected to the output from the alternator and everything else that needs power apart from the starter motor.

If the starter motor was running the whole time it would get very hot very quickly. They actually don't turn the engine over very fast compared to normal running speeds.

10 amps at 12 volts implies 120 Watts going into the battery.

I'm not overly worried as nothing is getting hot or not working but I would like to know what is going on.

Dont know if it'd get very hot as the starter motor wouldnt be working hard cos the engines already running....

However, as that article said, maybe the ammeter is inaccurate after the alternator conversion (if not the battery will be fried after a while) and this could easily be checked with a DC Tong ammeter if you can get access to one.

There is a reason, which I've forgotten, why a volt meter is normally fitted with an alternator, not an ammeter. Someone will know.

Tony.

Quoted from nang-

There is a reason, which I've forgotten, why a volt meter is normally fitted with an alternator, not an ammeter. Someone will know.

Tony.

I think its because a Dynamo only can charge at certain RPM when there is a full load so the Ammeter shows if its discharging. An Alternator should charge in all conditions so the Voltmeter should show a pretty steady reading across the rev range.... or something like that.  Plus wiring a voltmeter is so much easier!

Not quite.

Dynamo control boxes are mixed-mode electro-mechanical devices which are mostly sensitive to the dynamo's ability to provide charge. An ammeter shows whether that's actually working by showing the direction of the current flow. Alternators use pure voltage sensing and control, so a voltmeter shows whether that's working.

Also, dynamos were rated at quite low currents, where an ammeter was sensible. Trying to build an ammeter that could handle the 150A modern cars regularly use while still showing meaningful results at the 2A trickle you want into your battery most of the time... is hard. If the battery voltage is 14V then you know it's being topped up nicely, regardless of the actual current.

The car did 750 miles this weekend in the C2C without issue and the current going in has slightly lowered to 2 or 3 amps. I'm happy with how it is so thanks for all the comments and advice and for anyone else considering an alternator conversion it really is very easy. This video from Moss tells you everything you need to know:https://www.youtube.com/watch?v=4NsAYiUHsho

Hi Kevin,

having read websites and seen the Moss video I will assume that you have wired it correctly.

I didn't have that luxury a few years ago and I now have an ammeter that shows a charge if I apply  a large load to the system.  This is not actually a problem.

That bit doesn;t help you other than there are quirks in the TR system.

You say your battery is OK. The 10 amp flow reducing to 2 amps after a very long run would suggest you have a battery with a charging issue.

It may be that it wasn't charging too well with the dynamo and then when the alternator was installed it had a challenge to get the battery up to sorts.

No problem in using an ammeter instead of a voltmeter - it can give good information as to when systems are coming on line etc (rad fan )

Make sure that ALL the wiring behind the dashboard is in very good order.

The ammeter brown wire caries a lot of punch.

Roger