TR6 ammeter vs voltmeter

[pdplot]

Just returned from a meetup at a local farmstand. We had 7 TR 6's, all different years, different modifications, and colors; 2 red including mine, 2 blue, one black, one yellow and one green. My '71 was the only one with black instrument bezels. I prefer the look of the chrome but it just isn't worth the time and aggravation of wrestling with the instruments, cable and those cursed bulbs. Question - why did Triumph change from an ammeter - which mine has - to a voltmeter (or as we used to call it on my 1940 Ford sedan, a "battery condition indicator"? I would think an ammeter would be more useful. You can always check the battery condition with a multimeter.

 

[Geo Hahn]

Does an ammeter react as clearly with an alternator as it does with a dynamo/generator? I'm thinking than an ammeter doesn't show much with an alternator in place whereas a voltmeter would at least show an 'on charge' status.

I really do not know as my dynamo cars have ammeters and my alternator car has a voltmeter.

 

[dklawson]

The basic ammeter requires that all the power to and from the battery (excluding that to operate the starter motor) must pass through the gauge. That means when you move to an alternator (which puts out more current than a generator) you need larger wires and must take more care that those wires/cables are not damaged passing through the firewall. That's the basic ammeter. More sophisticated ammeters put a "shunt" in a heavy gauge cable inside the engine bay. A shunt-type ammeter is really a voltmeter that measures the voltage drop across the shunt. They are much safer than a high-current ammeter but cost more so they were not used on many cars.

As alternator output grew, ammeters generally gave way to voltmeters. You can still tell a lot from a voltmeter. In general, failures of the alternator electronics will result in a steady voltage that is much higher or much lower than about 14V when the engine is running. If the voltage is lower than 14V and continues to drop while driving, the alternator is not charging the battery and when the voltage gets low enough, the engine will stop because the coil can no longer create high enough voltage to make a good spark. If you see a volt reading above 15V, you should first check the accuracy of your gauge using a multimeter. If you find there really is more than 15V going to the battery, the alternator needs to be serviced as there is probably a problem with its diodes. Allowing more than 15V continuously to the battery can damage it. That said, I have seen some racing alternators which were designed and set to deliver 16V continuously.

So you can use a dash mounted voltmeter to monitor what is going on (in general) with the car's electrical system. Its advantage is that it requires small gauge wires which can safely be routed through the firewall compared to the heavy gauge wires of a typical ammeter. If you really want an ammeter, look for a shunt-type that will allow you to safely run small wires into the passenger compartment.

 

[pdplot]

Thanks for the explanation. I'll stick with my ammeter. Most of the time, the needle sits in the middle. When I've been stressing the battery, it shows a big charge until the battery is fully charged. Turning on the headlights shows a small discharge. I don't know how a voltmeter would work.

 

[TR3driver]

I ran with an ammeter and 60 amp alternator for many years in my previous TR3A. The type of charging system really makes no difference to the instrument, it still indicates the same things. Personally, I much prefer the ammeter, especially when compared to the voltmeters that Triumph used (which aren't very accurate and respond very slowly to changes in input).

In addition to avoiding the wiring to the ammeter, I think the voltmeter caused fewer user questions as well. Most people don't understand that generators and alternators don't work very well at idle; so they get upset when the ammeter shows discharge while idling. A voltmeter (even a fast responding one) takes much longer to dip below 12v.

BTW, there is a fairly simple modification that will allow the stock TR ammeter to work well with a higher output alternator. It's called a shunt, and is basically just a piece of wire that you connect across the ammeter terminals to take part of the current. Effectively, it recalibrates the ammeter to a higher full scale indication (eg 60 amps full scale instead of 30 amps).

 

[TexasKnucklehead]

I am glad to see Randall back on board.

I have a slightly different point of view regarding an alternator. I too like the ammeter because it is a real-time indicator. A voltmeter or ammeter is only a gauge, and the usefulness of either is dependent upon what it shows, as well as what is perceived from what it is showing.

True, if an alternator is installed, some re-wiring is required (assuming the old regulator will no longer be used to control the alternator output). Also true, if a higher output alternator is used, eventually the stock ammeter will probably fail (assuming it has been wired to see an excess current than which it was rated).

I have installed a 30a alternator and have not changed to a voltmeter, nor shunted my ammeter. I see no need for a higher output alternator -actually the generator was capable of meeting the normal electrical demands -when it worked. My (halogen) headlights draw less power than the stock bulbs. My electric cooling fan does take some power, but only runs with the engine running (and alternator producing). My cell phone charger and GPS are the biggest power "hogs" added. Combined they have not blown a 10a fuse.

The ammeter is showing current going to or from the battery, not the cumulative electrical load. The only time the ammeter should be showing an excessive charge, is after an excessive drain -like after continued cranking, but not starting. (And even then, my alternator is not expected to produce much more than 30a.) After a normal engine start, my ammeter goes a little higher than when the generator was installed, but it is not pegged. Otherwise, it's about the same. (If I had a failing battery I might see the re-charge take longer or at a higher rate.) I will not have another generator failure, because my alternator is a more rugged design. I do not anticipate an ammeter failure, or see a need to change anything.

My ammeter and alternator work fine for me.

 

[Tom74TR6]

Photo from Sunday - got you in there Paul

 

[TR3driver]

Ok, gotta ask, where did you find a 30 amp alternator and 40 watt halogen headlight bulbs?

When I did my first alternator conversion, I lived where it got cold in the winter (north of Indianapolis), and drove the TR3A I had then just a few miles each way to work. As I worked 2nd shift, that meant always running the headlights and heater; plus frequently the wipers too. So the generator had no chance to recharge the battery after each start and the battery would droop lower and lower. I can't tell you how many times I got off around 1:30 AM and found that there wasn't enough left to start the car! No cell phone, no AAA card, and since I was usually the last one out of the building, no way to even get back in where it was warm. Did you know it is possible to push-start a TR3A by yourself?

Anyway, that routine got really tiring after awhile, hence the big Ford alternator wired to recharge as quickly as possible. Never had a dead battery again, and in fact I used to give jump starts to others who weren't so fortunate (back then, many American cars suffered from similar problems). The previous owner had already replaced the ammeter with a cheap 60 amp unit, so that wasn't an issue on that car.

 

[TexasKnucklehead]

Ok, gotta ask, where did you find a 30 amp alternator and 40 watt halogen headlight bulbs?
Did you know it is possible to push-start a TR3A by yourself?

The bulbs are from the closest O'Reilly Sylvania H6024 -but it seems the specs for those bulbs are very generic. I think the ones from Moss are GE, but cross to the same part number.
The Alternator came from dbelectrical.com -a 12v, 30a Kubota Alternator that crosses to more numbers than I can look at (starting with 16231-64010). It is tiny, but I wish I had painted the shell black before installing so it wouldn't look so obvious.

Back when I was driving to Penn State as a student, I would sometimes drive my brothers TR4 (with a generator and *no* battery). At School, I always parked on a hill and backed into the spot, so I could coast down toward the stop sign and "catch it in gear". It had to work first try, because it was all up hill after that parking lot. Leaving home, I'd push it down the fairly level street and coast down the hill to "catch it in gear". I have pushed more than that car through an intersection. Cold weather didn't help. It's going to be 100 again today but I still don't miss trying to start a car on a cold day.

 

[pdplot]

That's my car - 2nd red one from the end