Dave Plowman (News) laid this down on his screen :
I agree, all but the very cheapest cars had an ammeter. When alternators appeared, there was much less need to know what was happening with regards to charging. The better models did then include a limited range voltmeter, instead of an ammeter.
A friend and I did that a couple of times. A reversal of the battery (usually requiring longer connecting cables) and a quick splat of the dynamo field terminal, and the job was done. Fortunately, the fuel and temperature gauges were hot-wire, and the indicator flasher was a bi-metal strip - so all were polarity insensitive.
And that's how an ammeter works. It is a voltmeter measuring the voltage drop across a shunt. The big difference is it gives you a direct reading - no guesswork needed.
The beauty of a suppressed zero voltmeter is it costs no more to make than an ammeter - but doesn't need heavy duty expensive cable to it. And also gives a (vague) indication of the state of the battery.
Some of the real cheapies appear to be remarkably accurate (well, my Fluke agrees with them!). Of course, you've got to carefully zero them beforehand.
You could obviously make a dynamo of any size - same as an alternator. The speed it runs at is determined by the gearing from the engine.
You would also obviously use electronic control these days with a dynamo.
Of course the lack of high current mechanical switching - commutator and brushes - on an alternator is a plus point - and I'd guess they are cheaper to make overall. And probably allow a far wider actual rev range than a dynamo, again because of the commutator. But you could use a viscous drive to limit the top speed of one too. But one thing is true - a dynamo produces more output at low revs than an alternator. So an alternator has to be geared to run faster relative to engine speed to match it.
In the end it's speed an flux density and that's the same for both. There were practical reasons why alternators DOD produce more, but that was down to the fact that materials and form factor changed AND the real gotcha, they didn't have an 'on off' type regulator, so overcharging could be controlled better,
In short they fitted BIGGER alternators. Not better ones as such.
Yes, you're right. While I think that it doesn't matter which way the wiper motor turned, obviously the heater blower motor would need to be reversed. However, on the couple of cars I was involved with, there didn't seem to be a problem. [Maybe we did swap the blower connections, but I don't recall doing that.]
There's a story there...
A friend and I did an elderly positive earth car for a bloke at work.
In those days, in many (if not most) cars, a radio was an optional extra, so he had bought one. He had managed to fit it himself, but it didn't work - so could we have a look?
We soon established that the reason that the radio didn't work was that it was negative earth (can't recall whether it had a polarity switch), and had blown up.
At the time, most modern cars and radios had gone over to negative earth, so to avoid it happening again, he asked us whether it was possible to modify his car. It turned out that it was, so one lunchtime we did the business.
After the change, the car functioned as normal - but a couple of days later, he came in, and reported that he had acquired another radio - but that too didn't work. We had a look, and found that it had a polarity switch - set to positive earth!
I'm glad to say that he gave up asking us for our assistance.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here.
All logos and trade names are the property of their respective owners.