Dymamos/Alternator

[Rosanne]

I was told recently that older cars (I.e 50 years or more) may have alternators that are unable to put any charge into the car battery, whilst the engine is just ticking over and that the engine has to be running at higher revs in order to do this.

Is this correct?

[V8forweekends]

They don't have to be 50 years old - although nearly. My 1968 Ford Cortina had a dynamo, and yes, at tickover it wasn't powering the electrical system or charging the battery.

Dynamo (US generator) = Older style DC output charging device.
Alternator = Newer style used for last 30/50 years - more power from lower revs, lighter, AC.

Edited by V8forweekends on Tuesday 30th September 16:25

[tomsugden]

My old 1965 Triumph Vitesse had a dynamo. I was under the impression that a dynamo takes it charge from a rotating wheel, rather than the engine?

[BL Fanboy]

Only if you are on a bike.

[Scuffers]

depends on the dynamo and car..

in the old days, the regulator for a dynamo was a electro/mechanical thing, they had two states, low and high, they were really there to prevent over-charging, but the net effect was they only really worked at optimum at two (engine) speeds.

(there were some later ones with electronic regulators that solved a lot of this)

Alternators are way more efficient and can be spun much faster, so work well at lower engine RPM's.

[matchmaker]

A dynamo won't charge at idling speed, hence when a dynamo equipped car is sitting in traffic all the electrical systems are being powered by the battery which is then discharging. The "ignition warning light" would be flickering on and off to warn you of this.

You had to switch off any unnecessary electrical equipment when in traffic.

On top of that the output of a dynamo is far less than that of an alternator. My 1964 Vitesse had a Lucas C40L dynamo which was a heavy duty unit putting out a massive 20amps maximum!

An alternator spins faster than a dynamo hence charges at lower engine speeds, and will have a far higher output. The main reason for this is that the dynamo transfers its output from rotating windings via a pair of carbon brushes, whereas the output from an alternator comes from fixed windings.

A bit non-technical, but I'm sure someone will explain better than me!

[Scuffers]

matchmaker said:

A dynamo won't charge at idling speed, hence when a dynamo equipped car is sitting in traffic all the electrical systems are being powered by the battery which is then discharging. The "ignition warning light" would be flickering on and off to warn you of this.

You had to switch off any unnecessary electrical equipment when in traffic.

On top of that the output of a dynamo is far less than that of an alternator. My 1964 Vitesse had a Lucas C40L dynamo which was a heavy duty unit putting out a massive 20amps maximum!

it's all relative, back then 20A was more than enough for everything on the car.

there were high output dynamo's, seen 60/80Amp ones on some late 60's cars

matchmaker said:

An alternator spins faster than a dynamo hence charges at lower engine speeds, and will have a far higher output. The main reason for this is that the dynamo transfers its output from rotating windings via a pair of carbon brushes, whereas the output from an alternator comes from fixed windings.

A bit non-technical, but I'm sure someone will explain better than me!

alternators still have brushed, but they are onto slip-rings, so very low wear and (as you said) the rotor windings are only the field windings on an Alternator - so low power as opposed to a dynamo's commutator made from segments that carry the full output power.

[Rosanne]

Thanks for your helpful replies. The car in question is a 1960 Ford Anglia 105 e which was converted from positive to negative earth at some stage. It also had its Dynamo replaced with an alternator, but I don't know when.

Could the fitting of a modern type of alternator improve things re battery charging ?

[matchmaker]

Rosanne said:

Thanks for your helpful replies. The car in question is a 1960 Ford Anglia 105 e which was converted from positive to negative earth at some stage. It also had its Dynamo replaced with an alternator, but I don't know when.

Could the fitting of a modern type of alternator improve things re battery charging ?

Yes, it will. A very common modification.

[tr7v8]

Rosanne said:

Thanks for your helpful replies. The car in question is a 1960 Ford Anglia 105 e which was converted from positive to negative earth at some stage. It also had its Dynamo replaced with an alternator, but I don't know when.

Could the fitting of a modern type of alternator improve things re battery charging ?

Alternators typically start charging from 1800rpm or so. Older ones tend to be lower output than current ones but will be much better than a dynamo. On an Anglia the total power drawn is much lower thn on a modern so less of an issue. Modern cars have heated rear windows, electric power steering, electric windows etc.

[Rosanne]

Thanks for your helpful replies. The car in question is a 1960 Ford Anglia 105 e which was converted from positive to negative earth at some stage. It also had its Dynamo replaced with an alternator, but I don't know when.

Could the fitting of a modern type of alternator improve things re battery charging ?

[Ray Luxury-Yacht]

It's well proven that magicians are rubbish at charging batteries

[Scuffers]

Rosanne said:

Thanks for your helpful replies. The car in question is a 1960 Ford Anglia 105 e which was converted from positive to negative earth at some stage. It also had its Dynamo replaced with an alternator, but I don't know when.

Could the fitting of a modern type of alternator improve things re battery charging ?

Simpler mod would be to replace the regulator with an electronic one..

http://www.dynamoregulatorconversions.com/conversi...

Makes a huge difference...

[tr7v8]

Rosanne said:

Thanks for your helpful replies. The car in question is a 1960 Ford Anglia 105 e which was converted from positive to negative earth at some stage. It also had its Dynamo replaced with an alternator, but I don't know when.

Could the fitting of a modern type of alternator improve things re battery charging ?

What is the current (sorry) issue? Which model of alternator is fitted. If it was done in period then it'll probably be an ACRxx or the Prestolite equivalent. It'll be around 30-40amps or so & should more than cover the drain of an Anglia, unless it is converted to electric.

[BL Fanboy]

tr7v8 said:

Alternators typically start charging from 1800rpm or so. Older ones tend to be lower output than current ones but will be much better than a dynamo. On an Anglia the total power drawn is much lower thn on a modern so less of an issue. Modern cars have heated rear windows, electric power steering, electric windows etc.

Can I pick you up on that statement? So for an Alternator, if my car is idling at say 850 rpm, provided it has enough fuel it'll eventually stop due to a flat battery since its not running at 1800 rpm for the alternator to start charging the battery as you say?

[Scuffers]

BL Fanboy said:

Can I pick you up on that statement? So for an Alternator, if my car is idling at say 850 rpm, provided it has enough fuel it'll eventually stop due to a flat battery since its not running at 1800 rpm for the alternator to start charging the battery as you say?

he's talking alternator speed, not engine speed.

dynamo's can only spin so fast (before the windings fall apart), so they are typically run on at only 2X engine speed, an alternator can easily manage being spun at 4-5X engine speed.

obviously, the max revs of the engine are the key here, but being something old, it;s not going to be doing Vtec yo revs.

back to dynamo's, with electronic regulators, they can work at idle, as the electronics are progressive in controlling field currents.

[TooMany2cvs]

BL Fanboy said:

Can I pick you up on that statement? So for an Alternator, if my car is idling at say 850 rpm, provided it has enough fuel it'll eventually stop due to a flat battery since its not running at 1800 rpm for the alternator to start charging the battery as you say?

An alternator will put current out from idle speed, but typically not much. As the revs rise, the output will rise. Modern alternators tend to be big enough that it's rarely an issue, largely because of the amount of electronics even at idle, but on anything roughly pre-injection, it's definitely the case.

If you chuck a voltmeter on, you'll probably see ~12.5v with the engine off, ~13.5v with the engine idling, and ~14.5v with the engine at 1500rpm+.

[BL Fanboy]

Scuffers said:

he's talking alternator speed, not engine speed.

dynamo's can only spin so fast (before the windings fall apart), so they are typically run on at only 2X engine speed, an alternator can easily manage being spun at 4-5X engine speed.

obviously, the max revs of the engine are the key here, but being something old, it;s not going to be doing Vtec yo revs.

back to dynamo's, with electronic regulators, they can work at idle, as the electronics are progressive in controlling field currents.

Ah, alternator speed - makes sense, thanks.