Dynamo vs Alternator

[Jack]

I think, at a very basic level, I now understand some of the differences between a dynamo and an alternator.

The question, given the limited power generated by a dynamo, especially on the Bradford and prewar cars, is why everyone isn't moving over to alternators? Is it purely for originality and appearance of the engine bay? Problems changing to negative earth? Or something about how they work that I've not understood?

I am trying to work out if less force is required to spin a dynamo or alternator (assuming both are in good condition and working properly) but my internet learnings haven't revealed that.

It does look like an alternator kicks out more power if spun at the same rate as a dynamo, but I am some distance away from understanding why. Some magic inside them that works differently between one and the other.

All input welcome. If nothing else because the explanations online are mostly way too advanced for my simple brain.

Jack.

[Jack]

One note on the Bradford, in order to fit the LED rear lights that I have planned they have insisted will only work with negative earth. I queried it, but apparently greater minds than mine have tried to find a simple solution to that problem and ended up switching to negative earth.

On that basis, I guess what I am really getting at is: What are the downsides of switching to an alternator?

Jack.

[Srenner]

From a utility aspect, it is superior to a dynamo. Problems pop up with fan belt dimensions, proper pulley ratio, mounting issues and IMHO, it will look totally out of place!

Modern v-belts are thinner and have a different angle to the sides of the belts. A modern belt in an old-style pulley rides on the outermost edge of the belt and quickly loses tension as the sides wear.

A Nippon-Denso forklift alternator is the choice among the budget-minded racers. It is a one-wire unit not requiring an external control box. Make sure to wire it so that no power is going to it with the ignition off or it will drain the battery.

An English outfit offers an alternator inside a dynamo body, so all of the problems are addressed. They are a bit expensive.
Cheers1

[Keith Clements]

Trevor Spero should be able to help on the LED front. LEDs are, as their name suggests, Diodes, so polarity is important. But that does not mean you cannot use them on positive earth systems, you just need to make sure you insulate from chassis (if required) and you connect them the opposite way round.
https://www.google.co.uk/?gws_rd=ssl#q= ... tive+earth
http://matchlessclueless.com/electrical ... -lighting/
But you will need to get the correct polarity LED units if they are on an assembly.
http://www.norbsa02.freeuk.com/goffyleds.htm

I visited Accuspark a couple of months ago and they had a prototype alternator in a dynamo case. Now on sale.

[Jack]

Thanks Scott and Keith for quick response.

If going for the alternator I think the accuspark unit is sensible, and at £125 seems more expensive than a cheap alternator but not huge compared to dynamo rebuild costs. Question is whether it will stay cool enough inside a solid housing and if heat has significant effect on output.

The negative earth makes sense to me anyway, the issue with the led units is they are earthed to a single wire and multiple wires come into the different functions.

Jack

[george garside]

presumably an alternator generating a greater current than a dynamo will, on the basis that ''there is no such thing as a free lunch'' require more power to turn it - so why waste part of your 25bhp generating power you probably don't need

as far as leds just connect them arse upards so to speak.

george

[Keith Clements]

George,
There may be a free lunch with the efficiency of alternators at lower engine rpm. Although I am still debating if that is true. Alternators have other advantages such as no spikes in their output caused by a commutator which can blow electronic components. No wear and need to replace brushes. Better power to weight ratio.
You have to understand that Jack needs 10hp to drive the music system in the back of the Bradford. It is unlikely he will venture up any hills in the van. If he does, he will have to point the speakers backwards.

[David Kemp]

My understanding is that, power output of both, is governed by the cars need for power, if you need 1000w your need is greater than 100watt. Your alternator adjusts accordingly, so in normal Bradford use , with no power options it is irrelevant what you have. If you need a 1000w stereo, electric pump/fan your needs increase, a dynamo will not supply your needs , without running a larger heavier dynamo or a lighter alternator.
Also polarity is irrelevant I changed my Bradford 35 years ago it takes ten minutes, not worth the hassle of staying with positive earth. This allows CD players & the like,

[Amy]

and IMHO, it will look totally out of place

Hahahaha....you ain't seen nothin' yet!

[BobCulver]

Hi Jack

The power required to drive a dynamo or alternator at any moment is closely related to the output power at that moment, volts x amps, and as always around 13 volts more or less proportional to peak current. So a 40 amp peak alternator, although more efficient, still needs something approaching twice the power of a 20 amp dynamo. But not a problem with a belt drive from crankshaft.
I do not understand the desire for an ugly modern alternator, unless running a powerful electric fan. Modern bulbs tend to be higher wattage but few drive exclusively at night. For long traffic waits at lights can switch to side lights. Here in NZ Lucas dynamos are very common. Price has increased with scrap value but would not expect to pay more than $20, L10 unless gauranteed OK. If the commutator has no burned or sunk sections, and the wiring is not scorched black, and it doesnt smell burned, with a little patience can usually be fixed. Ditto the regulator. Bearing usually benefits from repacking with grease. All described in the Manual. Much easier to trouble shoot than an alternator and its regulator with diodes etc. For cars little used the constant drain from the diodes can be bothersome.
It is a simple matter to reverse polarity.

Bob Culver

[Jack]

Thanks Bob. Interestingly we took the dynamo off last night and it looks to have been refurbished already, with new brushes and it seems to be chucking electricity out reasonably, so for the short term (and until we have the engine running properly and electrics all working and tested) we will stick with that.

The new dynamator units have a dynamo appearance but with an alternator inside - they certainly get around the appearance issue of an alternator but still the pulley etc will probably be different, and are very new so we may wait and see what the reviews are like before spending any money just yet.

Jack.

[Keith Clements]

Cyril White phoned me today about fitting an alternator. I pointed him to the write up in the very old website
But also added TOPIC some circuit diagrams to the Galleryas the one in the old website has suffered from upgrade of Internet Explorer.

NOTES ON REPLACING JAVELIN/JUPITER DYNAMO BY AN ALTERNATOR

Suggested Lucas alternators:—

ACR15 25amp Use 44/0.30 gauge wire

ACR16 30amp 65/0.30

ACR17 33amp 75/0.30

ACR18 40amp 84/0.30

ACR23/25 60amp 120/0.30

ACR15 is a direct replacement for the dynamo. ACR16&17 give a higher output for normal use. ACR18 to 25 are high output for special applications)

A special mounting bracket will need to be fabricated. The vehicle must he negative earth polarity. The Jav/Jup are positive earth and their polarity must be reversed.

Reversing Polarity

This is quite simple. You must first check that you have no accessories which require positive polarity. In all probability a wireless will be the only problem on Jav/Jup unless non-standard things like electronic rev-counters or transistor ignition are fitted.

First, swap the battery leads around i.e. put the positive (earthed) lead on the negative terminal — you will need to change the terminal clamps on the leads to fit the battery posts.

Second, swap the leads to the coil terminals marked either CB/SW or +/-

Third, take the wires off the “D” & “F” terminals of the voltage control unit on the bulkhead.

Fourth, (not required if you are never going to swap the dynamo back in again). Take the wire which was on the “F” terminal and brush it. against either the “B” or “A” terminal on the voltage control box several times. NOTE this will result in a flash as the wire touches the terminal, this is normal and reverses the polarity of the dynamo.

Fifthly, replace the “D” & “F” wires to the terminals where you found them to begin with.

Fitting the alternator.

Remove the dynamo and insulate the thicker of the two wires which is now not needed. Make sure you mount- the alternator pulley in line with the water pump and crankshaft pulleys.

Connect the thin wire previously on the dynamo to-the alternator terminal marked “IND”. Then connect from one of the large +ve terminals on the alternator to the live starter solenoid terminal using the wire size shown above. The starter solenoid is on the bulkhead of the Jup and under the floor of the Jav. The live solenoid terminal is the one which has the main cable from the battery attached. (If the alternator happens to be an early one which has two smaller terminals marked - & +, earth the - terminal and connect the + to the solenoid together with the 1arge positive terminal.)

At- the voltage control box, disconnect the thinner of the two wires from the “D” terminal and the wire from he “F”. Join these two together with a screw connector and insulate.

The control box could be removed (but it does make a useful terminal block). In this case wires from the “D” & “E” terminals must be removed and insulated separately. The wires from the “A” & “Al” terminals should be removed and joined with a screw connector and insulated.

KC Notes.

It is worth putting an isolator switch in the circuit between battery and starter. On the Jav this can be put next to the starter solenoid with a hole through the floor and, on the Jup you can put it on the floor under the gear lever or any other either convenient or concealed position (depending on whether the switch is for safety or security ). Note that this switch should not be opened with the engine running as the alternator diodes will blow. If your clock is still working, you will need to run a separate fused circuit to it. I have an A133/55 Lucas fitted to the Javelin suitable for Winter Rally driving. I have fitted the pulley from a Jowett dynamo to the alternators, on the Jup the fins were ground off and the pulley fitted to the original alternator fins to provide more cooling.