Alternator instead of dynamo

Mursal

Member
No the internal regulator switching off around 14.7 Volts will keep most batteries safe. To be honest overcharging is never an issue for us, we even have some tractors with a bypass switch on the regulators so the driver can control charging output with engine revs (to boost older batteries for starting). But that's a totally different thread, I must start one .............

But we'll not stress to much about which is better dynamo or alternator, as long as they are working, I'm happy
 

Ley253

Member
Location
Bath
No the internal regulator switching off around 14.7 Volts will keep most batteries safe. To be honest overcharging is never an issue for us, we even have some tractors with a bypass switch on the regulators so the driver can control charging output with engine revs (to boost older batteries for starting). But that's a totally different thread, I must start one .............

But we'll not stress to much about which is better dynamo or alternator, as long as they are working, I'm happy
Indeed, and on older kit the dynamo is original and up to the job. the original dynamo, that is, some pattern units are scrap before fitting! Batteries are another thing though, many many starters have been destroyed by poor batteries, too many amps but not enough volts, starter turns slowly ( volts) and cooks (amps)!
Modern tractors infested with electronics need Battersea powerstation let alone an alternator!
 

DrWazzock

Member
Arable Farmer
Location
Lincolnshire
Our MF135 year approx 1978 and still in use with transport box and lots of stopping and starting still runs without problems with original Dynamo. The only thing we have ever done is cleaned the control box contacts with some extremely fine emery paper and adjusted the voltage a bit. That was about 15 years ago. The MF565 has been through 2 alternators since then. I would check the Dynamo regulator and connections before chucking the Dynamo.

Test the Dynamo by connecting 12 v straight to its field at lowish revs. If it goes up to 17 v as you increase the revs then the Dynamo is usable. Sometimes a commutator clean up and brush service helps. But if the coils have shorted either to frame or to one another or gone open circuit then it's probably not worth repairing.
 

Netherfield

Member
Location
West Yorkshire
Many a time I've changed from dynamo to alternator and positive earth to negative earth still keeping the dynamo, one thing puzzled me,maybe @Mursal can answer, why doesn't the starter motor want to spin the wrong way, basic DC tells us change polarity to change direction.
 

Mursal

Member
Because, when you change polarity, the direction of current flow through the field windings, changes with current flow through the armature. So the field polarity changes with the armature polarity, so it still spins in the same direction.
If you have permanent magnets for the fields, you will change direction with polarity. Nearly all electric motors used now, are of the permanents magnet type, for that very reason.
@Netherfield
 

ford4000

Member
Livestock Farmer
Location
north Wales
Our MF135 year approx 1978 and still in use with transport box and lots of stopping and starting still runs without problems with original Dynamo. The only thing we have ever done is cleaned the control box contacts with some extremely fine emery paper and adjusted the voltage a bit. That was about 15 years ago. The MF565 has been through 2 alternators since then. I would check the Dynamo regulator and connections before chucking the Dynamo.

Test the Dynamo by connecting 12 v straight to its field at lowish revs. If it goes up to 17 v as you increase the revs then the Dynamo is usable. Sometimes a commutator clean up and brush service helps. But if the coils have shorted either to frame or to one another or gone open circuit then it's probably not worth repairing.
We've had problems with it for 3 years now, had 2 regulators and took dynamo to be done up last year, it had new bushes fitted, but it still won't charge, has a dim flickering light on the dash. Though I'd start from begining and fit an alternator
 

Ley253

Member
Location
Bath
Link D and F together on the dynamo then check voltage between d and earth. if you get around 15 volts or more dynamo is fine, problem as you have had new regulators, must then be wiring.
 

DrWazzock

Member
Arable Farmer
Location
Lincolnshire
We've had problems with it for 3 years now, had 2 regulators and took dynamo to be done up last year, it had new bushes fitted, but it still won't charge, has a dim flickering light on the dash. Though I'd start from begining and fit an alternator

A dim flickering light on the dash? That sounds like alternator wiring. When did a dynamo circuit ever need an indicator light?

Should have DEAF connections on control box. D to Dynamo, E to earth, A to ammeter then battery and F to Dynamo field terminal. What can go wrong? Can be positive or negative earth. But sometimes need to "flash the field" by temporarily connecting battery to field to magnetise the Dynamo the right way.
 

DrWazzock

Member
Arable Farmer
Location
Lincolnshire
Because, when you change polarity, the direction of current flow through the field windings, changes with current flow through the armature. So the field polarity changes with the armature polarity, so it still spins in the same direction.
If you have permanent magnets for the fields, you will change direction with polarity. Nearly all electric motors used now, are of the permanents magnet type, for that very reason.
@Netherfield

yes the field and armature are in series for big torque at low revs like a milk float motor, whereas parallel connection is more for constant speed lower torque.
 

Ley253

Member
Location
Bath
A dim flickering light on the dash? That sounds like alternator wiring. When did a dynamo circuit ever need an indicator light?

Should have DEAF connections on control box. D to Dynamo, E to earth, A to ammeter then battery and F to Dynamo field terminal. What can go wrong? Can be positive or negative earth. But sometimes need to "flash the field" by temporarily connecting battery to field to magnetise the Dynamo the right way.
If you dont have an ammeter, you have a low charge light, used to be called the ign warning light.
 

DrWazzock

Member
Arable Farmer
Location
Lincolnshire
If you dont have an ammeter, you have a low charge light, used to be called the ign warning light.

So your 'A' output from you regulator must still connect to battery, (maybe via fuse)? And the lamp? presume it detects imbalance by connecting across something somewhere and isolated by ign switch.

If the Dynamo has been reconned and two new control boxes then surely there must be incorrect wiring or bad / wrong connections somewhere.
 

Ley253

Member
Location
Bath
So your 'A' output from you regulator must still connect to battery, (maybe via fuse)? And the lamp? presume it detects imbalance by connecting across something somewhere and isolated by ign switch.

If the Dynamo has been reconned and two new control boxes then surely there must be incorrect wiring or bad / wrong connections somewhere.
I cant remember the wiring for the lamp, but I think its connected across the cutout points in the regulator. My thoughts are with wiring, if the reg cant excite the dynamo, then no charge. Just had a gem of a problem here, late Lucas dynamo which was perfect off the tractor, would not charge on it! Tractor had a new loom as well. Turned out that the "F" terminal on the dynamo, which was on the body, not the end plate, was shorting to earth via a fuel pipe, Tightening the belt a fraction moved the dynamo enough to give the required clearance!
 

ford4000

Member
Livestock Farmer
Location
north Wales
So your 'A' output from you regulator must still connect to battery, (maybe via fuse)? And the lamp? presume it detects imbalance by connecting across something somewhere and isolated by ign switch.

If the Dynamo has been reconned and two new control boxes then surely there must be incorrect wiring or bad / wrong connections somewhere.
I am far from an expert on electrics! !! But when I measure the Dynamo output coming straight out of the Dynamo where you attached the wires ,it fluctuates wildly between 2 and 9 v but not more. Would this not mean it's not working properly?
 

Ley253

Member
Location
Bath
As I said, you must link d and f to get a correct reading. Dynamo output depends on the regulator input to the "F" terminal. Linking the two for test puts the dynamo up to max output.
 

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