negative earth

[chriss]

am I right in thinking if a major is fitted with an alternater the battery should be negative earth, just bought another 55 major with replacement engine with alternater the more I look at it the rougher it looks

[atkiman]

Hi Chriss

You are correct, needs to be negative earth for an alternator. A dynamo can be changed from positive to negative by "re-flashing" an alternator would need to have the rectifier diodes removed and swapped around to convert to positive earth, much easier to swap the battery leads and run as negative earth.

[chriss]

thanks for the reply, does this affect the regulator?

[Pavel]

Other than very early alternators, all now have internal regulators. If it's a Lucas, check the model designation. Early ones, such as AC15, used a separate, external regulator. Later ones would have an R after the letters AC [ACR] denoting internal self regulatoring. If yours is an unregulated alt. and you are fitting it to replace a dynamo/ generator system, you must also use an external regulator dedicated for alternators, such as Lucas 4TR & 8TR.
If you have to re-polarise your system and have an ammeter, reverse the leads on it.

Pavel

[Timeee]

Dear Chriss

Your question "how does it affect the regulator", depends entirely on how the alternator has been "wired in" to your tractor's electrical system. When converting to an alternator, most people use a commonly available one, usually a 16 ACR, with internal regulator. The original regulator is then modified (a couple of terminals are bridged and a few changes are made to where the loom connects to things like the ammeter and light/ignition sw) to become a simple junction box to the original loom. This approach limits the amount of rewiring to the original (dynamo driven) loom. Sometimes, the loom is modified to do away with the original regulator altogether. So, you really need to examine what you have got; Presumably the alternator set-up works at the moment. Tim E

[chriss]

had the tractor started and had it running today you need to turn the key on which lights up the small light, the amp meter goes over to charge when I switch the light switch on , I'm in the process of building a shelter for it at the moment when that's done I can have a good look at whats to be done, I think there's a fair bit

[Pavel]

I assume this is your 'new' Major which is alternator equipped and it would appear that the charge system is working correctly.
But just to be sure --
When you turn the key on, and the red light shows, the ammeter should indicate a slight discharge ie the pointer moves slightly to the negative side. When the engine starts the red light should go out and the needle should then indicate 'charge' [as much as 10-20 amps depending on the alternator's output] as the alternator replaces the current used by the starter turning the engine over, plus current lost whilst the engine has been standing idle. Turning the lights on at the same time will probably increase the charge rate slightly. This maximum charge rate will de-crease as the battery approaches its normal capacity. Even then, with the lights off, it should still show a slight charge to account for wire resistance losses.
If this is what is happening -- you've got a good one!

Pavel

[chriss]

checked it out this morning and it does just as you say