wiring the alternator

[littlejim]

After wiring up my new alternator I found I was only getting a small negative reading, with no sign of charge.

Although I had gone to a bit of trouble wiring it in according to a couple of guides on the TR part of the web, I found it was only showing a minor discharge all the time.

 

The Guru I followed on the VTR site had recommended connecting the alternator wires carrying the current to the solenoid connector that goes directly to the battery. When I finished the rest of the rewiring and lit the blue touchpaper I found I was only using the negative side of the ammeter, nary a plus ever appeared.

 

Backtracking to try to work out why it wasn’t showing most of the charges and discharges, I found I hadn’t left myself much of a trail to follow, so I wasted a lot of time working out how I had wired things up.

 

I had to get behind the dash and recheck the ammeter connections * On the 4A there are thick brown and thick brown white wires going to the ammeter. Thick brown connects to the aforementioned solenoid connection where the big black wire from PLUS on the battery connects. That’s where all the plusses come from. (Yeah, I know the electrons go the other way.)

 

Brown white (from the ammeter) used to go to A on the voltage regulator.

I eventually worked out that that is where the generator used to put power into the system, where it then went through the ammeter to wherever, including the battery.

 

I won’t upset you with the heart wrenching, agonising time spent analysing every reference to alternator connections in old cars. I eventually worked out that despite the Gurus’ pronouncement the alternator had to connect to the thick brown and white wire to the ammeter, in order to show + as well as -. It should not connect to the solenoid.

 

This worked,

I now get Plusses as well as Minuses on the ammeter.

 

As usual once you have the answer you wonder why you were so dumb, but if you are just following somebody else’s guide and it doesn’t work out you are up that well known creek and where’s the paddle? You can spend a lot of time trying to work out the basic principles involved; a lot of the articles are written in a "do this" fashion rather than what the actual aim is.

 

Summary: despite the guru, the alternator has to connect to the brown/white wire to the ammeter. (I could do a coloured diagram if anyone needed one.)

 

I have the Moss alternator which puts out more current than the generator but it is not cooking the ammeter wiring or sending the ammeter nuts.

 

(God I hated that! It was one the worst parts of my life!)

* unless you are a professional contortionist take the seat (driver’s in my case) out first. Working behind the dash is a nightmare if you leave the seat in place. You may be able to infer that I didn’t do it straight away.

· I’ll get out of your way now.

Edited August 5, 2010 by littlejim

[RogerH]

Hi LittleJim,

regards the Alternator output.

The ammeter shows what is going in and out of the battery +/-30amps.

 

It could be possible to have enough services switched on for the battery to supply more than 30amps in which case the wiring/meter may be compromised, but unlikely.

 

The alternator could easily supply 30, 40 50 amps if required (size permitting) but this doesn't go through the ammeter.

 

A flat battery will take a high current for a few moments 25(ish)amps but then fall off sharply.

 

Thus, don't panic about your alternator being more powerful than the dynamo.

 

Roger

[littlejim]

Roger,

What the ammeter shows depends on how it is wired in, that's what I was trying to point out.

When done according to the VTR man it didn't show any battery charging, because the electricity went straight from the alternator into the battery, it didn't have to bother going through the ammeter. So it wasn't like you said, it wasn't showing what was going INTO the battery.

My final setup puts the alternator output (into the battery) through the ammeter just like the dynamo used to.

Edited August 5, 2010 by littlejim

[67_gt6]

Roger,

What the ammeter shows depends on how it is wired in, that's what I was trying to point out.

When done according to the VTR man it didn't show any battery charging, because the electricity went straight from the alternator into the battery, it didn't have to bother going through the ammeter. So it wasn't like you said, it wasn't showing what was going INTO the battery.

My final setup puts the alternator output (into the battery) through the ammeter just like the dynamo used to.

 

 

Hi Jim, if you wanted to you could have 2 wires of equal capacity (say 25 amps) coming from the alternator - one of them to the starter solenoid as you did originally and the other to the ammeter as you have done now. This would show you +/- on the ammeter but would split the charge and prevent all the amps going through the ammeter during periods of high load.

 

Andy

[badshead]

Hi Jim, if you wanted to you could have 2 wires of equal capacity (say 25 amps) coming from the alternator - one of them to the starter solenoid as you did originally and the other to the ammeter as you have done now. This would show you +/- on the ammeter but would split the charge and prevent all the amps going through the ammeter during periods of high load.

 

 

Another option is to fuse the charging circuit (just in case alternator goes off the scale) like so

 

 

Since fitting a 45A alternator about 6 months ago, mine has never exceeded/sustained -25A even when I accidently left it with the radiator fan running for nearly 1 hour and then started the car.

[stuart]

Another option is to fuse the charging circuit (just in case alternator goes off the scale) like so

 

 

Since fitting a 45A alternator about 6 months ago, mine has never exceeded/sustained -25A even when I accidently left it with the radiator fan running for nearly 1 hour and then started the car.

 

Neat solution!

Stuart.