Having To Fit An Alternator Back To The Race Pug

[wardy18 33 1 Cars]

So after finally realising its the Varley battery running out of charge that was causing the hillclimb pug to die half way throu my run i have now decided to stop all this fartin around with jump plugs/batteries to start it etc and just fit a good old alternator to charge a slightly larger Red Top 25 Battery i have now fitted.

 

BUT

 

cant remember the wiring for the alternator, im 99% sure that all i need is the main power cable from the alternator to teh battery positive but do i need that little thin wire that connects to the alternator too?!

 

its just because i have a bespoke wiring system purely for racing i have no where for this little wire, whats its actually for?! do i need it!?

[jackherer 543]

That wire is for the battery light but it also excites the alternator so without it you wont get any charge (some alts self excite over 3000 rpm or so but you probably shouldn't rely on that).

 

If you dont have a dash all you need is a bulb with 12v (fused and ignition switched of course) on one pin and the other pin goes to the alternator.

[wardy18 33 1 Cars]

ah ok but thinkin about it can i not just run this wire straight from the battery and fused in the middle as the car has battery cut of switches, so the wire would only be feeding the alternator when i flick the battery cut off swicth to "on" so to start the car and so acting as if it were ignition wired?! also what do i need the bulb for?!

 

just tryin to keep the wiring as simple as possible without too many running throu into the interior

Edited May 28, 2008 by wardy18

[tri_longer 25]

I know you probably fitted a Red Top for weight saving (so feel free to ignore me) but I run a shared car in hills/sprints with a standard battery and no alternator and we have had no issues with the battery discharging at all. In fact, we had it rolling roaded at Alson for a good few hours and then forgot to charge it and still managed 8 runs at Harewood (inclduing engine warming, queing etc) with no visible loss in volts. It migt be worth consdiering this than faffing around with re-wiring the car.

[wardy18 33 1 Cars]

i must say it would be better without one and i would love to stay away from an alternator but i just cant afford to buy another battery, i suppose it doesnt have to be a raccing batery like a varley at all as i can get a deep cell battery which can run down to nothin and be recharged without damage unlike normal batteries

 

will price one up before i go down the alternator route

 

this means i would have a Varley Red Top 15 and a 25 for sale if anyone interested

[wardy18 33 1 Cars]

ah ok but thinkin about it can i not just run this wire straight from the battery and fused in the middle as the car has battery cut of switches, so the wire would only be feeding the alternator when i flick the battery cut off swicth to "on" so to start the car and so acting as if it were ignition wired?! also what do i need the bulb for?!

 

just tryin to keep the wiring as simple as possible without too many running throu into the interior

 

ok so i gotta sort this out this week, can anyone help with this little wire on the alternator, will my above solution work?

 

thanx

[flipperthebushkangaroo 2]

ok so i gotta sort this out this week, can anyone help with this little wire on the alternator, will my above solution work?

 

thanx

 

Make sure the point that you connect the wire to is ONLY live when the cut out switch is on, if the wire is constantly live you risk burning out the exciter field of the alternator. The cut out switch needs to isolate the wire, sorry to repeat my self but if I'm understanding you right wiring the cable direct to the battery will give constant live as i guess the cut out isolates slightly away from the battery. never used them so sorry if I've got it wrong.

Otherwise it should work although you will not get any fail warning.

 

Hope this is some help

Roddie

[wardy18 33 1 Cars]

Make sure the point that you connect the wire to is ONLY live when the cut out switch is on, if the wire is constantly live you risk burning out the exciter field of the alternator. The cut out switch needs to isolate the wire, sorry to repeat my self but if I'm understanding you right wiring the cable direct to the battery will give constant live as i guess the cut out isolates slightly away from the battery. never used them so sorry if I've got it wrong.

Otherwise it should work although you will not get any fail warning.

 

Hope this is some help

Roddie

 

ah ok so i have a battery isolation switch which once tunred on i then flick another switch which turns the ignition on, if i were to run a new wire from this switch to the alternator would that work??

 

i hate wiring

 

can i run an ignition wire from the coil for the alternator?!?!? would that work

[Richie-Van-GTi 70 2 Cars]

run a wire from the ignition on switch to the excitation wire on the alternator, That way if the isolation switch or the ignition switch is off then so should that wire be off which is in effect the same set up as a normal car has. If you go straight from isolation it would mean even with ignition off the wire is still effectively live and chances are theres plenty of times between runs etc where this would be the case

[wardy18 33 1 Cars]

run a wire from the ignition on switch to the excitation wire on the alternator, That way if the isolation switch or the ignition switch is off then so should that wire be off which is in effect the same set up as a normal car has. If you go straight from isolation it would mean even with ignition off the wire is still effectively live and chances are theres plenty of times between runs etc where this would be the case

 

ok great ill do that, ive got one of those race electric boxes with 4 switches, so ill open it up and run a new wire from one of the terminals on the ignition switch

 

cheers mate

[wardy18 33 1 Cars]

this exciter wire has to be 12v i assume, i have run an extra wire from my ignition switch and sso will read 12v when the isolator switch is on an the ignition switc is on, so power will only be fed while the car is running

 

just need to find a alternator bracket now and geet it all fitted

[Richie-Van-GTi 70 2 Cars]

yes 12v, are you putting a small bulb inline with it? I know its an extra thing to mount but at least you can see its working when the light goes on and off.

[wardy18 33 1 Cars]

yes 12v, are you putting a small bulb inline with it? I know its an extra thing to mount but at least you can see its working when the light goes on and off.

 

 

dont think ill bother because if this isnt wire isnt fetting power then ill know cause the will have died as ill have no ignition

 

i will check the voltage regularly, what should be the voltage off the battery when the alternator is connecting and the engine running, am i right in thinkin its about 14v?

[pug_ham 240 3 Cars]

Yes, engine running the voltage across the battery terminals should be around 14v or more.

 

Graham.

[wardy18 33 1 Cars]

do i need to do anythin extra with the battery or just simply connect the wire from the alternator to the positive of the battery?

 

thanx

[pug_ham 240 3 Cars]

No, that should be all you have to do.

 

Thats all thats connected as standard so it obviously works.

 

Graham.

[wardy18 33 1 Cars]

fine job, gonna get it all fitted today if i can find my alternator bracket

 

will let you know how it goes

 

thnx for the help

[wardy18 33 1 Cars]

OK BIG PROBLEMS with the latest addition

 

one question first, my battery isolator switch has been run throu the negative lead from the battery, i thought this was a bit strange as i assumed it would run throu the positive wire to cut the power to the car whereas they way it is at the moment it simply cuts the earth

 

is this right?!?!?

[welshpug 1,622]

should be on the power really.

[Rob Thomson 6]

Every battery isolator I've ever seen or used has been wired through the positive. Can't think of a good reason why, but there probably is...

 

Regarding the excitor wire, I think you really do need a bulb or at the very least a resistor to control the current to the alternator. When the alternator isn't running the alternator end of the excitor wire is essentially grounded. If you've got the other end of a wire connected directly to the battery you'll get massive currents flowing that are bound to f*** things up. The bulb controls that current. Very important.

[wardy18 33 1 Cars]

ok thats what i thought

 

my problem is that i have now fitted the alternator and done as ive been told above as in run a new wire from my ignition switch to the alternator for the exciter and then run the usual power lead from the alternator to the positive on the battery.............i then started her up and yeh it was chargin the battery and workin fine, while running the battery had 14.2 volts

 

BUT THEN

 

i pulled the battery cut off switch to shut her down but nothing actually shut down, its just kept idling like normal, i then went in the car and switched off the ignition and fuel pump and still the car ran like normal, gettin very concerned and worried i then disconect the battery and pulled off the HT lead from the top of the coil and it shut down

 

WHATS GOIN ON?!?!?!?

 

i think that because my cut off switch is in the earth and not the positive that the wiring system and the whole car was then being powered by the alternator charge as i assume there are other seperate earths for the fuel pump and ignition switch

 

what do you reckon?!

im very concerned

[welshpug 1,622]

I think you've got it sussed yeah!

 

cut-off needs to be between the main live terminal and the rest of the system, normally its in the main line to the starter/alternator and the wire to the shunt box as well.

[wardy18 33 1 Cars]

Every battery isolator I've ever seen or used has been wired through the positive. Can't think of a good reason why, but there probably is...

 

Regarding the excitor wire, I think you really do need a bulb or at the very least a resistor to control the current to the alternator. When the alternator isn't running the alternator end of the excitor wire is essentially grounded. If you've got the other end of a wire connected directly to the battery you'll get massive currents flowing that are bound to f*** things up. The bulb controls that current. Very important.

 

sorry mate, im so confused about this bulb thing, sorry im very dumb when it comes to electrics

 

at the moment my excitor wire is connected straight to the ignition switch, so you mean put a bulb in the middle of this wire!?!? what sort of bulb do you mean, can u get me a link to one please sat on Demon Tweeks or somewhere

[jackherer 543]

Regarding the excitor wire, I think you really do need a bulb or at the very least a resistor to control the current to the alternator. When the alternator isn't running the alternator end of the excitor wire is essentially grounded. If you've got the other end of a wire connected directly to the battery you'll get massive currents flowing that are bound to f*** things up. The bulb controls that current. Very important.

 

That was my understanding but I wasn't confident enough to post it

 

I've seen two types of cut off switch, one just cuts the main live cable and the other type have extra terminals to run the ignition live through along with a ballast resistor that goes to ground IIRC. This is to prevent the running on the alt problem you have which I believe will damage the alternator.

[jackherer 543]

at the moment my excitor wire is connected straight to the ignition switch, so you mean put a bulb in the middle of this wire!?!? what sort of bulb do you mean, can u get me a link to one please sat on Demon Tweeks or somewhere

 

 

Just use a dashboard bulb like the battery light. They must be just a few hundred milliamps.