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Alternator and 3AW can

Acollin

Platinum Level Sponsor
1966 series v mostly stock
Hello all
sorry if I am being a pesky, but—-

ignition warning dash light— does not light.

i am afraid I still need a bit more advice on this issue and I want to be sure I am not damaging anything.

1) I want to know if I touch my grounded test light probe to the AL spade on the back of my alternator with the ignition switch “on” will I do damage to my alternator?

2) If I will not do damage to my alternator with my grounded test light probe on the AL spade, with the ignition “on”, will this tell me if current is traveling toward the 3Aw can?

I believe I need to know if my alternator is sending current to the 3AW. While my 3AW can may be my problem, I think I should probably test to see whether or not the 3AW is getting current. My alternator is unquestionably sending current— recharging- powering systems.

many thanks for tolerating my my many questions
Andrew
 

Scotty

Silver Level Sponsor
I’d just change the 3AW can (or get the 3AW relay replacement module) and see if that fixes it. Odds are the one you got is over 40 years old. The more you delve into this, the more that sounds like the likely culprit.
 

bernd_st

Bronze Level Sponsor
I'ld second to that statement. If your alternator charges with ~14V at least that component should be ok. Only remaining potential culprits would be the bulb, the wiring (contacts) or the 3AW. Originals are no longer available. If you Google Lucas 3 AW replacement you will find a couple of offers from companies in UK.
 

Acollin

Platinum Level Sponsor
Thanks for the replies

bulb works- 3AW on the way.
****Aside: fyi—- I did a little looking and found that any number of vehicles use 3AWs . From Norton motorcycles to XKEs. They seem to be readily available new and used and many look identical to the one in my Alpine.

Q: Can I use my grounded test light to check power flow from the back of my alternator?
Q: With the key on, should the AL spade light my test light or car running?. I have been afraid to touch anything since bernd_st suggested I could do some damage touching the wrong bit with my test light— if I read that right.

Thanks
Andrew
 

bernd_st

Bronze Level Sponsor
Yep, but acc. to my survey all the newly offered 3AW are more or less transistorized repros. So not sure about their quality. However the original Lucas ones weren't good either.

Regarding your 2 questions the WSM isn't very specific about that. It states " When at low engine speed, a small low voltage current from the alternator opens the switching device, the lamp will cease to illuminate." Whether this low voltage is good enough to make your test Probe lit or not I can't say. Would advise you to measure the AL output with a Multimeter instead. It has a much higher input resistance and will definitely not damage anything. How much voltage/current you need I can't tell you by heart , because so far I didn't measure it on a working system plus the WSM is not really specific for that.,.
 

Acollin

Platinum Level Sponsor
Thanks
I am , however, still struggling with the concept of — if I do not get an output acknowledgment from AL terminal on the back of my alternator with my test light, what is there for the 3Aw to read and transmit to the bulb?

My 3AWs are at the post office today— later , I will report what I find.
Be well
 

husky drvr

Platinum Level Sponsor
Andrew,

DON"T use your test light. Use your multi-meter.

The AL terminal will produce about 8V AC when running (probably not enough current to light your test lamp). Test on low voltage AC scale between AL terminal and ground, engine running.

The original - NOT new solid state - 3AW should show ~ 0.5 Ohms and ~ 16 Ohms testing between the Earth terminal and each of the other two terminals. Test on lowest Ohm scale, harness wires disconnected. Passing this test might not mean the 3AW is good depending on what failed. If either terminal tests to be open or no connection, then the 3AW is bad. Before testing, with the meter on the Ohm scale, touch the test leads together to see the difference between NO resistance -touching- and OPEN - NOT touching.

I found this on the internet so YMMV.

Have fun,
 
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Acollin

Platinum Level Sponsor
Question 1. What does “ YMMV “ mean? Sorry, but had to ask.

if touching my test light to the AL tang on the alternator is such a huge “don’t”, why are there no symptoms to me having done this? I have not used my test light since the initial warning, but I am near certain I did early on. The car was not running, but the ignition was switched to on. Or is a test light simply not up to the job and won’t read the weak current?

Had a small problem with the 3AW I was expecting today. I have to go shopping. Unless one of you —who have done the alternator upgrade and have an old 3AW and no use for it collecting dust on a shelf. Happy to buy it here!!!!!
Be well all
Andrew
 

Scotty

Silver Level Sponsor
Question 1. What does “ YMMV “ mean? Sorry, but had to ask.

if touching my test light to the AL tang on the alternator is such a huge “don’t”, why are there no symptoms to me having done this? I have not used my test light since the initial warning, but I am near certain I did early on. The car was not running, but the ignition was switched to on. Or is a test light simply not up to the job and won’t read the weak current?

Had a small problem with the 3AW I was expecting today. I have to go shopping. Unless one of you —who have done the alternator upgrade and have an old 3AW and no use for it collecting dust on a shelf. Happy to buy it here!!!!!
Be well all
Andrew

YMMV - Your Mileage May Vary. As in, your experience with the situation may differ from someone else in the same or similar situation.
 

husky drvr

Platinum Level Sponsor
What does “ YMMV “ mean?

YMMV = Your Mileage May Vary

My intended meaning > I found the data in a discussion forum like this one with 3AW's being discussed. There is No guarantee that the info is correct but probably might be = Use At Your Own Discretion!

Just a "be aware" type warning.

Good luck,
 

husky drvr

Platinum Level Sponsor
The car was not running, but the ignition was switched to on. Or is a test light simply not up to the job and won’t read the weak current?

This test doesn't actually test anything and the test light should not illuminate - no voltage or current to test or to cause damage.

That changes if the alternator is spinning and excited - switch on and engine running.

The AL terminal is connected between two ends of an output winding, before the output diodes. Must be a very small or restricted connection or it would short the winding, allowing no power to be produced by that field winding. The field windings are able to dump the generated charge through the output diodes to charge the battery (think AL garden hose compared to a diode street water main). The diodes are also how the generated AC current changes from AC to DC. The AL terminal is bleeding just enough non-rectified AC current to allow the 16 Ohm heater in the 3AW can to almost instantly heat to open the switch to cut off current to the charge indicator light.

The 16 Ohm heater is effectively a straight drain to ground. The heater's resistance limits the amount of current that can flow through that path. When the alternator is producing current giving the AL terminal an output, if you then use the test light to also short the current path to ground the new short is in parallel to the original 16 Ohm path and the the test light's bulb is potentially capable of several times more current than just the heater. The field winding produces a third of the alternator's total 35 amp output. Electricity always travels the least restrictive path. With the test light, you've just created a new path capable of flowing several times more current through the AL terminal connection than it's designed to carry.

Being a Lucas product, want to make a guess where the most likely "smoke escape point" will expose itself. Think low limit fuse.

Fun part is the alternator will probably still continue to charge, but even if everything else remains in good condition the charge indicator light wont turn off.

EDIT


Have fun,
 
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Acollin

Platinum Level Sponsor
Thanks for the electronics primer. There is good information here for me to learn from and grow my understanding.

I do find husky drvr’s last line “condescending”.
Does he think that I do not understand my already admitted to deficits? How does his last line help?
My greatest concern here is not for my ego, but for those owners of Sunbeams with minimal knowledge who may sit silent and not find out more about their cars. My belief is the only inappropriate question is the one that is never asked.
Where are we to begin learning if not from “zero based knowledge level”.
No hard feelings
Be well all
Andrew
 

husky drvr

Platinum Level Sponsor
Thanks for the electronics primer. There is good information here for me to learn from and grow my understanding.

I do find husky drvr’s last line “condescending”.
Does he think that I do not understand my already admitted to deficits? How does his last line help?
My greatest concern here is not for my ego, but for those owners of Sunbeams with minimal knowledge who may sit silent and not find out more about their cars. My belief is the only inappropriate question is the one that is never asked.
Where are we to begin learning if not from “zero based knowledge level”.
No hard feelings
Be well all
Andrew

Andrew, and other concerned SAOCA members,

Please accept my apology about my conveying a thought in an unclear manner. In no way did I intend to be condescending or patronizing. Actually, to do so is appalling to me.

All I can say now is I will try to do better in the future.

I'm sorry Andrew.

I hope you are able to sort out your issues.
 
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