Bright lights

[FranklinLeicester]

A strange thing happened the other night, on a dark unlit country lane my headlights flashed very bright for just a fraction of a second. It happened several times but the last time it was for about 2 seconds - long enough for me to notice a big discharge on the volt meter. I was worried that the bulbs might blow. It was as if I had got 24 volts. Once or twice recently in daylight I have noticed slight blips of discharge on the meter (it is usually rock steady) and also the fuel gauge registering full when I know this not to be true. Have I got some form of alternator malfunction?

[CABRIOBOB]

Re: Bright lights

If you have a volt meter I would check your charging with all the lights,heater fan ect switched on, as it seems the alternator is starting to play up. check all you battery leads and that you have good earth conections.

[h_m_cumming]

Re: Bright lights

That sounds as though your losing your connection from the alt to the battery and the alternator voltage is rising due to this. Is your alt. machine sensed or battery sensed? If machine sensed as most car alts. are it may be that the regulator is not getting good connections or is starting to fail, though usually when they go its completely. A not too good positive battery connection may also give this effect, although that would usually show in poor starting, as the alt would still be connected to the car circuits but not properly to the battery.

[CosworthCabrioLee]

Re: Bright lights

Franklin,
Your voltage stabilizer is on its way out, mine went on the V8 Cabrio and it blew all my bulbs in the dash,back lights and rev counter blew. Fixed with a £20 stabilizer job done.
Let me know how you get on

[FranklinLeicester]

Re: Bright lights

Thanks for your prompt replies. Bob, what reading should I get with everything switched on? I will check all battery and alternator connections. Hugh, I have a normal 1275 Marina alternator (I think). How do I tell if it is "machine sensed or battery sensed"? I have never come accross these terms before? It makes me reluctant to use the car at night. Is it likely that the headlight bulbs would blow?

[FranklinLeicester]

Re: Bright lights

Voltage stabilizer eh? mmm, where should I look for that and what does it look like? Is there a positive test for it before buying a new one?

[stevejgreen]

Re: Bright lights

All the above may be appropriate but I would check the alternator-battery connection first.
Possibly the voltage regualtor but that only supplies the temp and fuel gauge on a Marina based car.
Regulator is attched to the back of a Smiths rev counter, difficult to say without knowing your instrument cluster etc. Replacing it as Lee suggests will improve fuel gauge response if nothing else.
Sorry cant help with 1275 specific electrics.

[FranklinLeicester]

Re: Bright lights

Not checked anything yet but I can say that I have always had fuel gauge inaccuracy when more and more systems are activated. I put up with this because I know the car and regard it as one of its quirks. However, when I spoke to the builder of the car recently and mentioned this ammusing habit he said that it never did it in his day (20 years ago) because he remembers putting a VR on the back of the gauge. My temp gge. is temp sensed by the way so I have no probs there. So, I'll check the connections as suggested and have a look at the back of the rev. counter for a vr there. BUT, can anyone explain how a 12v. alternator can suddenly generate what seems like seachlight power?

[CABRIOBOB]

Re: Bright lights

Franklin

To test the alternator with a volt meter, clip your meter to the battery terminals and start the car, you should get about 13 to 14.5volts.
Then switch on all your lights, fans etc then the voltage will drop to around about 11 - 12.5 volts for a few seconds then when you rev the engine to 2000 rpm the voltage will rise again to 13 - 14.5 volts to replace the charge in the battery when the light etc switched on.
If you are getting more then 14.5 volts Its looking that you Regulator or surge protection diode is playing up in your alternator.
Also check that your alternator has good earth via the fixing bolts to the cars engine as this can cause charging problems.
Its your voltage stabilizer that controls your fuel and temp gauges and this is normally behind your dash and it might be working overtime if the alternator is giving a power surge.
The voltage stabilizer could have 2 or 3 terminals on it with the letters I,= Instruments B = + Battery or power feed, E = Earth if fitted.
I found on the Marina wiring that there is one V/S for both the fuel and temp gauge and if using a Ford fuel tank and float sensor the gauge reads 1/2 full when the tank is empty.
By fitting a a separate VS for each gauge the fuel gauge reads almost empty when the tank is empty then after tweaking the sender float max/min stops this made it spot on.
The VS I used for the fuel gauge was old FOMOCO one with 3 terminals fitted I,B,E

[h_m_cumming]

Re: Bright lights

There are two types of voltage sensing systems for alts. The vast majority of cars are machine sensed where the controling voltage is detected inside the alt.by the regulator. However, where you have a fair distance between the alt and the battery the sensing wire is taken to the battery to compensate for any volt drop in the longer run of cable. You find this on some trucks where the batts. are located down under the chassis and on boats where the batts are usually located some way from the engine. Hope that made sense.
Is your alt output cable taken to your starter motor terminal and then to the batt or straight to the batt +ve terminal?
Have you had any symptoms recently of low batt voltage on starting? These may provide some clues.
Best of luck, Hugh.

[neiltechspec]

Re: Bright lights

Here's how an Alternator can generate 'searchlight power'.

An car alternator by nature is a 3 phase AC Generator, the diode pack coverts the output to DC, the voltage regulator will limit the ouptut voltage to between 13.8 to 14.4 volts (approx). Without regulation the output voltage can rise to 120volts at 2000rpm.

As you have a BL/BMC 1275 engine, I guess you have a Lucas 16 / 17 / 18ACR alternator. While these were very popular at the time, it has to be said they are old technology now and relatively low output current and would benefit from being replaced by something a bit more modern.

I use an SEV 55A/h jobby from a Pug 205, it has the same physical mounts and just needed spacing to make pulleys line up (on my Triumph 4cyl which orginally had a Lucas 17ACR). This has doubled the output capability.

[FranklinLeicester]

Re: Bright lights

Right, I have just dismantled, cleaned and checked all the terminals between the alt. and battery, earths etc. However, having just read Bob's point about the earth connection between the alt. body and the engine, this didn't occur to me so I must do that too. Thanks for all the technical stuff too - well, I did ask. Actually, the flashing brightness has happened before now I come to think about it so if the earth/terminal clean up doesn't sort it then I'm tending to think that the 32 year old alternator is the culprit. BUT, I don't want to be stuck miles from home on a dark night with a load of blown bulbs so should I change the alt now? Going back to the voltage stabilizer question, I have had a good look and there is a little gizmo behind the fuel gauge, it is a simple 2 terminal in-line piece of alli with an "RS" logo and several numbers presumably signifying its capacity. It is not earthed, just dangling with the other wires. It can't be doing anything because of the fuel gauge deflections caused by other drains of current. Thanks for all your help chaps, I'll let you know the outcome.

[lizbillings]

Re: Bright lights

Doug suggests another possibility is a dipswitch problem causing main & full beam to come on at the same time giving very bright lights.

[h_m_cumming]

Re: Bright lights

The voltage stabiliser at the back of the gauges is for the gauges only and has nothing to do with any other circuit so will not affect the lights.

[h_m_cumming]

Re: Bright lights

Just to add, going by all that's been discussed I'd go for the alt. since you noticed the fuel gauge rise when the lights weren't on and this could be due to a rise in the alt output due to bad regulation, especially as you noticed a rise in the voltmeter in the car.