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MG Midget and Sprite Technical - Tacho overreading & battery draining - regulator?

Hi,

My tacho is overreading significantly, and the battery drains if I leave it for a week.

Could it be the regulator, or am I barking up the wrong tree?

I've got an early Mk3 midget, if that helps.

Nigel
N K Baker

I think it could be the condenser. Great that one David!! Must admit it went passed me to begin with then I doubled up!

Seriously

The voltage "stabilizer is not powered when the ignition is off so therefore would not be the cause of a battery drain You maybe confusing this with the voltage regulator which ought not to casue problems with the rev counter.


Like evrything else you need to fault find to determine what is causing a problem

Regarding the battery drain You could measure for current drain on each fuse or what do you have that requires power when the car is switched off. Do you have a modern CD/Radio with memory?

The Rev counter, how do you know it is over reading? do you have electronic ignition.

Bob England

how old is the battery?

first and most important question

I doubt if many of us have really accurate tachos
Bill

Ok, in answer to your questions.

No modern equipment in the car - no radio, just the three toggle switches on the dash - all off.

The rev counter shows very nearly 100rpm per mph in top.

I.e. 5000 at 50, 7000 at 70, and then on to being off the scale if I really push it (obviously on my own private test track)

I'm not an expert, but I've had quite a few cars and it certainly doesn't sound like it is revving that high.

Having said that, I'm not sure the speedo is that accurate, but then I think it overreads too, which makes the tacho problem worse, at an estimate about twice what it should read.

Finally, I don't know how old the battery is, it came with the car 18 months ago.

Thanks in advance for any suggestions. I can probably fault find the battery drain with a meter, but I don't know where to start with the tacho.

Cheers,

Nigel
N K Baker

Nigel, I posted a method used by "A certain large motor organisation" to test whether the battery is capable of retaining a charge on the SS&NB MASC website which maybe of help to you

http://ssnbmasc.freezoka.com/index.html

then navigate to the techy section

If the battery is OK but still draining power a reasonable test involves using the ammeter section of a normal automotive multimeter on its 10A setting.

If you do use the ammeter test please DO NOT attempt to start the engine with the ammeter in circuit because the amperages involved will blow the chip in the multimeter to electronic shreds... And may even blow tracks off the circuit board.

The test:
Disconnect the earth terminal from the battery
Set the meter to 10A
Assuming a digital meter read out
&
Assuming negative earth
Connect the black crocodile clip to the battery earth lead
Connect the red crocodile clip to the battery earth pole,
Turn on the meter completing the circuit and then the meter will tell you if there is power leaking
This will be an indication that the regulator points are sticking together allowing the drain

Digital meters get my vote because if you connect them the wrong way round you can still get a reading but with a minus sign in front of it.

Next installment soon please, tell us what you find

Remember not to try to start it up in this mode
Bill

What meter did your organisation use Bill? most of the ones I have come across would have a line fuse on the current/amps scale and thus that would blow before damage occured to the meter. I find it strange that a country wide organisation would use such unsafe equipment?
Bob (robert) Midget Turbo

No Bob

The organisation does and did use such equipment
I just emphasised that the users of multimeters should take sure not to allow high amperage through the meter

If I had advised doing the job without such assurance and the equipment got damaged who would have been the first target around here?

It isn't safe to assume that everyone has fused appliances or leads is it.

So now I get castigated for trying to help safely.

FWIW I have two such multimeters, one works one doesn't

The one that doesn't was given to me by a friend who mistakenly used unfused leads in the hope that I may be able to have it repaired.

For a possible second hand value of a tenner it isnt worth it, but the case is useful, I will also be able to salvage the LCD and the battery cable with its PP3 connection next time I have a need for one

I always use leads with a 10A fuse in both the positive and negative probe ends.

I do not wish to have to buy another, this one works well enough for me.
Bill

Yep point taken although fused leads are for another purpose and protect the operator. The meter is protected by the in line fuse within the meter which to my knowledge all meters have and is ONLY on the ammeter side of the wiring connections.

One day when I was 50 meters up a column at our local refinery, the multimeter that I had with me had a blown fuse and I needed to measure 20 milliamps. What to do? Well take some silver paper from my fag packet and wrap the fuse. (they were the days) Job done and unfortunately I forgot about it.

Unfortunately I had left my leads in the Ammeter connections when I decided to measure for 110 Volts. Anyone with knowledge of these thing will be laughing now as they will know the meter blew apart in my hands, no fused leads in those days but fortunately I survived but the meter was a write off and I had a lot of explaining to do to the refinery manager.
Bob (robert) Midget Turbo

Bob, between us I bet we could fill a moderately sized pamphlet with multimeter horrors to entertain and eddicate

one of my "Nicest!" was when working in the rain taking voltage readings from the alternator plug end of the charging circuit the red lead went alongside the plug leads on a Marina 1300. The rain caused some kind of HT induction into the meter and fried the chip and totalled the meter. The Marina's HT wire gave me a zizzle at the same time, didnt half make me jump I can tell you. Wet surfaces love to leak HT...

Bill

This thread was discussed on 01/04/2008

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