Battery keeps going flat

[shawn71]

It's not Type 3 or 4 related but it is still aircooled so...

Our 71 1300 Beetle has drained a new battery in a couple of weeks! I replaced the old one because I thought it was knackered but the problem still persist.

The charge light doesn't come on when the car is running and it's charging at 13-14volts.

What sort of power drain is likely to drain a battery in a week or so of daily use (about 25 miles a day)?

Therefore it seems that I have a circuit that is draining the battery when its not used. I read somewhare that you can test each circuit by removing each of the fuses in turn and measuring the voltage drop across each one in turn. Having never done this before my question is what setting would I need to put my circuit tester onto, would it be the same setting as I put it onto to test the charging? (I'll post of pic of my tester if needed)

Assuming that this shows a problem on one circuit (fingers crossed it will) how do I then narrow it down further and then repair the problem?

What else is a likely suspect to be draining the batteries over the period of a couple of weeks?

[JSR-69]

If everything's turned off then there should be no current through any of the fuses. If you take a fuse out and put an ammeter across the terminals, then the ammeter should read zero. If you get a reading, you've got current. If you don't have a suitable ammeter, try an instrument panel bulb (~2 watt) which will light up if the circuit is drawing current. Do that for each fuse in turn.

There are other circuits that aren't fused, such as the ignition, so check wire that might draw current.

Let us know what that shows.

Judi

[miketyp3]

Hi Shawn,
I only mention this as it happened to me recently.
I needed to move my Fastback during its winter lay-up and it seemed to have all the symtoms of a dud battery (would hardly turn the engine over even after a full charge).
I changed the battery for a new one and even bought a new starter before discovering it was the starter motor guide bush in the bell housing that had self destructed.
It looks like what was happening was that the unsupported starter motor shaft was allowing the pinion to bind in the ring gear of the flywheel which gave the impession of a flat battery.

Its worth considering if the symptoms sound simular.

Mike

[shawn71]

If I've used my tester correctly then I don't seem to have any drains on the battery when everything is turned off.

The dynamo seems to only put out a max of 13.6 volts at high revs and is barely at 12.5 volts on tick over, this reading is the same at both the battery and the dynamo.

I'm assuming then that the dynamo might be at fault?

[JSR-69]

Volts sound a bit low.

Judi

[shawn71]

I've the conclusion that the dynamo is dying a slow death and probably has been for some time, the problem is exasperated by the need to run with lights, wipers etc on almost every day.

I've checked the voltage drop and it's about 10 milliamps (whatever they may be?) so not enough to kill the battery.

I'll order another dynamo and see what happens

Thanks for the input peeps

[purplepeter]

Before you rush into the expense of a new one Shawn,Check the brushes-theyre about £4!
Also,even though youve convinced yourself its the dynamo,check for earth leakage-put the meter on volts,neg probe to a good earth on car body & positive probe to various random points on the battery casing..any reading indicates leakage..caused by muck/crap/electrolyte/grease etc on the casing allowing current to "escape" to earth...you cure it by putting a sheet of polythene under the battery & washing the casing down with bicarb soln
you never know...plus the test & cure are both free!

[shawn71]

Hi Pete, I've checked the brushes and they are still making good contact and are less than a year old although the commutor has several deep scores, the battery case is clean as its new. I will however check again tomorrow once the battery is charged.

This problem has been hovering for a while now and I've been trying to ignore the fact that the dynamo is dying but it would seem that could be the case. I will, however, welcome a free fix should one be available.

[Editor]

Do you still need a large (?36mm?) socket to undo the dynamo nut on the fan? I remember it was quite big on the old Beetle, but don't know if they've reduced it since.

You need to do the handbook tests first - it could still be the regulator, which is likely to be less hassle and cost than changing the dynamo. It's the regulator that limits the volts, unless the dynamo has shorted windings or similar.

[shawn71]

Don't know about the socket size Dave but I have the 36mm one as its the same size for rear hub nuts.

Just refitted a fully charged battery measuring 12.6 volts. Retested the drain by placing multi meter between the earth terminal and earth strap and it reads 0.01 amps, by my understanding that is well below any level that will drain batteries.

Everything connected properly with clean connections and at tickover I get 12.4 volts, increase the engine revs and it just about reaches 13.4 volts. Turn on lights, wipers etc and at tickover it reaches about 12.1 on tick over and at high revs about about 13.1

Pushed the brushes in to ensure good contact and this made no changes to the numbers.

It has been suggested that there is another test to confirm the dynamo is at fault that I can try. Disconnect the generator from the regulator by removing the wires on the dynamo and place a jumper wire from DF to the frame of the dynamo and mutli meter between D+ and earth and it should reach 35 volts at high revs.

[JSR-69]

It has been suggested that there is another test to confirm the dynamo is at fault that I can try. Disconnect the generator from the regulator by removing the wires on the dynamo and place a jumper wire from DF to the frame of the dynamo and mutli meter between D+ and earth and it should reach 35 volts at high revs.

If you do try that test, you must be very quick about it else you will burn out the windings! From memory, you may need a load resistance?

Judi

[shawn71]

I'm confused by this test as it jumped upto 60 volts at high revs! The D+ is the one that has the red/white stripped wire and another one and DF has the smaller single wire? And when it says DF to frame of dynamo it meant the dynamo casing?

Does this mean I did the test wrong? Or is the dynamo still good and the problem is the regualtor?

Plugged everything back together and its still charging way below what it should be.

[Editor]

That sounds OK - I don't think the high revs are needed. The regulator is basically controlling the cutting in of the field coils - when you ground the DF connection, it allows the full voltage on the field coils and the dynamo puts out its maximum at that rpm.

If you've got the Bentley Type 3 manual that gives the correct way to test the dynamo on its own. Note the rpm mentioned is dynamo rpm, not engine rpm. The procedure is:-
1) Disconnect both D+ and DF from thegenerator.
2) Connect DF generator terminal to ground
3) Connect voltmeter + to D+ on generator, and voltmeter - to to D- on generator (casing screw).
4) Run engine at slow idle 700rpm (= 1500 rpm on generator), output should be around 12V.
5) Run engine briefly at 1300rpm (=3000 rpm on generator), and output should be about 36V.

No more that 10 secs with DF grounded or you may burn out the field coils.

Note no high rpm.

Sounds like the regulator - that's good news; much less work and not too expensive.

[shawn71]

I might as well start with the regulator and see what happens, it is certainly the cheaper option at half the price of a dynamo

[Editor]

Just another little tip, don't allow the terminal posts to rotate when tightening or loosening the nuts, as the connection at the base of the terminal inside the generator can be broken.

You can do stage 2 after setting things up - simply touch the DF terminal to the dynamo body when testing the volts output. That's easier than starting with it connected and then having to dash round the back before it cooks!

[shawn71]

Having checked the dynamo was kicking out a decent voltage I have replaced the regulator with a new one and it now charges at 14 volts on high revs!

This is a lot higher than before so fingers crossed the problem is fixed

[Editor]

Sounds like it - here's hoping.