Dynamo regulator problems?

[jmwf]

We've owned four cars over the years with this problem, but I've never found an official explanation. Dynamo charges OK until on a long run (2+ hours) with wipers and lights etc. on. All OK until trying to start only to find that battery is flat! The regulator appears to gradually reduce the charge rate until the battery is only-just not being charged. Cars are 1x MG midget 1x MGBGT and 2x Minors. (all using the same regulator box)Whilst I have devised my own add-on electronic remedy, I can only presume that there must be others who have experienced the same?

[Willie]

Lo, the symptoms you describe certainly suggest that continued running with 'every
thing' switched on ends in an uncharged
battery, but I have owned 3 MGs,2 Minis,
5 Minors etc and have never experienced a
flat battery. The simple answer,of course,
is to fit an alternator(see latest test tips
in the magazine). I have also learned that you should NEVER try to adjust the charging
regulator.
Willie

[Willie]

basically, the dynamo charging system was
perfectly adequate for road conditions when
it was designed. There were few occasions
when you would crawl along for miles in long
traffic jams, in the dark, in the rain!not
able to go fast enough to get maximum output
from the dynamo. As congestion increased
the problem caused makers to fit Alternators
which not only give far greater output,but
do so at much lower engine speeds. A MINI
alternator works very well on the Minor and
it is easy to revert back if desired. As I
said,I have never had this problem,but I
don't have to commute to work!
Willie

[newagetraveller]

I also used to regularly do a two hour motorway trip with wipers and lights on and a dynamo to charge the battery but never experienced this problem.
Is the fan belt slipping?
Is something draining the battery when you switch off?
Have you tried fitting an ammeter to see if the battery is charging properly?
Normally the regulator reduces the rate of charge when the battery is fully charged.
Your message reads as if you are using the same regulator on all four cars (and not four regulators, one for each car).

[Gareth]

Hello there!

Surely he means the same type of regulator box...?

Using the same one would be silly - even by my standards!!

[jmwf]

Er yes... The same TYPE of regulator box... Using a DVM across the battery on each car shows that the charging rate eventually drops below 12.4V which suggests that the battery is being discharged?

[newagetraveller]

The regulator is fairly complex but there is a book that gives a very good description of how it works and how to fault-find the entire charging circuit.
The book is called: Automobile Electrical Manual
Author's name is: Tranter
Publisher is: Haynes
Unfortunately it is currently unavailable according to Amazon. However your library may have a copy.[ This Message was edited by: newagetraveller on 19-03-2002 09:43 ]

[Willie]

Well, yes,according to my book a voltage
across terminals 'D' and 'E' on the control
box of only 12.4v means that the charging
'cut out'will have opened thus stopping
charging. The cut out is meant to operate at
between 12.7 and 13.3volts thus starting to
charge the battery. You could check this,
and,despite my earlier remarks, it is adjustable. but all other adjustments are
temperature dependent which is bad medicine.
Willie

[tuning72]

Hi
Of course the system and circuit can be tested and adjusted. I have had five instances of this "falling off" of performance. It was always this type of dynamo/regulator set up.
1) Make sure all terminals are Soldered not crimped. Especially old ones.Poor connection and will o/heat BUT ok when cold!)Most common fault!)
2) Check the Dynamo FAN. If blades are damaged bent, then Dynamo o/heats.
3) Commutator needs u/cutting.(Brushes o/heat
through poor contact).
4) Fan belt.Slipping. Readings OK cold but will o/heat and drop voltage, check sides for "shine" or cracking.( New type "toothed") belt is great improvement.
These are just some mechanical faults that are often o/looked.
I suspect Heat has much to do with this problem.( Not mentioned in Manuals)?..Ivor

[jmwf]

I've read all the responses to my query but it looks as if nobody else has experienced a similar problem, but may of course recified it by replacing the offending part when their battery was not being charged and going flat. Whilst I have eliminated the problem in a round-about way, I believe that the problem lies with the reg. box itself. For a start, the car should run with headlights and wiperrs on ONLY should it not? this combination assured a flat battery after a long run. If the reg. cover was removed with the car stationary and a DVM across the battery with lights and wipers on, the battery showed a voltage of between 12.4 and 12.5 with the engine at about 2,500 or thereabouts. If, using a fingernail, the reg. coil is stopped from regulating the dynamo, the voltage immediately rises to 15+ volts (I didn't allow it to go higher as I'd proved my point). Thus the fan belt wasn't slipping and the dynamo itself was ok. I did have an ammeter on one of the earlier cars with the problem but it always showed a small charge. Bear in mind that if the battery is almost flat with a load across it, the ammeter will still show a charge as the dynamo might still be supplying current to keep the lights etc. up to a certain voltage - even if that is below the correct charging voltage. Confusing? I'll say! My solution in the end? I cheated and built a small add-on box with a few bits of electronics that monitors the output voltage from the reg, and if it finds it too low, overrides the reg and pulls it back up to a proper charging voltage. Problem solved.
Thanks guys for all the advice all the same!

[Willie]

You rogue you. anyone would think you knew
what you were doing!! Very interesting.
Willie

[catsoup]

Good solution!
Any chance of the circuit diagram?

I too had exactly the same problem. With both my MM's. I presumed that it was because the old dynamo was designed to top up the battry when the bulbs were alot less wattage than the modern ones. (My first MM had a halogen conversion, my other has a sealed beam.)

My heavyhanded solution was to fit an alternator. However the alternator has now let me down twice. After just a few months wear it stoped charging. I had it replaced. And the next one went again after a few months. This time I risked the guarentee, and took it apart. One of the burshes had gone completely. I cleaned the commutator, and replaced the brushes. ... I guess its due to go in about 3 weeks time! No, seriously I expect most people have no problems with alternators.

Cheers.

[jmwf]

Hi catsoup - so there are others out there with the same problem! Sorry to hear about your alternator problems - a guy 2 doors up from me has a Landy (series III) and he has been through either 3 or 4 alternators in as many weeks - all genuine Lucas replacements - I've seen them come shiny and new looking from new Lucas boxes - I diverse. Is your Morris + or - earth? My device was designed for - earth. You will need a scope and a good DMM to set it up though. I've left a message in your private mail box if you need more help.[ This Message was edited by: jmwf on 15-04-2002 00:06 ]

[winger300]

Im getting this flat battery problem on a long run also!

Would replacing the regulator box with a new one (I have a boxed spare one) solve it?

[rayofleamington]

winger300,
Did you get your battery and dynamo checked out yet?
As you were getting flat bettery also on a short run this may be jumping the gun.

[winger300]

I check the battery using a hydrometer, and all the cells seemed fine after a good trickle charge.

I tested the dynamo output again and it outputs upto 14.5v when revved hard, so i know its charging ok.

Its been fine most of the time, but when i think about it, i always end up with a flat about a day after a long run. Since the previous owner had the same trouble, but thought that the dynamo couldn't keep up when driving above 60mph, it makes more sense to suspect an overheating regulator is actually the fault.

My spare regulator is at my parents, so after the drive home i'll check the charging output again and should hopefully be able to identify the problem.