2long Posted November 10, 2014 Report Share Posted November 10, 2014 Hey guys: On a run this weekend, my ammeter gauge showed normal positive flow from the dynamo after I started up, but it stayed high as I drove, whereas normally it drops down to about zero as the battery is charged back to full (about 5-10 minutes). I have positive ground and no extra ancillaries. When I turned on my lights or indicators the needle did show the discharge. Does this suggest my battery is not holding the charge? Cheers Dan Quote Link to post Share on other sites
RobH Posted November 10, 2014 Report Share Posted November 10, 2014 It could mean that the battery isn't charging properly but you should be able to tell that if cold starting is poor, although a battery that has lost capacity can give the appearance of charging quickly which is the opposite of your symptom. It could also be a fault with the dynamo regulator of course. More information would help. Is it possible that the battery was a bit low on charge and that it just needed to recharge for longer than normal? How long was the run and what level of charging current was it - did the current stay constant or was it dropping slowly? Does the ignition lamp still work as normal and come on at idle? Quote Link to post Share on other sites
TomMull Posted November 10, 2014 Report Share Posted November 10, 2014 My generic response to dynamo issues is to check the battery terminals and grounds. Never hurts. Tom Quote Link to post Share on other sites
LGFromage Posted November 11, 2014 Report Share Posted November 11, 2014 When that happened on my car it turned out that the field coils in the dynamo had failed which meant that a replacement unit was required. Hopefully your the problem with your motor will have a simpler solution. Tim Quote Link to post Share on other sites
Ashley James Posted November 11, 2014 Report Share Posted November 11, 2014 Make sure the fan belt isn't slipping Quote Link to post Share on other sites
2long Posted November 12, 2014 Author Report Share Posted November 12, 2014 Here's a bit more information. I checked the battery terminals and ground, and the fan belt. All seem ok. Upon initial cold startup after a week of sitting, the gauge goes to just below 15 amps, and then after about 3-4 minutes it drops down to about 5-7 amps and stays there for the duration of a 30 minute run (except for at idle). At idle (about 700 to 800 rpm), the amps drop down to zero but the ignition light does not come on (and it never has at idle speed). Turning on the headlamps puts it at about 5-7 amps to the negative at idle or just below zero at 2500 rpm. My concern is that the amps seem to be staying at 5-7 even after a long drive, rather than dropping down to about zero due to the battery going up to a full charge. I have a standard dynamo and box. Thanks for the input! Dan Quote Link to post Share on other sites
peejay4A Posted November 12, 2014 Report Share Posted November 12, 2014 Given how inaccurate these gauges are I wouldn't worry about it. Quote Link to post Share on other sites
RobH Posted November 12, 2014 Report Share Posted November 12, 2014 Pete has a point Dan, and if you have access to another meter its worth checking that the ammeter i telling the truth. If its real though its definitely worth worrying about as 5-7 amps continuous will overcharge the battery and almost certainly damage it permanently. (quote: OVERCHARGING is the most destructive element in battery service. During overcharging, excessive current causes the oxides on the plates of the battery to "shed" and precipitate to the bottom of the cell and also heat the battery, thus removing water from the electrolyte. Once removed, this material is no longer active in the battery. In addition, the loss of water from the electrolyte may expose portions of the plates and cause the exposed areas to oxidize and become inactive, thus reducing additional capacity. --DC Battery.com) From your description it sounds as though the battery is behaving as it should. If you can swap the battery temporarily for another it would confirm that. If the same effect persists it means the regulator may be faulty which could also explain why the ignition light never comes on at slow idle (provided the bulb is not blown). Are all the connections OK on the regulator? - (particularly no short between the F and A or F and D terminals ? ) It is also possible that the regulator contacts have stuck closed but unless you know what you are doing its easy to mess up the settings while trying to fix that. This link gives some background info: http://matchlessclueless.com/electrical/how-it-works/lucas-voltage-regulator/ Quote Link to post Share on other sites
peejay4A Posted November 12, 2014 Report Share Posted November 12, 2014 Good point about overcharging. I might be worth checking the battery terminal voltage with the engine running. Quote Link to post Share on other sites
McMuttley Posted November 12, 2014 Report Share Posted November 12, 2014 I'm confused, some people have amnmeters that have needles that move - wow ! Quote Link to post Share on other sites
EdwinTiben Posted November 13, 2014 Report Share Posted November 13, 2014 ... the ignition light never comes on at slow idle (provided the bulb is not blown). If the bulb was blown, there wouldnt be any charge at all, the bulb is necessary in the circuit to get a field in the dynamo to have it charging. Quote Link to post Share on other sites
Lebro Posted November 13, 2014 Report Share Posted November 13, 2014 Wrong. This is true for an alternator, but not for a dynamo. A dynamo uses residual magnetism to start it up. Bob. Quote Link to post Share on other sites
RobH Posted November 13, 2014 Report Share Posted November 13, 2014 Not quite Edwin - that is true of some alternators but a dynamo and regulator work differently and do not need the bulb current. The residual magentism in a dynamo field should be quite sufficient to start it up. Quote Link to post Share on other sites
peejay4A Posted November 13, 2014 Report Share Posted November 13, 2014 Exactly so which is why one can flash the field coils of a dynamo to alter the polarity of the residual field and thereby alter the polarity of the dynamo output voltage. Quote Link to post Share on other sites
Lebro Posted November 13, 2014 Report Share Posted November 13, 2014 Below is copied from another recent post in the Technical area: Posted 11 November 2014 - 03:23 PM I would expect the warning light to come on at a slow tickover with a dynamo setup, but not with an alternator. The purpose of the warning light differs between the two setups: Dynamo The lamp is connected between the dynamo main output, & the battary -via the ign switch. it will illuminate as soon as ign is turned on as the dynamo has no output. When engine is started, & revs taken above a slow tickover the dynamo will produce enough voltage to activate the "cut in" contacts in the regulator box, This connects the dynamo output to the battery, thus shorting out the warning lamp - which will go out. The "cutin" contacts will not normally open again unless the dynamo output falls to a low level, (causing the battery to start discharging into it) this can happen at slow tickover, & when it does, the warning lamp will come on - but not as brightly as before engine start. The charging will take place perfectly well if the warning light is blown, or not present. Alternator The lamp is connected between the alternator field winding -(slip rings) & the battery via the ign switch. It has to be there in order to supply initial current to the field winding to start the alternator producing an output. Blown or missing bulb means no charging. When started, the alternator will immediately give an output which is rectified: A. By some high current diodes to provide the main output, & B. some lower current ones to provide the field current. These latter diodes connect to the same point as the warning light, & so as the rectified voltage rises from the alternator, it equals the battery voltage, and the light goes out. The earthy end of the field winding is connected (via the slip rings) to the regulator, which adjusts the field current to give the correct output voltage. It is very unusual for the warning light to ever come back on again until engine is stopped. If it does, then I would strongly suspect the alternator is at fault, either the rectifier diodes (either set) or the regulator, or the slip rings. All are worth checking. By the way anyone who wishes to update their dashboard illumination lamps, & the two warning lamps with LED types (I have) will find that the IGN warning lamp will not pass enough current to energise an alternator. The fix is to solder a resistor across it, to increase the current. Bob. Quote Link to post Share on other sites
Richardtr3a Posted November 13, 2014 Report Share Posted November 13, 2014 I had similar problems and it was the regulator. After a number of new stock failures from many different suppliers, I had the old one rebuilt and it has been fine now for years. Lucas made £5.00 every time a customer took the cover off the regulator. Good Luck Richard & H Quote Link to post Share on other sites
EdwinTiben Posted November 13, 2014 Report Share Posted November 13, 2014 I stand corrected. This is a language issue. In dutch we dont use seperate words for alternator of dynamo. in the spokenlanguage we call them both dynamo. cheers Quote Link to post Share on other sites
tthomson Posted November 14, 2014 Report Share Posted November 14, 2014 Hi Dan, You don't say how you checked the battery, but the situation you describe could be due to a failed battery cell (Short circuit) If you use a standard voltmeter, these have very high resistance and do not place a significant load on the battery and may therefore not show the problem. The only true test of the battery is to measure the voltage under significant load. (i.e. when it is supplying 5 Amps or more). You would also notice this when starting the car. It would turn over much more slowly. TT Quote Link to post Share on other sites
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