Nobag Posted September 13, 2019 Report Share Posted September 13, 2019 I have to rev the Barrus Shire engine quite fast to get the alternator working. I have put a larger 4w bulb in to try and boost the voltage from the charge light circuit. Checking the voltage at the alternator it was 1.45v on the charge light circuit, when I disconnected the wire from the alternator I got battery voltage. Is there a fix for this or is it new alternator time. Thanks for any help. Link to comment Share on other sites More sharing options...
WotEver Posted September 13, 2019 Report Share Posted September 13, 2019 What voltage and charge current do you get out of the alternator once it’s excited? The voltage on the exciter feed sounds correct as described. No voltage on the ‘Ind’ terminal until the alternator is running. Is the fan belt tight? Link to comment Share on other sites More sharing options...
Nobag Posted September 13, 2019 Author Report Share Posted September 13, 2019 Thanks, the voltage is around 13.8 and 27 amps when first started. The fan belt is tight about half inch free play. If I touch a wire from the battery positive to the D+ the alternator starts working and the warning light goes out on tickover. Link to comment Share on other sites More sharing options...
Tony Brooks Posted September 13, 2019 Report Share Posted September 13, 2019 (edited) 3 hours ago, Nobag said: I have to rev the Barrus Shire engine quite fast to get the alternator working. I have put a larger 4w bulb in to try and boost the voltage from the charge light circuit. Checking the voltage at the alternator it was 1.45v on the charge light circuit, when I disconnected the wire from the alternator I got battery voltage. Is there a fix for this or is it new alternator time. Thanks for any help. When you measured the voltage on the warning lamp terminal you were measuring the voltdrop across the alternator's rotor and as Wotever says that is probably about correct. A larger bulb is unlikely to alter this. When you disconnected the D+ (WL) wire from the alternator there was no path to negative so no voltdrop. Thus you found batery voltage. All perfectly correct. Edited September 13, 2019 by Tony Brooks Link to comment Share on other sites More sharing options...
Tony Brooks Posted September 13, 2019 Report Share Posted September 13, 2019 2 hours ago, Nobag said: Thanks, the voltage is around 13.8 and 27 amps when first started. The fan belt is tight about half inch free play. If I touch a wire from the battery positive to the D+ the alternator starts working and the warning light goes out on tickover. The alternator is an A127 and 28 amps at 13.8 volts sounds very low to me IF the engine was revving at around 1500 rpm or more. If the engine was on tick over then those readings are pretty much meaning less. Exactly what is causing your concern, what are you trying to cure? The alternator is probably rated at 50 amps or more so 28 amps (on a revving engine) is low but so is the 13.8 volts. As far as alternators are concerned the higher current the batteries demand over the alternator's rated out put the lower the charging voltage will go so your figures could be normal at tick over or at speed they are proabbly wrong. If wrong it suggests you have lost one of the three generating coils in the alternator, probably blown diode(s) Please give an estimate of engine speed when you took those measurements. Link to comment Share on other sites More sharing options...
Nobag Posted September 13, 2019 Author Report Share Posted September 13, 2019 21 minutes ago, Tony Brooks said: The alternator is an A127 and 28 amps at 13.8 volts sounds very low to me IF the engine was revving at around 1500 rpm or more. If the engine was on tick over then those readings are pretty much meaning less. Exactly what is causing your concern, what are you trying to cure? The alternator is probably rated at 50 amps or more so 28 amps (on a revving engine) is low but so is the 13.8 volts. As far as alternators are concerned the higher current the batteries demand over the alternator's rated out put the lower the charging voltage will go so your figures could be normal at tick over or at speed they are proabbly wrong. If wrong it suggests you have lost one of the three generating coils in the alternator, probably blown diode(s) Please give an estimate of engine speed when you took those measurements. Thanks, the engine was running around 1300 rpm . The problem that I have is that to get the alternator started, I have to run the engine at very high revs which I would rather not do, especially when it is starting from cold. Link to comment Share on other sites More sharing options...
Tony Brooks Posted September 13, 2019 Report Share Posted September 13, 2019 33 minutes ago, Nobag said: Thanks, the engine was running around 1300 rpm . The problem that I have is that to get the alternator started, I have to run the engine at very high revs which I would rather not do, especially when it is starting from cold. In that case as long as the drive belt fits properly and is correctly tensions I suspect its the alternator. Link to comment Share on other sites More sharing options...
Neil2 Posted September 13, 2019 Report Share Posted September 13, 2019 I've had a similar problem recently which started the same way, having to rev the engine quite hard to get the alternator started. But a few days ago the output ceased altogether. I limped in to Calcutt where they bench tested the alternator and initially got no output. We were all assuming a new unit was on the cards when Ian suggested reconnecting everything with the original securing nuts from the boat wiring and lo it sprang into life, and it's been fine ever since. None of the guys at Calcutt could fully explain what had happened so I can only assume that there must have been a duff connection somewhere which the process of removing and reconnecting the wires a few times resolved. Link to comment Share on other sites More sharing options...
Nobag Posted September 13, 2019 Author Report Share Posted September 13, 2019 14 minutes ago, Neil2 said: I've had a similar problem recently which started the same way, having to rev the engine quite hard to get the alternator started. But a few days ago the output ceased altogether. I limped in to Calcutt where they bench tested the alternator and initially got no output. We were all assuming a new unit was on the cards when Ian suggested reconnecting everything with the original securing nuts from the boat wiring and lo it sprang into life, and it's been fine ever since. None of the guys at Calcutt could fully explain what had happened so I can only assume that there must have been a duff connection somewhere which the process of removing and reconnecting the wires a few times resolved. Thanks, I going to refit it tomorrow. Might be lucky. Link to comment Share on other sites More sharing options...
Tony Brooks Posted September 14, 2019 Report Share Posted September 14, 2019 10 hours ago, Neil2 said: I've had a similar problem recently which started the same way, having to rev the engine quite hard to get the alternator started. But a few days ago the output ceased altogether. I limped in to Calcutt where they bench tested the alternator and initially got no output. We were all assuming a new unit was on the cards when Ian suggested reconnecting everything with the original securing nuts from the boat wiring and lo it sprang into life, and it's been fine ever since. None of the guys at Calcutt could fully explain what had happened so I can only assume that there must have been a duff connection somewhere which the process of removing and reconnecting the wires a few times resolved. The main output stud is often a splined interference fit in the positive diode heat sink plate. If this has worked loose then the movement caused by manipulating the fixings could be enough to re-establish a connection for now. It could also be worn brushes and it was just coincidence they remade contact while you were fetching the nuts & washers from the boat. Link to comment Share on other sites More sharing options...
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