More Alternator problems

[Dr Bob]

3 hours ago, nicknorman said:

if the regulation of the 90A is set to 14v the A2B is capable of getting plenty of output from it by pulling it down to 13v but of course that will only happen after the small alternator is at or around max output. But if a phase was out on the 90A, I suspect the A2B would still be able to get a few 10s of A out of it. So I am still unsure whether it’s a phase out or a low set regulator. The test would be how much current the system can produce with well-discharged batteries.

See post 141. When the 55A was taken out of circuit, the 90A produced 65A of current (on its own) in the first 5 mins after starting the engine with a battery bank only 5% discharged. That sounds like all the phases are intact and the probelm is therefore a low voltage regulation.

Good discussion  on the paralleling of alternators guys, but the AtoB is going to pull the voltage down to 13V isnt it, therefore both alternators will be below their regulated voltage? So both should output. How does the AtoB pull the voltage down? If it does it by drawing current but the 90A wont supply that current as it is seeing 14.6V from the other one, the voltage will still be high. BUT....the 55A is delivering lots of power so its voltage will drop below 14V so then the 90A should start delivering power and its voltage drop. Something is not right then. Hence the email to Charles. I will let you know his response. We are not going to be out on the boat for the next two weeks so I wont be able to do any more testing, but safe to say it is working fine now with the 55A on the engine start and the 90A to the domestic via the AtoB.

[nicknorman]

2 hours ago, Dr Bob said:

Good discussion  on the paralleling of alternators guys, but the AtoB is going to pull the voltage down to 13V isnt it, therefore both alternators will be below their regulated voltage? So both should output. How does the AtoB pull the voltage down? If it does it by drawing current but the 90A wont supply that current as it is seeing 14.6V from the other one, the voltage will still be high. BUT....the 55A is delivering lots of power so its voltage will drop below 14V so then the 90A should start delivering power and its voltage drop. Something is not right then. Hence the email to Charles. I will let you know his response. We are not going to be out on the boat for the next two weeks so I wont be able to do any more testing, but safe to say it is working fine now with the 55A on the engine start and the 90A to the domestic via the AtoB.

Depends on the load / ability of the batteries to take current. The A2B will only "pull the voltage down" when it can send lots of current to the batteries - and it does so by sending lots of current to the batteries! It is quite similar to a MPPT solar controller in that it will adjust the current "pull" to hit the target of the 13v or whatever - in the same way that an MPPT pulls the panel voltage down until the max power voltage is achieved. That combination of current and lower voltage is converted into a somewhat higher voltage and somewhat less current (power being constant, apart from inefficiencies) to convert the power to a suitable potential for optimum charging.

But if the load is light or even moderate, the A2B has no need to, and cannot, pull the alternator voltage right down.

So with your two mismatched alternators connected to the A2B input, I would expect the 55A to supply all the current when the load is light, up to a certain current whereby the alternator voltage has dropped to 14v, and for increasing currents thereafter, the 90A alternator will start to help it. This is probably exactly what is happening. If the alternators were more closely matched in regulation voltage, it would all be fine and they would pretty much play nicely together and share the load.

Edited April 3, 2018 by nicknorman