Alternator load sharing

[Tractor]

Installation:

Beta B 43 S

Victron ‘Combi’, 12/1600.

Alternator 45 Ampere, starter battery.

Alternator 150 Ampere, Service battery.

Battery combiner, Cyrix.

 

Question

With the ‘Battery Combiner’ closed, the two alternators are operating in parallel. Assuming one alternator will output a Voltage higher than the other, this unit will progressively take more load, and the other less load.

How does load sharing in this condition operate?

Does the higher voltage alternator take all the load until its current limit is reached, thereby shedding load to the other alternator?

I would be grateful for any opinion.

Many thanks

[Tracy D'arth]

Are your alternators simply connected together?

 

If so they will both supply current as long as the battery voltage is below both regulator settings.

As you say, the regulators will not be set to exactly the same voltage so as battery voltage rises and current falls the regulator with the lowest voltage setting will supply less and less current.

Alternators and batteries can be regarded as analogue devices, not on or off switching. 

[MoominPapa]

Assuming that the regulators have roughly similar voltage curves and maximum voltage settings, they will share the load, but the proportions taken by each depend greatly on subtle variations in regulator performance, so are not really predictable. If it matters, the easiest way to find out is to try it.

 

MP.

 

[nicknorman]

Yes the load will be shared roughly in proportion to the max output, eg at mid charge both alternators might be producing 50% ie 75A and 22.5a respectively, but as previously mentioned there will be some variation in that if the alternators have different set voltages and regulation curves.

[Chewbacka]

Apart from being technically interesting it doesn’t matter, so the op shouldn’t worry about it.

[Tractor]

Thanks for the feedback

Yes, the two alternators are parallel when the 'battery combiner', contactor closes.

Whilst the system has been operating for some time without fault and is I guess, a typical configuration, I have this question??

The next step would be for me to current clamp the two alternator outputs and tabulate the results.

Thanks, I appreciate all responses.

 

[Tony Brooks]

15 minutes ago, Tractor said:

Thanks for the feedback

Yes, the two alternators are parallel when the 'battery combiner', contactor closes.

Whilst the system has been operating for some time without fault and is I guess, a typical configuration, I have this question??

The next step would be for me to current clamp the two alternator outputs and tabulate the results.

Thanks, I appreciate all responses.

 

 

What is the question? If you want to know more about what is going on then you will have to monitor both alternator outputs and chart the results. However it is very unlikely to show anything apart from within an hour or so neither alternator will be delivering maximum output unless there is also a heavy domestic load running. I can't see any way to alter this so am tempted to ask why bother.

[Tracy D'arth]

19 minutes ago, Tractor said:

Thanks for the feedback

Yes, the two alternators are parallel when the 'battery combiner', contactor closes.

Whilst the system has been operating for some time without fault and is I guess, a typical configuration, I have this question??

The next step would be for me to current clamp the two alternator outputs and tabulate the results.

Thanks, I appreciate all responses.

 

As I now understand, the large alternator is connected to the cabin batteries, the small one to the engine Battery with the VSR connected across both.

I can see nothing wrong with that, you will get the best from both alternators. Is the VSR triggered by the cabin or the engine battery? Or is it bi directional, I don't know that model.

[WotEver]

27 minutes ago, Tracy D'arth said:

Is the VSR triggered by the cabin or the engine battery? Or is it bi directional

It’s bi-directional with some intelligence to  help prevent unwanted disconnects. 

[Tractor]

It is a Cyrix-ct 12/24 (Victron).

When the 'Start' battery is >13.6V, the contactor closes connecting start battery to the Service battery, which also connects both alternators in parallel.

 

Before I get into monitoring the alternators, I need to ask the question; which, yes, is a bit academic but worth the ask I am sure.

 

e.g. if the alternators have an inbuilt 'falling Volts with load' characteristic, then they will share naturally, this the detail which I do not know.

 

[Tracy D'arth]

2 minutes ago, Tractor said:

It is a Cyrix-ct 12/24 (Victron).

When the 'Start' battery is >13.6V, the contactor closes connecting start battery to the Service battery, which also connects both alternators in parallel.

 

Before I get into monitoring the alternators, I need to ask the question; which, yes, is a bit academic but worth the ask I am sure.

 

e.g. if the alternators have an inbuilt 'falling Volts with load' characteristic, then they will share naturally, this the detail which I do not know.

 

The voltage achieved by an alternator (or 2) is dependant on the state of charge of the batteries, rising volts, falling current as "full" is approached.

[nicknorman]

11 minutes ago, Tractor said:

It is a Cyrix-ct 12/24 (Victron).

When the 'Start' battery is >13.6V, the contactor closes connecting start battery to the Service battery, which also connects both alternators in parallel.

 

Before I get into monitoring the alternators, I need to ask the question; which, yes, is a bit academic but worth the ask I am sure.

 

e.g. if the alternators have an inbuilt 'falling Volts with load' characteristic, then they will share naturally, this the detail which I do not know.

 

Yes I think some people think that an alternator will produce full output right up to the point that the regulated output voltage is reached, but this is very much not the case for a normal analogue regulator. The regulation is very soft (low gain in the control loop) so there is a broad region of reducing current output as regulated voltage is approached. It probably starts around 0.5 to 1v below regulated voltage.

 

This is one area where after market alternator control gadgets can help - allowing max output until very close to regulated voltage. The downside being that forcing the alternator to work harder makes it run hotter and may shorten its life.

 

Edited August 23, 2020 by nicknorman

[Tractor]

The batteries in parallel, start and service, with rising Voltage internal resistance, a regulated supply Voltage, current reducing. There must be a natural balance throughout the system.

 

I am getting there, thanks again for this discussion.

 

Tractor