Alternator upgrade

[Molteni]

Presently running a Thorneycroft T80 with a 70A A127 Lucas alternator supplying 4 x 110Ah batteries. The system has a Stirling regulator and a FET charge splitter.

I was looking at a 120A alternator upgrade with a view to less engine running time to recharge batteries heavily discharged after a long sail.

Is this a viable solution, there seems to be conflicting advice online. Some say that an alternator only supplies the current demanded by the resistance in the discharged batteries; others that heavily discharged batteries will recharge with less engine time with an alternator with a higher nominal output.

Thanks in advance

Mike

 

[Boater Sam]

With the single v belt you will struggle to drive anything larger than 90Amps .

Changing to a double or polyvee belt on this engine is not easy, the crank pulley has to have a vibration damper built in.

 

[Buck Turgidson]

Presently running a Thorneycroft T80 with a 70A A127 Lucas alternator supplying 4 x 110Ah batteries. The system has a Stirling regulator and a FET charge splitter.

I was looking at a 120A alternator upgrade with a view to less engine running time to recharge batteries heavily discharged after a long sail.

Is this a viable solution, there seems to be conflicting advice online. Some say that an alternator only supplies the current demanded by the resistance in the discharged batteries; others that heavily discharged batteries will recharge with less engine time with an alternator with a higher nominal output.

Thanks in advance

Mike

Mastervolt probably know what they are talking about. LINK

 

[[70521]]

Have you ever measured how much charge your batteries absorb and the time it takes to charge it?

Had a trip on a boat last year with Lithium batteries and a massive alternator, we could either motor or charge!

 

[Stemar]

Someone who knows what they're talking about will be along in a minute, but my understanding is that a more powerful alternator will only be a benefit for a relatively short time. Once the batteries get to a certain level, they won't take more than a few amps, and that goes on for a long time.

I'd be inclined to keep the existing alternator and spend the money - and a good bit more, probably - on solar

 

[PaulRainbow]

Steve (post #5) is correct. With a bank of 4 x 110ah batteries the larger alternator might put some initial charge in a little faster, but that would quickly tail off to less than your current alternator output. Next time you run the engine to charge the batteries, closely monitor the current the batteries accept. I'll be surprised if you ever see 90a for more than a very short while, if ever.

I'd also agree with Steve that fitting solar is a better solution. You'll be taking less from the batteries whilst you're sailing (unless night sailing, of course), so less time required to charge at the end.

I would also question the statement "batteries heavily discharged after a long sail." Are you really "heavily discharging" a bank of 4 110ah batteries whilst sailing ? If so, you might want to look at your power usage, see if you can reduce it.

 

[pvb]

On my last boat, I had a 90A alternator and 6 x 110Ah batteries in the domestic bank. I rarely saw much more than 70A charge rate. The alternator, regardless of its rating, can only charge at a rate which the batteries can accept.

As already mentioned, around 90A is the biggest alternator you can easily drive with a single V-belt.

Another consideration is that larger alternators tend to be large-case versions, which are physically bigger and heavier and usually require custom mounting brackets, which need to be very substantial to cope with the vibration. On the other hand, around a 90A alternator is still small-case and could be a straight swap.

All alternators are not equal - best to go for one which has a good output curve, with reasonable current at lower revs. The Prestolite Leece-Neville range is good in this regard.

 

[Bobc]

You might find that swapping the diode splitter out for a VSR helps, as you can get quite a voltage drop from a diode splitters.

 

[Molteni]

Thanks for all the good points raised. We already have both solar and wind turbine, and by batteries "heavily discharged" I mean down to 60% capacity on the gauges.

The recent Splitter is an Argofet which does away with the drain caused by diodes.

The present 70A alternator will start charging heavily discharged batteries (60% capacity) at about 40 Amps, quickly dropping from about 20 Amps after an hour or so. There has been a big improvement in charge rate after installing the Sterling regulator but I'd like to improve still further. I'm told that the Sterling regulator has a "soft start" which increases the load on the belt gradually when the engine is started. Reported elsewhere is that a standard V belt will not slip because of this feature.

Without wishing to reduce our power consumption, the aim would be to reduce the time spent using the noisy engine. Is a 120A alternator the way to go?

 

[Boater Sam]

You will NOT drive an alternator bigger than 90Amps on a single V belt, end of.

 

[pvb]

Without wishing to reduce our power consumption, the aim would be to reduce the time spent using the noisy engine. Is a 120A alternator the way to go?

No.

 

[Molteni]

I'm not looking to drive the alternator at anything like 90Amps, just more than it supplies at the moment. An alternator rated at 120A is just a nominal figure.

 

[Paulg25]

The present 70A alternator will start charging heavily discharged batteries (60% capacity) at about 40 Amps,

This would suggest that it's not the alternator that is the limiting factor.

 

[RichardS]

I'm not looking to drive the alternator at anything like 90Amps, just more than it supplies at the moment. An alternator rated at 120A is just a nominal figure.

You don't have any choice in the matter, I'm afraid. If the batteries are discharged then whatever alternator you have fitted will produce its maximum current, although that will not be quite as high as the rating shown on the label. There are ways to limit the current being produced but that would be pointless.

Richard

 

[Graham376]

You will NOT drive an alternator bigger than 90Amps on a single V belt, end of.

If the alternator is still only outputting the 40 amps he has now, a V belt will cope but, if the alternator was trying to run at its full rated output then you would be correct. For reasons already stated in various posts, I think increasing alternator size would be a waste of money.

 

[pvb]

For reasons already stated in various posts, I think increasing alternator size would be a waste of money.

Yes, a better use of the money would be to buy more batteries. A bigger battery bank will be able to accept a higher charge rate and make better use of existing alternator capacity. Fitting AGM batteries would be an advantage, as they accept charge more rapidly than flooded batteries.

 

[TernVI]

Thanks for all the good points raised. We already have both solar and wind turbine, and by batteries "heavily discharged" I mean down to 60% capacity on the gauges.

The recent Splitter is an Argofet which does away with the drain caused by diodes.

The present 70A alternator will start charging heavily discharged batteries (60% capacity) at about 40 Amps, quickly dropping from about 20 Amps after an hour or so. There has been a big improvement in charge rate after installing the Sterling regulator but I'd like to improve still further. I'm told that the Sterling regulator has a "soft start" which increases the load on the belt gradually when the engine is started. Reported elsewhere is that a standard V belt will not slip because of this feature.

Without wishing to reduce our power consumption, the aim would be to reduce the time spent using the noisy engine. Is a 120A alternator the way to go?

40A is roughly C/10, so if your batteries are really down at 60% SOC, this suggests only about 13.4V is getting to the batteries.
If you could confirm voltages at the batteries you might get a clearer picture.
I tend to trust directly measured voltages much more than SOC indications.

It ought to be feasible to do some bulk charging at C/5, or a tleast maintain better than C/10 up to more than 85% SOC.
You could look at whether the Sterling regulator is achieving anything.
An alternator upgrade might be the way to go, but as others have said, it's very demanding on the belt, particularly at low RPM.
Does the current improve if the engine speed is increased?

It's easy to get more current out of a 90s-era car alternator (assuming the belt can get the power in!), but cooling it can be an issue on a boat installation. The alternator may reduce current as it heats up in the engine box.

 

[PaulRainbow]

Thanks for all the good points raised. We already have both solar and wind turbine, and by batteries "heavily discharged" I mean down to 60% capacity on the gauges.

That's still a lot of power, unless you are sailing for a very long time.

The recent Splitter is an Argofet which does away with the drain caused by diodes.

It has a lower voltage drop than an Olde Worlde diode pack, but it's not zero loss. Check the voltage at the ArgoFET input and the battery terminals. You may be able to compensate fro some voltage drop with the regulator (i don't use Sterling regulators, so not familiar with its settings).

The present 70A alternator will start charging heavily discharged batteries (60% capacity) at about 40 Amps, quickly dropping from about 20 Amps after an hour or so. There has been a big improvement in charge rate after installing the Sterling regulator but I'd like to improve still further. I'm told that the Sterling regulator has a "soft start" which increases the load on the belt gradually when the engine is started. Reported elsewhere is that a standard V belt will not slip because of this feature.

Without wishing to reduce our power consumption, the aim would be to reduce the time spent using the noisy engine. Is a 120A alternator the way to go?

If the batteries will only accept 40 amps (as you say above) then you can put a 1000a alternator on if you want, it won't get any more into the batteries.

You could reduce power consumption.
Increase solar generation.
Fit more batteries (as PVB said, a bigger bank would take more amps)
Fit batteries that can take a higher charge rate.

Exactly what batteries do you have and what is the terminal voltage when the alternator is charging them ?

What solar panels, controller and charging voltages ?

 

[TernVI]

If the batteries will only accept 40 amps (as you say above) then you can put a 1000a alternator on if you want, it won't get any more into the batteries.
... ?

What the batteries will 'accept' is a function of the volts across them.
Get a bit more voltage across them, by upping the alternator voltage or reducing losses and the current will increase.
The battery maker may give advice on recommended charging rates, C/10 is not high for some batteries.

 

[PaulRainbow]

What the batteries will 'accept' is a function of the volts across them.
Get a bit more voltage across them, by upping the alternator voltage or reducing losses and the current will increase.
The battery maker may give advice on recommended charging rates, C/10 is not high for some batteries.

That's part of it, which is why i said:

"Check the voltage at the ArgoFET input and the battery terminals. You may be able to compensate for some voltage drop with the regulator

and asked:

"Exactly what batteries do you have and what is the terminal voltage when the alternator is charging them ?

What solar panels, controller and charging voltages ?"