Alternator, fitting more power

[christophert]

Good afternoon all. I'm hoping someone can help. I believe my alternator has passed away so I need s new one. It is,was, a 70 amp, receipt from fitting in 2014 shows Alt 6039 alternator A127 R/H 12 volt 70 amp. 

My batteries,  X 3, are fine still and they are-

Exide er 650 142 AH 12v  

My relay is - Durite 120 amp 

Battery charger is Waeco Perfectcharge IU1512

(I believe this is suitable for one leisure bat only.)

 I'm presuming for my battery bank the alternator is/was not powerful enough to charge the bank,  (I'm aware it would if engine left running for s very long time.)

I was thinking a more powerful alternator but not sure what to go for. I will be replacing the battery charger which is good when when on shore line (24/7) but not up to it when out on the canal and using generator to power it.

I hope people can help.

Regards,

Sean

[Alan de Enfield]

 

You could replace it by a 90 amp, or even 100 amp but any more and you are likely to need to start replacing pulleys for different contoured belts.

 

Without investing in all sorts of electronic wizardry you will get very little time saving in recharging you batteries with a 100amp compared to a 70 amp as the batteries control the charge rate and after the first 20-30 minutes charging at high currents they demand that the alternator reduces the current to (example) 50 amps, then 10 minutes later to 30 amps, then 30 minutes later to 20 amps, and then progressively lower and lower currents to around 2 or 3 amps.

 

It will take many hours to get from (say 85% charge to 99.9% charge) and that is because the battery is demanding a smaller and smaller current. This will not change if you a 70 amp alternator or a 700 amp (exaggeration) alternator.

 

This is a funtion of ALL Lead Acid batteries - spend £5k on lithium batteries and the whole thing changes.

 

Suggestion - replace your 70 amp like for like and invest is 300 watts of solar.

Run your engine for the bulk-charge in the morning for (say) 1 hour and let the solar 'trickle' charge the batteries for the next 12-15 hours*

 

 

*This will work in Summer time but you will need extended engine or generator time in the Winter.

 

Edit for spooling errurs

Edited October 11, 2021 by Alan de Enfield

[Tony Brooks]

Here we go again. Simply fitting a higher output alternator will NOT make a significant difference to the overall fully charged time. It may make a small difference to the charge to 80%  time.

 

That and your perceived charger problem are a result of the way lead acid batteries charge. After the first half hour of charging on a tolerably well-designed  system it is the batteries that control the charging current and not the alternator. From that point onwards, the charging current starts to drop until it is only a few amps towards the batteries being fully charged.

[Alan de Enfield]

11 minutes ago, christophert said:

 I'm presuming for my battery bank the alternator is/was not powerful enough to charge the bank, 

 

My 70amp alternator was quite happy charging my 6 x 230Ah batteries.

[Tony Brooks]

1 minute ago, Alan de Enfield said:

 

My 70amp alternator was quite happy charging my 6 x 230Ah batteries.

 

As was mine, charging 430 Ah of batteries via a split charge system. Nothing wrong with the system, it's users realistic expectations that need addressing -  - - - - - - - unless he changes to Lithium batteries.

[Alan de Enfield]

Just now, Tony Brooks said:

 

As was mine, charging 430 Ah of batteries via a split charge system. Nothing wrong with the system, it's users realistic expectations that need addressing -  - - - - - - - unless he changes to Lithium batteries.

 

It is always difficult explaining to people with little knowledge of batteries that if you need to put 70Ah into your battery, that, running your 70 amp alternator for one hour will only 'put in' a fraction (maybe 25%) of what is needed - you get :

 

It is a 70 amp alternator there fore it must put in 70 amps.

 

Hopefully repeated spreading of 'the word' will help to increase boaters knowledge.

[christophert]

Thank you all for sharing your knowledge.  I was informed that a higher amp alternator is better as you do not need the engine running for longer periods. It seems I was misinformed.

[nicknorman]

Fitting a larger alternator gives diminishing returns because after initially speeding things up, as the batteries become more charged they take less and less current. That lengthy period of getting a battery from fairly well charged to fully charged, will take just as long. There is also the issue of how to drive the alternator. A large alternator presents a large mechanical load that cannot be dealt with by a conventional V belt. It depends on the pulley setup / how much belt wrap there is on your alternator setup, but the general consensus is that about 90A is the maximum to reliably drive from a V belt.

 

It might be worth looking at replacing the alternator with similar, but fitting something like a Sterling A2B or Adverc alternator controller thingy. These result in a significant reduction in time for the mid-charge phase.

 

As you say, a 15A charger is fine for permanent mains connection but insufficient for charging with a generator. But of course whatever charger you get has to be able to be powered by the generator, with some margin for surge load, so it depends on what generator you have.

[Tonka]

Do you have to consider what the wiring can take  ?

 

 

[Alan de Enfield]

19 minutes ago, Tonka said:

Do you have to consider what the wiring can take  ?

 

 

 

Which wiring ?

[christophert]

26 minutes ago, nicknorman said:

Fitting a larger alternator gives diminishing returns because after initially speeding things up, as the batteries become more charged they take less and less current. That lengthy period of getting a battery from fairly well charged to fully charged, will take just as long. There is also the issue of how to drive the alternator. A large alternator presents a large mechanical load that cannot be dealt with by a conventional V belt. It depends on the pulley setup / how much belt wrap there is on your alternator setup, but the general consensus is that about 90A is the maximum to reliably drive from a V belt.

 

It might be worth looking at replacing the alternator with similar, but fitting something like a Sterling A2B or Adverc alternator controller thingy. These result in a significant reduction in time for the mid-charge phase.

 

As you say, a 15A charger is fine for permanent mains connection but insufficient for charging with a generator. But of course whatever charger you get has to be able to be powered by the generator, with some margin for surge load, so it depends on what generator you have.

Thank you. The generator is a bit excessive. It's a 3 cylinder 1100 cc ! 

8 minutes ago, Alan de Enfield said:

 

Which wiring ?

That's why I'm on here, trying to get my head around it all 🙂

[Tonka]

13 minutes ago, Alan de Enfield said:

 

Which wiring ?

between the alternator and the battery

[Alan de Enfield]

5 minutes ago, christophert said:

That's why I'm on here, trying to get my head around it all

 

You asked the question about 'considering the wiring' - are you referring to the wiring from the alternator to the battery / split charger / batteries, or the wiring from the battery charger to the batteries ?

 

The wiring from the alternator the 'big thick black one' will be fine is you replace the 70a alternator with another 70a alternator, and, probably OK if you so decide replace it with a 90a alternator (but do not understand why you would)

 

If you replace the battery charger with a bigger one then you will need to use wires suitable for the current of the new charger AND sized to prevent volt drop and that can only be determined by the distance of the charger from the batteries, and the current rating of the charger.

 

For example a 50 amp charger should be wired using 16mm2 but if the charger is some distance away from the batteries, and you still want 'maximum' voltage to get to the batteries you may need to go up to 25mm2 if your battery charger is 5 metres from the batteries.

 

 

[Eeyore]

15 minutes ago, christophert said:

Thank you. The generator is a bit excessive. It's a 3 cylinder 1100 cc ! 

That's why I'm on here, trying to get my head around it all 🙂

3 cyl 1100cc diesel?

Just put a additional split charge relay between the generators battery charging alternator and the domestic bank and run it in parallel with the existing mains charger. That will speed up the bulk phase a bit without excessive expenditure.