Alternator upgrade or solar panel

[lumphammer]

For about the same sort of money I could either get an extra 100W of solar or upgrade the standard alternator on my beta 38 from 45A to 90A.

On my Moody 36 I've got 160W of solar at the moment and three 130AH batteries covering the domestic supply and a separate engine starting battery.

Where should I spend my money?

 

[robmcg]

Standard alternator on a Beta 38 should be 60amp.

 

[William_H]

The first question to ask is how much current your existing alternator is putting in to batteries. You need an amp meter to check. You may not get much more from a bigger alternator.
Solar panels are entirely dependent on having room to fit them. If you have room and need for more power when camping away from shore power then yes more solar if you have room. My guess is you need neither. ol'will

 

[PaulRainbow]

For about the same sort of money I could either get an extra 100W of solar or upgrade the standard alternator on my beta 38 from 45A to 90A.

On my Moody 36 I've got 160W of solar at the moment and three 130AH batteries covering the domestic supply and a separate engine starting battery.

Where should I spend my money?

I have a 35ft boat, 3 x 130ah batteries and 260ah of solar panels, during the Summer i am self sufficient with electricity. So guess where i'f spend the money

The solar panel will be charging all the time the Sun is shining, how long will the engine be running ?

 

[Pasarell]

I would go with solar everytime for the reasons mentioned above. The standard alternator on my VP MD22L was, I believe, 50AH. At some stage it was upgraded to a Balmar 100AH but it still only puts out what the batteries can absorb (I have 550AH of domestic batteries) and I don't think it is any more efficient than the standard alternator would have been. Solar, on the other hand, is what really charges the batteries and keeps them up to standard

 

[lw395]

I think I'd look at the way I use the boat and ask how often each option would earn its keep.
How much time do you spend with the exixting alternator current limited rather than voltage limited?
Is the existing alternator charging at a high enough voltage?
What do you actually want from your electrical system that it doesn't do at the moment?

 

[Minchsailor]

I have a Beta 35 (basically the same engine) with a 100A alternator. 450Ah of batteries. The only time I get more than 50A from the alternator is a for a few minutes after I have been at anchor/on a mooring for a couple of days and been using the batteries (but I do have a windmill which gives out an amp or two in these circumstances, so batteries not completely knackered ).

Not sure the bigger alternator is worth it. If I had the room I would go for bigger solar.

 

[Bobc]

If you want better charging from the engine, buy a Sterling A to B booster rather than upgrading the alternator. It will make a BIG difference to what the alternator throws at your batteries (I have a 60 amp alternator and 675Ah house bank, and I go from 12.2v to full float in about 3 hours on the engine).

Otherwise, add more solar.

 

[TQA]

As Bobc says there is not much point in the bigger alternator unless you get a 'smart' regulator.

Having said that I would go for the solar option every time. But I sail when ever I can and avoid running the engine.

 

[DuncanHall]

I would beware putting too large an alternator on. If you only have lead acid batteries then you should probably not give them more than 50A. I have 3 130AH Trojans for which the recommended peak current is about 52A. If you have AGMs then you may benefit. If your Solar controller can take it I would add another panel.

Looking at what my 60A alternator actually put in last August I rarely saw much more than 40A I have a Stirling Alternator to battery charger so it may not benefit you significantly to have the larger alternator.

 

[Graham376]

As others have said, solar is the way to go. Unless you deeply discharge your batteries, the larger alternator isn't going to output more than you get now and running the engine just to charge batteries isn't a good idea.

 

[Balticfly]

I have a 35ft boat, 3 x 130ah batteries and 260ah of solar panels, during the Summer i am self sufficient with electricity. So guess where i'f spend the money

The solar panel will be charging all the time the Sun is shining, how long will the engine be running ?

They do different things for you. If you like sailing, add solar panels

 

[lw395]

They do different things for you. If you like sailing, add solar panels

I don't think it's as simple as that.
Sailing a long season in the UK, it's frequently valuable to be getting as much out of the alternator as you reasonably can. If you motor a lot, any old low power alternator will be fine. If you don't motor much, one which delivers all the current you want at lower engine RPM can make a difference.
TBH, I see it as a false choice. If you are struggling to keep up with your 12V needs, are you really going to choose one or the other? It's often more a case of how much solar can you easily fit and not have most of it shaded. Solar enables us to use the fridge on a summer cruise. Keeping up with the eberbasto in the winter, a good alternator with a high charging voltage (equiv to an alt to battery charger) also really helps.
Some people would do better to buy more batteries instead.
Others should get a more efficient fridge.

 

[Graham376]

If you don't motor much, one which delivers all the current you want at lower engine RPM can make a difference.

Agreed but, unless the existing alternator is working at its limits which is unlikely, just replacing with a larger one with same internal regulator voltage isn't going to do anything. Best increase is by adding an Adverc or Sterling booster to increase charging voltage.

 

[PaulRainbow]

They do different things for you. If you like sailing, add solar panels

The solar panels will charge the batteries whether you are motoring or sailing, the alternator won't work without running the engine.

 

[sailorman]

I have a Beta 35 (basically the same engine) with a 100A alternator. 450Ah of batteries. The only time I get more than 50A from the alternator is a for a few minutes after I have been at anchor/on a mooring for a couple of days and been using the batteries (but I do have a windmill which gives out an amp or two in these circumstances, so batteries not completely knackered ).

Not sure the bigger alternator is worth it. If I had the room I would go for bigger solar.

Try an Adverc, one has transformed my charging, i also have an Aerogen 6

 

[PaulRainbow]

I don't think it's as simple as that.
Sailing a long season in the UK, it's frequently valuable to be getting as much out of the alternator as you reasonably can. If you motor a lot, any old low power alternator will be fine. If you don't motor much, one which delivers all the current you want at lower engine RPM can make a difference.
TBH, I see it as a false choice. If you are struggling to keep up with your 12V needs, are you really going to choose one or the other? It's often more a case of how much solar can you easily fit and not have most of it shaded. Solar enables us to use the fridge on a summer cruise. Keeping up with the eberbasto in the winter, a good alternator with a high charging voltage (equiv to an alt to battery charger) also really helps.
Some people would do better to buy more batteries instead.
Others should get a more efficient fridge.

You do raise several valid points here.

My reply was to the OP in particular, in this case. IMO, if he adds the 100w panel to his existing panels he won't need to worry about any other charging methods during the Summer. His panels will keep up with his demands (unless he wastes electricity), regardless of whether he runs the engine or not.

But, as you say, this might not suit everyone, a lot depends on how they use the boat, what they currently have installed and where they keep the boat. I was recently asked to visit a boat and discuss fitting some solar panels. I discussed how he used the boat, what equipment they used and how they currently charged the batteries, as well as looking at what he already had. The boat wasn't power hungry, it lived in a marina, connected to shore power when not in use and the owner used it for day or weekend sailing. It had a good mains charger, but only 220ah of batteries, which were 10 years old. If he spent the weekend at anchor he struggled for power and had to run the engine.

He'd already said he'd fit a solar arch and whatever panels i though he needed. Solar arch, a pair of 100w panels and a Victron controller would see that he almost never had to run the engine for a weekend at anchor or use his mains charger. It would also see a hefty sum of money vanish from his wallet. The batteries were on their last legs, so they'd need changing too. For this situation i think the solar panels are not cost effective, or even needed. His battery box is big enough to take 4 x T105s. Leaving the marina with those 4 fully charged he's extremely unlikely to need to run the engine and would arrive back at the marine with the batteries not dangerously discharged, leaving them on shore power until the next weekend he uses the boat. He needs new batteries anyway, so it's only an extra £300-£400 to upgrade to Trojans. If he still finds a shortfall (which i very much doubt) we can add a couple of small flexible panels and the money for the batteries is still well spent.

There is no one size fits all.