Downrating alternator from 90 to 70amp

[Peter]

Current alternator is a Presolite 90 amp alternator, approx 12 years old before going tits up. Been told this alternator is now not available by Presolite. But have been offered a Presolite 70 Amp as a replacement. They are other 90/120 amp alternator, although difficult to get alternator manufactor from suppliers, so dubious on quality etc. And quite like Presolite as been reliable items, to include stater as well.
Question what are the issues in downsizing the alternator apart from the obviously taking longer to recharge, 500amphr battery bank.

How is charging regulated (external device or standard inside alternator)? Standard, not a fan of adding addition bits to equipped
Type of useage (liveaboard, odd weekend sailing etc.). Liveaboard, but have 660 amp solar as well. So don't use engine to charge apart from when motoring
Type of batteries you have fitted. Lead acid, Trojan
Where do you sail (UK or extremely hot area). Hot, southern spain, med
Engine room ventilation (good or poor) average going poor

 

[Mistroma]

You would probably need to provide more information.
e.g.
How is charging regulated (external device or standard inside alternator)?
Type of usage (liveaboard, odd weekend sailing etc.)
Type of batteries you have fitted
Where do you sail (UK or extremely hot area)
Engine room ventilation (good or poor)

The normal built-in regulator will probably only result in quite a low charging current for a relatively short time and not be a huge problem. Possibly only 40-45A.
An external regulator will result in a higher charge current.

High temperature due to poor ventilation and/or high ambient temperatures will stress an alternator more.

Lifestyle will affect length of time spent charging. A liveaboard may be easier on an alternator than someone who spends every weekend on board, it all depends on kit fitted. A huge solar panel will avoid the need to spend hours using the engine to charge.

Lots of variables to consider but there's a pretty good chance that the smaller alternator will have a decent service life (especially if it is hot rated and the larger one wasn't). I'm assuming it is likely you don't have a lot of solar, not a liveaboard, sail in UK and have lead acid batteries (i.e. nothing exotic).

 

[yotter]

Peter,
I got a Prestolite alternator from these chaps in Plymouth. The 90A model was discontinued, but they did the 100A model for the same price, around £145 I recall, worth giving them a call? They dispatch by courier very quickly. No connection.
Angus

https://www.startermotor-alternator-store.co.uk/

 

[PetiteFleur]

Have you considered getting the alternator checked out by a suitable firm and getting it repaired? Try a car electrical repair firm locally. May be cheaper than a new alternator.

 

[Sandy]

Peter,
I got a Prestolite alternator from these chaps in Plymouth. The 90A model was discontinued, but they did the 100A model for the same price, around £145 I recall, worth giving them a call? They dispatch by courier very quickly. No connection.
Angus

https://www.startermotor-alternator-store.co.uk/

They are fantastic people to deal with. With the boat in Plymouth I've got the advantage of visiting the shop.

 

[pvb]

The Prestolite alternator is excellent quality, and spares are available, so I'd get it fixed rather than downgrade the charging current capability.

 

[yotter]

My local repair man in Paisley near Glasgow, tells me that a Presolite is actually a Bosch, he reckons they are pretty robust, so I agree with other posters, get it checkout/repaired, before further action.
Angus

 

[pvb]

My local repair man in Paisley near Glasgow, tells me that a Presolite is actually a Bosch, he reckons they are pretty robust, so I agree with other posters, get it checkout/repaired, before further action.
Angus

He's completely wrong.

 

[KompetentKrew]

Peter,
I got a Prestolite alternator from these chaps in Plymouth. The 90A model was discontinued, but they did the 100A model for the same price, around £145 I recall, worth giving them a call? They dispatch by courier very quickly. No connection.
Angus

https://www.startermotor-alternator-store.co.uk/

These guys are amazing - they have a couple of different locations and internet sites, so I'm not quite sure how they're organised (partners or a family business?) but I stopped for a chat when walking past their shop last winter and the bloke was so helpful.

If you live near I'd just take a couple of pics of your engine and take your alternator in. Otherwise phone them for a chat. Really they're the best kind of business.

 

[Boater Sam]

Prestolite have their own mobile repair van, try ringing them.

MAdams@prestolite.com
07771978746

Damn good alternators.

 

[Peter]

Anyone reccomend a overhauler in southern Spain/Portugal, around Ayamonte?

 

[Spirit (of Glenans)]

Anyone reccomend a overhauler in southern Spain/Portugal, around Ayamonte?

Try googling :
"auto electrico"
"reparacion de alternadores (y motores de arranque)"
These are the most useful looking results, but I can't vouch for either of them.
Taller de electricidad de vehículo en Ayamonte | PÁGINAS AMARILLAS
ᐅ Hospiauto (Huelva) - Tallermecanico.org
"Taller" is the word for a workshop, there seems to be a few of them on Calle Gibraleon.