12volt alternator and 24volt starter

[Bodach na mara]

While the arrangement sounds odd, it makes sense when you know how Westerly powered the larger boats in their production line at that time. The 31 footers (Renown, Longbow, Berwick and Pentland) were either fitted with a Volvo engine (and have probably been re-engined) or the Watermota like yours, in which case they are porbably happily running the original engine. The Sea Panther in the 31s had the 12 volt starter hit by a 24 volt starter battery bank, but also a 24 volt alternator to charge it. They carried a burden of four batteries, two to each bank! The weakness was that, to get a 12 volt supply for the electrics, they just tapped off the one battery in the domestic bank. This left the other as a sort of voltage dropper, which it did not like. My solution to this was to utilise 24 volt equipment for as much of the load as possible (fridge, central heating) and power the rest via a DC to DC convertor.

The long term solution to your problem may be to go the same way. Replace the charging system with a 24 volt one. In the short term, there is no easy way to re-connect the batteries in parallel, while ensuring that they can deliver the current to the starter. I did consider a changeover switch (2 pole 2 way) to parallel up my domestic batteries, but the switch needed to carry only the 30 amp charging current, and even that was going to be hard to find and expensive.

I hope this makes some sense and helps you. Electrical problems can ruin a cruise.

 

[ccscott49]

Somebody is not reading the other posts! /forums/images/graemlins/grin.gif

 

[ccscott49]

Somebody else is not reading the other posts! Jeeze! /forums/images/graemlins/grin.gif

 

[Gunfleet]

If my engine wouldn't start without heaters summer or winter I would get the head overhauled. Diesel engines rely on pressure. I've just done the same job to my formerly reluctant Yanmar. Now it starts as soon as you touch the button.

 

[brianrunyard]

[ QUOTE ]
Somebody is not reading the other posts! /forums/images/graemlins/grin.gif

[/ QUOTE ]
Oh yes I did.
It's just that so many others hadn't and they were suggesting changing to a 12v starter, that I thought it worth repeating that it was a 12v one.
But if it offends or upsets you, I appologise.

 

[cliffordpope]

Is a pre-heater the device I remember on the air intake of an old Perkins engine? It was an electrically-heated wire gauze onto which diesel was dripped for 10 seconds until nicely smoking, and then the engine turned over. Could one of these be fitted, and then the starting voltage reduced to the correct 12v with the existing starter?

( in very cold weather the system could be boosted by lighting the gauze with a burning rag while turning the engine over.)

 

[claredelune]

Westerly Centaur for sale. one careful owner and two new batteries!

Just to confirm is it a 12 volt starter?!!

I will try the 12volt to start and let you know. Engines can get 'used' to pre-heaters like the dreaded cold start spray.

The thought of some of my crew holding a burning rag on let alone in the boat scares me. The alcohol fumes would be a leathal combination.

 

[claredelune]

12v hardly turned the engine.

 

[ccscott49]

stick with the system you have obviously worked before, why repair something that isn't broken?

 

[claredelune]

the solution is a simple one. Keep the set up as it is but replace the solinoid that links the two balleries into 24volt with an isolator switch. Fit another isolator switch to connect the 'free' earth of the second battery to the engine earth. Throw one key away so that both switches cant be closed at the same time.

Simple.....

 

[VicS]

Good idea but only half way there. You'll need to switch the positives of the two together for charging as well unless you use a diode splitter but then you have to overcome the voltage drop the diodes cause. That can be done by a simple mod to the alternator to make it generate 0.6v more.

Ive got the details that SBC posted a while back but I dont think I've got the link.

It is still going to a pita having to manually switch over from 12 to 24 volt mode but better than having to physically swap batteries about .