Upgrade to Dual alternator on Mercruiser, Bad Idea?

[Shanestan]

In my restoration of my cuddy cabin, I am completely making over my electrical system. Several of the upgrades include adding AC system, microwave, TV, stereo system that will all be using 110 vac. This will also include an installed refrigerator, water heater and some service outlets for small stuff.. I just don't have the room or budget for a generator, but I found an 2000w marine inverter that provides 110vac from 12vdc when out to sea and will also charge the batteries when connected to shore power. I plan on 3 batteries for the house bank and one for starter.
I think a dual alternator will work, since I will be switching over from power assisted steering (deleting power steering pump) to hydraulic. Anybody have any thoughts on this? The search function didnt yield any results

 

[bruceb58]

Why are you removing power steering?

 

[alldodge]

I plan on 3 batteries for the house bank and one for starter.

Think you have a single motor, but just incase

If this is a twin engine boat with only one alternator, then not a bad idea.

If this is a single engine boat and you want to add another ALT to the motor, then bad idea. I would just get a larger output ALT, but keep in mind the batteries can only take it so fast. If you were using AGM's they could take it a bit faster.

Don't see your batteries lasting long if you start pulling some heavy loads.

 

[Scott Danforth]

agreed, simply get a good high-output (single) alternator. you wont need anything larger than 100 amp alternator. you will need to change your alternator cables

if it wasn't a boat, they make alternators that have a 300 amp output that you can also use as an A/C generator or a welder.

if your running A/C, you will need a generator, or you will need to run your motor to keep up. the A/C will pull more than that 2000 watt inverter would handle. not to mention the 2000 watts is a peak (intermittent ) rating. The batteries will not survive the high current draw for a long period of time

I wouldn't remove the power steering.

 

[RobertThoreson]

Honestly I don't see any problems with duel alts. I run duels on every one of my 5 trucks and two tractors. Even if you didn't need the extra output available, the fact that one could leave you stranded if it fails and it's nice to have a spare

 

[Shanestan]

Bruce,
I'm ditching the steering cable and going with SeaStar Hydraulic.

Alldodge,
Thanks for response but not seeing the reason for the bad idea. What makes it bad? And its a single engine.

Scott,
The AC I will be using is small and would draw about 300-400w max. Max btu I'm looking for is around 6000. Here is on on Ebay that is 4200 BTU that draws 320w for cooling and 430 for heating.

http://www.ebay.com/itm/4200-BTU-11...tioning-Unit-w-Control-and-pump-/231628969593

Here is another that is 6000 BTU and would draw 650w.

http://www.ebay.com/itm/6000-Btu-Ma...heating-systems-115V-AC-Control-/200784427887

I guess that I should say that one alternator would be for the start batt. and the other would be for the house which would have two~three batts in parallel.

 

[bruceb58]

Do you realize that 400W is going to be around 38 amps?

 

[bruceb58]

Isn't the Seastar system for outboards?

 

[alldodge]

Thanks for response but not seeing the reason for the bad idea. What makes it bad? And its a single engine.

Two ALT's on the same motor should be separated from my way if thinking. One ALT will be sensing the out put of the other and frankly I don't know what the mix would do, but I'm leaning toward a current loop. If a current loop is made it may melt things

On a twin engine setup, each ALT charges one start and one of them charges a start and house, they don't put the two ALTs together.

 

[RobertThoreson]

That is what he said he wants to do, one for his cranking battery and one for his two cabin batteries

 

[alldodge]

Thanks RT, overlooked the last line

So I will revise and say don't connect them together while the motor is running. Would also reassert to post 3, and just get a higher output ALT

 

[alldodge]

Should also add, need to add wiring from the second alt to the battery, do not use the key ignition switch to power on both ALT's, going to need another switch,

Bruce is the guy which would be better equipped to answer, that is unless RT can advise how its wired on trucks and tractors

 

[RobertThoreson]

It's simple, I'll try to post a pic. I'll draw both 1 wire and the older style

 

[RobertThoreson]

Ok, j got it drawn but can't get it to post. I checked google and they have images. I'll post a link

 

[RobertThoreson]

http://www.chargerr.com/Alternators/ALT.HTM


This is a great site for the older type. Just make sure you put ether a resisted or a light in where they call for one.

 

[Scott Danforth]

I must have designed at least 5 or 6000 diesel engine installations. Never once did a twin alternator. The complexity is not worth any of the percieved benefits. A battery isolator with a high output alternator is the simplest. Active battery management with a single alternator is the most robust.

Seastar hydraulic steering are for outboards or inboards (rudder), not I/Os unless there is something new I'm not aware of.

 

[alldodge]

http://www.chargerr.com/Alternators/ALT.HTM


This is a great site for the older type. Just make sure you put ether a resisted or a light in where they call for one.

RT your link is for a standard single three wire ALT install. The light is there so it the ALT shorts out then there is a ground and the light will light. This is the setup for just about all boats other then the light. I thought you would show us how your Trucks and tractors were wired up using two ALTs

 

[Scott Danforth]

Here is some reading on seastar on I/O's. http://forums.iboats.com/forum/engi...540494-mercruiser-power-to-hydraulic-steering

 

[RobertThoreson]

It's basically the same in the trucks. I have the factory set up then I take a second alt, make a bracket to mount it where the ac pump goes. Then wire it just the same as factory. That way I can run all my lights, wenches, and compresses off a separate battery. I do this to keep from relying on just one battery/alternator. Tractor field work sucks when you have no lights

 

[RobertThoreson]

Just like having the backup.