Upgrade to Dual alternator on Mercruiser, Bad Idea?

[alldodge]

RT still look forward to those pics. From your post, I think your saying its wired as I mentioned in post 12 using a separate wiring setup and switch.

Same thing happens using and ACR, isolator or simple bat switch with one ALT, or as boat folks say, different banks

 

[RobertThoreson]

But wouldn't you want the redundancy on a boat? Ik alts fail on cars and trucks all the time. On a boat, in a storm when you need all you electronics going, wouldn't a fail alt cause alot of problems? The op asked if it was a good idea and I said absolutely. Don't get why you think it isnt? Wiring up another alt is definitely not hard.

 

[Shanestan]

WOW! Got some people talking about this! Awesome!.
Alldodge(AD) I would never hook two alternators to run in tandem charging the same battery. The only thing that would be in common would be the ground wire. I am going to be using the Blue Sea System Switch with ACR. If I see the need to add another switch I will.
Bruce, Using 115vac source, it says its 400w, w/amp draw @ 3.8 (heater or reverse cycle). The cooling cycle draws 2.5 amps. There may be an initial surge but I think it will be negligible.
Scott, What do you mean by "active battery management"? Thank you for the link to hydraulic steering. It seemed the way to go, read some good things about it and they make the cylinder to adapt to the "tiller". Not so sure now.
I at least got RT on my side.

 

[alldodge]

A unit which draws 400W and runs on 110V draws 3.8 amps. Same unit which runs on 12V will be 38 amps.

Formula to calculate is P=E x I (P= watt, E=voltage, I=amps)
To find amps I=P / E

For 110VAC 400/110 = 3.6 amps
For 12VDC 400/12 = 33 amps

The differences in the numbers does not take into account friction and other circuitry (such as thermostat and such). When a inverter is used there is additional loss due to converting 12DC to 110VAC. The rule of thumb is to divide watts by 10, so 400w = 40 amps

 

[Shanestan]

AD, so what Bruce and you are saying is that the house batt would have a 12vdc 40 amp draw at a minimum from the inverter to provide 110vac 3.6 amp to the air conditioner? I really need to brush up on my electronics. Thanks for reminding me about power conversion formula.

Edit. Holy crap, I should have known better and I do. When stepping up or stepping down voltage, current is inversely proportional. I know i over simplfied that.

Still all the reason to have a second alternator. I would mind running the engine to keep batteries charged while i enjoy myself at sea making boat drinks and listening to the radio while watching the Blue Angels fly over in formation.

I've looked in other forums and did a search here without finding much on the subject which is why i have raised the question.

 

[alldodge]

AD, so what Bruce and you are saying is that the house batt would have a 12vdc 40 amp draw at a minimum from the inverter to provide 110vac 3.6 amp to the air conditioner?

Yep

 

[Silvertip]

It appears you have not considered the factor of "10" when figuring current draw for any device you connect to the inverter. Connecting a device that draws 350 watts of 115VAC to the inverter OUTPUT (roughly 3 amps) requires that you INPUT 30 amps at 12.6 volts DC. That's a pretty stout load and will flatten a group 27 deep cycle in less than three hours. Three batteries would be dead in less than 9 hours. And that does not consider the draw from the microwave, fridge, the other stuff you mention and the losses impossed by the inverter itself.

 

[bruceb58]

85% efficiency at best with an inverter and it better be a pure sine wave one if you are driving a AC

 

[Scott Danforth]

Running AC requires a generator.

Active battery management is a multi-bank battery charger/maintainer that keeps your batteries up to snuff separately.

 

[Shanestan]

Okay I am waving the white flag and surrender. I will settle for a generator and quit perusing a dual alternator system. Thanks for the input from all who responded.

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