Can I charge 1 battery from 2 engines???

[Any_Weather]

Gday guys, just interested in your thoughts regarding twin engines charging one battery? I am about to get a boat built that will have twin engines so my thinking was I would have a start battery for each engine and then a house battery for the rest. Is it possible to have both engines connected in such a way that when the start batteries are fully charged, the excess charge goes into the house battery? If I had a 120 amp hour house battery and was drawing a max of 10amps per hour, I should in theory get 12 hours of run time yeh? If I am charging this battery with 2, 40amp alternators, it should charge in 2 hours of run time yeh? If this is all possible it will eliminate the need for me to have a solar panel. Is my 10amps reasonable assuming I run a GPS and a radar and a sounder for most of the night and then a few LED lights as well?I was thinking a Glass Mat battery as the house as the house battery and normal marine batteries for the start ones?I am getting the boat wired professionally but I am just trying to get my head around the battery situation before I get in too deep. Any other ideas on batteries and charging systems is greatly appreciated. Thanks for your thoughtsLee

[scottar]

Not 100% sure but the two charge circuits may interfere with each other. Check with your engine supplier as they will be the ones deciding on warranties if the charging outputs toast each other. The other option would be 2 smaller house batteries. Means a bit more cost - additional vsr if you are going to use them and a bit more for batteries & switches, but would also allow extra redundancies.


I like the AGM's personally. I used them on my last boat. One of them was seven years old when I sold it and still going strong. I used them for everthing but it was only a 40hp so it started easily. Maintaining batteries is a pain on a lot of boats due to lack of space so I would be looking at their location and maybe even using them for starting batteries as well if they are hard to get to and the AGM's will do the job CCA wise.

With your power consumption figures, it will depend on what gear you are fitting. Some of the new electronic gear available these days is quite power hungry. Your electronic supplier should be able to give you power consumption figures for the sounder/gps/radar, add a couple of amps for radios - more if you have the stereo pumping, a few amps for the bait tank pump if you have one, and a couple of amps for minimum lighting.

[Any_Weather]

Gday Scott, cheers mate, I hadnt really thought about 2 smaller house batteries but yes I guess this could be an option. I hadnt really thought about the charge circuits interferring with each other, I guess I was more concerned about too much charge frying the battery but you do have a valid point.
How do any of you other guys with twin engines go about charging batteries and how many batteries do you generally run?

Lee

[Chimo]

Lee and others

Yes you can. That is how mine is set up with and Auto Battery Coupler (ABC) managing the connection between the motor battery and the house battery. Can also connect both motor batteries together, a feature that has been used once when one motor battery failed so that motor was started by the good battery and then the link was undone and the good battery started its motor and off we went with two operating motors. Handy to have that link

Dont know where you are but the guy who wired mine up is mobile and knows his stuff. He also makes the ABC

Cheers
Chimo

[scottar]

Chimo is right. There is aftermarket hardware available to do what you are talking about. There are reported cases of people frying charge circuits as well by simply hooking it up without said hardware. It can be done simply by using VSR's and blocking diodes but the house battery will only ever charge to 0.6 volts below where it should be. I wouldn't be concerned about 80 amps total output frying a battery unless a regulator failed. A standard 4wd altenator is usually 100.

A lot of the cats I have worked on over the years are set up with 4 batteries. One bank is a starting/house bank either with a standard battery switch or a VSR. The other is a start bank for the other motor using a switch. There will then be a third On/Off type switch that is used for parralleling in the case that the bank on one side has failed. This system can be set up with 3 batteries as well but as you had thought about already, you are only ever charging off one motor for the house bank under normal conditions.

[Any_Weather]

Cheers guys, great info. At least I now know it can be done if given to the correct people to do.
thanks again
lee