Altenator Charging 2 in parallel? Bad?
 

My boat is set up like So:
I have 3 switches one for each motor, and one for genny.

1 Bat for just the genny on its own switch.
1 bat connected to position (1) on either engines switch.
1 Bat connected to position (2) on either engines switch.

So when running each motor is charging its own battery.


I am going to add a battery to Position (2) connecting 2 group 27's in parallel for one big house battery.

Will the port alternator charge both battery's ok? i know slower, but will it hurt the alternator?

it will charge both batts....only issue you may run into is if one of the battery's has a bad cell...it can drain and ruin the other batt its connected to....i would install a battery isoaltor and let it do the switching between what ever battery need to be charged.

I personally like the alternators to only charge the starting batts and only charge house deep cycle batts off of shorepower.

While this is fine the charger will do that. when at a dock.

but lets say you run somewhere and anchor for the day, and the house is on the 2 27 tied together.

I have a battery to start the engines off of. but why would you not point one of the engines back at the set and let them get some juice that the motor provides?

the other motor is plenty for the other starting only battery.

Or what happends if you point BOTH motors to the same battery/batteris (when tied) does this help? or hurt?

It hurts, one alt will always be stronger then the other no matter how exact they are built...and it will back-feed the other one and eventually ruin the regulator inside and you will need to buy an new alt or have it rebuilt....
Not to say that it cant be done...but you get into different things like blocking diodes, voltage sensing equipment or battery isolators etc....

Good to know, thanks fort he input. I expected that but have to ask when talking this subject, and thinking of all the possibility's.

What about adding a battery combiner? I don't know how difficult it would be with the twin engines..

I've been reading alot about this lately, as I plan to add a 3rd battery to my rig. I currently have 1 battery for each motor.

I'm going the Blue Seas ACR route. ...and after doing some reading, that would be my suggestion to you, as well. About $80, a battery, and some 8g wire. Simple install.

What Charge Sources will an ACR work with? An ACR will work with all charge sources, including an alternator, AC charger, or solar panel. However, low current charge sources might not produce the voltage rise required to force the ACR to combine.

this would be bad in a float mode.. then you have one hot bat, and one not hot bat in parallel.


These are more of a smarter isolator. which is great when you want to keep one battery up and let your stereo or what ever kill the other one. But in my application. I want both batterys to function as one, all the time. ONE BIG Battery. if i kill it, thats still fine. i can charge it, I still have a separate starting battery that I can fire up with on both motors, and another battery that will start the genny and then the battery charger will charge all 4. but when sitting for a day, and night that one big battery needs to be ONE so it keep going for the fridge and stuff. the ACR would disconnect the second battery from the stuff I have it connected to in the first place as soon as it started seeing the voltage drop below a point, then its saves the other battery. I dont want to save it. i want them to die together, a LONG slow death haha.

if you want to run all the batt's as one big unit then I would check into something like this:
http://www.balmar.net/centerfielder.html

it requires external regulators on the alt's but then you can run all the batt's in parallel and the centerfielder would regulate how the Alts work in the charging mode....
I would still have one battery on a switch you can separate from the rest to have as a backup..

I dont want to run ALL my battery's as one. just 2 (of the 4) for a house bank. the other 2 will be seprated, one for genny, and one for starbaord motor.

and I dont NEED to combine the 2 altenators on one bank, I just wanted to know if this could cause damage. and it can from the responses.

From your original question....yes...it will hurt the alt if you run both together charging at the same time.
As far as adding another battery, you can set it up in parallel.... but like I mentioned before...IF one of the batteries has a bad cell develop....it can damage the other battery along with it so you could be potentially out two batteries at once. Not that it happens all the time but the potential is there....I think a smarter way would be to use a battery isolator for charging so the alternator is charging one battery at a time as they need to be topped off....and then add a 4th on/off switch between this new battery and the original one so when you need full capacity you can turn it on.
It just all depends on how much you want to invest in the setup. If you don't plan on keeping the boat for any length of time then I would just add the new battery in parallel and go buy some Wallymart batteries and change them out if they go bad....they have a decent warranty exchange deal for their batteries :D

Not trying to be a pain here. but I can take this both ways.

So for clarification.


2 battery's in parallel on one motor/altenator. will hurt not hurt the altenator, but if one battery dies, its going to take out the other with it.

2 alternators/motors, charging the same battery will hurt the alternators.



OR

are you saying that 2 batterys in Parallel will hurt the one alternator charging them?

:) :)

awesome reply Thanks for the clarification!

BTW, since you have the genny; it is tempting to run the genny when house batteries deplete and charge while still running the stereo.
This WILL burn up a battery charger. A buddy burns up a 40a charger every year running only a 700w Kicker amp. He gets it warrantied but that is pretty much abuse of the warranty because he is causing the failure. Most chargers try to use an ideal charge profile which is no condusive while a load is still on the battery bank.

A Power Supply like Iota or Kinetik can keep up with the draw and not burn up. http://www.iotaengineering.com/12vdc.htm
I know it was not the direct question but usually follows.........

That is a Very weird statement to me. As the boat is set up to use the battery charger with genny or Shore power. and while its charging you are using the boats electrical system, lights, stereo, vacuflush, what ever. the battery charger is what keeps the boat alive for ever with the systems running at the doc or what ever. so I think thats more of a VERY large draw in short bursts that the chager is not liking. he might could as a big Capacitor to help take the shock load off the battyer/charger.

If you put in one of these for your switching needs it will eliminate the possibility of a bad battery killing a good one.

http://www.bepmarine.com/home-mainme...lusters-manual

They have lots of configurations or you can put your own set up together. I have two of the single engine 2 battery bank clusters in my boat one for each motor and the house and starting batteries it charges. so if one of the banks gets below 13.4 or 13.8 volts it disconnects them, so they are only connected when being charge by and alternator or battery charger and you set it up so the starting battery is hooked up to the alternator so it always gets charged first. In practice they combine almost as soon as you start the engines at least for me. Ideally the start battery has no loads on it when off so you can never have a dead start battery and if for some reason it goes bad you can use the emergency parallel switch to start from the house battery.

I also have a blue sea systems remote switch which allows me to manually combine both house banks when I need the extra capacity when the engines are off.

http://www.bluesea.com/products/cate...ttery_Switches

So in my boat each alternator (80A) first charges its own start battery (group 27), then when it reaches the voltage setting of the voltage sensing relay (VSR) then it is also charging the two house batteries (group 24's).

For at the dock charging I have two dual bank chargers in the boat that charge all 4 banks at the same time, the VSR's do combine when they are on the charger but still works fine.

See I DON'T want it to cut off the extra battery, as stated, this was not my worry. I WANT the 2 in parallel to DIE TOGETHER. and charge together. like one big battery. all the time.

just wanted to make sure it was not a problem for the alternator.

I thought alternators did not like charging depleted deep cycle batteries? Is this an old wives' tale? Great info on this thread BTW.

I only run deep cycle batterys on the boat. and never had a problem.

not a problem for the alternator it will just take longer to charge two back up, but if you plug in when you get back to the dock that is irrelevant.

never had a problem either, the only alternator problems I had were from Eliminators ****ty rigging job pointing the air intakes right at the starboard alternator which here in the salt water meant if got a spray of salt everytime we went out, so I had to rebuild it yearly, the port never had an issue.

Yea I am not worried about it dieing really, as it sits now with only one house battery I am ok, and only SOMETIMES run it low enouhg that motor wont start. But I have genny and charger, and the whole extra battery and motor. i just want to make the house/port motor have extra capasity.

Sorry it seems foreign.
First consider the battery bank is depleted. He runs one large Kinetik but duals have similar or more capacity.
When batteries are allowed to run down to 11.5v and the HU/amps start to reset; 50% battery capacity or roughly 100a/hr depleted. The charger will do everything it can to push charging voltage to 14.5ish. It is also trying to monitor this state to provide an appropriate charge profile.
If the stereo continues to exert a load, in this case 50a+ transient (90a fuses) it is more than the charger can do to even keep up, let alone charge. Internal components WILL fail.
Using relatively low amperage, consistent pulls on charged batteries will take a long time, if ever hurt the charger. Starting the genny/charger at the beginning of the day will help relieve demand as for much of the time the batteries will at least remain charged but the constant fluxuation and negative net power will eventually damage a standard charger too.
As I stated however, many people wait til the batteries start getting low, then kick on charger while amped stereo is pushing hard (again late day usually = louder play).
This WILL damage a charger.

A power supply is built to identify the difference between charging profile and supplying power to the battery. It will say "hey, I can only give 12.9v based on draw so I will not even try 14.5". When the draw is reduced it will recharge the battery bank but will not go into full profile charge mode til is senses the major draw has stopped.
This does not mean you still might not trip a power supply but with a larger one and connected to batteries, this is highly unlikely.

Alt does not know the difference between deep cycle or any other type.

Good reading, as are the other 6 parts that would cover many other questions - http://www.bdbatteries.com/autosizing6.php

A larger battery bank will put excessive draw on the alternator if the battery bank has been depleted.
With average boat use this problem is compounded by two things. First, alt output is a function of rpm. Thus to achieve 90amps, the engine must be turning at least 3000rpm for example.
When you first fire up and idle to warm engine and leave cove for instance, alt is probably only putting out 1/3 that amperage, but it is still trying to push up to 14.4 volts. If the stereo still cranking as the party continues. this compounds the situation by placing further demand on limited output.

Alt will burn up its regulator or other diodes if there is too much difference in output vs draw. This is why in car audio, you see them adding huge 150-300a alternators.
Boats don't necessarily have to do this since much of their heavy output is with engines off but if motor is running, alt capacity needs to be factored. Many can get by bumping from a standard 70a alt to 110a and relieve the problem.

Boy, there is a lot of misinformation on this thread.

I have been rebuilding, repairing, and selling, starters, alternators, and batteries for about 35 years. I have retro fitted, designed and installed more charging, starting systems on boats, planes, cars, and trucks, than I can remember.

Following is a description of my system that I installed several years ago in my 42 Harley.

Boat has twin engines, a gen, four battery banks, and an on board charger/inverter. I use battery combiners between all banks with simple on-off battery switches for each bank. I also have one parallel bat switch between the two starting batteries, just in case. It is left in the off position under normal circumstances.

When the boat is plugged in to shore power, it will charge all four banks via the combiners, when one or both engines are running, it will charge all four banks via the combiners. When I am at anchor, I can start the gen and it will do the same. I frequently run the gen while under way, so the on board charger is operating, and both alternators are charging with no problems. Neither the alternators nor the on board charger will be harmed if ran at the same time.

Battery combiners when activated combine two battery banks in parallel. I stopped using isolators many years ago because they can ruin your alternator if they fail with an open circuit. They are also harder to install. Combiners are easier to install, and if they do fail in the open or closed condition, the worst that can happen is a dead battery.

I do agree that you should keep all of your batteries the same age if you can, but it's not the end of the world if you don't.

I have installed dual alternators on several applications. They do not have to be special, computer controlled, or a matched set, just hook them up and go.

I have never had a problem running multiple alternators to one battery bank. I have seen many problems with multiple batteries paralleled into one bank and sitting idle (not being charged or discharged).

It is true that the alternator generating the higher voltage will carry most, if not all the load. If the recharge current were more than a single alternator could live with - say a very large and very depleted bank - that alternator carrying the greater load could overheat. But the fact that a second alternator was also feeding into the bank would not make it work any harder.

Ideally I would have two banks, one for starting and essential loads and the other for a house bank. Use a 2 bank switch for each engine. Leave one engine and the generator on the starting bank and the other engine on the house bank. If the house battery is too discharged to start its engine, simply switch to the other battery. After all engines are started, switch one engine through "all" back to "house" to recharge the house bank. As already mentioned, using an automatic battery combining relay simplifies the process.

Never switch a working alternator to "off". The spike can kill it. But unless an alternator or regulator already has a problem (or there are other wiring issues, like a poor ground) it shouldn't hurt to combine them.