Battery Usage

J

jmeirhofer

Active member
Member
Joined
Jan 3, 2009
RO Number
30972
Messages
2,127
Any reason why you can not use one battery for both motors?

I currently have two 8D batteries. One of each motor and of course the alternator on each motor charging these batteries or the battery charger charging when they are not running.

One of the batteries is connected directly to the 12v house side. The other battery can be used via selector switch or even both can be used.

I have considered separation of the motor and house batteries completely. My intention would be to use one battery for both motors for starting. At the same time one of the motors alternators would charge that battery when running and of course the charger would maintain that battery.

A second thought I had would be to use two (one for each motor) group 27 batteries (1050cca) with a ACR like the blue seas unit to use the one alternator to charge both. My thoughts about using the two smaller batteries was the lifting of them 6' to the cockpit is easier for my old back.

For the house I would use the second 8D and another for 2 - 8D on the house. I would also add a higher capacity alternator to the other motor to charge these batteries while underway since these would have a deeper discharge. And of course the charger would maintain them when on shore power or genset.

of course I would leave the selector switch so that should it become necessary I could combine the batteries to start the motors.

I currently have the two 8D in the center bilge. Probably room for two more in there. Or two group 27 and three 8d. It does make it easy to service them.

The last part of this is my thruster and windlass. It would seem prudent that they have their own battery. There is 4/0 cable running forward to them and even a shut off for the thruster in that space under the bed. However, that seems like a lot of potential current loss with about 40' of battery cable running forward. It seems the only real option I have for placement of another battery would be in the anchor locker. While there is enough room in there for a couple hundred feet of chain and me, I think even the strongest battery box would be no match for the jostling chain. Anyone have any thoughts on this?

Of course it is all hypothetical for now since we will likely still have snow on the ground in May. lol
 
"Any reason why you can not use one battery for both motors?"

Brief discussion:

First, consider charging separately from usage. An engine could care less where it gets the juice for starting as long as the source can provide and maintain sufficient voltage at a large enough current flow to start the engine

So, given a strong enough source, anything will do, from the engine's standpoint. The "general rule of thumb" of "one start battery for each engine" is based upon redundancy and reliability. That is, in a twin engine vessel, should the port start bank be insufficient to start the port engine, you can start the starboard lump, then use the starboard start bank to start the port engine ( or vice versa ).

One other, ( imho, important, but less critical ) reason is that any "non-standard" wiring set-up will at a minimum irritate, and at worst, confuse, any mechanic who works on the vessel. Some may even try to "fix-it" which can be quite a problem. ( Do Not Ask... )

With those considerations out of the way, having a shared, dedicated stater bank is fine. But you must ensure that that starter bank can provide enough juice to reliably start two engines, both of which might be slow to start ( ie: cold weather etc ) Remember, you need to ensure reliability. So a minimum sized battery suitable of one engine would be too small to be shared for two engines.

Refer to the engine suppliers manual for your engines to help determine battery size. They often supply at least some info, and in my experience barely enough info to properly size the shared battery bank ( Drop a not to the eng mfgr tech support and ask. Who knows, they may provide useful info!!! )

But, back to generalities; a shared start bank, sized to provide three prolonged hard starts ( or more ) and with provisions made to have a strong back-up in the event of "issues", should work just fine.

I can throw out lots of battery suggestions, but you really need to go to the source ( documents and/or tech support ) to get a good answer. And since a minimum size bank will be worked very hard, consider "oversizing" the start bank for reliability and longevity.

-edit-

I'll bail out on the rest of the discussion except for a few comments. Thruste, imho, should be "locally sourced" with it's own bank, sized large enough to operate the thrusters reliably even during an extended operation cycle in the case of emergency.

House banks are sized based on house requirements ( time for research and spreadsheet ) as well as charger availability and cycling. It is a system and no one individual part can be altered without consideration of the rest of the system. Just remember to consider your battery's capacity based upon "95% charge to 40% charge" as being the the true capacity of the bank. Yes you can operate "deeper" but for longevity and reliability that is the range ( average; approximately ) you should plan on.
 
I like your idea. I would recommend the starting batteries be able to be paralleled just in case.

I understand your windlass / thruster concerns. However, do you really use them that much that it warrants the massive cost involved to install a separate battery system?
 
I had one group 31 battery isolated as a "start" battery only. It would start both engines and served no other purpose. It was charged when under way by one of the engine alternators and by one loop from the charger when on shore power or generator power.

My house bank consisted of 3 Group 31 batteries that were charged by the other engine alternator when under way and a loop from the charger when on shore power or generator power. These 3 batteries handled everything other than starting engines.

Worked very well. I liked always having a fresh start battery no matter how much house power I used up.

Bob
 
Bob, it sounds like you did pretty much exactly as I wanted to do. Sounds like it also worked as I envisioned.

Dave, I don't really use either very much. Especially with the thruster and that is only when maneuvering. But the windlass is something we hope to use a lot more of. And it is currently on the house bank. Seems like it would pull a quite a bit of juice from that bank but then maybe only when pulling up vs putting out. May not be much of an issue at all

Bill, I have checked the manual and with cat. The manual says 850cca and nothing more. The service tech I spoke with gave me the same answer, probably looking at the same manual. But he did add that really is not helpful information. I did not really consider and 8d for starting a minimal sized battery. Although I do question whether two gp27 would be sufficient. No real reason to change from the 8d for starting other than thinking of if I have to lift it out of there.
 
John, here's my 2 cents:

I personally think that if someone keeps an eye on their batteries via a good monitoring system (I have a Xantrex LinkPro), then having a larger house bank and modest starting bank is fine. I realize that's a long run to your bow for the thruster and windlass, but you're not using that many amp hours on those devices to justify another battery and charger. I also would just slightly over-size the starting bank over manufacturer's specs and make sure the house bank can be tied in to assist if needed. Cold starting diesels is difficult, but we're talking temperatures much lower than you'd be boating in!
 
John,

I use my windlass quite a bit. Granted it Is probably not as powerful as yours, but I see no degradation in performance after being on up the hook of long periods..

My situation.... If on the hook, gennie is running, Batteries are charging. Leaving anchorage, my bow is perpendicular to the rode. I'm only lifting the weight of the rode for most of the time then rode plus anchor for the last 20 or so feet. K
 
The best setup is for each engine to have its own start battery, incl genset(s) plus a house bank, but of course, there is theoryland and there is the realityland....

Second best would be a start battery shared by both mains, a dedicated genset battery and a house bank... Worst in my opinion is sharing a start battery with house loads.

For serious cruising and time on hook, dedicated start and house is what you need. If you only occasionally anchor out or always run on Genset then a single start and dedicated house is fine,
 
John, remember too, pretty much the only time you'll use either the bow thruster or windlass, the engines will be running and charging. I didn't have a thruster, only a windlass, and never saw any degradation at all.

The most power I ever used on the house back was the inverter powering my ice maker for evening beverages. :) as Kurt said, keep an eye on the monitor and all will be well.

But, I always slept better knowing that, no matter what, I always has a dedicated, fully charges start battery.

Bob

Bob
 
I agree, adding a battery system for the windlass might be a bit overkill.

I will be adding a link pro for both so I will have that covered. If I do choose to go with the two gp27 I do have a helm mounted combining relay switch. So when necessary they could be combined. I would also retain the battery switch that allows me to combine the house and motor batteries.
 
The best thing for you back might be to sh/t can the 8Ds and use multiple group 31s. Set up a bank of two for your starting bank, two or more for your house bank and two for your thruster bank. Then just install manual paralleling switches (or in the case of your starting bank a momentary paralleling switch) so if any bank goes dead you can switch in another.
 
I have a "standard" arrangement of two battery banks (each of which are connected to one engine) and a typical "Batt.1 - Batt. 2 - BOTH" switch. I have up-sized bank 2 to act as the house battery. I normally leave the battery switch in the Batt. 2 position to power the house circuits from this larger bank. When underway both banks get charged by the engines. If for some reason I were to unintentionally over-drain the house bank (and could not start that engine) I can always start the second engine, switch to BOTH and start the first engine.

Bottom line is I always have a dedicated starting battery which could be used on either engine; no special wiring was required.

Mike
 
Bill. I am right there with you on that one. Except that one 8d is three years old and the other I bought last year. But that is exactly why I want to use something smaller for the motors. One for each. I do,have the momentary parallel switch. My thought was to get separate smaller starting batteries now and when the time comes replace the two 8d with 5 smaller batteries.
 
I just talked the owner of a brand new sister-ship out of going with a LiFePO4 bank. Yeah, that might be the way of the future, but my boat (and his) can't charge a lithium bank with outboard engines. I caught some crap for it on the oowner's group because some guy who doesn't own the same boat claims "all the cruisers" are going this route. Really? If one of the 3.2-volt LiFePO4 batteries goes bad, where does one find a replacement in...the Bahamas...Bermuda....South Pacific..

Whatever you do, I suggest you "keep it simple, stupid". :-)
 
John last year I tied my two 8Ds together as my port /house bank and added a 3rd 8D as my starboard back of coarse I can select either bank as the house and I still have a parallel switch to bridge the banks if ever needed. I have not had a problem since the two 8Ds as a house bank has a huge standby stand while on a hook for the weekend. As many here know I like to run my generator a lot last year I ran it much less being my batteries never seemed to get low. I also replaced all of my bulbs with leds the year before which I'm replacing again this year with higher output no polarity sensitive bulbs.
 
Be careful when using different size banks connected to a two (or three bank) charger as you may have issues when charging on shore power.

There is really no reason to have a dedicated battery for the windlass.
 
Oh I replaced the charge as well. The charger has no issue with the different banks it can even handle different battery types in different banks and will charge them accordingly.
 
I went to a single dedicated start battery, an 8d. I see no reason in my system for a second start battery. I have multiple options including paralleling the house bank, as well as being able to hand crank the generator if needed. My alternators both charge my large house bank. My starting battery gets charged through its own multi stage charger supplied by the house bank, instead of a simple combiner. Since I only have one start batt, I ensure it gets charged on its own terms.

It took a lot of work to get reconfigured, but has been well worth it.

Key benefits was to make room for a larger house bank, the ability to significantly increase charge rate without fitting larger alternators while maintaining strict isolation irrespective of battery types and reducing issues related to differences in charge state.

The cascading charging also works well with my dc generator and inverter setup.
 
Thanks everyone for the comments. I think I have decided what I am going to do about it now. Of course I will have to wait until June for all the snow to melt first.
 
You must log in or register to reply here.
Back
Top