Alternator connection to batteries

[PAC3142]

I'm moving my batteries from the stern locker to under the aft berth to get more locker space, be able to add an extra house battery, and get weight out of the aft end. I'm taking advantage of this to improve the wiring layout, but I've hit a snag I'm having trouble finding an answer for.

Right now I have just one cable connecting the engine to the 1/2/both battery switch, so it does both power the starter and charge the batteries. I want to have a separate connection between the alternator and batteries and add an ACR, as in the diagram below.

My question is: Do I just disconnect the wire between the starter motor and alternator from the starter, and extend that back to the house bank bus? Is it that simple?

Engine is a Yanmar 3JH2E, Alternator is a Hitachi LR155-20. Photos show the alternator and starter, with the wire highlighted in yellow.

Thanks!
Paul

 

[LeslieTroyer]

Check out https://forums.sailboatowners.com/index.php?threads/1-both-2-off-switches-thoughts-musings.137615/

 

[seadaddler]

Yes I disconnected the wires from the starter to Alternator and both switch and have a fused heavy cable from the + side of the alternator straight to my batteries and just added a cable from a start battery for my Yanmar.
Nick

 

[PAC3142]

Leslie,
I've been through that chain many times, but there is nothing on what exactly happens at the engine.

Nick,
Thanks very much, that is what I needed to know.

Paul

 

[LeslieTroyer]

Alternator to battery connection - fuse at battery side 150% of alternator output. Starter to battery (with or without switch) optional (recommended) 200-300A fuse at battery. Fuses should be within 7 " of battery

 

[dlochner]

In one of Maine Sail's posts on his website or here, he mentions that OEM engine manufacturer's routinely attach the alternator output to the starter for a couple of reasons.

When the engine is running, by default the starter must be connected to the battery or it wouldn't start. This ensures that there is a load on the alternator when the engine is running.

Boat manufacturers like this arrangement because there is only one cable to run to the engine, thus saving money in labor and materials.

 

[jssailem]

Dave. True about the saving of money in the install. But as MaineSail has said it does nothing to help stop the Boat Owner from destroying his alternator when turning the 1/2/B switch to off while the motor is running.

 

[LeslieTroyer]

1-2-both is not the best choice for boats with big house and smaller start. Better is for the alternator to go to the house bank and use ACR or equivelant to top off the start battery.

 

[dlochner]

John,

Operator error is always an issue.

John,

Correct the alternator output is best lead directly to the house bank and fused at 150% of alternator output. Connect house and start batteries with an ACR or similar device.

OEM engine manufacturers are interested in not having warranty claims on their alternators. Hence the poor charging profiles of the Hitachis and connecting the alternator to the start battery.

 

[Stu Jackson]

Here's why:

OEM 1-2-B Switch Wiring History http://c34.org/bbs/index.php/topic,4949.msg30101.html#msg30101

Not sure what Hitachi alternators, connections to start banks and some other specious claims here are. Sure, it saves money, but surely doesn't help alternators by connecting the output to a switch! At all.

Here's why connecting to the house bank makes more sense: you can turn the bloody switch off when the engine is running and not hurt anything. How's that for simplicity and crazy brothers-in-law?

The Short Version of the 1-2-B Switch Stuff: http://c34.org/bbs/index.php/topic,5977.msg38552.html#msg38552 This is a link to the Electrical Systems 101 Topic, reply #2

 

[dlochner]

Stu,

Not sure what you mean by "specious claims."

If it about OEMs doing things to prevent warranty claims, you might want to look at this thread:
https://forums.sailboatowners.com/i...s-super-dumb-alternators.173324/#post-1226813 In which Maine Sail states: "These are cheap automotive alternators using bottom of the barrel cheap regulators and reducing voltage using a temp gradient is the least expensive way to get these alternators through the warranty period." (my emphasis)

Or do mean this comment from above:
"Correct the alternator output is best lead directly to the house bank and fused at 150% of alternator output. Connect house and start batteries with an ACR or similar device."

Or are you suggesting that "Operator error" is not equal to "crazy brothers-in-law?"

Dave

 

[Maine Sail]

Right now I have just one cable connecting the engine to the 1/2/both battery switch, so it does both power the starter and charge the batteries. I want to have a separate connection between the alternator and batteries and add an ACR, as in the diagram below.

Your diagram shows a three ON/OFF configuration not a 1/2/BOTH?

There is nothing wrong with doing this but you will need a fuse at the positive busbar. This fuse should be rated at approx 150% of alt output. Seeing as you will likely be upgrading your alternator sometime in the future, because the LR155 is a very lack luster performer, I would recommend sizing this cable for an 80A to 100A or larger alternator now so you don't have to repeat this in the future..

My question is: Do I just disconnect the wire between the starter motor and alternator from the starter, and extend that back to the house bank bus? Is it that simple?

Yes. Open the harness, remove the jumper wire, close the harness back up.

House bank, charger, alt and ACR all need fusing and it is also a very good idea to fuse the start battery. Fusing is size for the wire it is protecting but if starting the motor I would not fuse at below 250A and 300A is even better if the wire is large enough..

 

[jssailem]

Experience being a good teacher, I can affirm the recommendation of MaineSail that the starting motor needs a big fuse. Tried to fuse my starter with 150 fuse. Thats big right. Turned on starter, motor just kicked over one of the cylinders sounded like it fired ... then... phfffttttt. And silence. Looked at the $15 MRBF --- BLACK. Burned fuse.

 

[Ned Ludd]

Between this thread and Mainsails discussion on 1/2/both switches I need to junk my entire 41 year old electrical system...

 

[jssailem]

I feel your pain. I'm in the process. Made a few mistakes along the way but feeling a lot better about the direction I am taking then 12 months ago. Wanted to get the boat down to Portland for the winter so I could work on these tasks, but that did not happen. On the flip side I have had some nice 4 day work weekends and discovered the benefits of the Wallas diesel heater.
Keep telling myself it is the journey that feeds the soul.

 

[dlochner]

Between this thread and Mainsails discussion on 1/2/both switches I need to junk my entire 41 year old electrical system...

If planned out carefully, the upgrade can be completed in stages over several seasons. It eases the pain. I'm on year 3 of my upgrade and then maybe I'll be done?

 

[PAC3142]

Your diagram shows a three ON/OFF configuration not a 1/2/BOTH?

There is nothing wrong with doing this but you will need a fuse at the positive busbar. This fuse should be rated at approx 150% of alt output. Seeing as you will likely be upgrading your alternator sometime in the future, because the LR155 is a very lack luster performer, I would recommend sizing this cable for an 80A to 100A or larger alternator now so you don't have to repeat this in the future..



Yes. Open the harness, remove the jumper wire, close the harness back up.

House bank, charger, alt and ACR all need fusing and it is also a very good idea to fuse the start battery. Fusing is size for the wire it is protecting but if starting the motor I would not fuse at below 250A and 300A is even better if the wire is large enough..

Thanks, Maine. The 1/2/both switch is current, and I'm changing to three on/off switches as in the diagram. I spent more time this weekend than I'd like figuring out wire size and fuses, including the fuses to protect the cables you mentioned. By lucky coincidence the cable to the alternator will be oversized mainly because it is cheaper to buy 25 feet of the heaviest gage needed for the whole set up rather than shorter lengths of the minimum gage needed for each leg.

By the way, the sale prices this past weekend at Defender for battery cable were still more expensive than here at SBO.

Paul

 

[GonzoF1]

Between this thread and Mainsails discussion on 1/2/both switches I need to junk my entire 41 year old electrical system...

Yea... Tell me about it! Two boats has equaled two complete overhauls of the OEM DC system. One was a 1986 Taiwanese trawler (which you would expect), but what was surprising to me was that our 2000 model year motoryacht made in the USA was equally wonky of a DC system. 3x8D batteries with a single 1/2/O/B switch and a single on/off... it must have been designed for people to only sit in marinas and never anchor out. *sigh* However, I can't thank MaineSail enough for all his help here. The new design is far better!

 

[FlyingAloha]

Does the 3GF need ONE starter battery or TWO ? Im completely new to this motor and have bot hooked power yet to the motor. I have a 1983 Yanmar 3GF
Thanks