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Old 15-01-2014, 15:26   #1
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DC Battery Rig

I'm working on a rewire plan and I'm starting off with the 'heart' of the system. This setup is based on the 'use the house to start' camp, with the aux (starter) batt only being used as a backup. There will be a battery monitor on the house bank.
I would appreciate any comments, especially around the large pos bus bar, fuses & fuse positions.
many thanks...
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Old 15-01-2014, 16:04   #2
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Re: DC Battery Rig

Well, I am not a big fan of your basic premise of using the house to start and having a standby battery to start the engine in an emergency or ??? But coming back to that issue later, what you have sketched works fine.

The DC + buss is no real problem as long as it is beefy enough to take the engine starting load. Do not fuse the starting circuit. ABYC doesn't require it and for a number of reasons I don't think it is a good idea. But obviously you need to fuse everything else connected to the DC + buss.

I prefer to take the opposite approach: use the starting battery to start so that you can monitor how it works. Have all of your charging sources charge the house bank and charge the starting battery with an Echo Charger or similar as you have shown. Only use the house batteries to start in an emergency.

With big house banks and particularly big AGM banks, it doesn't matter so much. But my main reason is to monitor how the starting bank starts, so you can do something about it before you have to. In your diagram it may not work when you need it.

But if you want to do it that way, test the aux battery periodically to make sure it will start.

David
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Old 15-01-2014, 16:31   #3
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Re: DC Battery Rig

I don't see why the charging loads need fuses at the +bus. Seems like the fuse should be on the other end (close to the alternator for example).
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Old 15-01-2014, 16:54   #4
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Re: DC Battery Rig

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Originally Posted by RainDog View Post
I don't see why the charging loads need fuses at the +bus. Seems like the fuse should be on the other end (close to the alternator for example).
I didnt notice them on the layout but if that is them at the batteries, ABYC likes them within 7" of the battery.
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Old 15-01-2014, 17:04   #5
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Re: DC Battery Rig

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I don't see why the charging loads need fuses at the +bus. Seems like the fuse should be on the other end (close to the alternator for example).
The alternator can only put out a limited amount of current, the max of which the wires should be sized for, so no need of a fuse at that end. Batteries on the other hand put out way more current in a no load condition, so ideally a wire on the positive post is fused before it can touch anything negative.
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Old 15-01-2014, 17:12   #6
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Re: DC Battery Rig

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Originally Posted by mtompson View Post
I'm working on a rewire plan and I'm starting off with the 'heart' of the system. This setup is based on the 'use the house to start' camp, with the aux (starter) batt only being used as a backup. There will be a battery monitor on the house bank.
I would appreciate any comments, especially around the large pos bus bar, fuses & fuse positions.
many thanks...
I'm also in the camp of how do you know the aux battery is good enough to start the engine.

My setup has the ignition switch cross connect the batteries. So both are in circuit during starting and charging. I thought that I would regularly start with the house bank off to use/test the engine battery. I got lazy, and thought that I had gotten 9 years out of the start battery, that is until it got so bad it was pulling the house bank down so I couldn't start. Solution of problem was to turn off the start battery main, so I could start off of the house bank to get home. I now make sure a couple of times a year I start only off of the start battery.

If I ever get a 3 stage regulator I'll go alternator straight to the house and Echo to the start.
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Old 15-01-2014, 17:56   #7
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Re: DC Battery Rig

I have a similar setup and I like to leave the start battery as emergency only. 2 things to warrant this. 1st is I will use it from time to time to make sure it is still good and second I change it out every 3 years no matter what. On my boat its only a group 24 so 150$ every 3 years is fine by me. I'm not rich but I will always spend extra money for reliability when needed.
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Old 15-01-2014, 23:28   #8
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Re: DC Battery Rig

Thanks for all the comments! I do agree on checking the aux bank with occasional starts or regular jobs around the boat. I've always been a fan of maine sail's ( of Compass Marine ) work & methods, and this rig is based on that.
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Old 15-01-2014, 23:51   #9
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Re: DC Battery Rig

I've had the same setup, including the EchoCharge, for 19 years and a lot of cruising. It works fine.

As for the state of the start battery - monitor it! My 19 year Link2000 monitors two battery banks as does almost any inexpensive or expensive battery monitor.

I always start using the house bank but I carefully monitor the voltage and amp hour discharge status of the start battery.
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Old 16-01-2014, 00:09   #10
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Re: DC Battery Rig

Yes, some way to always check the start batt's condition, Victron do a monitor to watch two banks? (at least the voltage of the 2nd? & I think you need a 2nd shunt? ) sorry about all the ? I'm too rushed to check this morning!
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Old 16-01-2014, 00:37   #11
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Re: DC Battery Rig

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Originally Posted by RainDog View Post
I don't see why the charging loads need fuses at the +bus. Seems like the fuse should be on the other end (close to the alternator for example).
because when those wires get damaged and shorted the current is going to be flowing from the battery to the short. in your case with an unfused wire...

the chargers and alts are already self limited how much they can put out. and chargers are normally fused inside.

back on topic I think your battery idea is silly. run the engine battery to the starter and house battery to the panel. you have different choices on how to switch them.
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Old 16-01-2014, 00:55   #12
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Re: DC Battery Rig

won't that mean a complete loss of house DC while I start the engine, and I would have to go and put the battery switch over to #2 before ( & after ) starting!
To stop a complete loss of house DC you could use the 'both' switch, but that worries me if one bank is in a poor SOC?
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Old 16-01-2014, 07:33   #13
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Re: DC Battery Rig

Might be worth a read on this method...
Battery bank design recommendations - Page 9 - SailNet Community
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Old 16-01-2014, 12:20   #14
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Re: DC Battery Rig

The 1,2,all switch should not be used for the house side. Only for the starting side. House stays connected to house through another cutoff swsitch regardless of switch position.

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Old 16-01-2014, 12:33   #15
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Re: DC Battery Rig

I saw issues with the house bank (3) being used as a starter battery. There was enough voltage drop when cranking for the Electronics to blink off and on. Not good for that stuff. Moved the motor to a dedicated battery and the issues went away.

Steve in Solomons MD
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