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Old 12-01-2010
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Battery bank design recommendations

I'm about to acquire a 34 foot sailboat and will modify the electrical system for offshore/alternative energy use. I want to end up with 2 banks consisting of a single 12V start battery plus a house bank consisting of four 6V golf cart batteries. A battery monitor will track the house bank and measure the Voltage only of start battery. I want to satisfy these criteria:
  • Allow house bank to start engine in case start battery fails
  • Allow (rarely used) battery charger, alternator & wind generator to charge house bank
So far I figure that one of those "Off, 1, 2, All" switches can be wired to connect house bank to starter motor in an emergency ie, position 1 goes to start battery, position 2 goes to house bank, and common goes to starter. Normally the switch would be set to position 1 ie, connect the start battery directly to starter and isolate house bank.

Now I need to figure out the charging circuit. By default I want the charger, alternator and wind generator to charge the house bank. I suppose either the alternator alone or common charging circuit could charge the start battery. I do want to take care not to over-charge the start battery given it's limited usage. Does this call for a combiner or is something else simpler and less expensive? I really believe in the KISS principle and am also trying to be budget conscious. Comments and suggestions much appreciated.
Pete

Last edited by prroots; 12-01-2010 at 05:26 AM.
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Quote:
Originally Posted by prroots View Post
I'm about to acquire a 34 foot sailboat and will modify the electrical system for offshore/alternative energy use. I want to end up with 2 banks consisting of a single 12V start battery plus a house bank consisting of four 6V golf cart batteries. A battery monitor will track the house bank and measure the Voltage only of start battery. I want to satisfy these criteria:
  • Allow house bank to start engine in case start battery fails
  • Allow (rarely used) battery charger, alternator & wind generator to charge house bank
So far I figure that one of those "Off, 1, 2, All" switches can be wired to connect house bank to starter motor in an emergency ie, position 1 goes to start battery, position 2 goes to house bank, and common goes to starter. Normally the switch would be set to position 1 ie, connect the start battery directly to starter and isolate house bank.
Doing it this way requires a second switch, as you really should have a switch between the house bank and the main DC circuit breaker panel. You could use a BlueSeas Dual Circuit Plus switch instead, which has three positions--Off, Run (where the house bank goes to the DC panel and the start bank goes to the starter motor), and Combine (where both the house and start banks are combined to support both the house and start loads).

This keeps your house electrical loads isolated from the starting loads under normal usage.

Quote:
Now I need to figure out the charging circuit. By default I want the charger, alternator and wind generator to charge the house bank. I suppose either the alternator alone or common charging circuit could charge the start battery. I do want to take care not to over-charge the start battery given it's limited usage. Does this call for a combiner or is something else simpler and less expensive? I really believe in the KISS principle and am also trying to be budget conscious. Comments and suggestions much appreciated.
Pete
Put all the charging sources onto the house bank. Then use one of the following to charge the starting bank whenever the house bank is being charged:
  • Balmar Digital DuoCharge
  • Xantrex EchoCharger
  • BlueSea ACR
This will keep the start bank basically topped off without any user intervention.
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Last edited by sailingdog; 12-01-2010 at 07:13 AM. Reason: edited brand names
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Old 12-01-2010
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Quote:
Originally Posted by prroots View Post
I'm about to acquire a 34 foot sailboat and will modify the electrical system for offshore/alternative energy use. I want to end up with 2 banks consisting of a single 12V start battery plus a house bank consisting of four 6V golf cart batteries. A battery monitor will track the house bank and measure the Voltage only of start battery. I want to satisfy these criteria:
  • Allow house bank to start engine in case start battery fails
  • Allow (rarely used) battery charger, alternator & wind generator to charge house bank
So far I figure that one of those "Off, 1, 2, All" switches can be wired to connect house bank to starter motor in an emergency ie, position 1 goes to start battery, position 2 goes to house bank, and common goes to starter. Normally the switch would be set to position 1 ie, connect the start battery directly to starter and isolate house bank.

Now I need to figure out the charging circuit. By default I want the charger, alternator and wind generator to charge the house bank. I suppose either the alternator alone or common charging circuit could charge the start battery. I do want to take care not to over-charge the start battery given it's limited usage. Does this call for a combiner or is something else simpler and less expensive? I really believe in the KISS principle and am also trying to be budget conscious. Comments and suggestions much appreciated.
Pete
You could always do everything off the house bank and use your 12V battery as a "reserve" or back up battery if you want.


As Dog said using one of the devices above will keep the reserve bank topped up but the Balmar unit is called a Digital Duo Charge not an Echo the Xantrex unit is called the Echo Charger.

There's no need for needless switching back & forth between house & "start" to start a small diesel. Keep it simple, go to boat switch to house bank, leave boat switch off, and let the combiner or Echo type charger do the behind the scenes stuff to keep the reserve/start battery topped up.

Using a 1/2/BOTH/OFF I prefer switch settings of 1=Primary or house bank and 2=secondary or reserve bank.

The 1/2/BOTH/OFF, if wired appropriately, gives you excellent most redundancy by allowing the complete isolation of either bank, either bank can become the start or house bank and you still retain the ability to "combine" the banks if that need were to arise such as a failed ACR or Echo charger, which would be very rare.

If you wire your alt directly to the house bank you will also prevent the inadvertent frying of the alternators diodes by moving the switch through the OFF position accidentally. The ACR or Echo will still charge the reserve bank...
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Last edited by Maine Sail; 02-16-2012 at 11:13 PM.
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Quote:
Originally Posted by Maine Sail View Post
Just do everything off the house bank and use your 12V battery as a "reserve" or back up battery. It is far more simple..

As Dog said using one of the devices above will keep the reserve bank topped up but the Balmar unit is called a Digital Duo Charge not an Echo the Xantrex unit is called the Echo Charger.
my bad

Quote:
There's no need for needless switching back & forth between house & "start" to start a small diesel. Keep it simple, go to boat switch to house bank, leave boat switch off, and let the combiner or Echo type charger do the behind the scenes stuff to keep the reserve/start battery topped up.
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Old 12-01-2010
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Thanks alot for the feedback; food for thought. Here are my immediate thoughts. I like the concept of direct connecting all charging devices to house bank. This makes sense and follows the KISS principle. I like the wiring of the "Off, 1, 2, All" as mentioned in my original post which provides for emergency engine start from house bank (and emergency combining if an automatic device fails). Of the 3 devices mentioned, it seems that two (ie, Balmar and Xantrex) follow the same philosophy of charging start battery from house battery when charging is detected. The Xantrex is substantially cheaper and seems to do the job (ie, $126 vs $225). The BlueSea ACR seems to be a different device which doesn't follow the above philosopy. It appears that the ACR does not provide direct connection of charging devices to house battery and, therefore, seems inherently more complicated and less reliable. Guess my immediate reaction is to select the Xantrex Echo-charger. Please tell me where I went wrong!
Pete

Last edited by prroots; 12-01-2010 at 08:24 AM.
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Quote:
Originally Posted by prroots View Post
Thanks alot for the feedback; food for thought. Here are my immediate thoughts. I like the concept of direct connecting all charging devices to house bank. I like the wiring of the "Off, 1, 2, All" as mentioned in my original post which provides for emergency engine start from house bank (and combining if combining device fails). Of the 3 devices mentioned, it seems that two (ie, Balmar and Xantrex) follow the same philosophy of charging start battery from house battery when charging is detected. The Xantrex is substantially cheaper and seems to do the job (ie, $126 vs $225). The BlueSea ACR seems to be a different device which doesn't follow the above philosopy. It appears that the ACR does not provide direct connection of charging devices to house battery and, therefore, seems inherently more complicated and less reliable. Guess my immediate reaction is to select the Xantrex Echo-charger. Comments please.
Pete
On other point I should mention is that it is a good idea to add a fuse/breaker within 7" of the battery for the direct feed alt wire and I sometimes add a "service switch" into the alt feed wire so when working on the engine you can simply disconnect the alt from the batts. This is usually a hidden switch not highly visible to guests. It is also a good idea to fuse your banks.

As always there is no one right way to wire banks, unless you do it dangerously, but on small boats it makes little sense to not a perfectly good 1/2ALL/OFF, if you already have one, when a simple re-wire will give you everything you need with simplicity and total redundancy should a combiner fail..

#1 Assign house bank to batt switch position #1
#2 Install reserve battery to position #2
#3 Wire alternator output directly to the house bank with sufficient size cable & fuse.
#4 Install ACR or Echo Charger between banks.
#5 Use boat in position #1 for starting AND house loads. Switch to OFF when you leave it's that simple.



So why do I want to wire my alt direct to the house bank??


I prefer to feed the alt directly to the house bank and not the reserve bank as the start bank is for back up or emergency, in this situation, and would usually be at or near 100% SOC anyway.

1- No more worries about fried diodes.

2- Accurate voltage sensing of the discharged bank & less chance of voltage drop over the generally very small factory wiring.

3- If you use an Echo Charger you need to do this anyway

You should NOT however wire the alt directly to the house battery unless you have either a VSR/ACR (voltage sensitive relay/ automatic charging relay) or a unit like the Echo Charger or Balmar Duo Charger.

Follow me on this one.

If you sense/wire directly to the house bank, bank 1, but do not have an ACR or Echo type unit installed, this means you could physically select the battery being used via the 1/2/BOTH/OFF switch.

If you select bank two as your source and the alt is connected to bank 1 you will draw down bank two and not replenish it unless the ALL function is selected during charging. In short, without an ACR or Echo type charger I would not wire directly to the house bank and instead would leave it wired through the common post of the battery switch.

With an ACR/Echo you can still select bank 2 but it will automatically be getting charged via the combiner or Echo even with the house bank being direct wired...


So what is a battery combiner / ACR / VSR??

Blue Sea ACR Si Series (LINK)

An ACR is an automatic charging relay. ACR is Blue Sea Systems trade name. They are also know as VSR's or voltage sensitive relays. A VSR is essentially a high current automatic relay that senses voltage and combines banks when the voltage rises. If it senses 13.6 volts for more than 30 seconds it combines and if it sense more than 13.0 volts for two minutes it also combines. When the VSR senses a drop in voltage below roughly 12.35V for more than 10 seconds it disconnects or when it sense 12.75V or less for more than 30 seconds it also disconnects the banks. These devices are very simple and fully automatic requiring no human intervention at the battery switch. Truly "set it and forget it"..

Start the engine and when the charge voltage begins to rise the VSR/ACR automatically energizes the relay, closes it, and "combines" the banks for charging, just like if you flipped the 1/2/BOTH/OFF to BOTH. The best feature is that it NEVER forgets to disconnect the banks when a charge source is not present. When the batteries are not seeing a charge source they are disconnected from one another. These devices are relatively inexpensive $65.00 - $150.00 depending upon model. They are also very easy to wire. The Blue Seas ACR has three wires to connect, ground and house and start bank jumpers. Yandina also makes a battery combiner/VSR. The Blue Seas models should have a fuse installed in the ground wire as well.

The unit labeled ACR is a Blue Seas ACR:



So what is an Echo Charger?


Xantrex Echo Charger (LINK)

The Xantrex Echo Charger is an electronic 12v to 12v charger. The banks and the banks remain isolated but you don't have the voltage drop issues associated with diode based isolators. It simply takes or "bleeds" it's power from the charge source or the house bank and when it senses over 13.0 volts energizes and begins charging the reserve bank. When it senses below 13.0 volts it turns charging off. It can supply up to 15 amps of charge current to the reserve battery while borrowing/bleeding it from the house bank. Normally that battery will be at or near full and you'll rarely ever see it pull more than an amp or two anyway so 98% of the time your alts full output heads directly to the house bank. The Echo Charger is also a voltage follower and will follow the incoming voltage to the house bank. When the house goes into float mode so does the reserve bank.

The Echo Charger is also a simple three wire hook up but needs to feed the reserve bank, and pull from the house bank. All charge sources should be fed to the house bank, solar, alternator, wind and shore side charger.


The Balmar Duo Charger is similar to the Echo but more expensive and can supply up to 30 amps of charge current. It does have a few flaws so I'd stick with the Echo or ACR.


By simply adding an ACR or ECHO only, you can still go to your boat and select HOUSE and when you leave select OFF. That's it, simple...

Some folks complain of voltage drop out for electronics when starting off the house bank. I have never experienced this in any of my installations but my battery cables and system wiring are of sufficient size and my house bank even at 35-40% SOC never drops out the electronics during engine starting. I can start my engine and not reset any of my electronics even down to about 35-40% state of charge. You should not normally be dropping below 50% SOC anyway. If this is a concern then your batts may be ready for replacement or you have some bad connections. To avoid this you can start the motor, then flip on the instruments.

You can direct wire a dedicated start battery but it will be more complicated if you want to retain the ability to start off the house bank in an emergency. This is why the 1/2/BOTH/OFF is such a good tool despite it often being incorrectly maligned.

I still wire the alt direct to the house bank even with an ACR for the reasons mentioned above.
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Quote:
Originally Posted by Maine Sail View Post
#1 Assign house bank to batt switch position #1
#2 Install reserve battery to position #2
#3 Wire alternator output directly to the house bank with sufficient size cable & fuse.
#4 Install ACR or Echo Charger between banks.
#5 Use boat in position #1 for starting AND house loads. Switch to OFF when you leave it's that simple.
Thanks a million; lots more food for thought! The above connections make sense, but I do have one preliminary question. Where do you connect the common of the "Off,1,2,All" switch. My idea was to connect it to starter motor and the switch becomes essentially a starter motor selector switch (or emergency combiner). I suspect you're recommending a different connection.

Edit: I'm guessing that you tie both the DC loads and starter motor to the common of switch. I was proposing that only the starter motor be connected to the common of switch. Your method has the advantage that the start battery could feed the DC loads. The disadvantage is that starter current draw could raise havoc with sensitive electronics. In my proposed connection, the start battery is connected directly to starter motor and does not affect the DC loads. The disadvantage is that I can't feed DC loads from the start battery. Both schemes allow starting engine from either bank and emergency combining. Did I guess correctly? Are there other issues involved?

Last edited by prroots; 12-01-2010 at 10:30 AM.
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Originally Posted by prroots View Post
Thanks a million; lots more food for thought! The above connections make sense, but I do have one preliminary question. Where do you connect the common of the "Off,1,2,All" switch. My idea was to connect it to starter motor and the switch becomes essentially a starter motor selector switch (or emergency combiner). I suspect you're recommending a different connection.
Usually two wires on that post, one to house loads/panel and one to the starter. You can also run to a + buss bar and then branch the panel & starter but I prefer the starter to have as few connections as possible and two lugs on that post is usually doable.
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Old 12-01-2010
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Quote:
Originally Posted by Maine Sail View Post
Usually two wires on that post, one to house loads/panel and one to the starter. You can also run to a + buss bar and then branch the panel & starter but I prefer the starter to have as few connections as possible and two lugs on that post is usually doable.
I was editing my post while you posted. Guess I guessed correctly! I would appreciate any pros and cons you might add to my proposal vs yours.
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