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Old 11-20-2014, 11:39 AM   #1
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Question 6VDC Golf Cart Battery Question

I am redoing my house battery situation (it currently comes off the start batteries). I understand that you have to hook 2 of the 6Vdc batteries in series to achieve 12vdc, then when adding additional banks you connect them in parallel. So now I have 2 12Vdc banks, each bank has 4-6Vdc batteries. Each bank has a positive and negative wires for the 12vDC connection to the house. Already have the positive wire figured out as it is already provided.
Question:

Where do you connect the negative (ground) wire on the bank? Hook it to a negative post on the start battery or ground point on the engine?
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Old 11-20-2014, 11:50 AM   #2
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Either connection might work as long as the house loads somehow ground to them.

But it would be better to look at where your house loads connect their grounds. Often there is a buss that these grounds come back to and you connect that buss to the negative terminal of the house batteries. That should be a more direct ground path.

But why two house banks. It is better to wire them as one big bank.

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Old 11-20-2014, 11:57 AM   #3
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Quote:
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But why two house banks. It is better to wire them as one big bank.

David

Depends on how you plan to charge it or them.
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Old 11-20-2014, 12:05 PM   #4
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When I did ours, I used several BusBars to manage all the connections to avoid stacking too many onto battery posts. https://www.bluesea.com/products/cat...sBars/PowerBar

There is some discussion both ways as to using the engine block as a grounding point for the house bank. You have to for the starter battery anyway, just to finish the loop to the starter motor. However, if you are going to be able to combine house and start for whatever reason, the house ground will need to find its way to the block at some point for that to work. So I used a busbar and then took a very heavy gauge wire to a solid ground on the block.
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Old 11-20-2014, 12:27 PM   #5
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Good points all.

I plan on two banks, with 4-6Vdc batteries in each bank. The reason for this is because of the way the boat manufacture wired it. On my DC panel I have a battery switch (as most of us do) with a Off, #1, #2 and both. In the engine bay where my batteries are located, I have two red heavy gage wires for the house, one for #1 and the other is #2. Both #1 and #2 run ALL of the DC needs on the boat doesn't matter if the switch is selected for #1 or #2 all DC is powered. Placing the switch to both will just increase my amp hours as I am now tying in both banks.

As far as charging, the banks will be charged two different ways. The first will be a battery charger. I have one that is a 3 bank charger, but will only be using two legs. My start batteries will not be on the charger as there is no need to as I start and run my boat all the time, thus charging the start battery.

The second way the house bank will be charged is when the engines are running as I am installing a two engine battery isolator.

Good point on the ground to the engine block in case I have to jump start from the house batteries. I believe this is the way it is currently set up. I also think the two start batteries are tied together with the ground between the two batteries and then each battery is grounded to the engine starter.
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Old 11-20-2014, 03:45 PM   #6
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Normal battery isolators have a forward voltage drop of a half volt or so. This voltage drop means that there is not enough voltage at the batteries for efficient charging.

Look at the FET isolators by Victron here- Argo FET Battery Isolators - Victron Energy

They have a very low voltage drop and eliminate this problem

OTOH I am a big fan of battery combiners for this purpose. Look at Yandina Marine Electronics

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Old 11-20-2014, 05:53 PM   #7
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Thanks david. Good info!
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Old 11-20-2014, 07:38 PM   #8
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Normal battery isolators have a forward voltage drop of a half volt or so. This voltage drop means that there is not enough voltage at the batteries for efficient charging.

Look at the FET isolators by Victron here- Argo FET Battery Isolators - Victron Energy

They have a very low voltage drop and eliminate this problem

OTOH I am a big fan of battery combiners for this purpose. Look at Yandina Marine Electronics

David
I wouldn't even consider a battery isolator of any kind. Battery combiners are much more efficient. In addition to Yandina, many other companies make these, often calling them automatic charging relays (ACR).
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Old 11-20-2014, 10:01 PM   #9
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Folks in the know with battery isolators and capable charging systems can adjust their charging systems to accommodate that 0.5-1.0 V loss during charging. I know folks here who have done just that. At the time, I didn't have a charging system capable of adjustment, so I installed a Yandina combiner. Blue Sea also makes quality ACRs.
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Old 11-21-2014, 07:00 AM   #10
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>I plan on two banks, with 4-6Vdc batteries in each bank. The reason for this is because of the way the boat manufacture wired it. On my DC panel I have a battery switch (as most of us do)<

That was the standard 30 years ago ,which is far less common today.

Low voltage takes a toll on the batts , so by using one large bank, the same amp draw shows as less V drop to the bigger bank.

Your rotary switch should allow this to be set.

IF you have two engines , the house banks may be charged faster with the house sets not joined .

Be sure the rotary switches have the field disconect circuit wired in , to save the alt should you make a bo bo with an operating engine. IF there are no small terminals on the back of each rotary , discard them.

A battery combiner is just an $18 RV relay , with electronics added.

KISS works better.
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Old 11-28-2014, 02:46 PM   #11
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I am also in the process of doing some rewiring of batteries / alt / charger and agree w/ the comments so far...

I am wondering why you wouldn't use the third bank on the charger to keep the starting battery at full charge? Most smart chargers today do a better job at fully charging than the alternator does (I believe)

Most of the combiners / ACT's recommend wiring the alternator primary to the largest bank (house) and then connecting to the start batty.Name:  series batty hookup.jpg
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The attached shows the recommended hookup for parallel batteries / banks - I'm not sure exactly why but I have seen references that state this will charge & discharge more evenly and improve performance & life.

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Old 11-28-2014, 03:00 PM   #12
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I agree, Don, but I have split my loads and charges to provide complete control of both at all times. There is no shared cabling between the two as there was when I purchased the boat.

Assuming each battery depicted in your diagram represents a series-connected pair of 6V GC batts, that's how loads are connected. I run all my loads through 1-ALL-2-OFF switches outside the ER before they connect to any buses to allow me to select, isolate and share loads.

I am configured differently for my charge currents. In my twin engine/alternator boat, I have the high output alt connected directly to the house bank and the smaller stock alt connected directly to the start batt. My single-bank charger is connected to the house bank with a switched Yandina combiner to share the charge with the start batt when needed.
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Old 11-28-2014, 06:50 PM   #13
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I am wondering why you wouldn't use the third bank on the charger to keep the starting battery at full charge? Most smart chargers today do a better job at fully charging than the alternator does (I believe)

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Hey Don,

There is no need to have a charger connected to the start batteries. I start and run my boat a lot, so the start batteries are always charged full, thus no need to charge them.
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Old 11-28-2014, 07:15 PM   #14
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I like the old oil pressure activated switch connected to a charger relay for tying the engine alternator to the house bank. Simple.
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Old 11-29-2014, 07:48 AM   #15
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An oil pressure switch Is simple , BUT you are not in charge.

With the charge solenoid wired to the ACC position on a key switch , you can once a month place it in acc while dockside and charge the start batt.

Starts age and loose internally , like every batt , so after a few weeks or a month dockside it will live longer being recharged.
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Old 11-29-2014, 10:51 AM   #16
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Why would anyone not take advantage of the technology of the battery combiners or automatic charging relays commonly and inexpensively available?

No need to remember anything no need to switch anything.
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Old 11-29-2014, 02:02 PM   #17
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You don't always want the start battery taking the charge being provided to the house bank or it can overcharge resulting in excessive water loss.

For me, a switchable combiner is the best of both worlds. YMMV

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Old 11-30-2014, 06:42 AM   #18
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>Why would anyone not take advantage of the technology of the battery combiners or automatic charging relays commonly and inexpensively available?

No need to remember anything no need to switch anything.<

RVs have been doing this since 1950 , with an $18 buck relay.

>You don't always want the start battery taking the charge being provided to the house bank or it can overcharge resulting in excessive water loss. <

I dont think so. Start batts in todays cars and trucks are used with the alt charging almost all the time.

Lights , blowers, hot seats,boom boxes and the rest mean most cars are at 14+ volts as the numerous users draw juice.

A good 3 stage V regulator will bring the house to 14.4 (or so) before cutting back to float.

No harm with a batt created to operate 99% of the time at 14V + in overcharging.
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Old 11-30-2014, 08:42 AM   #19
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Quote:
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Hey Don,

There is no need to have a charger connected to the start batteries. I start and run my boat a lot, so the start batteries are always charged full, thus no need to charge them.
Not always the case. Many vessels, mine included, have separate chargers for the engine start batteries. Why not? Redundancy is great with the availability of the start battery charger to charge the house bank if the inverter charger for some reason not performing.

In my case the dinghy davit is powered from the engine starts. To monitor the health of engine starts we have a separate Magnum BMK.
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Old 12-01-2014, 01:32 PM   #20
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Not always the case. Many vessels, mine included, have separate chargers for the engine start batteries. Why not? Redundancy is great with the availability of the start battery charger to charge the house bank if the inverter charger for some reason not performing.

In my case the dinghy davit is powered from the engine starts. To monitor the health of engine starts we have a separate Magnum BMK.
Good point. I don't have any inverters (yet). My battery charger is a fairly new one, with 3 legs. I also have a portable charger onboard just in case and that is powered when I run the genny.
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