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Old 10-10-2016, 13:35   #1
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Single House Battery Bank, Split Between 2 Locations?

Current house bank is three group 31 FLA deep cycle batteries (110 Ah x 3). Way too little for cruising on the hook. With freezer and refrigerator compressors plus minor typical house loads (e.g. fresh water pressure pump, anchor light), we can only go 24 hours when cycling between 80% and 50% SOC.

I want to add three additional group 31 FLA deep cycle batteries, but the only suitable location is 12 wire feet away (one way). Realize that the cable between the two portions of the bank will need to be HD, like 1 AWG. Batteries within each of the two portions is in existing portion / going to be in new 4 AWG.

Is this technically correct approach? Once I implement the forgoing, I will install soloar consisting of 2 x 100W of moncrystal panels with PWM solar from Defender (currently $1050). BTW, I also have a 3.5 Kw genset, which I hope to use only to run the A/C and make water as necessary.

Regards to all - Alan
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Old 10-10-2016, 13:40   #2
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Re: single house battery bank, split between 2 locations?

Why not install the solar panels first and then see if you need a larger battery bank?
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Old 10-10-2016, 14:04   #3
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Re: single house battery bank, split between 2 locations?

I think it's fine to physically separate portions of the house bank. However, it is important that all of the batteries see about the same voltage. Most of the voltage drop does not come from lengths of cable, but from the connections. So if you want to do this well, I think you should:
  • Use the right tools and process to crimp lugs onto your cables. It's easy to have a good looking but poorly done crimp that adds quite a bit of resistance. There are inexpensive hydraulic crimpers on ebay.
  • Wire it so that there are the same number of connections between each battery and your bus bar or switch. One should run each half of a bank directly to the battery switch or bus bar, rather than connecting the second half of your battery bank to the first half, and then the first half to the bus bar.
  • I am overly cautious about fusing. I would be uncomfortable having a long run of cable coming from the batteries that is not fused. Consider either getting the fuses that fit on top of your battery terminals, or some other system. But, again, pay attention to the number of connections between the batteries and the load.
  • Test it to be sure. Make a high load (like a space heater or heat gun on the inverter) and check that the voltage at each battery is close. I've thought I've done everything right and then seen a big difference due to a small detail, like finding a stainless washer (which has high resistance) between a terminal and a fuse block.
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Old 10-10-2016, 14:23   #4
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Re: single house battery bank, split between 2 locations?

If you draw this out as a simple schematic, it looks fine. In reality, it is not because of the resistance of 24 feet of cable. Your batteries won't be discharging or recharging equally and for high current draws such as a windlass or bow thruster, you will not receive the expected voltage and current from some of the batteries.

I think you would be better off having two separate house banks and assigning each to certain loads. You will need a three bank charger (common) and two automatic charging relays.
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Old 10-10-2016, 14:29   #5
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Re: single house battery bank, split between 2 locations?

I have been running a system 4 6V GC midships and 2 in the fwd bilge for 11 years. This entire bank also serves as starting battery and the fwd bank is tapped for bow thruster and windlass. Imbalances will exist with heavy usage but they will all equalize in time. The connections between the two banks is #2 AWG and fused at 200 amps on each end of the positive connection. Never able to tell that this shortens the battery life in any significant way.
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Old 10-10-2016, 16:23   #6
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Re: single house battery bank, split between 2 locations?

it is not an ideal setup. as it'll be hard to properly wire end to end or wire in a battery monitor. without doing this the batteries will not be evenly used and will wear differently.

6 in the same spot wired correctly would probably last longer. however 6 apart will probably last longer then staying with only 3 and draining them lower. so if it's your only choice then do it.

also how big is your battery charger? with an onboard gen and 600ah of batteries you should be in the 80-100a range to best make use of the genny run time. many boats have tiny useless chargers.

also group 31 aren't the best choice for house batteries.
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Old 11-10-2016, 12:31   #7
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Re: single house battery bank, split between 2 locations?

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Originally Posted by Pete7 View Post
Why not install the solar panels first and then see if you need a larger battery bank?
First, do an energy audit. Without it, everyone is just guessing.

If you are frugal, with a fridge and separate freezer you are likely using at least 100 A-hrs per day, but calc (or better yet measure) the real number.

If you are 125 A-hrs per day, then you need 400 A-hrs storage minimum (standard lead acid), just to handle one days consumption before re-charging (assuming a 50% to 80% charge cycle). 50% more would be smart.

If you will typically be anchoring in an area of 20 knots or more, also consider wind. (If less than 15 knots typical, forget it.)

To satisfy a 125 a-hr per day energy demand with solar, you will need 500W min for sunny days, genny back up on cloudy.

If you go up to 800W, that would allow you to meet needs on most days. (Else 600W solar with 400W wind if in windy areas.)

Be sure to mount your solar where it won't be shaded (usually high above the cockpit aft of the boom).
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Old 11-10-2016, 13:45   #8
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Re: Single House Battery Bank, Split Between 2 Locations?

Thanks to all for some really good comments. Keep them coming

In response to some of the comments:
1. I have a separate bank for my thruster.

2. Not sure whether my house or start bank powers my 1200 watt windlass. I'll check that out. I always have the engine running when using the windlass.

3. Space constraints prevent me from adding more than one additional grp 31 in current bank location. This will require me to move the start battery to where I planned to expand the house bank, which is not an issue, except that adding one grp 31 only gets me to 440 Ah which still seems inadequate (but better than current setup as pointed out by smac999), given the preceding (thanks ramblingrod) energy usage analysis (which corresponds to my analysis using a 50% duty cycle for both the frig and freezer).

4. Boat purchased in 2015, and the grp 31s deep cycles were new from PO installed in 2014. He was on shore power virtually all the time.

5. I recently bought and installed a 50 amp charger from Maine Sail dedicated to the house bank. Sounds like I would need to 'stack' a second charger if I expand total bank capacity to 500 or 600 Ah.

6. We just left the Great Lakes for the ocean, and hence expect to run the genset for two hours every other day to make water (Rainman 37 gph, admiral requires copious water to be happy) and charge batteries. So it seems like 2 x 50 Ah charges indeed are required.

7. If I ran the genset at night, the solar would then be supplemental to push SOC past 80% in the day. The spec of the Go Power that I am considering are: 200 Watts, 17.8 Volt DC / 11.24 Amps. So, conservatively, I am hoping for 60 Ah per day which if I have a 600 Ah bank would push the genset provided 80% SOC to 90%, which is probably max given charge acceptance rate realities.

8. If I do configure as a single bank, I would use 1/0 AWG wire to connect the bank halves (with 2 AWG interbank halve). I have been buying premade cables from genuinedealz.com so I assume that the crimps are good.

One ah ha is that the existing charger round trip will be significantly extended since one cable will need to go to the end of the new partial bank ... OR ... could I charge one half as currently set up and the new added half with a separate charger?
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Old 11-10-2016, 22:39   #9
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Re: Single House Battery Bank, Split Between 2 Locations?

Quote:
Originally Posted by Jeanneau 45.2 View Post
Thanks to all for some really good comments. Keep them coming

In response to some of the comments:
1. I have a separate bank for my thruster.

2. Not sure whether my house or start bank powers my 1200 watt windlass. I'll check that out. I always have the engine running when using the windlass.

3. Space constraints prevent me from adding more than one additional grp 31 in current bank location. This will require me to move the start battery to where I planned to expand the house bank, which is not an issue, except that adding one grp 31 only gets me to 440 Ah which still seems inadequate (but better than current setup as pointed out by smac999), given the preceding (thanks ramblingrod) energy usage analysis (which corresponds to my analysis using a 50% duty cycle for both the frig and freezer).

4. Boat purchased in 2015, and the grp 31s deep cycles were new from PO installed in 2014. He was on shore power virtually all the time.

5. I recently bought and installed a 50 amp charger from Maine Sail dedicated to the house bank. Sounds like I would need to 'stack' a second charger if I expand total bank capacity to 500 or 600 Ah.

6. We just left the Great Lakes for the ocean, and hence expect to run the genset for two hours every other day to make water (Rainman 37 gph, admiral requires copious water to be happy) and charge batteries. So it seems like 2 x 50 Ah charges indeed are required.

7. If I ran the genset at night, the solar would then be supplemental to push SOC past 80% in the day. The spec of the Go Power that I am considering are: 200 Watts, 17.8 Volt DC / 11.24 Amps. So, conservatively, I am hoping for 60 Ah per day which if I have a 600 Ah bank would push the genset provided 80% SOC to 90%, which is probably max given charge acceptance rate realities.

8. If I do configure as a single bank, I would use 1/0 AWG wire to connect the bank halves (with 2 AWG interbank halve). I have been buying premade cables from genuinedealz.com so I assume that the crimps are good.

One ah ha is that the existing charger round trip will be significantly extended since one cable will need to go to the end of the new partial bank ... OR ... could I charge one half as currently set up and the new added half with a separate charger?
I would go larger on the cables. I wire battery banks with a minimum of 1/0 for all including interconnects between batteries, more often 2/0.

You can do better on the solar. I am assuming you are getting 2 flexible panels and the Go Power 30 amp Pwm controller. I sell the same in Canada. The panels are 379 each if you purchase 2. I sell very few Pwm controllers, maybe one every month, but sell Victron MPPT controllers as fast as I can get them. The Victron 75/15 handles 200 watts of panels and is fully adjustable as far as absorption and float voltages as well as many other functions and sells for 169. These prices are Canadian so when converted would be well below the prices you are looking at.

ps I am not trying to sell you anything - I am in Victoria. Just suggesting that there are much better values available.
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Old 12-10-2016, 06:08   #10
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Re: single house battery bank, split between 2 locations?

Quote:
Originally Posted by Jeanneau 45.2 View Post
Current house bank is three group 31 FLA deep cycle batteries (110 Ah x 3). Way too little for cruising on the hook. With freezer and refrigerator compressors plus minor typical house loads (e.g. fresh water pressure pump, anchor light), we can only go 24 hours when cycling between 80% and 50% SOC.

I want to add three additional group 31 FLA deep cycle batteries, but the only suitable location is 12 wire feet away (one way).
Quote:
Originally Posted by Jeanneau 45.2 View Post
3. Space constraints prevent me from adding more than one additional grp 31 in current bank location. This will require me to move the start battery to where I planned to expand the house bank, which is not an issue, except that adding one grp 31 only gets me to 440 Ah which still seems inadequate (but better than current setup as pointed out by smac999), given the preceding (thanks ramblingrod) energy usage analysis (which corresponds to my analysis using a 50% duty cycle for both the frig and freezer).
Quote:
Originally Posted by rwidman View Post
I think you would be better off having two separate house banks and assigning each to certain loads. You will need a three bank charger (common) and two automatic charging relays.

Maybe combine some of this. Change the existing 3xG31 configuration to at least 4xGC (~440Ah). FWIW, you may be able to fit 6xGCs in the same space as 4xG31s. Might be worth a look.



Then add another 4xGC (or 6xGC) bank. Then split the overall load into two "houses." A decent multiple-bank charger could handle that, especially with solar augmentation.

Our boat came with two separate house banks, two separate "houses." Works well enough. The two individual house banks are 300 Ah each, and I don't think I'd notice much difference compared to one 600 Ah bank. A technical difference likely exists, but practically-speaking... not so much.



-Chris
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Old 12-10-2016, 07:06   #11
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Re: Single House Battery Bank, Split Between 2 Locations?

Quote:
Originally Posted by Jeanneau 45.2 View Post
Thanks to all for some really good comments. Keep them coming

In response to some of the comments:
1. I have a separate bank for my thruster.

2. Not sure whether my house or start bank powers my 1200 watt windlass. I'll check that out. I always have the engine running when using the windlass.

3. Space constraints prevent me from adding more than one additional grp 31 in current bank location. This will require me to move the start battery to where I planned to expand the house bank, which is not an issue, except that adding one grp 31 only gets me to 440 Ah which still seems inadequate (but better than current setup as pointed out by smac999), given the preceding (thanks ramblingrod) energy usage analysis (which corresponds to my analysis using a 50% duty cycle for both the frig and freezer).

4. Boat purchased in 2015, and the grp 31s deep cycles were new from PO installed in 2014. He was on shore power virtually all the time.

5. I recently bought and installed a 50 amp charger from Maine Sail dedicated to the house bank. Sounds like I would need to 'stack' a second charger if I expand total bank capacity to 500 or 600 Ah.

6. We just left the Great Lakes for the ocean, and hence expect to run the genset for two hours every other day to make water (Rainman 37 gph, admiral requires copious water to be happy) and charge batteries. So it seems like 2 x 50 Ah charges indeed are required.

7. If I ran the genset at night, the solar would then be supplemental to push SOC past 80% in the day. The spec of the Go Power that I am considering are: 200 Watts, 17.8 Volt DC / 11.24 Amps. So, conservatively, I am hoping for 60 Ah per day which if I have a 600 Ah bank would push the genset provided 80% SOC to 90%, which is probably max given charge acceptance rate realities.

8. If I do configure as a single bank, I would use 1/0 AWG wire to connect the bank halves (with 2 AWG interbank halve). I have been buying premade cables from genuinedealz.com so I assume that the crimps are good.

One ah ha is that the existing charger round trip will be significantly extended since one cable will need to go to the end of the new partial bank ... OR ... could I charge one half as currently set up and the new added half with a separate charger?
All sounds reasonable. A couple of things to consider.

1. Far better to run the genny in the morning, say after 9am. At this time of day, the bank is likely to be lowest (no solar overnight) so the bank will be able to take everything the charger can dish out. This also will not annoy neighbours so much. Then in the evening if at sunset you find solar hasn't brought the bank up full enough, you can run the genny a bit to bring it up a bit.

2. Battery cables should always be sized for the max current they may see under normal use, and fused to limit unusual max current (provide overcurrent
protection for the word nazis among us). In your case it sounds like the cables between the thruster bank and house bank should be able to handle the full thruster current.

3. Because you are planning on running the genny every second day anyway, I recommend keeping the thruster / windlass bank isolated from the main house bank, and using a discrete AC charger for the forward bank. This will eliminate the need to run the heavy cables betweeen the banks.

4. I would definitely recommend increasing the house bank to the 4 x Grp 31, and moving the start battery. (I had a 3 battery house bank plus start battery, and opted to swap the start battery for a 4th house battery. I don't recommend this for all, but I watch my batteries closely enough to ensure I always have enough to start. If the exisiting batteries are in good shape, it doesn't make sense to scrap them to put in 6 volt batteries. When the house bank is due for replacement, 6 volts could be considered then (though I'm not convinced they are sufficiently better than Grp 31s to warrant the cost of the new boxes and wiring mods.
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Old 15-10-2016, 20:11   #12
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Re: Single House Battery Bank, Split Between 2 Locations?

I have the same boat as you and was able to fit 3 x DC31's in the locker under the bed behind the original bank. We got a thick piece of marine ply, faired it to the shape of the hull and expoxied it in place, making a stable platform for the additional 3 batteries. There's not much room but it just fits. I now have 675ah house bank. Ventilation isn't too much of an issue as they're sealed (Ca+Pb) batteries.


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Old 15-10-2016, 21:11   #13
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Re: Single House Battery Bank, Split Between 2 Locations?

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I have the same boat as you and was able to fit 3 x DC31's in the locker under the bed behind the original bank. We got a thick piece of marine ply, faired it to the shape of the hull and expoxied it in place, making a stable platform for the additional 3 batteries. There's not much room but it just fits. I now have 675ah house bank. Ventilation isn't too much of an issue as they're sealed (Ca+Pb) batteries...
This is WAY better.

And the cables previously suggested are ridiculously under size.
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Old 16-10-2016, 09:32   #14
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Re: Single House Battery Bank, Split Between 2 Locations?

Stefan. Good information. Perhaps your boat is slightly different but I don't have a second compartment behind the battery bank, at least not obvious. The decking behind the battery bank is one piece of solid wood. Did you have to cut the wood and add a removable cover? I'll PM you. Thanks, Alan
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