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post #1 of 11 Old 08-22-2013 Thread Starter
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House bank sizing

I am replacing my house bank of batteries as part of my refit and I have have a lot of room. Can anyone provide a rule of thumb for sizing a house battery bank on a 33' sailboat. Also what type of battery?

My biggest load will probably be the cold plate in the ice box, second load would be the freshwater pump but it would only run intermittently. All lighting is led and I do not have a microwave or ac. If I add AC it will only used at the dock so that should not affect the size of the bank.
The new beta 20 motor is equipped with a 75 amp alternator on serpentine belt and I have an echo charge that will be installed between he house bank and the starting battery.

Thanks in advance

dan

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post #2 of 11 Old 08-22-2013
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Re: House bank sizing

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Originally Posted by katsailor View Post
I am replacing my house bank of batteries as part of my refit and I have have a lot of room. Can anyone provide a rule of thumb for sizing a house battery bank on a 33' sailboat. Also what type of battery?

My biggest load will probably be the cold plate in the ice box, second load would be the freshwater pump but it would only run intermittently. All lighting is led and I do not have a microwave or ac. If I add AC it will only used at the dock so that should not affect the size of the bank.
The new beta 20 motor is equipped with a 75 amp alternator on serpentine belt and I have an echo charge that will be installed between he house bank and the starting battery.

Thanks in advance

dan
Start with a battery monitor so you know your daily averages. A Victron BMV-600 is a very good value.

Once you have a good idea of consumption you can then size a bank for your intended use. 1 day on the hook, 2 days on the hook, 3 days on the hook before recharging..?

Remember you should only use 50% of the capacity so as to get the most cycles per $$ spent. 50% is a guideline however and shallower cycling will simply mean longer life. How do you cycle less deeply? Size the bank larger and re-charge at 65%, 70% or 75% SOC vs. 50% SOC...

BUT, there is always a but......

When off cruising you can really only use about 30-35% of the capacity due to declining acceptance during the last 15-20% of the charge cycle. No real sense in charging beyond 80-85% SOC because you just waste fuel and lightly load the engine.

So in reality you need a bank that is about 70-75% larger than your daily use.

If always tied to a dock after each use you can get away with 50% larger than daily use...

If you use say 50Ah per day then a 130Ah - 150Ah bank would be about right if you only want to go 1 day on the hook without re-charge. If you want to go two days then a bank of about 300Ah's would be much better...

Also the larger the bank, compared to daily use, the shallower the cycles and the longer the bank will last.

50Ah per day takes a 100Ah battery to 50% SOC

50 Ah per day takes a 200Ah bank to 75% SOC

50Ah per day takes a 300Ah bank to 83% SOC

The less deeply you cycle a bank the longer it will last.....


That Peukert guy...

Also there is the Peukert effect. 50Ah per day is approx 2Ah every hour or, a 2A average load.

A 2A load on a 100Ah 1.25 Peukert bank is a 1.59A effective load or makes it effectively a 125Ah bank (a 25% increase)

A 2A load on a 200Ah 1.25 Peukert bank is a 1.3A effective load or makes it effectively a 300Ah bank (a 50% increase)

A 2A load on a 300Ah 1.25 Peukert bank is a 1.2A effective load or makes it effectively a 500Ah bank (a 67% increase)

A 2A load on a 400Ah 1.25 Peukert bank is a 1.1A effective load or makes it effectively a 710Ah bank (a 78% increase)


The larger the bank is the better the cycle life will be and the shallower the effective cycles.........

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post #3 of 11 Old 08-22-2013
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Re: House bank sizing

Can you fit 2 golf cart batteries? 4 would be better.

If yes go for those! about $150 each.
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post #4 of 11 Old 08-22-2013
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Re: House bank sizing

Start with 4 6-volt golf-cart batteries....about 450AH total. Wire them in series/parallel to make a single house bank. FWIW, I just bought six Crown golf-cart batteries for $99 each.

Run the alternator output and all other charging sources (battery charger, solar, wind, generator, etc.) directly to the house batteries.

Use the EchoCharge to keep the start battery topped up.

From what you described, that should be just fine for your boat.

Bill
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post #5 of 11 Old 08-23-2013
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Re: House bank sizing

Agreed. Simple rule of thumb is that with a fridge even with LED lights, you'll use around 100 amps per day.

Record of Daily Energy Use of 100 ah per day:

"Breaking In" New Wet Cell Batteries

It's all up to you as to how large a house bank you want, since it's size will determine how long you can stay without recharging. Solar's a good bet to help to avoid using the engine/alternator. BTW, nice engine, nice alternator.

Good luck.

Stu Jackson, Catalina 34, 1986, M25 engine, Rocna 10 (22#), Maple Bay, BC, Canada
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post #6 of 11 Old 08-26-2013 Thread Starter
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Re: House bank sizing

Thanks all. I didn't mention it in my earlier post but I picked up a Victron BMV-600 and the pricey blueseas 3/8 terminal strips a couple months ago. Still need the galvanic isolator and wire to complete the house bank and grounding side of the rewiring project.
Next will be a new panel and charger/inverter or just continue to use my existing charger and add a small inverter for charging electronics.

I spent part of my weekend stuck in the mud, literally!

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Re: House bank sizing

Next question

Do I connect my starting battery to the starter terminal and connect the house battery to the Battery connection on the alternator with the echo charge installed between the house and starter batteries?

MaineSail to the white courtesy phone please.

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The victron is a nice tool. But they don't tell you about resetting it often, which it needs.

After a while of cycling up and down the logic circuit gets confused or can't keep up or just falls asleep. So it needs resetting.

How?

Wait until, during charging, your I number is only reading 2% of bank capacity. If you have a 500 a/h bank you need to see the I number down to about 10 amps. That is REALLY full and not almost full. When you are at this 2% level, press the top and bottom buttons simultaneously until the display switches to 100% SOC. Now the system is recalibrated to a true 100% SOC.

Did I do OK MS?
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Re: House bank sizing

[QUOTE=katsailor;1079649]Next question

Do I connect my starting battery to the starter terminal and connect the house battery to the Battery connection on the alternator with the echo charge installed between the house and starter batteries?


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post #10 of 11 Old 08-27-2013
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Re: House bank sizing

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Next question

Do I connect my starting battery to the starter terminal and connect the house battery to the Battery connection on the alternator with the echo charge installed between the house and starter batteries?

MaineSail to the white courtesy phone please.
It all depends on how you want to wire it.

Basic Battery Wiring Diagrams This is a very good basic primer for boat system wiring: Basic Battery Wiring Diagrams

This is another very good basic primer for boat system wiring: The 1-2-B Switch by Maine Sail (brings together a lot of what this subject is all about)
1/BOTH/2/OFF Switches Thoughts & Musings - SailboatOwners.com

Echo Charger:

Echo Charger Use Warning from Maine Sail: Xantrex Echo Charger Rant

For your Victron:

or everyone installing a battery monitor: The "Gotcha Algorithm" thread, a "MUST READ"

Link-series Charging Algorithms -- The "Gotcha" Factor!

DEFAULTS are factory settings that are made to be modified to suit your setup.

Stu Jackson, Catalina 34, 1986, M25 engine, Rocna 10 (22#), Maple Bay, BC, Canada
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