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Old 27-11-2014, 14:36   #16
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Re: Adding a battery bank

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Hi there,
I am looking at buying a catamaran here in Australia and I am really I terested in your electric propulsion. Can you give me more details as to how you went about the conversion and how you keep the batteries charged enough to provide you with enough " engine" power when needed?
Thanks
My conversion thread:
It Begins: Converting Cal 2-27 to Electric Propulsion!

Lots of ways to charge your propulsion batteries. Diesel genset, portable generator, windcharger, solar panels, engine alternator, regeneration, and good old fashioned plug in to shore power. You want to maximize use of renewable energy, of course, but a diesel or gasoline powered source is a great backup, and you can live with the inefficiency therein, if you get at least some power from wind or solar. If you are just day sailing or weekending with no motoring except docking and maneuvering for locks or bridges, shore power is cheaper than gallons of diesel. If you motor a lot, then maybe electric is not a good idea. Unless you just want to go electric. Even at only 10 amps, you will draw down your 220 to 260 ah bank in just 10 hours or so. You should only discharge to 50%. Bigger bank lasts longer of course.

If you only need an engine for maneuvering, electric is perfect. If you motor a lot, then you will have to live with a lot of tradeoffs and compromises if you go electric.
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Old 27-11-2014, 17:26   #17
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Re: Adding a battery bank

I'm a big believer of battery banks. I would install your second set of batteries as a second house bank for all the reasons others mentioned, aka, guarding against wake up with dead batteries... although your separate started battery goes a long way toward such protection. But desperate banks allow deprecate monitoring of voltage. (You can 't manage what you don't measure.). It so easy to set- up a two bank system... buy the switch and run just your normal new bank Red to #2 terminal and the black to the sNe ship's ground as the other bank black went. Charge wire goes to the common terminal. Charges bank 1 when SW on 1. Charges 2 md bank when SW in 2. Charges both in Both. Done!


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Old 27-11-2014, 19:34   #18
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Re: Adding a battery bank

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I'm a big believer of battery banks. I would install your second set of batteries as a second house bank for all the reasons others mentioned, aka, guarding against wake up with dead batteries... although your separate started battery goes a long way toward such protection. But desperate banks allow deprecate monitoring of voltage. (You can 't manage what you don't measure.). It so easy to set- up a two bank system... buy the switch and run just your normal new bank Red to #2 terminal and the black to the sNe ship's ground as the other bank black went. Charge wire goes to the common terminal. Charges bank 1 when SW on 1. Charges 2 md bank when SW in 2. Charges both in Both. Done!


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+1. Just remember to never turn switch to or from the OFF position while the engine is running. It CAN pop the regulator though it usually doesnt. You should be able to switch between 1 and 2 and BOTH though.

Look how many new boats are sold with exactly that setup.
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Old 27-11-2014, 21:55   #19
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Re: Adding a battery bank

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I'm a big believer of battery banks. I would install your second set of batteries as a second house bank for all the reasons others mentioned, aka, guarding against wake up with dead batteries... although your separate started battery goes a long way toward such protection. But seperate banks allow separate monitoring of voltage. (You can 't manage what you don't measure.). It so easy to set- up a two bank system... buy the switch and run just your normal new bank Red to #2 terminal and the black to the negative ship's ground as the other bank black went. Charge wire goes to the common terminal. Charges bank 1 when SW on 1. Charges 2 bank when SW in 2. Charges both in Both. Done!


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Not a great idea really. A large battery bank is more efficient than 2 banks half the size both when using power and when charging. The batteries will last longer if in one large bank as well.

As far as the original poster is concerned I agree a charging relay (like a Blue Seas ACR) is a great idea and run all charging to the house bank.
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Old 28-11-2014, 00:14   #20
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Re: Adding a battery bank

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Not a great idea really. A large battery bank is more efficient than 2 banks half the size both when using power and when charging. The batteries will last longer if in one large bank as well.
Lots of other posts to support this.

Use the search function or see my post @ Battery Configuration #49
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Old 28-11-2014, 01:04   #21
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Re: Adding a battery bank

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Lots of other posts to support this.
Lots do, but I don't

For a long distance cruising boat two house banks (with a separate starting battery as well) ads a lot of versatility.

You can use batteries of different ages and even different chemistries with care. It is easy to occasionally equalise, or fully charge a battery bank. Finally if have a defective battery/ cell it is easy to diagnose this and isolate the battery concerned.

I lot of people get the wrong idea about two banks and assume you must run them independently. With a flick of switch they can be combined and this is sensible most of the time. However with a simple and cheap extra battery switch you gain a lot versatility.
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Old 28-11-2014, 04:57   #22
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Re: Adding a battery bank

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Not a great idea really. A large battery bank is more efficient than 2 banks half the size both when using power and when charging. The batteries will last longer if in one large bank as well.
+1 Used to set up my boats with dual house banks but after reading all the latest discussions I set up my current boat with one large house bank and one isolated state bank.
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Old 28-11-2014, 05:05   #23
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Re: Adding a battery bank

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Lots do, but I don't

For a long distance cruising boat two house banks (with a separate starting battery as well) ads a lot of versatility.

You can use batteries of different ages and even different chemistries with care. It is easy to occasionally equalise, or fully charge a battery bank. Finally if have a defective battery/ cell it is easy to diagnose this and isolate the battery concerned.

I lot of people get the wrong idea about two banks and assume you must run them independently. With a flick of switch they can be combined and this is sensible most of the time. However with a simple and cheap extra battery switch you gain a lot versatility.
I can see the point that dual banks adds some additional options and the additional wiring to set up or combine the banks minimal but for most boaters I see no reason or advantage to mixing battery types or chemistries. Also, if you use 6 V batteries in series it's about the same amount of work to check individual batteries with either system, basically pulling one cable off to check individual voltage.
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Old 28-11-2014, 10:15   #24
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Re: Adding a battery bank

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I can see the point that dual banks adds some additional options and the additional wiring to set up or combine the banks minimal but for most boaters I see no reason or advantage to mixing battery types or chemistries.
Batteries are very expensive in out of the way places. Shipping is difficult and batteries are regarded as harazadous goods so arranging delivery is complicated.
House battery banks have a very unpredictable life, so it is hard to always replace them in a timely manner.

With two battery banks if your house battery bank fails you can replace half your battery bank with local batteries. Keep the best of the old batteries as a separate bank. In the near future a lot of cruising boats are likely to be using lithium batteries. To source these in remote places will be difficult for some time to come. Two house battery banks allow for the use of lithium and lead acid if a problem develops with the lithium bank.


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Also, if you use 6 V batteries in series it's about the same amount of work to check individual batteries with either system, basically pulling one cable off to check individual voltage.
Batteries often choose offshore sailing as a great time to fail . On most boats this is time when the house battery bank is most deeply discharged. In addition, the pounding can cause mechanical problems with the battery. If you lose a cell in one battery the whole bank is defective.

With two house banks it easy to diagnose where the problem battery is and with the flick of switch continue on the remaining good bank. The alternative of trying to switch over battery cables, offshore, especially in boats where the batteries access is poor is much more difficult. Throw in the loss of autopilot, navigation instruments and running and interior lights while you are making the switchover and a redundant battery bank system has a lot of appeal.

Two house banks is not essential by any means, but cruising boats have become very dependent on their battery supply. Having a separate battery bank that can be isolated is a nice extra. It has no drawbacks other than the slight extra cost. You can, and should, operate the two house banks as a single bank in most circumstances and this is easy to do.

For some reason people get very upset at the mention designing an electrical system with two house banks. It can be argued that it is overkill, but it is not an expensive addition and is at least worth some consideration.
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Old 28-11-2014, 10:58   #25
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Re: Adding a battery bank

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Originally Posted by noelex 77 View Post
Batteries are very expensive in out of the way places. Shipping is difficult and batteries are regarded as harazadous goods so arranging delivery is complicated.
House battery banks have a very unpredictable life, so it is hard to always replace them in a timely manner.

With two battery banks if your house battery bank fails you can replace half your battery bank with local batteries. Keep the best of the old batteries as a separate bank. In the near future a lot of cruising boats are likely to be using lithium batteries. To source these in remote places will be difficult for some time to come. Two house battery banks allow for the use of lithium and lead acid if a problem develops with the lithium bank.




Batteries often choose offshore sailing as a great time to fail . On most boats this is time when the house battery bank is most deeply discharged. In addition, the pounding can cause mechanical problems with the battery. If you lose a cell in one battery the whole bank is defective.

With two house banks it easy to diagnose where the problem battery is and with the flick of switch continue on the remaining good bank. The alternative of trying to switch over battery cables, offshore, especially in boats where the batteries access is poor is much more difficult. Throw in the loss of autopilot, navigation instruments and running and interior lights while you are making the switchover and a redundant battery bank system has a lot of appeal.

Two house banks is not essential by any means, but cruising boats have become very dependent on their battery supply. Having a separate battery bank that can be isolated is a nice extra. It has no drawbacks other than the slight extra cost. You can, and should, operate the two house banks as a single bank in most circumstances and this is easy to do.

For some reason people get very upset at the mention designing an electrical system with two house banks. It can be argued that it is overkill, but it is not an expensive addition and is at least worth some consideration.
+1. I don't know why none of us though to point that out before, but replacement of a bad bank with whatever is available is an important capability. Thanks for that.

FWIW I always had switch on "both" unless I was sleeping on the hook, or there seemed to be a problem with a bank. On "Both", essentially you have a single bank.

Right now I have one 12v house bank and one 48v propulsion bank, but that will change next year when I add a reserve 48v bank. Might get rid of the 12v altogether.
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Old 28-11-2014, 11:04   #26
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Re: Adding a battery bank

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Originally Posted by noelex 77 View Post
Batteries are very expensive in out of the way places. Shipping is difficult and batteries are regarded as harazadous goods so arranging delivery is complicated.

Absolutely no argument with this.

House battery banks have a very unpredictable life, so it is hard to always replace them in a timely manner.

This however has not been my experience. Yes, occasionally a battery may die an early death or die unexpectedly but have not seen this to be a common problem.

With two battery banks if your house battery bank fails you can replace half your battery bank with local batteries. Keep the best of the old batteries as a separate bank.

With my setup I can just remove or move a max of 2 jumpers and I can remove a pair of the 6V batteries from the system. Might take 5-10 minutes max.

In the near future a lot of cruising boats are likely to be using lithium batteries. To source these in remote places will be difficult for some time to come. Two house battery banks allow for the use of lithium and lead acid if a problem develops with the lithium bank.

I guess sourcing batteries could be a problem in some remote area of the south Pacific but most places in the world if you have a major battery problem you would typically be no more than a few days, max 8-10 days sail to a place where you can buy whatever you need.



Batteries often choose offshore sailing as a great time to fail . On most boats this is time when the house battery bank is most deeply discharged. In addition, the pounding can cause mechanical problems with the battery. If you lose a cell in one battery the whole bank is defective.

Again, my experience has not shown this to be a significant problem.

With two house banks it easy to diagnose where the problem battery is and with the flick of switch continue on the remaining good bank. The alternative of trying to switch over battery cables, offshore, especially in boats where the batteries access is poor is much more difficult. Throw in the loss of autopilot, navigation instruments and running and interior lights while you are making the switchover and a redundant battery bank system has a lot of appeal.

I had a boat with pretty tricky battery access but once again, for something that might happen once in several blue moons I don't think it makes sense to plan my battery installation for something with a very low chance of happening. As long as the cable changes are doable I prefer to design my battery installation for the optimal day to day use.


Two house banks is not essential by any means, but cruising boats have become very dependent on their battery supply. Having a separate battery bank that can be isolated is a nice extra. It has no drawbacks other than the slight extra cost. You can, and should, operate the two house banks as a single bank in most circumstances and this is easy to do.

Certainly the cost is minimal and yes you can use two banks like one but I think you can get all the advantages you describe with minimal cost and effort with one bank.



For some reason people get very upset at the mention designing an electrical system with two house banks. It can be argued that it is overkill, but it is not an expensive addition and is at least worth some consideration.
What, me worry? Upset, not at all and hope you aren't either. In fact based your arguments I see some advantages and minimum downside to running two banks as one. Keep responding and I might almost be convinced.

Like different ships, different long splices. I see it as a matter of preference and not a critical safety issue either way.

In my setup with 3 pairs of 6V batteries in one large box it just makes sense to wire it as one bank. Also let me set up the house bank as backup starting with 2 switches only.
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Old 29-11-2014, 08:46   #27
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Re: Adding a battery bank

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Batteries are very expensive in out of the way places. Shipping is difficult and batteries are regarded as harazadous goods so arranging delivery is complicated.....
It's worth noting that AGMs are classed as non-hazardous so can be shipped anywhere. The extra cost of shipping may still make them cheaper than the same AGM brand that may eventually be sourced "locally".
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Old 29-11-2014, 12:51   #28
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Re: Adding a battery bank

I have personally witnessed a boat with 2 house banks, a 1,2,all switch for house banks (seperate switch and battery for engine) dual bank battery monitor. With one bank 8' farther from switch then the other

When running the house switch in all The close bank was always around 25% more discharged then the further one.

Both banks were same size, same batteries, but at different ends of seat bench for space

This boat was tied up and fully charged after each trip

2 banks ruins day to day use. If you only use one at a time, you have a loss of capacity from perkurs curve, and if you run in both you have a loss from inprober wiring by not going end to end.

I rely like the "it's better to have 2 because its cheaper to buy them". Lol

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Old 29-11-2014, 14:14   #29
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Re: Adding a battery bank

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When running the house switch in all The close bank was always around 25% more discharged then the further one.
It is sensible when splitting a battery bank in two to keep the resistance in the battery cables equal, but the imbalance in SOC should not be 25% if the banks are combined. (Remember as the charge current drops off the voltages will tend towards the same.)

It sounds like in the quoted example one bank had a defective battery, or high resistance connection somewhere in the system, or it may have been a simple miscalibration of one monitor.

One extra advantage of two systems is that their performance can be compared. A discrepancy like the one noted indicates that there is problem that needs investigation. A bit like if there was difference in oil pressure between the two engines in a cat.

If the banks are operated independently you do need to consider Peukert's law, as you say, during discharge and the reduced current acceptance during charging. This is one reason why it is sensible to keep the banks linked as much as possible.

Typically the batteries would only isolated for testing, where a battery has developed a fault, to keep electronics running while equalising, or to occasionally fully charge the batteries (especially AGM) when power is limited.

Even if you were forced to use LA batteries are different chemistries the banks can be linked much of the time. If you are using say gel and flooded batteries the batteries would be isolated during the last part of charging to allow the flooded batteries to reach the higher charge voltage they need.
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Old 29-11-2014, 15:06   #30
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Re: Adding a battery bank

I'm not trying to refuel the debate on one vs. two battery banks, but just want to share our real a World experience with a two bank battery that has worked exceptionally well for us. As an EE and long term user of a large two battery bank sailboat... I've had no battery life issues/ nor can I get my technical head around why there would be any REAL, not theoretical bank , life issues with a two bank system. In our case, my wife and I went 7+ yrs before any measured decrease in either battery bank efficiency on lead-acid 8Ds (2 + 2 lead acid 8Ds). I could have possibly gone another year or two... but I voluntarily changed them out (one bank at a time to soften the $$$impact). I don't think 7+ yrs of typical use/ about equal lost of efficiency on both banks shows much loss of life in a two bank environment. One of the new replacement batteries developed a shorted cell (manufacture's defect) very soon (1st month) after replacing and we would have been in duck soup being where we were waking up with all batteries dead (I never sleep with battery SW in 'both.' As it was, all we had to do was switch over to the other bank. I then remove the bad battery from its brother, recharge the remaining battery and reconnected it back as a single battery into Bank 2. What could have been a stressful and expensive situation was a tiny event that I had totally forgotten about until this discussion. And we continued our journey, still with the protection/ safety of a two battery bank system, although one with now 1/2 capacity of the other. Maybe our long life two bank experience was due to having plenty/ over capacity on either bank so that our typical use never taxed either bank that may be been working alone. Also both of us are good about battery management/ routine of flipping between banks... Monday was bank 1, Tuesday 2, ... But other than drawing down an under capacity bank, I'm still having a hard time understanding why a two bank battery system spoils the stew... if you are rotating their use about equality. Again... our real-life experience seems to prove it out. We now have 2+ 2 AGM 8D banks going on 4-6 years with still just about equal measured efficiency's.


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