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Battery, charging, isolation, inverting, switching questions

Old 07-07-2017, 05:06 AM
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Default Battery, charging, isolation, inverting, switching questions

Hello I have a new to me 30 year old 27 foot Tiara with twin engines and no generator.
I’d like to set it up for my needs and am looking for suggestions and answers to electrical questions.

My objective is to be able to overnight on the hook and run interior fans, refrigerator, lights, and charge phones off of battery power and still be able to start the engines in the morning.
I’d like to be able to charge any battery from either alternator. Does a battery isolator do this? I’ve seen isolators advertised like PROMARINER 1 ALTERNATOR 3 BATTERY ISOLATOR 70 AMP that seem to do this but its not clear to me if the alternator input is switched to all batteries. For example, if one of my alternators dies will the other still charge all 3 batteries?...if so how would I know if one of the alternators went bad?
I’d also like to be able to switch any battery bank to start either engine in an emergency.

Current setup is:
• Two gas engines
o Mercruiser stern drive 5.7 L V8 Alphas carburated
• Two alternators
o Each tied to it’s own battery
• Two starting batteries
o Port battery also powers windlass
o Starboard battery powers all onboard house loads
• 30 year old permanent battery charger (no inverter)
o Question: is it advisable to leave the charger on while on shore power or will it cook my batteries? Boat sits at the dock during week and runs about 4 to 8 hours every weekend depending on the weather.
• An on / off battery switch for each motor/battery
• An on/off switch for the windlass
• An emergency momentary parallel switch on the dash

My first questions are about batteries. I’d like to leave the house bank on overnight to run things.
1. How much battery do I need to run the fridge, 3 small fans and phone chargers?
2. Is it ok to just let the battery run down overnight till it’s out of power
a. Will that hurt the fridge?
b. Will that hurt the battery?
3. Should I add a dedicated 3rd house bank or beef up one or both of the current two batteries?
4. Should I do a 2 battery setup and make one the starting battery for both motors and one the house bank?
5. What kind of batteries?
a. Lead acid, AGM, other?
b. Run dual 6 volt batteries serialed to equal 12 volts?
c. Deep cycle vs startup for house and starting batteries (I assume there’s a reason for the term “start up”.
My next question is about inverters and isolators
1. When and why would I want to run ACHs vs a multi bank isolator?
2. Should I replace my old technology battery charger with a modern charger/inverter?
a. Does my AC/DC fridge run more efficiently on AC or DC?
b. It would be convenient to power on the electrical outlets for AC phone charging but I can also charge them on DC USB chargers…again is AC or DC more efficient?
c. What’s better inverter for my intended use (or do I need one at all)? Sine Wave VS modified Sine Wave
3. If I upgrade the charger can I leave it on all the time on shore power?

next questions are on battery switches
1. If the answer to the battery question is to set up a 3rd house battery bank, what is the recommended battery switch configuration that enables any of the 3 batteries to be switched to start either engine in an emergency
2. This question is easier if two battery banks are used…I’ve seen Blue Sea sells this set up pre configured
Lastly, I plan to install a multifunction battery gauge that measures volts and Amps and can be switched to read up to 3 banks of batteries.

Thanks for reading this far and any recommendations you can offer.
I’m sure to have follow up questions 
Old 07-07-2017, 07:35 AM
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Originally Posted by outobie View Post
Current setup is:
• Two starting batteries
o Port battery also powers windlass
o Starboard battery powers all onboard house loads
• 30 year old permanent battery charger (no inverter)
o Question: is it advisable to leave the charger on while on shore power or will it cook my batteries? Boat sits at the dock during week and runs about 4 to 8 hours every weekend depending on the weather.
• An emergency momentary parallel switch on the dash

My first questions are about batteries. I’d like to leave the house bank on overnight to run things.
1. How much battery do I need to run the fridge, 3 small fans and phone chargers?
2. Is it ok to just let the battery run down overnight till it’s out of power
b. Will that hurt the battery?
3. Should I add a dedicated 3rd house bank or beef up one or both of the current two batteries?
4. Should I do a 2 battery setup and make one the starting battery for both motors and one the house bank?
5. What kind of batteries?
a. Lead acid, AGM, other?
b. Run dual 6 volt batteries serialed to equal 12 volts?
c. Deep cycle vs startup for house and starting batteries (I assume there’s a reason for the term “start up”.

My next question is about inverters and isolators
2. Should I replace my old technology battery charger with a modern charger/inverter?
a. Does my AC/DC fridge run more efficiently on AC or DC?
b. It would be convenient to power on the electrical outlets for AC phone charging but I can also charge them on DC USB chargers…again is AC or DC more efficient?
c. What’s better inverter for my intended use (or do I need one at all)? Sine Wave VS modified Sine Wave
3. If I upgrade the charger can I leave it on all the time on shore power?

1. You can look up how much power the fridge uses. See fridge specs. The rest, not a lot... except continuous "hidden" loads -- CO detectors, stereo memory, etc. -- can add up, so "lots" (as much capacity as you can reasonably stuff in there) is usually an OK approach.

2 and 2a, Absolutley NOT and yes it'll toast your batteries. Most makers recommend disharging to no less than 50% of capacity.

3 and 4. I suspect easiest is to just add battery to your starboard bank, and use your port battery as reserve (with the parallel switch). Might not hurt to add battery to you port bank, too, but I'd guess space will come into play. Maybe high CCA/MCA dual-purpose battery(ies) for your port side. Maybe high dual-purpose or deep cycle amp-hours for your starboard bank. (Cranking amps are additive within a battery bank, so more deep cycle batteries on a combo starting/house bank can still work for starting your engine. Engine specs will list minimum cranking amps.)

5. Depends. If you can easily service, flooded lead acid is least expensive. If you can't easily service, and/or if off-gassing in an issue to avoid, AGMs can be viable. You might have to study sizes (physical dimension and layout possibilities) and capacities first, though. Certainly 6V golf cart batteries can be part of your examination, but if you only have room for one pair -- and if one of those in the pair develops a short -- you're temporarily hosed... so I'd guess 6V batteries in series/parallel are only a better choice if you've got room for four of them.

2. Maybe, maybe not. If your current charger is working OK and not boiling batteries... maybe only adding an inverter on your starboard bank could be fine. Or another approach might be (again assuming current charger is OK) to add an inverter/charger to starboard bank, and dedicate the original charger to only the port bank. Or maybe the gold solution is to replace the current charger with one appropriate for your port bank, and put an inverter charger on the starboard bank. (Inverter/chargers will often service only one battery bank... without some relays or echo chargers or whatever... so I've only mentioned maybe the easiest approach.)

2a. Depends. Some dual-voltage fridges always run on DC, even with being fed AC,, and some may be the opposite. Check fridge specs, or ask the manufacturer. But if the dual-voltage fridge runs on DC (for example), converting AC to DC is usually slightly less efficient... and vice versa.

2b. Ditto.

2c. Depends, but some appliances reportedly really prefer pure sine wave. I think some microwaves fall into this category...

3. Very likely. You may be able to do that with your current charger, too, but that depends on how it's acting, whether it's designed for that or not.

-Chris
Old 07-07-2017, 07:43 AM
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Some great advice above.

Those two engine batteries are "starting" batteries - designed to supply power quickly for an engine cranking over.

What you really need is a "house" battery setup. House batteries are both a separate battery bank and a different type of battery. Most house setups are deep cycle batteries (designed to be run down lower and recharged many times) and they are of course wired separate from the engine starting batteries.

When you have a house setup you run all of your 'stuff' off the house battery bank. In the morning even if the house bank is 100% depleted - your engine batteries are still ready to go and start the engines.

Two group 31 deep cycles batteries, wired on a separate bank, with a dedicated switch, and you will be good to go for overnights.

I've posted on this before, but you should look at a solar panel setup. The solar panels obviously won't charge anything overnight however they will provide a small stream of charge during dawn/dusk and of course output a healthy amount of charge during peak sun.
Old 07-07-2017, 08:53 AM
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I've got a fair amount of space to add batteries. my boat had the option of fitting it with a hot water heater, generator and AC unit...all of which are not on my boat. so I do have decent space in the engine compartment to add batteries...there's enough space to double up each of the current batteries and to add a double battery 3rd bank so I have room to go from 2 to 6 in the engine compartment ...if that's the best solution...I like the idea above of doubling up both the port and starboard banks...that sounds simple and balanced without adding too much weight to the stern

I thought about solar but ruled it out for lack of mounting location...I don't have a hard top or any arch...only a bimini. a tubular arch for radar and spreaders, etc is on the list for a possible future project but that's a year or more in the future
Old 07-08-2017, 05:49 AM
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Originally Posted by outobie View Post
I've got a fair amount of space to add batteries. my boat had the option of fitting it with a hot water heater, generator and AC unit...all of which are not on my boat. so I do have decent space in the engine compartment to add batteries...there's enough space to double up each of the current batteries and to add a double battery 3rd bank so I have room to go from 2 to 6 in the engine compartment ...if that's the best solution...I like the idea above of doubling up both the port and starboard banks...that sounds simple and balanced without adding too much weight to the stern

In that case...

An example approach might be to double your port bank, assuming you're starting with something like a single G27/29/31... to 2x Odyssey 12V PC-2150 AGMs (BCI Group 31) in parallel. Huge cranking amps, and that'd give you 200-Ah total capacity, 100-Ah usable to now less than 50% discharge.

Then increase your starboard bank, again assuming you're starting with a single G27/29/31, to 4x Lifeline GPL-4CT AGMs (BCI GC2 equivalent, I think) in series parallel. Decent cranking amps (good for the windlass, too), but more importantly that'd give you 440-Ah total/220-Ah usable on that bank for your fridge and so forth.

Or for the latter, and if you have vertical space, 4x of the taller GPL-6CTs would give you 600-Ah total/300-Ah usable.

Just meant as an example, and not an inexpensive one since these are premium batteries, but you can look at specs for those and other similar battery options (and less expensive brands) to see how much your wallet can stand. AGMs gets you out of some service work over their lifetime, and you wouldn't have to pay as much attention to off-gassing... but then again, if service is easy, flooded lead-acid (FLA) batteries are good value for $$$.

Also... your charging capability may come into play, in two ways. First is that AGMs can accept charge faster, and most makers recommend a higher-rate charging capability. Second is that two banks, one 200-Ah and one 440-Ah aren't all that well balanced. Modern "smart" chargers are expected to accommodate that, though, at least within reason... so they only charge a given bank with the amount of current that bank will accept.

OTOH, that gives you another opportunity for improvement. Add an inverter/charger to your starboard bank, and dedicate your original old charger to the port bank. Or maybe see if you want to get a new charger for the port bank, too, if you feel the older one isn't really "smart" enough, perhaps a distinct possibility.

"I'm on a..." suggested separate start and house batteries, and I would agree, that's a common set-up intended to keep you from getting stranded...

But that'd be more work, too, and probably just beefing up your current start/house combo banks would be sufficient, also assuming you pay attention.

-Chris
Old 07-09-2017, 10:25 AM
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Thank you ranger42c. I like your suggestions

So if I understand

In your top description of dual batteries port and quad batteries starboard, are the port batteries providing start for both motors or just start for port? If only start for port is the reason for adding a second battery just for redundancy?

Are my 65 amp alternators sufficient for charging 6 batteries?

Also when you parallel batteries how do you isolate them so one failed battery doesn't bring down its paired good ones

Thanks again for the great info

I ordered a marine electronics book to educate myself as well
Old 07-09-2017, 11:55 AM
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Originally Posted by outobie View Post
In your top description of dual batteries port and quad batteries starboard, are the port batteries providing start for both motors or just start for port? If only start for port is the reason for adding a second battery just for redundancy?

Are my 65 amp alternators sufficient for charging 6 batteries?

Also when you parallel batteries how do you isolate them so one failed battery doesn't bring down its paired good ones

Thanks again for the great info


I ordered a marine electronics book to educate myself as well
I suspect easiest to leave the starting arrangement as is: dual port batteries start port engine and run windlass, quad starboard batteries start starboard engine.. and run house functions, too. Second port battery is mostly to give you headroom for the windlass, and plenty of cranking amps if you happen to draw down the starboard start/house bank so much that you need to use your momentary parallel switch to start starboard.

Might not even need a second battery there if you don't use the windlass all that much (not often, or only for very short periods), but then a two-battery bank can also speak to your question about parallels and isolation (more on that, below).

I can't speak well to the alternator question, but as I speculated above, you have a battery charger (that you might replace) for one bank (e.g., port) and you might add an inverter/charger to the other bank (e.g., starboard)... and both of those (assuming well-selected during your shopping phase) would be sufficient to charge batteries when you're on shore power.

With alternators.... one would be charging the 2 port batteries. The other would be charging the 4 starboard batteries. How well they can do that depends on how much "left-over" juice they have available after servicing whatever DC loads that are on while the engines are running. This would be a good question for engine/alternator guys...

And it's also a factoid that it's difficult to get batteries quickly recharged that last little bit to 100%. Usually engine alternators and even generators running battery chargers for a few hours a day isn't enough to bring battery banks back up to fully charged... whereas shorepower chargers -- over the course of a day or two or three -- usually do better at that.

When batteries are in parallel, one battery crapping out the other is a risk you decide to take. But that's also why a common rule of thumb is to buy a whole bank at once, i.e., all new batteries, same type/size/age/maker/etc.... so you're hoping all of those new batteries work equally well.

And then if you get a short in a battery within a bank... often you can just disconnect the bad one, at least to get home. In a two-12V-battery bank (as in the port example, disconnecting the bad battery still leaves you with a 12V source. In a 4-6V-battery bank, disconnecting one pair (the pair with the bad 6V battery in it) still leaves you with a 12V source (and that's why four 6V batteries can be better than just two).

Nigel Calder's book on electronics if a good one.

-Chris

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