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My last boat was very minimalist, with only a 27ah house battery and only lighting loads, and most of the places we went we had access to shore power if needed, so I don't have a lot of experience with power management.

Our new boat has significantly more than that! We have a 550ah bank of flooded cell batteries providing power for a Webasto heater, refrigeration, electronics, auto helm, audio system, and even a 200w inverter powering a 22" led TV, (although I doubt I will use the TV much).

This weekend was our first time taking the boat "off grid", so I was watching battery voltages carefully to get some idea how long we could go without recharging. Unfortunately the boat is not yet equipped with an ammeter, so I don't know how much we were drawing. We started with fully charged batteries at 12.8v. Our main loads were the refrigeration and the heater. I have already upgraded all lighting to led so that is a negligible load. After 24hrs I saw the voltage dropping as low as 12.3v, but that was when both the heater and the fridge were running. When both units cycled off, voltage recovered to 12.5v

So when judging how discharged the bank is, should I be referencing the voltage under load, or at rest? My understanding is that you don't want to discharge more than 50% or about 12.2v. It seems to me my batteries were already getting low. I would have expected to be able to go longer than 24hrs without charging with my relatively large bank.

What should I expect from my batteries?

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You really should expect nothing until you get a battery monitor and find out how much you are using on a daily basis. Voltage measurement should be at rest for guestimating SOC, but this is almost impossible to achieve on an actively-used boat.
 

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You really should expect nothing until you get a battery monitor and find out how much you are using on a daily basis. Voltage measurement should be at rest for guestimating SOC, but this is almost impossible to achieve on an actively-used boat.
Yeah a voltage monitor is on my to-do list once I do my homework, and decide which one to get. Apparently all I need is a shunt for my panel to display amp draw. Don't ask me why that would not be installed from the factory...seems like it should be standard equipment on such a boat! Regardless, it doesnt give the whole picture because not all loads go through the panel. The heater, and power winch are not on breakers from the panel.

If resting state is the best way to check SOC, it's not hard to shut off all major loads once in a while to check it.

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Hey,

it's been my experience from my RV days that a forced air heater consumed a lot of power. If it was 50 or below the house battery would be dead by morning. If it was 60 and above I didn't use the heater and the battery would last 2-3 days. If you will be using the heater often then you better find out how much power it uses. If you won't be using the heater then your will use a lot less power.

Barry
 

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Welcome to the fight. Power management and tracking can be quite consuming, especially on a power hungry boat. Triple if your OCD about things like this.

A shunt and battery monitor are minimum ante into the game. You need to know how much draw you typically have, but you also need to know how much charge is going back in. Knowing how much charge is going back in may even be more important, because it's the only way to really know if you've properly topped up a flooded acid bank. You need to see how much acceptance amperage there is, not just count amps. Topping up increases longevity (is saves money) and maximizes capacity.

You are right, the rule of thumb is that one shouldn't use more than 50% of lead acid capacity, but capacity lowers as batteries age. It's hard to know what capacity really is after a few years. On the other hand, there is no law about that. It's simply considered the level that balances the number of useful charge cycles in the battery's lifetime against useable capacity. You can discharge to a lower State of Charge SOC, getting more useable capacity, but the batteries will die sooner. Vice versa, as well. Be light on their usage and they last longer, but of course, are less useful.

Balmar sells a Smartguage that is supposed to be able to determine SOC in a percentage, after it automatically "learns" you bank over a few cycles. I have one. It has allowed me to identify some real flaws in the OEM setup, which I've fixed. It also caused me to identify that I wasn't maintaining full charge, due to poor charge settings. I'm still not fully convinced it works, but I have to give it credit for causing me to debug. This will be my first season with both new wiring and charge settings, so I'll know over the next month or so, if I think it's SOC is accurate. Some swear by it.

Finally, 550 ah may not be enough for a power hungry boat. We only have 440ah and there is not way I can make it 24 hours with everything on...... ie cruising. I have to run the generator at some point. When I run this bank to it's demise, I'm upgrading to lithium. Twice the capacity in the same footprint and much more efficient charge profiles, without the need to top up to prevent decay.
 

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Yeah a voltage monitor is on my to-do list once I do my homework, and decide which one to get. Apparently all I need is a shunt for my panel to display amp draw. Don't ask me why that would not be installed from the factory...seems like it should be standard equipment on such a boat! Regardless, it doesnt give the whole picture because not all loads go through the panel. The heater, and power winch are not on breakers from the panel.

If resting state is the best way to check SOC, it's not hard to shut off all major loads once in a while to check it.

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Those won't be a problem to measure because a battery monitor shunt is wired so that all loads go through it, not just the panel - panel, alternator, all loads.

You want more than a voltage monitor. Get one that monitors voltage, amps, cumulative Ah.

Mark
 

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Using an electric heater when boat is off grid is way too optimistic. Put on some extra clothes and a hat. You will be pushing it with just your refrigerator running. You definitely need an ammeter to figure out what your equipment draws. When we lost generator and engine off the Honduras Banks, our 200 W solar panels were barely adequate for keeping navigation equipment running. It was not enough to keep our running lights on all night. We would only turn them on when we spotted another ship. Conserving power is very important.
 

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Use a clamp multi meter to get accurate draw...by item.
Then learn how long they run...24/24..4/24..etc
Quick to figure out
I have a bmv-700 but only use it to display voltage.
 

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Welcome to the grid
We have a victron to monitor usage as well is charge

540 ah is plenty unless you want to be running a condominium. Remember usable amp hours are 1/2 of your total bank.

With the victron you can figure out our electric diet . How much you use and or each piece uses. From there you can figure out how to manage it. Doutful a heater figures in as it uses mega amps. Refrigeration dies also.
 

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Does you new Jennaeu have a generator? If not you'll be like the 95% of us. You need to also match your batteries, and charging mechanism to prevent uselessly spending money, or burning up/ sufficating any battery bAnk you have.

Electrical systems require some reading up on.. but most can easily understand the basics.
 

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Discussion Starter #13
I am actually looking forward to delving into this stuff more, although I wouldn't consider myself OCD about it, it's the kind of thing that interests me.

As it stands right now we don't have any charging methods other than alternator or shore power. Generators have always been a pet peeve of mine, so at this point I anticipate my focus to be on clean, quiet energy sources.

Currently our cruising style has us frequently stopping in places that have shore power available, but I expect that will change now that we have a bigger faster boat, and will certainly change once I retire and we have time to venture to more remote locations for longer periods of time.

I underestimated how much power the Webasto draws, just based on the voltage drop it creates when it cycles on. I don't anticipate using it at all in the summer, but early and late season does get chilly at night. We didn't leave the heat on continuously, and we threw an extra blanket on the bed and turned it off overnight.

I don't think our boat is overly power hungry, with refrigeration being the main load. We don't use the power winch for much other than hoisting the main. I would assume if we used the auto helm a lot while sailing could consume a fair amount of power. That is something else I have never had, so I'm not sure how much I would use it. I am guessing only for short periods while I make trim adjustments etc, and maybe while I eat lunch. I'm the kind of guy who likes to be on the helm!

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You certainly don't need a generator, but you do need something more than an alternator, while out cruising, to be able to efficiently get a lead acid bank to 100% charge routinely. The alternator can play a role, but tons of solar or wind gens can help. Unless, of course, you're willing to replace the batteries more often. Either that or upgrade to Lithium, which doesn't care if you get back to 100%.
 

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Shock - do you know how old and how much use the batteries on the boat have had? That can make a big difference in what to expect from them going forward....

I would definitely second the previous suggestions about getting a Balmar Smart Gauge and a Victron battery monitor. These are awesome pieces of kit that will give you all the info you need to understand and manage your batteries and electrical system. Voltage readings alone can be somewhat useful, but they can also be very misleading.

And, if you haven't already check out Mainesail's Marine How To website....tons of educational material there!

For a point of reference, I have two 6V 215AH golf cart batteries on my boat, powered primarily by 400W solar, and can regularly go several weeks at a time without having to run the engine for a long period or plug into shore power.....running refrigeration, lights, VHF, chartplotter, autopilot, etc. as well as charging phones and laptops.
 

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Discussion Starter #16
Shock - do you know how old and how much use the batteries on the boat have had? That can make a big difference in what to expect from them going forward....



I would definitely second the previous suggestions about getting a Balmar Smart Gauge and a Victron battery monitor. These are awesome pieces of kit that will give you all the info you need to understand and manage your batteries and electrical system. Voltage readings alone can be somewhat useful, but they can also be very misleading.



And, if you haven't already check out Mainesail's Marine How To website....tons of educational material there!



For a point of reference, I have two 6V 215AH golf cart batteries on my boat, powered primarily by 400W solar, and can regularly go several weeks at a time without having to run the engine for a long period or plug into shore power.....running refrigeration, lights, VHF, chartplotter, autopilot, etc. as well as charging phones and laptops.
The batteries were replaced in 2016, and as far as I can tell they have spent most of their life on a smart charger at the dock. It is a 2011 boat and only has 650hrs on the engine, so I don't think it was used a lot.

I suspect I will use the current battery bank for a few years and then upgrade to modern battery technology once I have figured out what our needs are. We have an enormous battery compartment...we currently have 5 lead acid 12v batteries and we have space for one more at least!

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A shunt goes in the battery negative line, as close to the battery as you can get it, before the battery is connected to the rest of the system. You can place a DC clamp meter in the same location.

Reason being that no matter where things are powered from, they all normally join into a ground bus that goes through that ground cable, so you can measure the consumption of everything from that spot. Then all you have to do is rig a wifi webcam to broadcast a view of that meter from that inaccessible place to somewhere you can watch it.(G)

For the best life of wet lead batteries, you actually don't want to use more than 50% of their capacity, 30% of you can get away with it. Or you can go down to 80% but that's really going to use up the batteries fa$ter.

There are also low-voltage cut-outs that you can install. The good ones are adjustable, you can set it to 11.9 volts and if you draw the battery down that low, it cuts off all power until you reset it. (Usually manually, some by remote fob.)

The voltage after loads have been shut, the resting voltage, is what you want to measure by. If the batteries drop a little lower when loads are on, it just means you really need some more battery to keep running those loads.
 

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I underestimated how much power the Webasto draws, just based on the voltage drop it creates when it cycles on.
This is a diesel heater, correct? If so, then shouldn't the power be only for the fan (and maybe a small fuel pump)? If so, then that shouldn't draw more than 5A, and only when running - no? If similar to an AC runtime, then maybe 50% duty cycle, so 60-70Ah over 24hrs. Not too bad.

Disclosure: I don't know anything about these and am only guessing.

Mark
 

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The batteries were replaced in 2016, and as far as I can tell they have spent most of their life on a smart charger at the dock. It is a 2011 boat and only has 650hrs on the engine, so I don't think it was used a lot.

I suspect I will use the current battery bank for a few years and then upgrade to modern battery technology once I have figured out what our needs are. We have an enormous battery compartment...we currently have 5 lead acid 12v batteries and we have space for one more at least!

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We've got 6-6volt Lifeline AGM for720 ah. Daily diet in mid summer with refrigeration running is 65 ah. That includes many LED , radar and chartplotter and charging of phones etc. Caframo fans (3) and refrigeration use most of power. Don't forget the pumps etc. 360 usable ah. We never worry about electricity. Alternator is a 100 amp Balmar with ACR regulator .
AGM charge more quickly...but more expensive. Wilth proper equilization they have lasted 9-10 years and 500 cycles. That more thann covers their added exp see need of AGM.

The new lithium are super expensive and worth it if your sailing is mainly cruising or you switch from a desiel engine to electric. For most of us this type of battery is not cost effective.
 
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We've got 6-6volt Lifeline AGM for720 ah. Daily diet in mid summer with refrigeration running is 65 ah. That includes many LED , radar and chartplotter and charging of phones etc. Caframo fans (3) and refrigeration use most of power. Don't forget the pumps etc. 360 usable ah. We never worry about electricity. Alternator is a 100 amp Balmar with ACR regulator .
AGM charge more quickly...but more expensive. Wilth proper equilization they have lasted 9-10 years and 500 cycles. That more thann covers their added exp see need of AGM.

The new lithium are super expensive and worth it if your sailing is mainly cruising or you switch from a desiel engine to electric. For most of us this type of battery is not cost effective.
We’ve got 4ea 27 series AGM house batteries and one 24 series starting battery—also AGM. They are now 9 years old. We have dock power, but rarely use it. Motoring down the channel and back keeps the batteries charged for day sailing. When cruising, we might run the motor for about an hour per day to maintain hot water (via engine coolant) and to keep the voltage up to assure the 12V refrigerator keeps the beer, wine and perishables cold. We have a 70A Balmar (having downsized from 100A to minimize risk of damage to our 3GM30F water pump bearings from high loads) and have a Balmar smart charger set for AGMs. We don’t have a battery monitor, but have voltmeters on the panel to monitor bank voltages. We try not to get down to 50% SOC and normally keep the voltage from dipping below 12.3V. That has worked for us, so we don’t miss a monitor.

Our batteries stay in the boat for the winter and I periodically check them. As of last week the batteries are all at 12.5 V or higher. They have not been charged since haul out in October. Love these AGMs!
Agree that Lithium would not be cost effective for our use.
 
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