SailNet Community banner
  • SailNet is a forum community dedicated to Sailing enthusiasts. Come join the discussion about sailing, modifications, classifieds, troubleshooting, repairs, reviews, maintenance, and more!

Realistic expectations for my house batteries

13K views 137 replies 22 participants last post by  SanderO 
#1 ·
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?

Sent from my SM-G960W using Tapatalk
 
See less See more
#4 ·
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.

Sent from my SM-G960W using Tapatalk
 
#5 ·
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
 
#6 · (Edited)
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.
 
#9 ·
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.
 
#11 ·
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.
 
#12 ·
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.
 
#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!

Sent from my SM-G960W using Tapatalk
 
#18 ·
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
 
#14 ·
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%.
 
#15 ·
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.
 
#16 ·
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!

Sent from my SM-G960W using Tapatalk
 
#17 ·
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.
 
#21 ·
With battery technology progressing as fast as it is I would not be surprised if Lithium storage becomes more cost effective by the time I am ready to replace my old school lead acid bank.



Sent from my SM-G960W using Tapatalk
 
#23 ·
My two cents.

I ran calcs on amp use under different conditions

I got a 120 amp alternator w/ smart regulator (Balmar 614)

I have had 2 - 55 watt panels since before monitors existed and used only the voltmeter. They have a PV 14 regulator.

I have an Optima Blue Top 55 AH for a designated start batt

I have 2 8D AGMs total ~540 AH as the house bank. They are 8 years old.

I use a Link 20 monitor. Most of the fancy features go out of sync and are useless. The precision voltage, amps used / amps in are useful.

Boat is on a mooring all season and in a slip for winter. I don't usually use the shore charger.

I have an Espar Airtronic 4 diesel forced air heater. It works fine and if it runs all night will drain a lot of amps. We close of the outlets except where we sleep so the demand is small and heat is fine. It has a maintain mode which is quiet and low draw.

We changed all lamping to LEDs

Windlass is wired to house bank and only runs when engine is run.

Refer is engine drive and we run engine 2-3 hrs min when we are on board .. getting to and off mooring or anchor. We often bring ice in the summer.

We use a NUC w/ HP monitor at anchor

We have several chartplotters but use only 2 and navionics occasionally on the smart devices.

We have no lack of power and no need to add more solar or wind.
 
#24 ·
As I think SO is mentioning, the amp hour counters, if set up correctly, will do a good job of counting amps in and out, but there ability to determine state of charge is suspect at best. You start by telling it what your bank capacity is at the standard 20hr rating. The truth is, it’s probably just below that the day you install and just gets lower with time. The counter can’t tell. Secondly, capacity is afected by the rate at which a load is applied. If you draw at a load greater than the 20 hr rating, it will have less capacity and vice versa. Some counters allow for a ratio to deal with this, but almost no one knows what that ratio should be. I’ve never seen it in any paperwork, that comes with the batteries, and you’d likely have to contact the manufacturer. Some counters don’t account for it at all, which makes SOC calcs wrong for sure. It’s pretty unlikely anyone draws at exactly the 20hr rate.

The other malady, which a buddy of mine does all the time, is manually resets the counter’s SOC to 100%, when he thinks it’s become out of whack. He’s probably right that it is out of whack. However, he looks at voltage and charge stage, not acceptance amps, to convince himself the batteries are fully charged. At one point, I asked to take a look at his monitor, after he reset to 100%. His bank was still accepting 2+% of capacity in Float, which I took as a sign his charger went to float prematurely. The double whammy is that he’s probably not at 100% and, due to poor charge profiles, probably has much less than published total capacity anymore.

On my counter, it typically says 100% charge, while I can still see acceptance that disclaims. I ignore the counter’s SOC calc.

As a matter of disclosure, I’m no battery expert. This stuff gives me a headache, but I think it’s important to study up, if one plans to be off the dock for extended periods of time.
 
#25 ·
Who cares what the state of charge is... really. Our house bank is topped off and the drains are usually only a fraction of capacity. Using the dumb approach and having solar to keep them batts charging and charged when we are away during the week... we have no power problems. Why obsess on something which is not a problem?

Compute your daily typical loads... get batts which this represent a small fraction and have passive charging to replenish amps used.

Then enjoy your boat.
 
#29 ·
....Compute your daily typical loads... get batts which this represent a small fraction and have passive charging to replenish amps used. ....
That is one approach, but it also means one has significantly more capacity and battery cost than necessary. Over sizing a bank is one way to accommodate poor charging and it's resultant degradation of capacity too.

As to having enough passive to replenish daily use, that depends on how power hungry one's boat is and how much space they have for passive (plus whether they want to look like a solar farm, if that matters).

In our case, on a long cruise, this is what would be running.......

2 chartplotters
VHF radio, with remote
Radar
Autopilot
SSB occasionally
2 refrigerators
3 electric heads
Running lights as needed
Cabin lights, of course.
All sorts of parasitic loads from gauges to the system monitoring of the inverter/charger.

I'm sure I'm forgetting some. While much of our systems burn more juice than their most modern equivalents, I've been trying to improve. All cabin and nav lights have been updated to LED, for example.

Still, it's not uncommon for me to see 15 or more amps of draw, while underway. If making a long passage, I'd need a ton of real estate to be able to replace that with solar. Especially considering that solar will rarely be 100% efficient. Wind is less reliable and I find them pretty annoying, but that's personal opinion. Nevertheless, the sun doesn't always shine and the wind doesn't always blow.

On my most recent 26 hr passage, I slipped our mooring line with pretty fully house bank. We had the rare opportunity to sail the entire passage. Sounds nice, but it was really because it was blowing stink, with nasty seas. Nevertheless, I'm about 20 hours in and our house is down to 12.4 volts under load. That should be fine and I'm hoping to make landfall, before needing to recharge. About an hour or two later, our radar stops working. I fiddle, but assume it's just failed. Shortly, thereafter, I notice the house bank is down to 12.2v, so I turn on the generator. The radar starts working again.
 
#26 ·
Looking at different battery monitors, why is it they all look like 1990's technology? What's with all the round instruments? I guess they are meant to go on the dash of an RV or something.

Except for Simarine! It looks pretty slick with a decent amount of information available without having to scroll through a tiny 10 digit display that looks like an '80s digital watch!

Of course it is also a bit pricier...

Does anyone have any experience with Simarine?

Sent from my SM-G960W using Tapatalk
 
#27 ·
Cool looking and accurate for SOC are two entirely different things. If you don't mind fiddling with an Ah counter, testing for actual Ah capacity, etc., etc. then the SimMarine can give you a lot of good info but currently it does not track SOC as well as it should.

If you want super easy, the original Balmar Smartgauge is about as simple and accurate as it gets but it will not work with LiFePO4.

The new Balmar SG200 expands on the accuracy of the Smartgauge and adds a shunt and a state of health feature. The new SG200 also works with LiFePO4 and is self-learning meaning no continual fiddling to keep the monitor in sync with your bank as it ages and gets PSOC cycled.. The longer it remains connected the more accurate it gets. The way the self-learning SG200 works is the complete opposite of the rest of the Ah counters currently on the market.

Also keep in mind that you really only need to know your SOC perhaps once per day so the display does not even need to be prominent, and can even be mounted inside a cabinet etc.. The original Smartgauge is very antiquated looking but also very accurate. The SG200 is better looking, expandable, less money and also very accurate.
 
#37 ·
No one's saying it's not a great product overall.

Just that they haven't got SoC accuracy to a great level yet. Apparently after Bruce's comparative test their next firmware updates did improve things a bit, so maybe that will continue.

Even the best SoC meters aren't **that** accurate anyway, so if the unique aspects of the Pico are important to you, just get a SmartGauge as well to calibrate against.

And no, only that and SG200 have that learning feature, at least among non-military consumer systems.
 
#39 ·
Aside from a few "showboats" so to speak, no one has built a real boat powered 100% by solar. Nowhere near it.

You'll find launches that are kept up by solar, and small sailboats that basically having docking engines capable of being run at 3 knots while the sun is overhead, and then really short distances in flat water when it isn't, but nothing that approaches the ability of a typical built, to motor head into adverse wind and waves for 24-48 hours straight.

If you chase down the numbers for fuel density for diesel or petrol, and then compare that to what the very best of batteries can store, and the most optimistic of solar panel claims, the number still come down to fossil fuel, or highly limited purposes for the solar propulsion. They certainly can be enough--but if you run the numbers, solar still comes down to a docking or maneuvering engine, or other light use. (No pun intended.)
 
#45 ·
Aside from a few "showboats" so to speak, no one has built a real boat powered 100% by solar. Nowhere near it.
I would say you're correct. But I wasn't referring to electric propulsion. I meant the goal would be 100% solar for electric requirements so that a generator is not required at all. Main engine would be a backup, but we all know that running the main to recharge batteries is not a proper practice.

So my point was that based on above, that lithium sounds like it will capture every watt generated from solar panels, as opposed to FLA which only captures a small percentage for that last 20% (absorption/float) or so while it is topping up.
 
#46 · (Edited)
As soon as the LFP bank is Full, then the panel output is just as "wasted".

Don't worry about avoiding that "waste" for now, a minor issue, and inherent in proper sizing for variable weather conditions.

The key differences are the higher CAR and no need to get to Full.

So yes, you could in theory just expand the bank until every watt hour of solar output is captured.

But that would be silly if far larger than your usage requires.

Yes, how much solar you can fit and still have a beautiful well-sailing boat is usually your limiting factor.

Best to have a supplementary ICE source. LFP lets you "capture" all of **that** output to reduce run time drastically compared to lead.

Which means an owner that prefers fewer panels has greater flexibility.

So, size the bank for your usage requirements, use solar to reduce ICE runtime, yes LFP is a great improvement but not required, nor are its advantages directly tied to solar specifically
 
#47 ·
Thinking about replacing batteries myself. 4 - 12v GC batteries, 430AH capacity.

Low load boat, all LED, we keep the vHF on 24/7, reffer runs about 15-20 mins/ hour in the Carribean heat. We charge our iPhknes and laptops. That’s about it.

Wind generator output is related to wind speed: very roughly 40A @ 45 knots, 10@25, 2.5 @ 15. So if you are exposed to the fill tradesmen D’s you are getting good juice, elsewhere not so much.

My solar panels have a lot of shade. Something silly I had not considered is that in the trades you may E-W, so obstructiknsnin the S side of the panels really screws with them. I’ll be relocating the panels and moving the radar to partially address this.

We are on the boat about 6 months/year, living on the hook. Honda generator. No opportunity to hit the FLA batteries with a equalization charge. I’m not feeling the love for spending big bucks on batteries. I’m kinda in the mood to get what I can from what I have and accept a shorter life span, just part of the boats consumables. Part of keeping it simple.
 
#49 ·
Thinking about replacing batteries myself... I'm not feeling the love for spending big bucks on batteries. I'm kinda in the mood to get what I can from what I have and accept a shorter life span, just part of the boats consumables. Part of keeping it simple.
And that's probably the most realistic attitude!

There are some on these threads who have the budget and inclination to install the best of everything on their boats. Then there was one guy I remember who commented that he goes to Walmart and buys a big cheap starter battery (not deep discharge), uses it for a year or so until it is dead, then buys a new one.

Now that is being practical :)

I suppose the only thing more "simplistic" than that is buying oil lamps and being old school. However, oil lamps are much more harmful to the environment that a tiny solar panel, small motorcycle battery and a bunch of LEDs (IMO).
 
#48 ·
Time flies, and our Smart gauge is still working fine. Or, at least it has bamboozled me into believing in it!
At the time of the install I was influenced by Maine Sail's endorsement, and am still glad I made this change.
2016: New Batteries, New Smartgauge - Blogs - EY.o Information Exchange

Like so many problems with our boats, this might just be one of several "correct" solutions!
:)
 
#51 · (Edited)
I look at batts as consumables... The OEM batts were flooded acid type and there were two and not terribly large capacity. The alt was a dumb 55AH one. First upgrade was to do large gels... and when those died I removed / rebuilt the bat box and put in AGM 8Ds (now on 2nd set) and a separate start batt, a new monitor... Link 20 (somewhat useless), 120 am alt with a smart regulator. The box rebuild was not all that difficult. The bilge aft or the engine was where the box was between 2 fore-aft panels and a berth was over it. The start lives on the starboard side of the starboard panel. No need to have a pan to contain battery acid or add water. Maintenance free is definitely the way to go. Amp rating is almost 500. I could add a 3rd battery aft of the two, but the existing capacity is fine. All the cables, busses and so forth were new. Regulators and echo charge are mounted on the plywood hold downs. Shunt lives in this compartment along with numerous fuses.

So I have in 34 years upgraded 3 times... gel, AGMs and the present AGMs. Cost per season is not all that much. Upgrades - cables and so on should outlast me. ;-) Not having 12v refer was probably a good idea as far as batteries go.
 

Attachments

This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.
Top