Smartgauge w/ 3 batterys

[Exile]

Originally Posted by Dockhead

The reason why I don't think it matters for most of us is that getting the batts to 100% takes a long, long time. It only happens on my boat if I'm on shorepower overnight. So it's REAL easy for me to know when I got to 100% -- Shore power overnight = I got there! No shorepower overnight = I didn't. No electronics needed.

I guess if you have a large solar installation the question might be more complex, but still -- why do you really care? It's not like you can leave the sun running an extra hour. It is what it is.

Good points. If you're using a genset exclusively when away from the dock then you're not likely to charge batts. more than 80-85% for obvious practical reasons, and if you exclusively use or supplement with solar/wind/hydro then you're done whether or not you achieve 100%. The bottom line is that your batts. are going to take a certain amt. of abuse when away from shore power no matter how diligent you are. This is why equalizing/conditioning can become the only means of recovering capacity, but as a practical matter that also requires shore power!

[john61ct]

Originally Posted by Dockhead

The reason why I don't think it matters for most of us is that getting the batts to 100% takes a long, long time. It only happens on my boat if I'm on shorepower overnight.

Now I think we're getting to a major difference in attitude.

Having large expensive banks in multiple locations, wrt to the lead ones, I strive to get to 100% Full every cycle. Yes I believe the difference between 97% and 100% could mean an extra hundred cycles, especially with AGM banks.

I do watch trailing amps to verify / calibrate charge sources and SoC meters, best way to define Full.

I don't consider that goal at all optional as a design principle. I accept that sometimes circumstances don't allow getting to 100%, but would shoot for less than once a month.

Another big one is I design around never having shore power available at all.

When it is, that's great, makes things very easy, but it is not factored in up front.

[ramblinrod]

Originally Posted by Exile

As a layman maybe I missed something (corrections always appreciated), but I thought this was the entire point of RamblinRod's advice all along. Not that the SG is inaccurate, faulty, or unhelpful, but that it may be unnecessarily redundant for most of his customers. If you want or feel you need more precision then great, but I can't see how a VM reading of 12.2v (or whatever your batt. mfg. specs) with light loads applied can possibly indicate anything other than a true SoC somewhere at or above 50%. For most, this is the most important thing you need to know, right?

Exactly, with one caveat, the charge voltage must be off for a chunk of time (and normal loads limited from about C/100 to C/50) to make this 12.2 Vdc reading approximate 50% SOC correlation.

If a 12.2 Vdc reading is obtained, and a charging system is on (with significant charge current going into the batteries vs loads) then the SOC could be considerably less than 50%.

This is why the morning DVM reading around (or shortly after) sunrise is so important.

One potential disadvantage is I keep reading posters with newly-installed SG's and solar/wind claiming that their batts. have reached "100%". Have they really, or are they looking at an inflated reading due to their solar/wind charging sources?

You've got it.

It seems like an amp counter is most useful on this upper end, i.e. to see whether the batteries are only accepting amps at or below .05C (or whatever your battery mfg. specifies). My battery charger has a read-out which shows amps going into the bank, so once it's on float I can simply monitor that (or my Victron BM). Is there anything misleading that could shorten the life of my batts. with this approach?

Mostly correct, an ammeter (vs an amp counter) is ideal for determining when batteries are no longer accepting anything more than float current.

To determine this, assuming your charging source is going directly to your batteries and you have a distribution panel isolation switch, all you have to do is measure current with the switch on an off. If the difference is less than 1A / 100 A-hrs of capacity, your batteries are pretty much full.)

Having said that, I could very well wind up installing a SG once I go long-distance cruising, if nothing else than to have an add'l and easier way to monitor my batts. when I'm away from shore power for extended periods of time.

As indicated prior, I do question the validity of this. If neither the DVM nor SG is accurate while charging, and the best points to measure SOC with either device are sunrise and sunset, how does reading SOC between 50 and 100% vs 12.2 and 12.8 Vdc, really make life easier?

But I wouldn't be doing so because it's a "necessity," at least in my mind. In the meantime, I'm still at a loss to figure why RR's advice became so "controversial."

There is one particular poster who has been promoting the installation and use of the Smart Gauge very heavily and who becomes quite insulting if anyone suggests they can easily get by with a DVM.

In my experience with forums over the last 20 years, people tend to become adamant when they have financial gain or personal financial expenditure justification to others, at stake. Others have a strong need to be recognized as correct. (I really fall into this category; I normally have a strong opinion and have given an issue considerable thought before posting, and become quite vehement if I believe a post by others may lead fellow boaters astray.) When one poster becomes insulting a few more opportunists sometimes jump on the band wagon.

Compared to VM's & amp counters, the SG is a fairly recent arrival on the scene, right? Has everyone who understands how to properly read VM's been unduly shortening the life of their batts. before the SG came along?

Another excellent question. In my opinion, those who monitor their batteries with a DVM and keep sunrise above 12.2 Vdc and sunset near 12.8 Vdc, have been enjoying long battery life for a long time before any application specific battery SOC display device was ever invented. Those who have not done this, may have experienced short battery life. If one of these people installs a BM and starts using it, they allocate their longer battery life to it (and may then feel a need to continuously justify their purchase decision). But IMHO, every single one of them could have enjoyed the improved battery life by just monitoring their sunrise and sunset battery voltages.

[conachair]

Originally Posted by Dockhead

I guess if you have a large solar installation the question might be more complex, but still -- why do you really care? It's not like you can leave the sun running an extra hour. It is what it is.

Cruising if you don't have enough solar you need to guess how long to run the genny in the morning in order for solar to get them back full before sunset, otherwise risk not getting maximum life out of them which is a whole new set of unknowns, cost, will they last across another ocean, and can you even get good batteries where you happen to be that year.. Very important indeed full time cruising imho. Maybe not such a big deal if you frequent marinas with shore power but living constantly off the grid with batteries never ever getting fully charged isn't the road to happiness.. personally I think it's the only question you need to ask, am I getting to 100% most days? Everything else is secondary.

[john61ct]

Originally Posted by Exile

This is why equalizing/conditioning can become the only means of recovering capacity, but as a practical matter that also requires shore power!

Monthly manual equalizing (for appropriate batt chemistries) is to me an essential tool for longevity, but I see it as maintenance, *preventing* problems.

I believe it doesn't significantly repair capacity loss caused by long-term suboptimal care.

With the exception of Firefly, a special case.

[Exile]

Originally Posted by john61ct

Now I think we're getting to a major difference in attitude.

Having large expensive banks in multiple locations, wrt to the lead ones, I strive to get to 100% Full every cycle. Yes I believe the difference between 97% and 100% could mean an extra hundred cycles, especially with AGM banks.

I do watch trailing amps to verify / calibrate charge sources and SoC meters, best way to define Full.

I don't consider that goal at all optional as a design principle. I accept that sometimes circumstances don't allow getting to 100%, but would shoot for less than once a month.

Another big one is I design around never having shore power available at all.

When it is, that's great, makes things very easy, but it is not factored in up front.

Very boat-dependent, and often not practicable. With boats that use a lot of power you'd want to at least do a cost-benefit given the add'l solar/wind/hydro that would be needed.

[john61ct]

I have stated throughout, that if one has small or inexpensive banks, or otherwise doesn't care about details like SoC accuracy, then they needn't invest in any SoC meter.

My disdain arises from repetition of false information that would lead astray those who do care about SoC accuracy.

[john61ct]

Originally Posted by conachair

Cruising if you don't have enough solar you need to guess how long to run the genny in the morning in order for solar to get them back full before sunset

Bingo!

But when you are getting maximum information from sources you trust, over time you get ever farther from "guessing", the subconscious intuition gets accurate indeed, until only unpredictable weather or guests interfere with a near-perfect record.

Since most genset running cost is the hourly depreciation, an extra 30-90 minutes of runtime to tip the odds is a small investment in the early stages.

And of course when the captain is actually in charge of House loads, conservation is the ultimate weapon 8-)

[Exile]

Originally Posted by john61ct

Monthly manual equalizing (for appropriate batt chemistries) is to me an essential tool for longevity, but I see it as maintenance, *preventing* problems.

I believe it doesn't significantly repair capacity loss caused by long-term suboptimal care.

With the exception of Firefly, a special case.

I'm not sure I understand the distinction you're making. I thought equalizing reduced the amount of sulfation that builds up on the plates, mostly from chronic undercharging. Wouldn't this restore capacity?

Firefly looks interesting, and I hope they introduce more sizing options. Personally I might wait awhile for such new technology to get more developed. I just read that they changed the spec for their float voltage, for example. Think I'd rather let others serve as the testing lab.

[Dockhead]

Originally Posted by conachair

Cruising if you don't have enough solar you need to guess how long to run the genny in the morning in order for solar to get them back full before sunset, otherwise risk not getting maximum life out of them which is a whole new set of unknowns, cost, will they last across another ocean, and can you even get good batteries where you happen to be that year.. Very important indeed full time cruising imho. Maybe not such a big deal if you frequent marinas with shore power but living constantly off the grid with batteries never ever getting fully charged isn't the road to happiness.. personally I think it's the only question you need to ask, am I getting to 100% most days? Everything else is secondary.

Yeah, that's a different use pattern from mine, completely.

I can't even imagine getting to 100% EVERY DAY off the grid. I'd have to run the generator all day.

I normally charge to about 80% or 85% -- I shut down the generator after an hour of absorption. It can be more if I'm using the generator for something else. I go into a harbor of some kind at least once or twice a week, and most weeks out cruising I have a good long motor probably once a week or so (I have a jumbo 2.5kW school bus alternator). So two or three times a week at least I will get to 100%.

I equalize fairly often in months when I'm off the grid a lot.

Until last year, I kept my boat on a mooring in the Hamble River with no shore power, and lived on board a fair part of the year. That is pretty hard usage on the batteries, but even like that my light duty cheapish 12v Trojans were lasting four years or so, which I considered to be perfectly fine. Works out to a few hundred pounds a year. No big deal at all compared to the ten thousand pounds a year I was saving by not being in a marina.

Now I've given up the mooring and have gone back to keeping the boat in a marina 8 months out of the year (negotiated 8 months of winter rate ), so battery life is hardly a factor any more. I will get sick of this set and get tired of waiting to install LiFePo before I wear them out, or I'll sell the boat.

In any case, batteries are consumable items, and I am sure as heck not going to make my cruising life revolve around coddling them to eke out the last possible extra week of life out of them. They are there to be used up, and I use them up, and replace as necessary. Use them up rationally but not obsessively. They are very far from the biggest operating expense.


My Dad was a power nazi (and water nazi) on the boat I grew up cruising on, and I swore when I had my own boat, I would be more relaxed about it (both water and power), worry less, and enjoy life more. That was a really good decision. He would even turn off the ***** pressure water pump at anchor so we would pump with the foot pump -- to save electrical power on the pump I bought a solar phone charger so I wouldn't have to suffer his nervous glances when I charged my mobile phone

[noelex 77]

My experience with coulomb counting battery gauges has been positive. I have found them accurate and useful. They need to be correctly wired, set up and they also need to be a good quality design. It is interesting that some posts report a more negative experience. I suspect part of the difference is these meters are less accurate when the batteries rarely reach 100%.

Those boats relying on generator power often cycle the batteries between 50 and 80%. Any slight counting error is not corrected and gradually accumulates. Those boats using solar or shore power will periodically reach a 100% SOC. The meter can reset and does not have to keep track over a very large number of cycles.

Knowing the battery's SOC as accurately as possible is not essential, but it is useful information. A SOC of 50% is often quoted, but there is nothing magical about this number. Batteries will last significantly longer if the SOC is kept higher, and occasional excursions below 50% are not the end of the world.

A simple example where knowing the SOC accurately can be helpful is a question such as "Should I boil the water today on the gas stove (using propane which will have to be replenised) or should I use the electric kettle?". If the SOC is good and the solar output is likely to raise the batteries to 100%, it would be silly to use up propane. On the other hand, if the battery SOC has been gradually falling each day indicating that solar power has not been keeping up with demand then using propane rather than electricity might be more sensible. Another example is radar use on a long passage. A gradually falling SOC indicates that the currant radar pattern is not sustainable (unless you anticipate solar power will increase, or other electricity usage will decrease). On the other hand it would a shame to turn off the radar when there is no need to make power conserving steps.

These are only some of the examples when knowledge of the SOC (and particularly if production is keeping up with demand) can be useful.

[ramblinrod]

Originally Posted by john61ct

Now I think we're getting to a major difference in attitude.

Having large expensive banks in multiple locations, wrt to the lead ones, I strive to get to 100% Full every cycle. Yes I believe the difference between 97% and 100% could mean an extra hundred cycles, especially with AGM banks.

I do watch trailing amps to verify / calibrate charge sources and SoC meters, best way to define Full.

I don't consider that goal at all optional as a design principle. I accept that sometimes circumstances don't allow getting to 100%, but would shoot for less than once a month.

Another big one is I design around never having shore power available at all.

When it is, that's great, makes things very easy, but it is not factored in up front.

I believe you are overestimating the value of a 100% charge.

I agree it is important to get close to full charge often for max battery life.

But if one gets to 95% 6 nights out of 7, and 100% the remainder, I believe there will be negligible difference in battery life, and it certainly would not be worth it to spend time or money to achieve a higher SOC those 6/7 nights.

If one has a battery bank worth $1000 or less (which I assume is the case for the vast majority of cruisers), and getting to 100% every single night gets them 2% longer battery life than 100% vs 95% 1 out of 7 nights, then this likely translates to a battery life extension from about 4 years (typical well cared for cruiser batteries) for maybe an extra month. For life cycle cost, this represents a savings of $20, translating to an annual savings of $5.

I just cant financially justify the cost of purchasing, installing, and maintaining a more sophisticated battery monitor, for those little savings. Even looking at a purchase price of C$384 (Defender) and ignoring customs brokerage and shipping, installation cost, and replacement cost or damage repair cost when it gives up the ghost, that's a 76.8 year payback. I'll never see it. The boat (and I) will be long gone.

Frankly, for anyone who has a bank with 20 hr capacity less than 400% over average daily A-hr load, I would recommend spending their money on another battery instead. I believe this would cost way less, and have a much greater impact on battery life, by reducing depth of discharge significantly from maybe 50% to 40% (60% SOC or 12.35 Vdc at sunset). (These DOD variation figures are just figures for figures sake, one would have to know the bank nominal capacity and loads to accurately estimate the impact of increasing capacity a given amount.)

[Dockhead]

Originally Posted by john61ct

. . . Yes I believe the difference between 97% and 100% could mean an extra hundred cycles, especially with AGM banks.
. . ..

Really? How can that possibly be? How did you calculate that?


Someone on here made a convincing case that it is economically rational to work a smaller bank harder, discharging to 80% instead of 50%. He provided math. This is contrary to what we all believe.

In any case, I think it is a bit of superstition to imagine that our batteries are going to melt down if we discharge them to 49% once in a while, or even to 30% or 40% occasionally. The effect on cycle life is -- actually not even linear, the curve becomes shallower towards the end.


My approach to lead acid batteries is to be really, really careful not to leave a load on when I'm off the boat that could flatten them completely -- this kind of incident does really shorten life. Don't have any accidents with the battery bank. I think that may be more important than any other single measure. Then, don't spare the generator too much -- let it run for a few hours in the morning and a couple of hours in the evening, while doing other power-intensive tasks. Avoid discharging below 60% too much, and try hard to avoid discharging below 50%, but don't have a nervous breakdown if I hit 40% for some reason (like a multiday passage under sail in hard conditions where you have to shorten sail or heave to to run the generator). Equalize pretty often if I'm off the grid. Be careful to keep the water up. And don't worry about them too much otherwise. Use them and enjoy life.

[ramblinrod]

Originally Posted by noelex 77

My experience with coulomb counting battery gauges has been positive. I have found them accurate and useful. They need to be correctly wired, set up and they also need to be a good quality design. It is interesting that some posts report a more negative experience. I suspect part of the difference is these meters are less accurate when the batteries rarely reach 100%.

Those boats relying on generator power often cycle the batteries between 50 and 80%. Any slight counting error is not corrected and gradually accumulates. Those boats using solar or shore power will periodically reach a 100% SOC. The meter can reset and does not have to keep track over a very large number of cycles.

Knowing the battery's SOC as accurately as possible is not essential, but it is useful information. A SOC of 50% is often quoted, but there is nothing magical about this number. Batteries will last significantly longer if the SOC is kept higher, and occasional excursions below 50% are not the end of the world.

A simple example where knowing the SOC accurately can be helpful is a question such as "Should I boil the water today on the gas stove (using propane which will have to be replenised) or should I use the electric kettle?". If the SOC is good and the solar output is likely to raise the batteries to 100%, it would be silly to use up propane. On the other hand, if the battery SOC has been gradually falling each day indicating that solar power has not been keeping up with demand then using propane rather than electricity might be more sensible. Another example is radar use on a long passage. A gradually falling SOC indicates that the currant radar pattern is not sustainable (unless you anticipate solar power will increase, or other electricity usage will decrease). On the other hand it would a shame to turn off the radar when there is no need to make power conserving steps.

These are only some of the examples when knowledge of the SOC (and particularly if production is keeping up with demand) can be useful.

Excellent point - 50% is not a magic number, 49% is slightly less good, and 51% is slightly more good (WRT battery life days).

It is just a generally accepted target number, plus or minus 10% is not really a make or break issue.

According to tables I have observed, 60% DOD will actually yield the greatest number of discharged A-hrs over the bank life. Surprisingly 50% is only slightly less, whereas 70% is considerably less.

That is correct, discharging to 50% SOC will actually net you more charge/discharge A-hrs than discharging to 70% SOC before the batteries are toast. (The batteries will last longer in days of life, if only discharged to 70% SOC but they will actually deliver less A-hrs to loads before requiring replacement.)

I hope this doesn't make the subject any more confusing; I just think this is another consideration that helped land the 50% SOC rule of thumb.

[Exile]

Likewise, it's approx. 80-85% -- or at a point after charging goes from bulk to absorption -- when you would want to shut your genset down. I'm no expert, but none of this seems amenable to being looked at in absolutes. Which in turn supports the use of VM's as a perfectly adequate way of monitoring batts. Maybe not as precise as a SG, but certainly adequate when the goal -- maximizing battery life -- is not itself a precise endeavor.