Recommendations for Battery Monitor - Page 7 - SailNet Community
Old 03-12-2015
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Re: Recommendations for Battery Monitor

Quote:
Originally Posted by UnionPacific View Post
The \$200 gauge will tell you how much power you have taken out,

I'm having a tough time believing you've looked at any of the links I've posted for you...?

It will tell, you how many Ah's you've removed or % removed when calculated factoring in Peukert and temp. Looking at Ah's out screen tells you little about the batteries actual SOC, unless you discharged it at the 20 hour rate, from a known confirmed capacity at 77F. This is why they TRY and compensate for such things as charge efficiency, Peukert and temp.

Also please understand that by purposely under-programming your BM by 20% this throws another monkey wrench into your Peukert calculation... You are actually inducing more miscalculations than you are solving....

If we assume an average 10A load with an 860Ah bank and a Peukert of 1.2

860Ah @ 10A & 1.2 Peukert = Peukert corrected load of 7.5A and usable capacity of approx 1150 Ah's

688 Ah @ 10A & 1.2 Peukert = Peukert corrected load of 7.8A and usable capacity of approx 881 Ah's

The Ah counter is using the Peukert you give it to make its calculations. If the bank is not really 688Ah's then your Peukert is even further from being accurate. These devices are already disadvantaged by counting errors, due to ever changing capacity, Peukert and charge efficiency as well as temp, why confound the issue more by programming it inaccurately?

Quote:
Originally Posted by UnionPacific View Post
and how much you have put back, if setup correctly.
Actually they don't show you what you put back because they eventually hit zero then stop counting. In a flooded GC battery it is likely you need to replace 120-130% of what you removed in order to get to full, but the counter stops at 100% of removed. Return 100% of what you removed and you are NOT at 100% SOC as many incorrectly assume by simply looking at the Ah screen. The last 20 - 30% needed for full, beyond what you removed, takes hours & hours to replace. The BM can show you what went in but does a pretty poor job of showing you what portion of that went into waste energy and what went into actual usable capacity....

They can't show you accurately what you returned, in terms of usable energy, especially if you did not complete a full 100% recharge. Charge efficiency is not a static figure like an Ah counter treats it. In bulk you may be close to 98% charge efficient but the higher you go in SOC the less efficient the conversion becomes.

Ah counters have no way to calculate properly for charge efficiency unless you get back to 100% with every cycle. These counting errors begin to add up by cycle #2 away from "full".

Quote:
Originally Posted by UnionPacific View Post
It will give you a solid idea how far into your AH reserve you are.
It will only be solid if you've done the proper programming, which you don't want to do. Even then they are not very accurate after just a few cycles away from a full recharge and thus require manual known-full re-sets......

I honestly think you'd be better served by a Smart Gauge or this:

When your battery bank is accepting less than 1.5% in charge current, of it's Ah capacity, about 13A, while at absorption voltage, you can "consider" it full enough. This is still not full, but full enough for cruising...

Ah counters can be good tools if they are used properly. Unfortunately most owners don't want to use them properly and thus a simpler tool like a volt meter (most owners don't know how to use these properly either) or Smart Gauge is often the better choice.

Doing what you plan to do I think you can save \$200.00 and just not let the bank dip below 12.2V, unless starting the engine or using the windlass.

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Last edited by Maine Sail; 03-12-2015 at 12:31 PM.
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Old 03-12-2015
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Re: Recommendations for Battery Monitor

Quote:
Originally Posted by UnionPacific View Post
I am more concerned during a crossing then at anchor. During a crossing the autopilot is running. A very uneven load. Not only that, right now I do not have a digital voltmeter, I have analogue. Its wildly inaccurate. However a nice digital multimeter is almost as much as the 702.
A "good enough for this purpose" multimeter is less than \$20. You don't need a Fluke for this.
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Re: Recommendations for Battery Monitor

I have a BM-1 on one of my boats.

I like it. I like it because one display mode allows me to simultaneously monitor battery voltage and charge/discharge rate, in LARGE digits with a quick look.

That display mode also has a thermometer-style state of charge indicator (in percentage), which I have found to be useless. With a fully charged battery, and the battery switch OFF, and the indicator at 100%, after turning on the switch and starting a 12V fan and an LED saloon light on high intensity (about 1.3A total, actual and indicated), the thermometer indicator goes to 85 percent after a few minutes...which would mean almost 33AH (rather than the actual fraction of an AH) had been discharged, if accurate. The indicated battery voltage generally will be unchanged, or down 0.1V.

When I want to know the actual state of charge of the battery, I check specific gravity of each cell.

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Old 03-12-2015
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Re: Recommendations for Battery Monitor

Trojan Battery Company

Trojan guidance on s.g. testing of flooded batteries is at the link.

The web makes everywhere the same place. - Fred Reed, from "Fred on Everything"
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Re: Recommendations for Battery Monitor

"A "good enough for this purpose" multimeter is less than \$20. You don't need a Fluke for this."
I might not disagree, but you've got to put it in context.
If you didn't know that a <\$20 multimeter COULD BE OFF BY 1/2 VOLT on the 20v scale, it would not be good enough.
Most have great specs on paper. But some just aren't anywhere near calibrated. I've seen "12" volts that were anywhere from 11.5 to 12.5 in reality. So if you're just going to use a cheap digital meter and say "It says 12.4, that's normal for us in the morning" you can just as easily use the cheap old analog meter that's in so many boats.
I tried to calibrate one of those (easy enough) but if it was showing 11.5 at 11.5, it would be off by 1/2 volt at 14.4 charging voltage. So we had a choice, totally false when charging? Or totally false when discharging?
Didn't matter if you know to ignore the numbers and say "this is normal for us now".
But most people DO get distracted by numbers, and mistake them for having meaning.
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Re: Recommendations for Battery Monitor

Having multiple meters that you ARE SURE are reading correctly is a real help. A lot of hand-held DVMs have not-so-good accuracy. Maybe you don't need my Fluke's 0.09% but you need better than the Blue Sea 0.75%. And having multiple meters can save you from my recent mistake of replacing some batteries because they wouldn't hold a charge only to find out that the Victron 602 was randomly reading between .2 and .5 volts low. They replaced it instantly without question. But having multiple, known-good meters (if I had looked at them at the right times) was a real plus.
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Re: Recommendations for Battery Monitor

Quote:
Originally Posted by hellsop View Post
A "good enough for this purpose" multimeter is less than \$20. You don't need a Fluke for this.
I was talking about a good installed meter. I carry 3 cheap hand-held meters.

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Re: Recommendations for Battery Monitor

Quote:
Originally Posted by Maine Sail View Post
Doing what you plan to do I think you can save \$200.00 and just not let the bank dip below 12.2V, unless starting the engine or using the windlass.
Good point. I guess I could spend the \$200 and just grab 2 more batteries and hit 1000AH.

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Re: Recommendations for Battery Monitor

Quote:
Originally Posted by svinshallah View Post
Having multiple meters that you ARE SURE are reading correctly is a real help. A lot of hand-held DVMs have not-so-good accuracy. Maybe you don't need my Fluke's 0.09% but you need better than the Blue Sea 0.75%. And having multiple meters can save you from my recent mistake of replacing some batteries because they wouldn't hold a charge only to find out that the Victron 602 was randomly reading between .2 and .5 volts low. They replaced it instantly without question. But having multiple, known-good meters (if I had looked at them at the right times) was a real plus.

Add to that the sad reality that most volt meters are installed incorrectly and sensing voltage way downs stream of the battery terminals thus picking up all the voltage drop along the way. Any installed volt meter should be accurate and wired directly to the battery terminals if you desire accuracy..

Folks often forget that every 10% of a battery banks capacity is represented by a 0.1V change in the rested open circuit voltage. On an 860Ah bank, like we are discussing, 0.1V is 86 Ah's or an entire days energy just by being 0.1V off......

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Easy Meter Calibration

Everyone knows the native voltage of miniature Altoids in exactly 10.00 volts. So if the pictures will attach...one is an infamous cheap meter that was calibrated a year or two ago. The other meter is a respected name brand, also calibrated at the same time. One still says 10.00 volts when connected to the Altoids, the other has drifted.

So how much should I be selling "Altoids" for? Including the two alligator clips, a power switch (under the leads on the side of the case so it can't get nudged) and running on a 12v remote control battery, included.

NOT suitable for low-impedance high power devices, like the self-powered LED voltage displays. Designed for the usual high-impedance LCD digital multimeters. If your meter doesn't say "10.00" when on the 12 or 20 volt scale, your meter has a screw loose.

[IMG][/IMG]

[IMG][/IMG]
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