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Old 03-03-2010, 15:56   #1
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Battery Condition Gauges - Your Views, Please

I'm looking at fitting a battery condition gauge, and have seen this device.Having read the tech spec and rationale, it looks unique in as much as it does not use a shunt, and cannot get out of synch. It seems to be very highly regarded by the canal boat community in the UK, who rely heavily on their own power systems. I'd appreciate some feedback from the experts on this site as to the technical wizardry behind this.
Her's the link to the techy stuff.....
SmartGauge Electronics - SmartGauge compared to Amp Hours Counters
Bryan
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Old 03-03-2010, 16:24   #2
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From the wiring diagram it is a Volt meter that claims to use some advanced 'algorithms' that closely 'represent' some battery types.

I would not trust this. A voltmeter is a voltmeter is a voltmeter. At some X Volts the bat is full, at Y it is half-full, at Z - empty.

The shunt-based Volt / Amp meters measure a specific, not generic, battery and if supplemented by a temp sensor, battery bank size input and type, can give some sort of insight into what is going on.

But the same insight you will get with a good V/A meter and the lecture of Calder's book (at probably half the price of any 'advanced' battery instrument.

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Old 03-03-2010, 16:39   #3
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You might want to read the Limitations section on their link as well - it pretty much says it won't work except under ideal battery condition none of us could reasonably expect while cruising. Don't know the cost but even if it is half that of a real battery monitor, when you amortize the cost over it's useful life, this seem like a false economy to me.
My view is either use a voltmeter and extrapolate what you want to infer from a voltage reading or do it right and invest in something which actually measures amps in/out.
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Old 03-03-2010, 17:04   #4
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I installed a vitron bm and the info it gives is very useful
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Old 03-03-2010, 17:19   #5
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Quote:
I would not trust this. A voltmeter is a voltmeter is a voltmeter. At some X Volts the bat is full, at Y it is half-full, at Z - empty.
Voltage alone is never enough, but it would confirm the bank is stone dead. Without knowing more it may be a poor idea. There are many other approaches that use an integral approach measuring amps * time as a way of knowing how much energy has been added or subtracted. In the the end anything else would be foolish.
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Old 03-03-2010, 17:20   #6
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I too would recommend the Victron BMV. It is the unit we installed and it does a great job of providing us more than we need to know about our battery and charging system. WG
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Old 03-03-2010, 18:46   #7
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Bryan,

The "SmartGuage" looks like a clever attempt to improve upon pure voltage measurements, by monitoring system voltages over time and comparing them to a number of stored profiles. It attempts to represent remaining energy capacity, which is not the same thing as amp hours.

Though the SmartGuage folks have tried to simplify things and, in the process, have included some technical inaccuracies, much of the discussion re: the problems with shunt-type battery monitors is revealing, and should be read by those who "swear by their battery monitors", as well as those who've noticed that the readings they're getting don't necessarily correspond to reality.

I don't particularly like battery monitors and, like Barnakiel and Calder, believe that the intelligent use of an accurate digital voltmeter -- coupled with a knowledge of your particular boat -- will give you all the insight you need into battery condition and state of charge.

However, the shunt-type battery monitors have come a long ways. Some, like the Victron, include compensation for Peukert's equation, taking account of the rate of discharge and monitoring the rate of charge over time. This, coupled with other information, allows a fairly accurate calculation of remaining capacity of the battery bank. However, it is necessary to calibrate the meter when installed and, at least once a month to re-calibrate it (set it to zero) when the batteries are fully charged. Failure to do this will result in the types of inaccuracies we often hear about from boat owners.

I like the Victron stuff. On my boat I have a MultiPlus inverter/charger and have installed and programmed several others on customer's boats. The build quality of these machines is very very high, though some of the mechanical design "features" could stand a re-work as has been noted elsewhere. The new Victron BMV600 battery monitor looks very good indeed. Maybe good enough to put one on my boat this year and get rid of my very RFI-noisy Blue Sea Systems digital voltmeter :-)

JMO,

Bill
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Old 03-03-2010, 19:05   #8
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Quick Peukert's Example

You have a fully charged 100AH battery.

You put a 100A load on it for 30 minutes.

You've now drawn 100A X 0.5 hours = 50 amp hours from your 100AH battery.

That means you've still got 100AH minus 50AH or 50AH left in the battery. Right?

No, not right.

The 100AH rating is at the 20-hour discharge rate, or about 5A load for 20 hours. But you put a 100A load on it for a half-hour. And, in the process, you effectively diminished the AH capacity of the battery by 50AH x the Peukert factor for a 100A draw. Say, Peukert for this draw equals 1.5. So, effectively, you drew 50 x 1.5 or 75AH from the battery's capacity, leaving only 25AH remaining .... at the 20-hour rate.

The good news: Peukert works both ways. Let's say you had only a 1A load applied for 20 hours. 1A x 20 hrs = 20AH. So, you've used 20AH and that leaves 100AH minus 20AH = 80AH capacity in the battery. Right?

No, not quite. That 100AH battery (at the 20-hour rate) is more like a 110AH battery at the very low discharge rate of 1A. So, you actually have 110AH minus the 20AH or 90AH capacity left in the battery.

The figures used above are for example only.

Now, wasn't that fun? If this leaves your head spinning, maybe you need a good battery monitor!

:-)

Bill
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Old 03-03-2010, 19:17   #9
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When my fridge stops cooling I think about charging the battery.

When my lights dim, I know it's time to charge the battery.

When my GPS starts beeping due to low voltage I have the incentive to go take care of it.
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Old 03-03-2010, 19:25   #10
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Always been a voltmeter guy but my buddy has this on his boat and I'm beginning to weaken...

Xantrex Technology Inc. - LinkLITE Battery Monitor - Product Information
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Old 04-03-2010, 02:31   #11
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The Xantrex LinkLite and the Trimetric are the two most popular battery monitors. Xantrex products, as usual though, sometimes have long lead times.
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