Any smartgauge owners? Installation details query.

pteron

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I stumbled onto the smartgauge site from a discussion of battery monitors and was interested enough to do a spot of searching on the forums.

Some of the discussion was intriguing, and set me thinking, especially the claims that it was measuring parameters other than voltage. Can any owners tell me what sort of cable is used to connect the smartgauge to the battery terminals (length and diameter)? What value fuse does it use in line?

Thanks
 

Gumpy

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I stumbled onto the smartgauge site from a discussion of battery monitors and was interested enough to do a spot of searching on the forums.

Some of the discussion was intriguing, and set me thinking, especially the claims that it was measuring parameters other than voltage. Can any owners tell me what sort of cable is used to connect the smartgauge to the battery terminals (length and diameter)? What value fuse does it use in line?

Mine has 1mm with a 5 amp fuse in line you will need ferules to get the cable into the device. I have had mine since the first pre production release.
It is a clever device, there are only a handful of people that know exactly how it works.
 

oldmonsty

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Smartgauge

Why not ask the man who knows, Chris Gibson, he is not a very nice person but he is ever willing to explain and discuss the issues. But you must listen to him otherwise...........................................................
 

oldmonsty

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I only know him from his many extremely nasty comments on two other boat forums and yes he doesn't suffer fools very gladly but his 'stuff' is apparently marvelous and he is always prepared to explain and to support users.
 

prv

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I've just fitted one, so I've poked about at it but haven't used in anger yet.

It doesn't come with any wire (though it does have the crimp fittings, fuse holders, etc) and doesn't make any specific recommendation as to type. So I used the same 1.5mm tinned flex as for all other general wiring.

I didn't look at the fuse value (should do though, so I can get spares) but I doubt it's critical. The thing uses very little current indeed, so any fuse ought to be ok. The fuse is just in case something shorts the wire, because it's live all the time even when the battery isolator, if you have one, is off.

Pete
 

pteron

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Thanks for the info everyone. I wanted to apply a bit of electronics theory to the claims of measuring anything other than volts down two thin wires.

1mm copper wire is about 18 mOhms/m - say 3 meters each connection, so about 100mOhms overall.

A bit of googling reveals the following table of internal resistance http://www.alber.com/BaselineRef.htm which gives a range of values but all are measured in micro ohms, and are generally less than 10mOhms.

To measure impedance, you have to know the delta V for a delta I, i.e. you pull a bit of current and measure the change in voltage. Given the noise present on an unshielded cable, we are going to want a signal in the 100mV or more range, so across 10mOhms, we'd have to pull

I = V/R, I = 100m/10m = 10 A.

That's going to blow our fuse and I certainly haven't seen a power FET in the drawings of the Smartgauge that could pass that amount of current. In addition, that is at the battery terminals - the additional resistance in the cables will have to be taken into account. We will lose much of our signal across that resistance, so I think we can safely say that the Smartgauge is not measuring DC resistance.

A similar analysis applies for AC impedance - the references I can find indicate an AC impedance around 10mOhms up to 100kHz so a similar current would need to be pulled to measure it and the same issues appear for the smartgauge at the end of 100mOhms of wire.

Why do this analysis? Well in http://www.ybw.com/forums/showthread.php?t=73924 pvb was ridiculed for claiming that the smartgauge is just a fancy voltmeter with loads of pseudo science about measuring

"internal resistance measurement", "internal impedance measurement", "AC impedance spectrography", "surface charge" and "battery recovery".

These are valid techniques for analysing batteries but all but the last requires direct connection to the battery and the ability to perturb the battery conditions.

The only thing you can do down a variable length of thin wire is measure the voltage. You can infer much more - as I suspect the smartgauge model does, which is why it needs to measure the voltage over time.

So pvb, I'm with you on it, it *is* a fancy voltmeter. :D

(I am an electronics engineer and have been working in power management for many years. I designed a chip for Dunlop batteries many moons ago to monitor the state of the battery, indicating when it needed charging and/or replacement. It did this by monitoring the battery voltage over time and under load.)
 

oldmonsty

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Related to Mr Sterling? there is possibly no greater insult for Gibbo. It is a seriously good job that he does not post on this forum, we would never hear the end of it. A PhD thesis would have nothing on it!:)
 

Gumpy

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OK this is as I understand it but it has never been confirmed by Gibbo !

SG has "maps" of the discharge cycle of various battery types within its memory, These have been compiled from data drawn from many types of batteries.
SG then compares the discharge profile (taken by sampling the battery voltage many times a second) of the users battery bank to the selected "map" and works out the % of charge left. SG also can modify the "map" on the fly to more reflect the discharge cycle of the connected battery bank. I know for a fact that it is the most accurate battery meter available having run tests with it alongside various others and the others, without exception go out of sync with the batteries after a few charge discharge cycles.
I am now on my second set of batteries with SG, my usage is just about the same every day and towards the end of their life instead of using 15% per day I was using 25% a day which reflects the fact that after 6 years the battery capacity had reduced. Find me another meter that can do this automatically.
Gibbo is working on a new meter that will have many more functions I will be interested to see the results.
 

pteron

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That's pretty much what I'd expect it to do. My post was to point out that previously there have been claims that it doesn't simply measure voltage, but in reality that is all it can do.

I don't dispute that its accurate or that you need to measure anything other than voltage to predict the SOC of a battery bank.
 
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