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ammeter


Johny London

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1 hour ago, smileypete said:

By my reckoning, 22cm of 25mm2 cable should have the same resistance as a 500A shunt. (0.00015 ohms)

I make it 21cm but as you say, it’s only rough & ready and for £2.99 is it worth the hassle?

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11 hours ago, Mike the Boilerman said:

 

Given the BM2 also makes a reasonable stab at SoC, it too tells you when to start charging.

Agreed you need to reset it occasionally but it saves spending a further £120 on the SG.  

No it doesn’t. Well it would do if it was set to the actual remaining capacity of the batteries but since the user has no means of knowing that, it doesn’t once the batteries start to lose capacity.

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On 08/11/2017 at 22:40, nicknorman said:

No it doesn’t. Well it would do if it was set to the actual remaining capacity of the batteries but since the user has no means of knowing that, it doesn’t once the batteries start to lose capacity.

 

Yes they do. The BM2 can be used to determine that, once in a while. 

Take a resting voltage. Discharge a measured quantity of AH, take another resting voltage. Do a bit of arithmetic.

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8 minutes ago, Mike the Boilerman said:

 

Yes they do. The BM2 can be used to determine that, once in a while. 

Take a resting voltage. Discharge a measured quantity of AH, take another resting voltage. Do a bit of arithmetic.

Good luck with that. Let us know how you get on. In the mean time I’ll just read a couple of displays in the morning. 

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On 08/11/2017 at 22:53, WotEver said:

I’ll just read a couple of displays in the morning.

 

So how does reading two displays in the morning tell you battery capacity?

I have a BMV702 and a SG. I'll follow your instructions tomorrow morning and report back the results.

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11 minutes ago, Mike the Boilerman said:

 

Yes they do. The BM2 can be used to determine that, once in a while. 

Take a resting voltage. Discharge a measured quantity of AH, take another resting voltage. Do a bit of arithmetic.

Agreed, that's what I do. Every month or so you could do it accurately but if you track volts in the morning and Ahrs used overnight (from full) then you can easily see if something bucks the trend or drifts futher away. It takes seconds to work it out in your head. Of course the BM2 can be used to determine capacity.

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2 minutes ago, Mike the Boilerman said:

 

So how does reading two displays in the morning tell you battery capacity?

I have a BMV702 and a SG. I'll follow your instructions tomorrow morning and report back the results.

Well you could, but you can’t be bothered to get your faulty tools repaired. So I can do it but you can’t :P

4 minutes ago, Dr Bob said:

Agreed, that's what I do. Every month or so you could do it accurately

Or you could get a life ;)

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On 08/11/2017 at 23:04, WotEver said:

Well you could, but you can’t be bothered to get your faulty tools repaired. So I can do it but you can’t :P

 

I bought a Smartgauge. It turned out to be faulty.

So I bought another. That turned out to be faulty too. I really can't be arsed with Merlin products. They are unreliable in my personal experience.

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Just now, Mike the Boilerman said:

 

I bought a Smartgauge. It turned out to be faulty.

So I bought another. That turned out to be faulty too. I really can't be arsed with Merlin products. They are unreliable in my personal experience.

Fair enough. So you can’t do it but I can. 

I bought a G-Tech vac. It turned out to be faulty.

So I returned it and they replaced it with one that worked. It never occurred to me to just go out and buy another. 

  • Haha 1
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On 08/11/2017 at 23:08, Mike the Boilerman said:

 

I bought a Smartgauge. It turned out to be faulty.

So I bought another. That turned out to be faulty too. I really can't be arsed with Merlin products. They are unreliable in my personal experience.

I bought my Smartguage 9 years ago and at the same time removed the 1,2,both,off switch and installed Smarbank Advanced.  I have had not a moments trouble with Gibbo's stuff.

Nick

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  • 1 month later...

I see there are no fuses in the wires (that do the measuring) on the shunt resistor. I guess because one side is 0v and the other nearly 0v? Just about to wire up so got to thinking about this - maybe a fuse and holder (on the nearly 0v side) would add to much resistance/inacuracy?

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24 minutes ago, Johny London said:

I see there are no fuses in the wires (that do the measuring) on the shunt resistor. I guess because one side is 0v and the other nearly 0v? Just about to wire up so got to thinking about this - maybe a fuse and holder (on the nearly 0v side) would add to much resistance/inacuracy?

Why would you want to put a fuse in a negative connection on a boat?

What’s going to happen if it shorts to the hull? What would such a fuse protect?

Edited by WotEver
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On 11/8/2017 at 13:33, David Mack said:

That looks good.

The installation wiring diagrams are shown below.

s-l500.jpg

 

If I want to install this with the display remote from the battery, presumably I can just connect the three 'positive' wires together at the meter and run 3 wires (rather than 5) back to the battery/shunt like this:

Untitled.png.4a99857cc7c6946ba71e1bf975315566.png

NO  The wires from the shunt are carrying a tiny voltage from the shunt into the input of a very sensitive measuring device, if the current for the meter allowed to flow through those wires the voltage measured would be totally meaningless, the current for the meter would probable cause errors of several hundred percent.  The voltage on those shunt wires at 10 amps will be  1.5 millivolts(unmeasurably small current) the voltage drop caused by the display power current about 30 milliamps) will probably be in order of 10 millivolts, a huge amount greater.

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  • 1 month later...

Meanwhile - I went to fit my shunt after doing all the wiring and the panel etc. But thanks to the incredibly poor access to the batteries, I was unable to. I had planned to bolt the shunt to a terminal and the wires to the other side of the shunt, but the orientation it needs to be in coupled with no access means I'll have to get a short lead - even then it is almost impossible. So looks like another project in the offing - I'm going to cut out the deck (on both sides for the sake of symmetry) and raise it up a bit and have a removable top probably made from deck board - it will look very smart and the extra height on the other side will mean that I can one day fit a built in genny. Just a few other little jobs to do before then though.

Too bad as I really wanted to be able to check tail current and what the inverter uses.

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