WotEver Posted November 8, 2017 Report Share Posted November 8, 2017 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? Link to comment Share on other sites More sharing options...
Detling Posted November 8, 2017 Report Share Posted November 8, 2017 A lot of people like this one as the display can be anywhere https://www.ebay.co.uk/i/172278832577 Link to comment Share on other sites More sharing options...
nicknorman Posted November 8, 2017 Report Share Posted November 8, 2017 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. Link to comment Share on other sites More sharing options...
MtB Posted November 8, 2017 Report Share Posted November 8, 2017 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. Link to comment Share on other sites More sharing options...
WotEver Posted November 8, 2017 Report Share Posted November 8, 2017 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. Link to comment Share on other sites More sharing options...
MtB Posted November 8, 2017 Report Share Posted November 8, 2017 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. Link to comment Share on other sites More sharing options...
Dr Bob Posted November 8, 2017 Report Share Posted November 8, 2017 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. Link to comment Share on other sites More sharing options...
WotEver Posted November 8, 2017 Report Share Posted November 8, 2017 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 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 Link to comment Share on other sites More sharing options...
Dr Bob Posted November 8, 2017 Report Share Posted November 8, 2017 2 minutes ago, WotEver said: Or you could get a life I'd sooner have a Smartguage. 1 1 Link to comment Share on other sites More sharing options...
WotEver Posted November 8, 2017 Report Share Posted November 8, 2017 Just now, Dr Bob said: I'd sooner have a Smartguage. Sorry, you’re not allowed. Link to comment Share on other sites More sharing options...
MtB Posted November 8, 2017 Report Share Posted November 8, 2017 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 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. Link to comment Share on other sites More sharing options...
WotEver Posted November 8, 2017 Report Share Posted November 8, 2017 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. 1 Link to comment Share on other sites More sharing options...
Theo Posted November 10, 2017 Report Share Posted November 10, 2017 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 Link to comment Share on other sites More sharing options...
Johny London Posted January 6, 2018 Author Report Share Posted January 6, 2018 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? Link to comment Share on other sites More sharing options...
WotEver Posted January 6, 2018 Report Share Posted January 6, 2018 (edited) 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 January 6, 2018 by WotEver Link to comment Share on other sites More sharing options...
Detling Posted January 8, 2018 Report Share Posted January 8, 2018 On 11/8/2017 at 13:33, David Mack said: That looks good. The installation wiring diagrams are shown below. 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: 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. Link to comment Share on other sites More sharing options...
Johny London Posted February 15, 2018 Author Report Share Posted February 15, 2018 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. Link to comment Share on other sites More sharing options...
system 4-50 Posted February 15, 2018 Report Share Posted February 15, 2018 I don't think putting the shunt on top of the batt would be a good idea anyway. They can get quite warm (hot?) and putting an additional heat source near the batt seems unwise? What do the rest of the panel think? Link to comment Share on other sites More sharing options...
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