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Last edited by joerossjr; 03-10-2018, 12:01 PM. -
What current are you interested in monitoring? That determines where the shunt or shunts go. You cannot see all currents with 1 shunt. To see everything you need 3 shunts and a micro-controller to derive the 4th current in a system.
1. Panel Current
2. Controler Current
3. Battery charge/discharge current
4. Load Current.
With 3 shunts you can monitor all 4 points.MSEE, PE -
Are you using a Grounded System or Floating?MSEE, PEComment
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Here you go. The 3rd Shunt I spoke of is not shown, but would be between the Panels and Controller on the Negative line like you see below.
Last edited by Sunking; 08-08-2017, 08:11 PM.MSEE, PEComment
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You are welcome.Originally posted by joerossjrMSEE, PEComment
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Hmmm... If those 3 green grounds are actually connected in any way, the shunt is going to
be "shunted" and read low. Might need to relocate in the other lead. Bruce RoeComment
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That is possible if the Inverter and Controller Chassis are bonded to Batt NEG. You would be right as we created a parallel path with the Battery Negative supply conductor. OTOH if they are not internally bonded and open circuit, there are no issues with parallel paths. To facilitate proper operation of OCPD the battery Neg Term must be solidly Grounded, so that eliminates one great solution to move the Shunts.
The issue I struggled with is Metering OEM's making their equipment use the Negative Polarity rather than Positive. They know dang good and well most manufacturers bond Chassis to Bat NEG, thus compromises the system. This is why NEC will not allow that to happen on AC systems.
I know why they do it like that, I just don't care for it. They put it in Neg because that is a Grounded Circuit Conductor referenced to Ground aka Neutral with no voltage on it. That way when you run those little Shunt Wires outside the battery area, thet are not Hot Battery looking for a place to get loose if pinched or cut.
Move the Shunts to Positive polarity problem solved, or FLOAT your system.Last edited by Sunking; 08-08-2017, 10:41 PM.MSEE, PEComment
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There are two types of electrical systems:Originally posted by joerossjr
1. Grounded System.
2. Non Grounded of Floated.
Look at the two diagrams and note what is different. Floating system the battery is NOT BONDED to Ground and uses fuses on both positive and negative polarities. Now look at the Grounded system.
Your problem is you are associating Ground with Dirt or Earth. Stop doing that. Ground is a reference point and can be anything. Like the chassis of a boat, car, plane, or space ship.
MSEE, PEComment
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Same here Silent SerrviceOriginally posted by joerossjr
Just so I understand... Are you saying my shunts really should go on the positive side of the circuits to avoid ground loops or anything similar? .[/QUOTE]
They should but most OEM add-on units use return of the Grounded Circuit Conductor because it is Neutral. That way you are not taking Hot Raw Battery outside. There would not be a problem if equipment manufacturers did not bond Chassis to the NEG BATT Terminal. That forces all Negative Battery current to flow on Ground Conductors. Extremely dangerous practice.
MSEE, PEComment
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Sunking-
I'm again clocking through this data on shunt based battery meters. From how I currently understand the system, most OEM shunts are either unsafe or inaccurate depending on how they're installed. If the shunt is connected to batt (-) and all wires are run through it including chassis bond, then it is unsafe because other chassis bonded components have potential to not clear a fuse properly if they're internally faulted. Most manufacturers that I see instruct to do it this way, which would only really work in a full floating system (which is rare in vehicle applications).
The safe way of wiring is to have shunt installed between batt (-) and return wires and have a separate chassis bond bypassing the shunt from the same batt terminal. This wouldn't register current flow if it were to occur from chassis bond to other components. How often does this current flow happen? It seems like the system has some inaccuracy but maybe it's enough to get a rough estimate of energy consumption this way?
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Donkey the issue is with the support equipment having the Battery Return Conductor (negative polarity) bonded to the chassis and the Ground Terminal Post. What that does is puts the vehicle chassis in Parallel with your battery return conductor and thus bypassing any shunt you put in-line. There is no way to determine how much current is bypassing the shunt. Offending items are the charge controller, inverter, and any 12 volt DC loads running off DC power. Example most charge controllers have the bond, but some manufactures like Midnite solar isolate chassis and battery return. However I cannot tell you with any certainty if any Inverters isolate chassis from battery.
Having said that even if you could keep the support equipment isolated, the battery monitors are basically worthless. They cannot tell you what state of charge your battery is at with any meaningful significance. Remember cars with Check Engine and Hot Lights. By then it is too late. It is clear the OP does not want to hear that.
Now what can work is a Hall Effect Transducer installed Between the two Battery Fuses. But all that tells you is the same thing of either the battery charging or discharging. Counting Amps in/out and battery voltage just does not tell you anything useful.MSEE, PEComment
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Ok. So the whole setup doesn't tell you much more than a simple voltage reading would.
Does a significant amount of energy usually pass through the ground connectors or does it vary a lot? I know you said it's impossible to tell...Comment
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Very well could be more than 50% bypasses the shunt, depends on the resistance ratio. Example lets say the ground references is the I Beam of the frame which trucks (RV's) still use. The majority of current would be in the I Beam because it is a massive conductor. In a vehicle safety is not an issue because voltage is so low, and the chassis is low resistance. Most of the problems would be encountered with sensitive electronic equipment like radios, GPS/NAV, TV's etc...
Now if it were me, I know how to work around it. I would install something like a piece of plywood and mount all my equipment to the Plywood to isolate the equipment chassis and would not use any of Ground Terminals. On second thought, I would just use a Hall Effect Transducer on the Positive load side.
MSEE, PEComment
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Maybe, maybe not. I have not looked at every battery monitor out there. But I have looked at a few like TriMetric, and if you placed a Shunt on the Positive would let the magic smoke out. It is made to use ground reference, and when you place battery on its sensor, it goes POOF the Magic Dragon.
The reason manufactures use the return is strictly liability and cost issues. Running raw battery is dangerous and would require using dual fuses for each lead of the Shunt which cost money. Why they do not Use Hall Effect Transducers is beyond me. Hell a good Hall Effect does not cost more than than a Shunt.
MSEE, PEComment
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