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Old 07-16-2021, 05:54 PM   #1
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Routing of Solar Power to Battery

I have two dealer installed solar panels on the roof of my TT and their power cables are routed individually down the fridge vent in the rear to the electrical area under the fridge. All the 120 and 12v connections and converter/fuse panel come together in this area. The two solar panels are tied together in parallel under the fridge and connect to a #6 gauge wire to the MPPT controller which in turn ties into a #6 wire that heads through the floor to the front battery box. Somewhere underneath, it changes to a #8 wire which appears at the front in the battery box. The cable has a fuse installed on the positive side at this point. Is there any reason the charge cable has to go all the way to the battery when it could have easily be tied into a common power block at the back where the #6 wire comes back from the battery?

I have installed a hall effect ammeter on the battery cable to monitor current coming from the battery. I'm thinking of connecting the solar cable to the distribution block at the back and let the current flow back and forth on the larger battery cable as demand dictates. This way I can see the net current in and out of the battery on the ammeter. Positive flow when drawing from the battery and negative when the solar system is putting power back into the battery. As it is, I monitor the solar power going into the battery on my bluetooth and the power coming back on the ammeter.

Is it possible the battery is somehow buffering the power? I can't see it any difference whether I hook up near the power distribution block or at the battery. The battery should buffer the same.
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Old 07-16-2021, 09:43 PM   #2
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Quote:
Originally Posted by DougSick View Post
I have two dealer installed solar panels on the roof of my TT and their power cables are routed individually down the fridge vent in the rear to the electrical area under the fridge. All the 120 and 12v connections and converter/fuse panel come together in this area. The two solar panels are tied together in parallel under the fridge and connect to a #6 gauge wire to the MPPT controller which in turn ties into a #6 wire that heads through the floor to the front battery box. Somewhere underneath, it changes to a #8 wire which appears at the front in the battery box. The cable has a fuse installed on the positive side at this point. Is there any reason the charge cable has to go all the way to the battery when it could have easily be tied into a common power block at the back where the #6 wire comes back from the battery?

I have installed a hall effect ammeter on the battery cable to monitor current coming from the battery. I'm thinking of connecting the solar cable to the distribution block at the back and let the current flow back and forth on the larger battery cable as demand dictates. This way I can see the net current in and out of the battery on the ammeter. Positive flow when drawing from the battery and negative when the solar system is putting power back into the battery. As it is, I monitor the solar power going into the battery on my bluetooth and the power coming back on the ammeter.

Is it possible the battery is somehow buffering the power? I can't see it any difference whether I hook up near the power distribution block or at the battery. The battery should buffer the same.
I'm not familiar with the way you're monitoring your amps "from and to" the battery. I only know how my Victron BMV-712 monitors the battery (through a 500A shunt on the negative wire).

But that aside, your question is can you connect your MPPT output to the the buss bars at the 12v power center where the charger/converter and 6ga battery lines all come together. Yes, you can. Especially since, for some reason, your wires presently from the MPPT start as 6ga and reduce to 8ga.

Technically, I think you should have a fuse or breaker between the MPPT and the power center. I'd use a breaker so you can easily disconnect the MPPT from the batteries.

Some people may disagree.
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Old 07-22-2021, 05:59 PM   #3
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Thanks. That's what I had thought.
The ammeter i have is a cheapie from Amazon. It uses a Hall Effect pickup which is basically a coil that surrounds a wire and senses the DC current passing though the wire routed inside it. The advantage is there physical connection to worry about. The pickup senses the amps going either way so i have it set up so that a positive reading means power is coming from the battery and if the reading is negative, the power is going to the battery. The readout is hard wired to the sensor. They run in the CDN$40 range which is much cheaper than a bluetooth power monitor using a shunt system.
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Old 07-22-2021, 08:37 PM   #4
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Originally Posted by DougSick View Post
The pickup senses the amps going either way so i have it set up so that a positive reading means power is coming from the battery and if the reading is negative, the power is going to the battery.
Maybe I'm just dense.

So, is this an instant read of power use (flow)? Or is this cumulative? For instance, after sunset you're pulling power from the battery all night long. By morning I can be down 35-45Ahs of my 200Ah (yes, it would seem we're power hogs).

You said a positive number represents power coming FROM the battery.

If I were using your equipment, would it read +35Ah?

Shouldn't it read -35Ah?

Or if I used 35 of 100, shouldn't it read +65?

I guess my thinking is stuck in the cumulative mode.
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Old 07-23-2021, 02:39 PM   #5
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Quote:
Originally Posted by DougSick View Post
I have two dealer installed solar panels on the roof of my TT and their power cables are routed individually down the fridge vent in the rear to the electrical area under the fridge. All the 120 and 12v connections and converter/fuse panel come together in this area. The two solar panels are tied together in parallel under the fridge and connect to a #6 gauge wire to the MPPT controller which in turn ties into a #6 wire that heads through the floor to the front battery box. Somewhere underneath, it changes to a #8 wire which appears at the front in the battery box. The cable has a fuse installed on the positive side at this point. Is there any reason the charge cable has to go all the way to the battery when it could have easily be tied into a common power block at the back where the #6 wire comes back from the battery?

I have installed a hall effect ammeter on the battery cable to monitor current coming from the battery. I'm thinking of connecting the solar cable to the distribution block at the back and let the current flow back and forth on the larger battery cable as demand dictates. This way I can see the net current in and out of the battery on the ammeter. Positive flow when drawing from the battery and negative when the solar system is putting power back into the battery. As it is, I monitor the solar power going into the battery on my bluetooth and the power coming back on the ammeter.

Is it possible the battery is somehow buffering the power? I can't see it any difference whether I hook up near the power distribution block or at the battery. The battery should buffer the same.

If I understand your question, the amp draw should be monitored on a battery cable before it is split up at a junction block. The charge source can be connected at any point that is NOT between the current loop and the battery. In other words there should be no current flow that has not gone thru the current loop (hall effect device).

If the sign (positive or negative) is a problem turn the current loop around.
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Old 07-23-2021, 03:36 PM   #6
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Originally Posted by Mikec557 View Post
Maybe I'm just dense.

So, is this an instant read of power use (flow)? Or is this cumulative? For instance, after sunset you're pulling power from the battery all night long. By morning I can be down 35-45Ahs of my 200Ah (yes, it would seem we're power hogs).

You said a positive number represents power coming FROM the battery.

If I were using your equipment, would it read +35Ah?

Shouldn't it read -35Ah?

Or if I used 35 of 100, shouldn't it read +65?

I guess my thinking is stuck in the cumulative mode.
This meter just gives the instantaneous current flow in Amperes. With lights on, it shows just under 3A of current coming from the battery. With lights off, I get about .2A of parasitic draw to various devices in the trailer so I don't have much of an issue with keeping the batteries full. On warm nights, I have installed some computer fans in my overhead vents to draw in cool air from the outside. With both running, I can pull another .7A which is still not very much. The meter does provide a continuous voltage reading of the battery so it gives a rough idea of what capacity is left but it does not accumulate the Ah.

I do have a 3000W pure sine inverter to run the coffee maker, microwave or TV when off grid. I don't have a current meter on that as yet. Still thinking of a way to use this Hall Effect meter so I can see what it draws when under load. The battery voltage does drop to 11.7v when the micro is in use so I expect it's pulling a lot of AMPS. The inverter is in the storage boot at the front near the batteries so I'd have to put that meter at that end of the trailer.
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Old 07-23-2021, 03:55 PM   #7
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Originally Posted by Rick the Rocket View Post
If I understand your question, the amp draw should be monitored on a battery cable before it is split up at a junction block. The charge source can be connected at any point that is NOT between the current loop and the battery. In other words there should be no current flow that has not gone thru the current loop (hall effect device).

If the sign (positive or negative) is a problem turn the current loop around.
I think you have it. The Hall Effect sensor has an arrow that points to the positive terminal so the direction the arrow is in determines the +/- shown on the meter. It's pretty good as it does show 1 decimal point so it's pretty sensitive to the current flow. The maximum on mine is 200A but I never expect it would go that high just for house lights etc. I need one on the inverter to see how much that pulls. At 3000 watts, it could theoretically pull well over 200A which will put a lot of stress the two GC2 Trojan batteries. Can't run the micro for very long in that case.
As an idle thought, I wonder what the meter would read if I put two wires through the sensor, one charging from the MPPT and one coming from the battery. Would it just get confused or would it provide a net reading? I remember doing an experiment like this with two parallel loops of wires that could swing. Depending on the direction of flow on each wire, they would pull together or push apart, thereby demonstrating the presence of the magnetic field around the wires when current flowed. It would save me changing the wiring set up. Have to think on that.
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Old 07-27-2021, 01:39 AM   #8
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My only caution would be if the battery disconnect would also disconnect your solar. Some scc can be damaged by leaving panels connected but disconnecting controller from battery (but probably rare). More importantly, while your rv is sitting between trips there would be no way to allow solar system to charge battery while having small drains disconnected. I personally wouldn't do this if it did go through the battery disconnect.
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