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beachman
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# Posted: 21 Dec 2014 09:11am
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I want to hook up a battery monitor to supplement a solar system and the monitor requires a shunt. I have done a little research about the set up and from this I plan to put the shunt in a combiner box along with a few other things. Since I plan to have mostly AC wiring but will have a DC water pump, do I need to attach the DC neg. wire to the shunt also? Or can I attach it directly to the battery?
Also, since so many wires and cables are attached to the right side of the shunt, can I use a neg. bus bar or is there some other way of attaching several connections? Also, I seem to think that the neg. wire from the panel has to go to the right side of the shunt before going to the neg. on the lead (leed) battery. Does this sound right?
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MtnDon
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# Posted: 21 Dec 2014 10:40am
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Quoting: beachman mostly AC wiring but will have a DC water pump, do I need to attach the DC neg. wire to the shunt also?
I find that a confusing question. AC and DC in the same question about a single shunt and a battery monitor? The AC has nothing to do with the battery monitor.
If that monitor is designed to work with a single shunt then the shunt must be placed so all current passes through the shunt in the negative line. Yes, you can have a buss to facilitate the connecting of many wires. I would not place the shunt right on the battery as I would not want to take the chance of acid contacting the shunt.
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beachman
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# Posted: 21 Dec 2014 11:05am
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Don - thanks for the info. I understand that the monitor just relates to the batteries as to the state of charging and usage - regardless of type of current. Being an electrical dunce, I am trying to determine the proper set up for the monitor which uses the shunt as a resister to make the measurements. I plan to keep the shunt away from the batteries as you have suggested, but the directions call for a cable at least as large as the cable tying the 6v batteries together for the 12v system.
I think you answered my question in that all current must pass through the shunt, whether going directly to a 12v appliance, or to an inverter. Thanks so much!
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beachman
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# Posted: 21 Dec 2014 11:11am
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Oh, the combiner box would hold the shunt, another lightning arrestor (Midnight Solar with the led), some breakers, and a couple of bus bars - and be far enough away from the potential gases from the batteries. In designing the system, I just realized that even the Charge Controller should be wired through the shunt.
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MtnDon
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# Posted: 21 Dec 2014 12:07pm - Edited by: MtnDon
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Quoting: beachman , I just realized that even the Charge Controller should be wired through the shunt.
Yes, everything, all the current into and out of the batteries has to pass through the shunt. That means BIG wires for the main connections to the shunt.
Some systems like the fancy Outback Fkexnet DC use a separate shunt for CC, inverter, wind gen, etc etc.
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beachman
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# Posted: 21 Dec 2014 03:06pm
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Great. Think I got this now and many thanks. In "bonding" the system, I think I have to run a ground connection to the neg. bus in the converter box probably with a small fuse for protection. Any negatives to this thought?
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MtnDon
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# Posted: 21 Dec 2014 04:28pm
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1. I don't know what you mean by "converter box"
2. grounds never have fuses; neither do negative lines in DC
No more comments w/o more details.
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beachman
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# Posted: 22 Dec 2014 01:38pm
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OK - finally got a schematic made up - good as I had to do this anyway to make sure I had everything I needed before heading out into the wild. Note to anyone looking at this - use at your own risk as I am not sure if I am doing any of this correctly. Appreciate any comments - negative or positive.
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MtnDon
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# Posted: 22 Dec 2014 02:14pm
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First quick look....
No fuse or breaker in + wire to inverter?
No equipment ground on CC, but maybe the BlueSky folks did not provide one?
I would keep the lightning arrestor / surge protector grounds separate from the other grounds. How close is the PV panel to the rest of the equipment? If within 20 feet or so you can use just one ground rod at the PV as shown and run a wire direct to the inverter to ground the it. Nothing else has a ground lug so that would help keep the high voltage surges away from the other stuff. Lightning caused spikes in one conductor parallel to another can induce a spike in the second wire.
I;m not sure where the best placement of the MN SPD would be. Nearer the inverter or nearer the CC? Partly depends on distances.
Why don't you run the diagram by the folks on the NAWS forum or the Midnite Solar Forum. That's where I ask questions.
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MtnDon
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# Posted: 22 Dec 2014 02:24pm
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And a 1 amp fuse to a water pump is too small most likely. Also, remember that a fuse is there to protect the wire, not the device. Size the fuse to the wire and you can not go wrong.
Where wires are oversized to reduce voltage drop it would be okay to run fuses or breakers are that closer to the expected maximum amperage.
You have many circuits in your home that are never used to capacity. Nobody reduces the breaker size because they are running nothing but low amperage devices on some circuits. It is common to run a circuit off a 20 amp breaker, use 12 ga wire, but use nothing but 15 amp outlets, for example. The breaker there is sized to the wire's safe current rating.
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beachman
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# Posted: 22 Dec 2014 03:03pm
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Great thoughts! Yes - plus wire to inverter definitely needs a breaker or fuse. CC does not have a ground attachment. The PV is about 40 ft from the camp - I have #10 AWG from the panel to the CC right now which works well but theoretically it loses some power. I have the Delta SPD at the panel hooked to a ground wire (bare) that goes from the panel to the ground and buried this bare wire about 20 ft to the ground plate and continued this ground wire (coated) up under the camp to the system. I wanted to keep everything under the camp but accessible except for the battery monitor which will be on the wall inside. You are right on with the single ground as with the distances noted - all material that I have read states to keep the grounds all on one system so that lightning would not seek the other ground. But - you seem to indicate that the ground should run directly to the inverter rather through the combiner box. Also - not sure if I need to "bond" the system by attaching one ground wire to a negative bus in the system. Some diagrams appear to indicate this for some reason.
I was not sure about the size of the fuse for the 12v pump - it is a 12v - 8 amp pump, something more robust sounds necessary - say 5 or 8 amp? One diagram at Midnite Solar showed the Midnite SPD attached to the "combiner" box as I had shown but I will check out your link for sure. I was also thinking of putting in another ground rod nearer the panel and run the ground wire through this as one continuous wire. The distance from the batteries to the box/shunt would be a couple of feet and from the batteries to the inverter no more than 5 feet. I will definitely run this by the NAWS as suggested and thanks for the link.
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MtnDon
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# Posted: 22 Dec 2014 03:55pm
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My thinking on running the ground wire away from as much stuff as possible is that after our lightning strike is to keep any spikes as far away from other stuff as possible. I found a couple places in our disaster list where I am convinced the surge leaked in along the ground wire back towards devices rather than to the earth.
The PV panel is the biggest target for lightning. If it was struck any current being directed to ground by the arrestor/SPD could induce current in other stuff. Maybe even jump to another wire, especially if the ground wire makes any sharp bends.
I could be wrong, and there are probably many ways to do the wiring that would provide protection.
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beachman
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# Posted: 22 Dec 2014 05:48pm
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Thanks Don, I read your thread about the lightning and it was quite sobering.This is one of my big fears and I am trying to get as short and direct of a line to the ground from the PV. Frankly, the SPD at the PV might be useless because lightning travels so fast. I have heard where fuses and breakers have proven useless in the event of a strike. You looked to be well protected but you suffered much damage. I guess nothing is perfect. I would normally try to separate the grounds but I do not appear to have sufficient separation.
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MtnDon
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# Posted: 22 Dec 2014 06:19pm
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There is nothing much that will prevent damage from a direct strike which is what I believe got us. I think it was a cluster attack. Some meteorological info I tracked down indicated that the area was hit by a huge number of strikes in a short time. Good thing it was also rainy very heavily. Best of luck.
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