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Old 02-08-2022, 02:59 PM   #1
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Solar installation

I have a 210 watt solar panel. Thinking of connecting it to the controller and then going to a buss bar. From there I would connect 2 wires , one for each battery (for some reason the 2 house batteries are on opposite sides of the boat, to be corrected later) and fuse both individual wires. Has anyone done this?
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Old 02-08-2022, 04:19 PM   #2
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Try to make the wiring distance equal from the controller to each of the two batteries so one doesn't have a lower voltage drop and get all of the charging current. Otherwise, I don't see any problem.

Oh, and the fuses need to be near the batteries, right?

David
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Old 02-08-2022, 04:29 PM   #3
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Originally Posted by dosched View Post
I have a 210 watt solar panel. Thinking of connecting it to the controller and then going to a buss bar. From there I would connect 2 wires , one for each battery (for some reason the 2 house batteries are on opposite sides of the boat, to be corrected later) and fuse both individual wires. Has anyone done this?
Will this be the interconnection that makes the two separate batteries into a single "house" bank, or is that done somewhere else? If the latter, connect the solar at that connection?
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Old 02-08-2022, 08:00 PM   #4
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Try to make the wiring distance equal from the controller to each of the two batteries so one doesn't have a lower voltage drop and get all of the charging current. Otherwise, I don't see any problem.

Oh, and the fuses need to be near the batteries, right?

David
I think prevailing wisdom is circuit protection for the wiring. Fuses should be near controller, not battery.

Rather than run from controller to a bus bar, maybe run to a 25 amp circuit breaker, then run dual leads from that to each battery. Kills two birds with one stone. Anyone see a problem there?

Peter
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Old 02-09-2022, 12:27 PM   #5
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I think prevailing wisdom is circuit protection for the wiring. Yes, absolutely. Fuses should be near controller, not battery. No, No, No!

Peter
You need to protect the wire from high currents from the battery, not the controller. The current from the controller is absolutely limited by the wattage of the solar panels connected to it. It can never exceed that current. The wire size is such that it is 2 or 3 sizes above what is needed to carry that current.

The batteries OTOH can supply hundreds of amps if that wire is shorted. So you need to put the fuse near the battery. I think ABYC says 6".

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Old 02-09-2022, 12:42 PM   #6
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Check the amps on the 2 wires running to your house batteries when solar charging.
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Old 02-09-2022, 02:50 PM   #7
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I think prevailing wisdom is circuit protection for the wiring. Fuses should be near controller, not battery.

Rather than run from controller to a bus bar, maybe run to a 25 amp circuit breaker, then run dual leads from that to each battery. Kills two birds with one stone. Anyone see a problem there?

Peter
Sorry but I disagree. THe batteries are the far more dangerous of the two. NOt for long but long enough to cause all kinds of trouble.
Batts. can supply thousands of amps under short circuit conditions. If a short occurs between the charge controller's over current protection [fuse or C.B.]
and the batteries the batteries will fry the wires and maybe cause a fire.
I would expect the wire would disappear. However there is a worse case scenario which includes the wire fry but adds a battery explosion if the short is bad enough.

Best would be protected at both sides for protection for all of it.
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Old 02-10-2022, 12:55 AM   #8
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Batts. can supply thousands of amps under short circuit conditions.
Can you give an example? I am not getting how a short circuit sends amps upstream past the point of short.
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Old 02-10-2022, 08:11 AM   #9
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Hoping an ABYC electrician will chime in. I can see both sides. One being fuse right after the source (low amp solar controller). Can certainly understand the argument for circuit protection nearest largest possible source (battery) even though that would mean a serious reversal of fortunes.

Anyone?

Peter
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Old 02-10-2022, 08:31 AM   #10
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Solar installation

OCP close to the current source that could supply a high enough current to overheat the wire.

Solar has energy sources at both ends, but only one would need the OCP.
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Old 02-10-2022, 11:20 AM   #11
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OCP close to the current source that could supply a high enough current to overheat the wire.

Solar has energy sources at both ends, but only one would need the OCP.
Yes, let's take the example of the OP's 210 watt panel to illustrate the point. Assume it is a nominal 12V panel which can produce the most current. It has an Isc value of about 13 amps. That means that it can never ever generate more than 13 amps no matter what the sun, controller or anything is doing. So in this case it may be wired with 10 gauge which is good for 60 amps. So, there is no need to protect that wire.

Some people like a disconnect switch between the controller and the panels so they can work on them and often use a breaker to do that. Fine, but it isn't necessary for over current protection.

Now let's look at the output of the controller. If it is an MPPT controller it will boost the current a bit since the battery voltage during charging is 12-13 volts. So, let's use 12 volts and divide that into 210 watts which gives us about 18 amps. That side will be wired with maybe #8 gauge to limit voltage drop and is good for 80 amps. So, no need for a fuse at its output since the current will never go above the wire's rated current carrying capacity.

Now let's look at the battery. Depending on size and type it can deliver hundreds, maybe thousands of amps of current if it is facing a short to ground. There is no reasonable size wire that can carry that much current, certainly not the #8 gauge it is probably wired with. So, you put a fuse to protect the wire against a short to ground between the fuse and the controller and you mount it within 6" of the battery so there isn't much that can cause a short between it and the battery.

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Old 02-10-2022, 11:43 AM   #12
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OCP close to the current source that could supply a high enough current to overheat the wire.

Solar has energy sources at both ends, but only one would need the OCP.
Overheated wire is more likely to occur than a short when a load source that needs more amps than the wire size is rated to supply. The fuse at source blows. Remember the old days when a penny was added to overcome blowing the fuse.
So the wire size needs to meet the need of the load and fused accordingly at source.
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Old 02-10-2022, 12:29 PM   #13
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If the positive lead running between the solar controller and the batteries is shorted to ground somehow the solar will only supply what it can supply. A few amps although it still needs protection..

However the other end of that wire is connected to the batteries positive and now you have an unintended ground. THat battery does not care about the controller end of things. It is now grounded between the controller OCP and itself.

In this situation you have two energy sources. One at each end of the wire, not just one energy source. Both need to be fused or otherwise protected.

Of course the current from the short depends upon many variables, battery bank size, the quality of the short and the total resistance back to the battery bank ground.

I am not suggesting the battery will always dump thousands of amps due to those other variables, but it could and it is that you are protecting against.
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Old 02-10-2022, 03:13 PM   #14
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For what it's worth, Victron sample circuit arrangements show protective devices before and downstream of the controller. The diagrams are somewhere on their website, just don't remember where.
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Old 02-10-2022, 03:42 PM   #15
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You need to protect the wire from high currents from the battery, not the controller. The current from the controller is absolutely limited by the wattage of the solar panels connected to it. It can never exceed that current. The wire size is such that it is 2 or 3 sizes above what is needed to carry that current.

The batteries OTOH can supply hundreds of amps if that wire is shorted. So you need to put the fuse near the battery. I think ABYC says 6".

Daavid
Yes Dave, IMHO you are absolutely correct!!! Solar panels are current sources and have zero problems working directly into a short circuit. ABYC states somewhere a fuse should be 18 inches from the battery negative connection. I do not see the importance for not attaching a fuse to the positive connection. Either will provide protection.
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Old 02-10-2022, 03:47 PM   #16
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You must have OCP within 7” of the battery (72” if sheathed), period, no exceptions. So the question is, do you need it in both locations?

Re. the solar panel and regulator, ABYC’s language applies…

11.10.1.1.2 In addition to the provisions of E.11.10.1.1.1 the ungrounded conductors to a battery charger, alternator, or another charging source shall be provided with overcurrent protection within the charging source, or within seven inches (178 mm) of the charging source, based on the maximum output of the device.
EXCEPTION: Self-limiting devices.

11.4.30 Self Limiting Device - a device whose maximum output is restricted to a specified value by its magnetic or electrical characteristics.
NOTES:
1. The output remains at a value or will automatically decrease to a value such that it will not damage the battery charger or inverter/charger after application of a short circuit at the output terminals.
2. The output current will not exceed the ampacity of the conductor that is specified for connection to the battery charger or inverter/charger by the manufacturer.

While there is added resistance for every connection, there is no harm in including OCP at the panels, but strictly speaking, if it meets the above exception, it is unnecessary.
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Old 02-10-2022, 05:30 PM   #17
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Solar panels are current limited eliminating the need over current protection. Now as to ‘’7 inches’’ from battery to an overload protection device, nonsense! ABYC would be better recommending that protection be as close as reasonably possible to batteries instead issuing ridiculous distances

People should NOT get hung up with ABYC’s rules. They have zero enforcement authority. Yes, their recommendations provide value but remember, there are no laws that I know of as dogma pertaining to this topic. It is better to have some protection some where in the wiring than none.
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Old 02-10-2022, 05:55 PM   #18
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Solar panels are current limited eliminating the need over current protection. Now as to ‘’7 inches’’ from battery to an overload protection device, nonsense! ABYC would be better recommending that protection be as close as reasonably possible to batteries instead issuing ridiculous distances

People should NOT get hung up with ABYC’s rules. They have zero enforcement authority. Yes, their recommendations provide value but remember, there are no laws that I know of as dogma pertaining to this topic. It is better to have some protection some where in the wiring than none.
I am a decent shade tree mechanic. Additionally, I have done several down-to-stud remodels of homes and apartments. I appreciate codes and ABYC guidance. Even code inspectors will often use common sense.

7-inches tells me much more than as close as possible. As close as possible could mean several feet. 7-inches tells me damn close.

Bottom line is I may decide to set aside ABYC requirements. But I really appreciate knowing exactly what I am setting aside.

BTW - big thanks to Steve D for contributing, and to DavidM for first calling out that OCP should be near batteries. I learned something today.

Peter
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Old 02-10-2022, 06:56 PM   #19
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Originally Posted by Steve DAntonio View Post
You must have OCP within 7” of the battery (72” if sheathed), period, no exceptions. So the question is, do you need it in both locations?

Re. the solar panel and regulator, ABYC’s language applies…

11.10.1.1.2 In addition to the provisions of E.11.10.1.1.1 the ungrounded conductors to a battery charger, alternator, or another charging source shall be provided with overcurrent protection within the charging source, or within seven inches (178 mm) of the charging source, based on the maximum output of the device.
EXCEPTION: Self-limiting devices.

11.4.30 Self Limiting Device - a device whose maximum output is restricted to a specified value by its magnetic or electrical characteristics.
NOTES:
1. The output remains at a value or will automatically decrease to a value such that it will not damage the battery charger or inverter/charger after application of a short circuit at the output terminals.
2. The output current will not exceed the ampacity of the conductor that is specified for connection to the battery charger or inverter/charger by the manufacturer.

While there is added resistance for every connection, there is no harm in including OCP at the panels, but strictly speaking, if it meets the above exception, it is unnecessary.
Am I misunderstanding this bolded? The solar panel MPPT is the charging source, not the battery. So why is it said to be within 7 inches of the battery.
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Old 02-10-2022, 08:13 PM   #20
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How did ABYC allow the term “self limiting device”. I’ve worked on output systems on 1.2GW nuke plants. Even those are “self limiting”
Our battery banks have internal R with a more or less fixed V in series.
Maybe the sun itself is not “self limiting”?
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