Wire too big for Victron charge controller

[Statistical]

Originally Posted by noelex 77

Contrary to popular belief there is sometimes the need to provide circuit protection between the solar controllers and the solar panels in addition to the always mandatory protection between the controller and the batteries.

The basic general rule (with some exceptions) is that three solar panels or above in a string need circuit protection. The reason is to provide protection for the wire within the solar panels. These wires are kept small to minimise the shading of solar cells, but in the event of of fault condition these wires can overheat which is not ideal especially when installed on top of flammable canvas structures.

This. PV side shutoffs/breakers are rare on boats but they are very common on land and in most places mandatory for the obvious safety benefits. Now I am going to tell someone they are wrong for not having a PV breaker/shutoff but they do serve a purpose and having one wouldn't be a bad thing especially as PV arrays on boats continue to grow. Ten years ago 200W or less was pretty common. Today people have 1KW, 2KW, hell even 5KW solar arrays. It isn't crazy to have a safe and quick way to shut that off if things go wrong.

[Wotname]

Originally Posted by Statistical

God not solder. Just no. There are a half dozen ways to resolve this of various degrees of good. None involve solder.

100% AGREE - NEVER use solder here!

Victron specifically profits the use of solder on these connections. From their Wiring Unlimited document (link upthread).

Also, never use rigid cable starts or solder the cable strands together, this will create poor contact inside the screw connector, the wire might come loose, or this creates too much contact resistance. Too much resistance will cause the connector to heat up.

My emphasis.

[Statistical]

Originally Posted by Wotname

I completely disagree. In this case, both the battery and the CC are power sources but the CC is current limited, the battery is not.

The battery is almost unlimited uncontrolled current source. A fuse needs to be placed close to the battery.

The Victron charge controller is a current limited source. Its internal circuit design prevents it from supplying more current than the rated current for the model in question. The wire size is selected to safely carry the max output current thus there is no need to fuse at the CC end.

Fair point. I don't wire anything directly to the battery and the battery already has its own fuse from the battery to the busbar but that isn't universal. My response was vague to the point of being dangerous. Thanks for the correction.

[Wotname]

Agree with noelex 77 & Statistical that there are times when circuit protection is necessary at the PV end of the circuit just as there are times when it is not necessary. In the OP's case who is using a very small CC (75/15) I (and many others) would not bother with switch/breaker in the PC wiring but when circuit protection is needed, it really should be used.

[noelex 77]

Originally Posted by Statistical

This. PV side shutoffs/breakers are rare on boats but they are very common on land and in most places mandatory for the obvious safety benefits.

The provision for PV shutoff certainly has advantages. For example, some solar controllers demand the solar supply is disconnected before the battery supply.

The high input voltages of large modern solar panels are often above the capacity of marine switches (marine switches are often limited to 32v DC) so DC circuit breakers are sensibly employed in this capacity even if the circuit protection is not required or utilised. These circuit breakers often act only as suitable high DC voltage switches. They are not wired to provide effective circuit protection for the input to the solar controller.

Nevertheless, circuit protection on the input side of controllers is needed in some instances. This requirement is mysteriously neglected on many boats that otherwise have adequate circuit protection on all other devices. There is a belief that the maximum output of solar panels is self limited (which is accurate) and therefore fusing before the solar controller is never needed (which is wrong).

[Wotname]

Dependant on mounting architecture, many PVs can be switched off by shading or in the worst case, waiting 'till dusk. These 'switches' are not voltage dependant

[noelex 77]

Originally Posted by Wotname

Dependant on mounting architecture, many PVs can be switched off by shading or in the worst case, waiting 'till dusk. These 'switches' are not voltage dependant

It is very important to disconnect the solar supply before switching off the main battery supply on some boats. Without a battery in the circuit the solar controllers will struggle to keep the voltage within acceptable limits and major damage to sensitive electronics can occur in some instances.

In situations such as lightning in the local area, or just working on the DC system, many boat owners sensibly choose to disconnect the electrical supply and in these cases (depending on equipment and wiring) it is important to first disconnect the solar panel input.

An isolation switch for the solar panel input is not essential, but you need to very careful if this is not installed that the solar panel input cannot power the house systems directly if the batteries are disconnected as well as observing the correct disconnection sequence for your solar controller.

[Wotname]

^^ all valid points.

[skipperpete]

Originally Posted by Wotname

Crimp a bootlace ferrule onto the 8AWG wire and it will fit into the Victron terminal nicely. I do this routinely.



In fact, bootlace ferrules should be used all 'bare' ended wiring.

I totally agree, I saw them used as a matter of course in Europe but never seen em in Australia, not even for sale.

[Uncle Bob]

Originally Posted by skipperpete

I totally agree, I saw them used as a matter of course in Europe but never seen em in Australia, not even for sale.

I can assure you that they are for sale here in Aus, I just bought one today along with three sizes of ferrules.

[s/v Jedi]

- Always a fuse near the battery so for solar controllers as well.

- Solar panels connected in series do not require a fuse/breaker, because they are current limited and the current can not do harm anywhere. The wiring must be rated for Isc. Often, a switch or breaker/switch is added anyway, for convenience reasons.

- When three or more solar panels are connected in parallel, EACH panel must have a fuse/breaker. When a panel is shaded or has a failure and it doesn’t have a blocking diode or that is failed too, then it can become a short circuit and the other panels connected in parallel start dumping their power into it, causing a fire in the panel. This happens often. The fuse/breaker of the failed panel will protect it in that case. Check your docs but I think the fuse/breaker must be 1.5x Isc.

- When you have multiple series strings of panels and want to connect those strings in parallel, then you must follow the same rule as for individual parallel panels like above. That said, this is a large installation and it is custom to give each string a breaker even when there’s only two strings.

- Soldering creates hard spots. People who write that soldering creates the best contact are wrong. A high pressure crimp as with a battery lug has better contact. For smaller wiring it isn’t the contact resistance (we call it insertion loss) that is the problem with soldering, but it creates a hard spot that is likely to break copper strands just next to the soldering (copper work-hardens and any movement must be spread out over a length of wire, but the solder abruptly ends that and a stress riser is created). Also, solder easily melts with heat, which is a possible failure point during a fire or when the circuit is overloaded by a short with another, much higher amperage circuit.
You can solder these connections, but you need specific skills, techniques and practice to eliminate those issues. I still do soldering, but I try to prevent it where I can. One good way, recommended by me and also mentioned in the Victron document, is using Wago 221 series connectors. They interconnect wire of different diameters, solid or stranded. I’ll attach a picture when ai can find it, as well as for soldering connections done right on miniature switches.

- if you have your wire and crimped ferrules at the terminal but the crimped ferrule doesn’t fit, then you didn’t test this with a piece of scrap wire first, so do that at this time. Try remove strands and the same size ferrule first if it appears it is only a tiny bit too big. Otherwise take the next size smaller ferrule and count how many strands must be removed to fit in there. Crimp and test until you have the solution, then toss the scrap test piece in the bin and do all the connections right.
It doesn’t matter that there are strands cut off because what is left is more than capable of carrying the current (it only just fits the terminal). Also, the ferrule has added surface area. If this wire is reused for a different setup in the future, the ferrules must be cut off and replaced anyway. Using a butt crimp connector to go a size down is not wise and prone to failure. It’s hard to find crimp connectors going from 8AWG to 10AWG anyway, but they do exist. They cause a lot of trouble. The Victron document shows which crimp terminals are okay and which are not okay to use. Butt connectors will be in the “bad” category.
If you really, really want to use a different solution then use Anderson Powerpole crimp connectors. The small ones work for 1- or 2 conductors and they are reliable.

- to switch a solar controller on or off, you don’t have to blank a oanel or disconnect it. The Smart Victron controllers can be switched on/off using the Bluetooth app or a remote switch and the “dumb” ones all have that remote on/off as well afaik.

Edit: first picture shows soldering wires to miniature connectors. The connection is at one end supported by the switch itself, and the other end has glue lined heat shrink for strain relief, as well as bundling to reduce movement as much as possible.

Second picture, on the lower left side is where all the wires from those small switches are handled and you seethe Wago 221 connectors in action. They can hold up to 20 wires, interconnecting all of them. Four small wires per ferrule and five ferrules per Wago.

Third picture, if forum allows another edit, is the front of this panel with all the small switches illuminated.

[GordMay]

Originally Posted by Wotname

I completely disagree. In this case, both the battery and the CC are power sources but the CC is current limited, the battery is not.

The battery is almost unlimited uncontrolled current source. A fuse needs to be placed close to the battery.

The Victron charge controller is a current limited source. Its internal circuit design prevents it from supplying more current than the rated current for the model in question. The wire size is selected to safely carry the max output current thus there is no need to fuse at the CC end.

Indeed.

[CaptainRivet]

Originally Posted by s/v Jedi

- Always a fuse near the battery so for solar controllers as well.

- Solar panels connected in series do not require a fuse/breaker, because they are current limited and the current can not do harm anywhere. The wiring must be rated for Isc. Often, a switch or breaker/switch is added anyway, for convenience reasons.

- When three or more solar panels are connected in parallel, EACH panel must have a fuse/breaker. When a panel is shaded or has a failure and it doesn’t have a blocking diode or that is failed too, then it can become a short circuit and the other panels connected in parallel start dumping their power into it, causing a fire in the panel. This happens often. The fuse/breaker of the failed panel will protect it in that case. Check your docs but I think the fuse/breaker must be 1.5x Isc.

- When you have multiple series strings of panels and want to connect those strings in parallel, then you must follow the same rule as for individual parallel panels like above. That said, this is a large installation and it is custom to give each string a breaker even when there’s only two strings.

- Soldering creates hard spots. People who write that soldering creates the best contact are wrong. A high pressure crimp as with a battery lug has better contact. For smaller wiring it isn’t the contact resistance (we call it insertion loss) that is the problem with soldering, but it creates a hard spot that is likely to break copper strands just next to the soldering (copper work-hardens and any movement must be spread out over a length of wire, but the solder abruptly ends that and a stress riser is created). Also, solder easily melts with heat, which is a possible failure point during a fire or when the circuit is overloaded by a short with another, much higher amperage circuit.
You can solder these connections, but you need specific skills, techniques and practice to eliminate those issues. I still do soldering, but I try to prevent it where I can. One good way, recommended by me and also mentioned in the Victron document, is using Wago 221 series connectors. They interconnect wire of different diameters, solid or stranded. I’ll attach a picture when ai can find it, as well as for soldering connections done right on miniature switches.

- if you have your wire and crimped ferrules at the terminal but the crimped ferrule doesn’t fit, then you didn’t test this with a piece of scrap wire first, so do that at this time. Try remove strands and the same size ferrule first if it appears it is only a tiny bit too big. Otherwise take the next size smaller ferrule and count how many strands must be removed to fit in there. Crimp and test until you have the solution, then toss the scrap test piece in the bin and do all the connections right.
It doesn’t matter that there are strands cut off because what is left is more than capable of carrying the current (it only just fits the terminal). Also, the ferrule has added surface area. If this wire is reused for a different setup in the future, the ferrules must be cut off and replaced anyway. Using a butt crimp connector to go a size down is not wise and prone to failure. It’s hard to find crimp connectors going from 8AWG to 10AWG anyway, but they do exist. They cause a lot of trouble. The Victron document shows which crimp terminals are okay and which are not okay to use. Butt connectors will be in the “bad” category.
If you really, really want to use a different solution then use Anderson Powerpole crimp connectors. The small ones work for 1- or 2 conductors and they are reliable.

- to switch a solar controller on or off, you don’t have to blank a oanel or disconnect it. The Smart Victron controllers can be switched on/off using the Bluetooth app or a remote switch and the “dumb” ones all have that remote on/off as well afaik.

Edit: first picture shows soldering wires to miniature connectors. The connection is at one end supported by the switch itself, and the other end has glue lined heat shrink for strain relief, as well as bundling to reduce movement as much as possible.

Second picture, on the lower left side is where all the wires from those small switches are handled and you seethe Wago 221 connectors in action. They can hold up to 20 wires, interconnecting all of them. Four small wires per ferrule and five ferrules per Wago.

Third picture, if forum allows another edit, is the front of this panel with all the small switches illuminated.

Wago 221 are genius and my go for especially with small wires.
Big wire lugs i crimp and solder too but only front part.
The heavy wire lugs i use have a small hole in the front, so you don't enclosure air in a pocket. After crimping i use a solder iron and solder with a small amount of silver solder this hole close to make connection gas tight and connect the front part with the lug. You need to be careful and need a very hot slolder iron as you need to prevent the solder from creeping along the wire and prevent getting to rear part of the crimp. This is only for experienced persons with soldering !!! and if you not 100% sure what you are doing better not do it.
Done correctly gives the best longlasting contact and rear part stays flexible. Use heat shring with glue inside to seal crimping on the other side.
This way also non tinned stranded wire keeps corrosion free a long time. In US tin stranded is widely avaliable while in europe you often get fine stranded wire in stock for car installation but thats not tinned. Tinned is on special order...

[Senojev]

Response to Wotname

I don’t want to extend the debate on to ferrule or not to ferrule but only to post my source of information on Victron recommendation which is as follows. Guy is the Victron Community Manager and Produces a number of the Victron Training videos.

“Guy Stewart (Victron Community Manager) ♦♦ alaskannoob commented · Feb 16 2023 at 7:17 AM

I’ll make some resources to demonstrate why.
Ferrules make for a much neater installation, but they limit the contact surface area.

In some cases this isn’t an issue, but in others it can be.

A square crimpted ferrule will be better than a loose round one over thick stranded cable, but all will be inferior to fine stranded cable inserted with care and then torqued correctly.

Failure of an MPPT due to insufficient contact at the terminals is all too common unfortunately, though many MPPTs are also installed without optimum contact and without issues as well.

Best practice is a clean job, with fine strand to spec, and maximum contact surface area.”

[Emmalina]

Originally Posted by s/v Jedi

How it’s done for clean, reliable installation; I know it’s a lot more work than slapping some wires on, but it is required to achieve the results.

Wow reminds me of the 70's when we used to strip ww2 stuff. Whipping wires is an old art...