Wire too big for Victron charge controller

[nash_sailing]

Hey all, we recently installed some solar panels on our sailboat and are about 80% done with the project, with one small hiccup - the 8 awg wire we installed is too big for the 75/15 Victron MPPT charge controller, which can take 10 gauge max. We have a long run from panels to battery locker (~50’ round trip) due to awkward battery placement, so we can’t downsize the cable. I see three options: trim the strands to make it fit (seems sketchy), use a pin terminal (seems like it could vibrate loose) and upgrade to a 100/30 charge controller ($$$). Does anyone have any insight on this? Thanks in advance!

[Knotical]

Feel your pain, this is probably the only situation where oversizing wire gauge is not a good idea.

I have (non-expert) 2 ideas:
1. Crimp and heatshrink a 10 AWG wire to it
2. Use a terminal trip between the 8 & 10

[fourlyons]

Originally Posted by nash_sailing

Hey all, we recently installed some solar panels on our sailboat and are about 80% done with the project, with one small hiccup - the 8 awg wire we installed is too big for the 75/15 Victron MPPT charge controller, which can take 10 gauge max. We have a long run from panels to battery locker (~50’ round trip) due to awkward battery placement, so we can’t downsize the cable. I see three options: trim the strands to make it fit (seems sketchy), use a pin terminal (seems like it could vibrate loose) and upgrade to a 100/30 charge controller ($$$). Does anyone have any insight on this? Thanks in advance!

As the other poster said, just put a 10 gauge tail on it. You've got 8 gauge for the long run to deal with the voltage drop, a short length of 10 won't matter. You're not using 8 gauge due to the amperage.

[nash_sailing]

Originally Posted by Knotical

Feel your pain, this is probably the only situation where oversizing wire gauge is not a good idea.

I have (non-expert) 2 ideas:
1. Crimp and heatshrink a 10 AWG wire to it
2. Use a terminal trip between the 8 & 10

I know, I’m so annoyed - the wire sizing information was buried so deep in the manual!

[nash_sailing]

@fourlyons No, it should only be 15A. Thank you, I didn’t realize this was an option!

[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.

[fourlyons]

Originally Posted by fourlyons

As the other poster said, just put a 10 gauge tail on it. You've got 8 gauge for the long run to deal with the voltage drop, a short length of 10 won't matter. You're not using 8 gauge due to the amperage.

Ok, I didn't say that very well. You are using 8 gauge due to the amperage, lower the amperage and you won't have as much voltage drop and you could use 10 gauge for the 50 foot run.

What I meant to say is that adding a short length of 10 gauge, when the vast bulk of the distance is 8 gauge, will not add enough resistance to cause significant voltage drop or overheat the wire. Have you ever compared the size of the conductor in a fuse to the wire it's protecting?

[fourlyons]

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.

Even better. Much cleaner.

[jordanbigel]

trim the strands to make it fit

I've done this before, several times in this exact type of situation - seems like it is no worse than adding a short distance of 10awg (spliced with a butt connector). Since the butt connector must add some small resistance, how is that any better than just trimming some of the strands off the 8awg?

The end result is that you have appx. 1/2" of 10awg thick wire which then transitions to 8awg wire.

If this is bad, why?

[GordMay]

I wouldn’t assume that a #8AWG Pin Terminal (bootlace ferrule) would fit into a #10AWG (Victron) screw clamp (compression plate) terminal.
If it does fit, use it.
If it doesn’t fit, I’d trim the strands (on #8) to make it fit the terminal.

[GordMay]

Originally Posted by Wotname

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

In my view, a proper wire terminal has a compression clamping plate, that bears against the wire/conductor. The set screw bears against the clamping plate - not the wire.
When the equipment terminal has only a set screw, bearing directly on the wire, a Crimp Pin Terminal (bootlace ferrule), or better yet, a ring/captive spade crimp terminal must be used.
Otherwise, use of the pin terminal is not advantageous. It’s extra (unneeded) work/cost, and adds a small amount of circuit resistance (extra connection) to the circuit.

I can't tell what exact type of power terminals the OP's Viictron unit uses.

ABYC Section E-11 specifies:
“... Wiring connections shall be designed and installed to make mechanical and electrical joints without damage to the conductors...
Terminal connectors shall be the ring or captive spade types.
... Connections may be made using a set-screw pressure-type conductor connector, providing a means is used to prevent the set-screw from bearing directly on the conductor strands ...”

[thomm225]

How many watts worth of panels do you have going in to your controller?

I have a 75/15 Victron Smart Controller also and use both 10 and 14 gauge wire.

I have 10 gauge coming in from my 50 Watt Renogy Panel since that is what it came with I just bought the additional 10 gauge wire extension.

I have 14 gauge coming in from my old 65 watt panel for a total of 115 watts.

I have 14 gauge going to my two 6 volt golf cart batteries from the controller. The batteries are only 2'-3' from the controller.

Panels are 8'-10' away from the controller.

Current has never gone over 10 amps coming into the batteries.

[Maine Sail]

Even with a ferrule 8AWG is not going into a 75/15..

this may help:

https://marinehowto.com/terminating-bare-wire-ends/

[nash_sailing]

Thanks for the replies everyone. I’m only expecting 11 amps max from the panels (100 watt x 2 in parallel) but the large gauge is needed for voltage drop (used ABYC for this). I’ve heard anecdotally that even 10 AWG is very difficult to fit into the controller, which is why I don’t think a bootlace ferrule could work on 8 AWG. The most promising way forward seems to be to splice some 10 AWG, possibly fused or with a terminal block. A pin ferrule is another option, but for this wire size I’m only seeing packs of 50 online, and I’m impatient to finish this job!

[CharlieJ]

@nash_sailing: I would use a dual power post (Blue Sea p/n 2016; 5/16" studs) and then use ring terminals on the AWG 8 from the panels and on the AWG 10 from the dual power post to the MPPT. Ferrules on the AWG 10 "whips" make a more professional job.

If you go this route, you are going to have to protect the B+ power post with a boot or some other means.

A pro installation would have a circuit breaker in the AWG 8 feed from the solar panels so that the solar panels can be easily isolated for maintenance, troubleshooting, etc. The line and load sides of this circuit breaker can also be used to "downshift" from the larger AWG 8 to AWG 10.