Are my wires properly fused and sized?

[Peregrine1983]

Hey all,

Thanks for all who responded to my last thread when I was purchasing my solar system - http://www.cruisersforum.com/forums/...up-185887.html

I have all the bits and pieces laid out on my boat and I'm about to hook it up for the first time. I'm absolutely terrified of under sizing wires and the associated fire risk, so I always tend to over size when I do electrical work.

I've checked my wire sizing chart for 3% loss critical circuits and I believe I'm in the clear here, but I just wanted to get some input as I still have a few questions specific to my system.

This is my system:

2x100w 12v panels wired in series for 24v - at 12v they are max 5.62 amps current each - https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

These are connected to 25' of 8 Gauge ANCOR Marine wire into a...

Victron BlueSolar 75/15 MPPT Charge Controller - https://www.amazon.com/gp/product/B0...?ie=UTF8&psc=1

My first question at this point is this - The charge controller terminals are not large enough for 8 Ga wire. I have butt connected and heat shrunk 6" of 14 gauge wire at the end of this 8 ga wire so I have a secure connection into the input terminals on the charge controller. According to my wire sizing chart, 14 ga is good for up to 20amps for runs up to 6'. Am I OK to use this 6" run of 14 ga wire into the charge controller? I don't see how I could fit a much thicker wire into this thing.

My second and third questions are for the wire run to my house bank of 4 golf cart batts - There is a 20 amp fuse on the charge controller. I can't tell from the manual if this is a fuse for the output of the charge controller... is this the fuse for the wire run to my battery bank? If so, I should be fine once again with 14 ga wire as the run from the charge controller to my house bank is only about 2 feet. Am I correct to assume this?

Thanks in advance everyone...

[john61ct]

#1 yes NP as long as the connectors and crimps are sound. Get a cheap infrared gun to check for hot spots, test under as high a load as you expect.

Periodically as the system grows and ages.

Re fuse, yes but you still want a "battery master fuse" rated 115% of the smallest wire, within 7" of the positive post.

Device-level fuses are rated to protect that device only, not relevant to those protecting wires.

[Peregrine1983]

Really appreciate the input. I'll add an appropriate fuse on the pos lead going to the battery. So then should there also be a fuse on the pos lead from the panels, right?

[john61ct]

"battery master fuse" means just that, between the bank and any further connections. Should have a master switch just after the fuse to isolate the bank, but many smaller banks skip that.

Then comes buss or other direct connections, including to distribution panels and charge sources.

No need to place wire CP on both ends, usually goes on the side toward the battery, except for the device-protective ones.

Some like to separate a charge buss from a loads buss, especially if monitoring/protection gear, low-voltage cutoffs etc.

[Peregrine1983]

Understood. I should be good then. Thanks very much. Really appreciate the input.

[moseriw]

One Thing to mention: My electrician decided that the new MMTP 150/35 is scrap and I ordered TWO! - PWM BlueSolar-DUO-Charger-12V-24V-20A one for each sunny/shadow side.

Think it is worth for you to crosscheck this with your electrician.

[john61ct]

Hope you took advantage of Victron's 5-year worldwide warranty.

Why did you go from MPPT to PWM?

[foufou]

Instead of adding 6" of smaller wire to accommodate a smaller connector you can easily trim some of tbd strands of the #8 wire till it fits the #14 connector

[mitiempo]

Victron 75/15 will accept 10 gauge wire. I would not use any wire smaller as there is no reason to.

Fuse the controller output positive wire close to the batteries. I would use a fuse of 20 amps probably - more than the output but less than wire ampacity.

[mitiempo]

Originally Posted by john61ct

Re fuse, yes but you still want a "battery master fuse" rated 115% of the smallest wire, within 7" of the positive post.

Main fuse should be less than 100% of wire ampacity.

[Tessellate]

Hi,
I commented on your previous post, I'm doing basically the same install as you (2x100 to Victron 75/15, but wired in parallel rather than series). Hooked up on Saturday and it's working great.

As others said, Victron 75/15 will take 10 gauge. That's what I have in it. The manual shows that in section 5 > Power Terminals: 6 mm^2 / AWG10.

The 20a fuse on the controller protects the controller itself. I confirmed this with Victron support, but after thinking about it more it's a slightly silly question because device fuses always protect just the device - think about what would happen if the wires pulled out of the device and started flopping around, contacting a ground.

I would not step down to 14 gauge wire because that's now the weak link in your circuit, mostly defeating the purpose of your 8 gauge. I also would not use 8 gauge when 10 gauge is sufficient, but if you already got it, it's fine. There's no benefit to "over protecting" a circuit and I don't think 8 gauge is providing additional safety here. That's a myth that seems to get often propagated.

Oversizing is sometimes beneficial to reduce voltage loss over long runs. However there's debate over how beneficial that really is with solar panels, and personally I would go with what the controller manufacturer designed their controller for. (10AWG). There's no real harm in doing 8AWG, other than wasting a bit of money and introducing a step-down connection which is an additional failure point.

http://www.cruisersforum.com/forums/...s-90356-2.html

You asked "so then there should also be a fuse on the pos lead from the panels, right?" No, because solar panels are a current limited source. There were some other helpful CF threads on this which helped me understand:

http://www.cruisersforum.com/forums/...-177153-2.html
(see posts by ramblinrod, he knows what he's talking about)

Regarding your wire run from batteries to controller being only 2 feet long, and what's the point in fusing something so short? I also had that question, because mine is also only 2 feet, and well secured - it's hard to imagine how a dead short would ever occur on a 2' run. But ABYC says 7" from battery, and if you have high amp MRBF fuses on your batteries already, those are *not* protecting 14 gauge. So I put a 30a fuse a few inches from the pos distribution point (PowerPost).

Fusing is mainly about reducing a very low probability to an even lower probability.

[Peregrine1983]

Tessellate - Great post.. and thank you for answering my question about the fuses on the hot leads from the panels.

I'm glad you're having luck. My system seems to be working really well too. It brought my near-dead house bank back to full charge over just a couple of days. Considering it wasn't that pricey, this is possibly the best upgrade I've done to my boat.

I decided to go 8 ga because I had a 25' run from the panels to the controller and wanted, as you said, to mitigate current loss over what I felt was a long run. Of course, I failed to anticipate that 8 ga would be too thick for the terminals on the controller. I saw the bit about 6mm wires in the manual as well. I may just swap out my short 14 ga runs for 10 ga.

I know specific conditions on a boat dictate whether someone opts for series or parallel, but just curious why you decided to wire your panels in parallel. Do you have shade issues from your rig? I would think - and I may be totally wrong about this - that you'd want to wire in series to keep the voltage above the +5v needed to start the controller and the +1v to charge in a place like the Pac NW where you often have to contend with long stretches of cloud cover.

[Tessellate]

Originally Posted by Peregrine1983

I know specific conditions on a boat dictate whether someone opts for series or parallel, but just curious why you decided to wire your panels in parallel. Do you have shade issues from your rig? I would think - and I may be totally wrong about this - that you'd want to wire in series to keep the voltage above the +5v needed to start the controller and the +1v to charge in a place like the Pac NW where you often have to contend with long stretches of cloud cover.

My panels (GoPower) are at 17-18v even in overcast conditions. So the +5/+1 is not a problem. I'm not sure the specs on your panels but I suspect it's similar. Overcast/shading affects the current much more than the voltage.

I did parallel because many vlogs / sites I read said it has better performance on typical sailboats. On my bimini setup, one panel can get partially shaded by the radar tower at certain angles, so I think parallel will be better. Also my solar kit came with MC4 parallel connectors already. Here's a vlog I liked where they tested parallel vs series:

https://www.youtube.com/watch?v=1qD3mN8VotQ

The past couple days have varied from heavily overcast to mostly sunny. When it's heavily overcast (as dark as Mordor on a cold day) they put out only 1-2 amps. With the sun peaking out between clouds it's gotten to a peak of 150w / ~8-10 amps so far. Since we have 16 hours of daylight currently, even a mostly cloudy day isn't bad.