How to fuse 2 MPPTs into the same lug?

[mantis_solar]

Hi, I'm putting in a small system with a Lynx distributor. I have 5 cables and the Lynx only has 4 lugsn besides batther. I was thinking doubling up on the two Victron MPPTs, one is 75|15 and the other 100|50. If I size both cables for 50a then can I safely just have a 60a fuse in the Lynx, or do I need to put inline fuses in each cable?

In case anyone has other insights, the other inputs are an Orion 30a, a WFCO 25a and a Phoenix 1800 inverter. 600w of panels. Battery is a 270 ah Li Time, and I expect to add a second one in parallel soon. Eventually I'm planning on adding an ip43 to get around the WFCO current limits which will create another 2 cables - 1 lug situation.

Thanks!
Jim

 

[FilterGuy]

Technically the fuse should be at least 50 * 1.25 = 62.5A Round it up to 65A. Physically, you are going to find it very difficult to get that size wire into the 75/15 connectors.

 

[mantis_solar]

Thanks! They are short runs, so the wire calculator says 10 AWG is fine as the size for both current loads. I don't have the MPPTs in front me since they're arriving next week, but the data sheet for the 75/15 shows a max of 10 AWG and the 100/50 shows a max of 6 AWG. The Mega fuses in the Lynx only come (as far as I can see) in 60a and 80a. Do you think I should go with 80a?

 

[chrisski]

If the SCCs are capable of pushing 65 amps, are you sure you have want be short of that?

 

[crossy]

I wouldn't under-fuse!

Correct me if I'm wrong, but I believe the Lynx units can be daisy-chained.

The "correct" solution, particularly if you're looking at further future expansion, would be to add another Lynx.

 

[mantis_solar]

Lynx can absolutely be daisy chained and I'll certainly consider that when I get to the ip43, but they're big and I've got limited real estate in a travel trailer cabinet. I mean a single one is bigger than all of the other components except the inverter.

80a fuse it is!

 

[chrisski]

I have the 75/15 and the terminal on the SCC can’t handle a wire rated for 50 amps. I remember it only taking 12 AWG because its built not to push more than that.

One thing I didn’t like about the Victron is the terminals are built for the SCC rating. If you wanted to oversized the wiring for voltage loss, you need to come up with some way to downsize the wire.

I would fuse the 75/15 with a 20 amp ANL fuse and holder and join it elsewhere, and then fuse the lynx for 60 amps.

 

[timselectric]

Do not put a #10 AWG wire on an 80a fuse.
For a fuse to work, it must be the weakest link.
You might as well not fuse it at all. Because the wire is now the fuse.

 

[mantis_solar]

I have the 75/15 and the terminal on the SCC can’t handle a wire rated for 50 amps. I remember it only taking 12 AWG because its built not to push more than that.

One thing I didn’t like about the Victron is the terminals are built for the SCC rating. If you wanted to oversized the wiring for voltage loss, you need to come up with some way to downsize the wire.

I would fuse the 75/15 with a 20 amp ANL fuse and holder and join it elsewhere, and then fuse the lynx for 60 amps.

Ok, this sounds like the plan!. Reasonable to use an inline blade? Space on the cabinet side is a bit limited so I'd rather not screw down an ANL fuse holder.

 

[mantis_solar]

Ok, this sounds like the plan!. Reasonable to use an inline blade? Space on the cabinet side is a bit limited so I'd rather not screw down an ANL fuse holder.

Oops thinking about this further, I don't have a clear way to "join it elsewhere." But if instead I pair the 75/15 SCC with the Orion at 30 amps, at 45 amps I can use 10 AWG for both, fuse it at 60a and as far as I can tell, the math works out. A bit hard for me to believe that 10 AWG can handle 60 amps, but that's what the calculator tells me.

 

[mantis_solar]

Oops thinking about this further, I don't have a clear way to "join it elsewhere." But if instead I pair the 75/15 SCC with the Orion at 30 amps, at 45 amps I can use 10 AWG for both, fuse it at 60a and as far as I can tell, the math works out. A bit hard for me to believe that 10 AWG can handle 60 amps, but that's what the calculator tells me.

And continuing in my stream of conciousness, I think can connect the inline fused cable from the 75/15 into the end unfused connection of the Lynx. The one that is intended to connect to another Lynx in parallel. So then I have no doubled lugs. Thanks @timselectric !

 

[Supervstech]

Oops thinking about this further, I don't have a clear way to "join it elsewhere." But if instead I pair the 75/15 SCC with the Orion at 30 amps, at 45 amps I can use 10 AWG for both, fuse it at 60a and as far as I can tell, the math works out. A bit hard for me to believe that 10 AWG can handle 60 amps, but that's what the calculator tells me.

The calculator is incorrect.
It is saying the voltage loss won’t be too bad with short conductors. It is not telling you that 10awg will handle 60A unless you use silicone high temp insulation… and that wire will be HOT and limiting charge current.
Size AMPACITY first, size acceptable voltage loss next.

 

[mantis_solar]

The calculator is incorrect.
It is saying the voltage loss won’t be too bad with short conductors. It is not telling you that 10awg will handle 60A unless you use silicone high temp insulation… and that wire will be HOT and limiting charge current.
Size AMPACITY first, size acceptable voltage loss next.

Thanks. I was just using one of the wiring calculators on the solar websites. This makes more sense.

 

[scrubjaysnest]

For joining different wire sizes I think in terms of terminal strip or buss bar.

 

[yodamota]

I was suprised by the 75/15 wire terminals. I have 10awg in mine. Luckily the batteries are close.
I was under the impression that the 75/15 came with its own blade fuse.... Maybe its only for the load side?

I find the calculator in my signature handy for what size wire to use for a given circuit.

 

[chrisski]

I was suprised by the 75/15 wire terminals. I have 10awg in mine. Luckily the batteries are close.
I was under the impression that the 75/15 came with its own blade fuse.... Maybe its only for the load side?

I find the calculator in my signature handy for what size wire to use for a given circuit.

10 AWG would not fit for me. I used 7 Strand copper wire. Maybe the multistrand would have fit.