What size fuse between mppt (40ah) and batteries?

peterboat
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What size fuse between mppt (40ah) and batteries? Nov 4, 2016 9:19:23 GMT

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Post by peterboat on Nov 4, 2016 9:19:23 GMT

I cheated when I did my installation the controller is fused, also because of the setup the panels are fused [solar panel industry guidelines], the cables from the controller go to the cables that my inverter run from and these cables are fused in the engine compartment! far to many fuses but it was the easiest method of doing things plus on a sunny day the panels are first in line to supply the leccy

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smileypete
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What size fuse between mppt (40ah) and batteries? Nov 4, 2016 9:38:42 GMT

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Post by smileypete on Nov 4, 2016 9:38:42 GMT

For 16mm² cable I'd use a 50A fuse (using "amps divided by three"), allows a bit of headroom over the MPPT output

As Nick says it could probably take a lot more but best play it safe if you can, engine areas can get quite hot.

Last Edit: Nov 4, 2016 9:39:10 GMT by smileypete

Telemachus
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What size fuse between mppt (40ah) and batteries? Nov 4, 2016 10:01:20 GMT

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Post by Telemachus on Nov 4, 2016 10:01:20 GMT

Nov 4, 2016 9:18:12 GMT geo said:

Nov 4, 2016 9:11:21 GMT Telemachus said:

Not if there is one 100w panel

Disagree, the unit is capable thus additional panels can be added just because it is a 40A unit and will take 400W plus, without checking the wiring from the MPPT to the battery. Basic good practice and safety.

You miss the point. Of course the installation should be able to cope with the controller's max output, but we are talking about having plenty of headroom on the fuse rating to avoid thermal fatigue. The relevant point is to know what the max expected current will be under the present circumstances, so as to determine whether the 50A fuse will be operating near, or well below, its rating.

Telemachus
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What size fuse between mppt (40ah) and batteries? Nov 4, 2016 10:02:46 GMT

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Post by Telemachus on Nov 4, 2016 10:02:46 GMT

Nov 4, 2016 9:19:23 GMT peterboat said:

I cheated when I did my installation the controller is fused, also because of the setup the panels are fused [solar panel industry guidelines], the cables from the controller go to the cables that my inverter run from and these cables are fused in the engine compartment! far to many fuses but it was the easiest method of doing things plus on a sunny day the panels are first in line to supply the leccy

And whilst on the subject, let's clarify the position about fuses for the panels. There is no Point in having the panels fused unless there are at least 3 parallel strings of panels.

Last Edit: Nov 4, 2016 10:03:15 GMT by Telemachus

peterboat
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What size fuse between mppt (40ah) and batteries? Nov 4, 2016 17:21:36 GMT

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Post by peterboat on Nov 4, 2016 17:21:36 GMT

Nov 4, 2016 10:02:46 GMT Telemachus said:

Nov 4, 2016 9:19:23 GMT peterboat said:

I cheated when I did my installation the controller is fused, also because of the setup the panels are fused [solar panel industry guidelines], the cables from the controller go to the cables that my inverter run from and these cables are fused in the engine compartment! far to many fuses but it was the easiest method of doing things plus on a sunny day the panels are first in line to supply the leccy

And whilst on the subject, let's clarify the position about fuses for the panels. There is no Point in having the panels fused unless there are at least 3 parallel strings of panels.

In my case there are I have 3 x panels in series x 3 which then go back to the controller which has the fuse gizmo in front of it. But the instructions are if its 2 strings upwards fuse gizmo to be used, and given that they are a multi million pound company and much more important the warranty is void if you dont why not comply

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Last Edit: Nov 4, 2016 17:30:49 GMT by peterboat: to add ifo

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quaysider
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What size fuse between mppt (40ah) and batteries? Nov 4, 2016 19:12:12 GMT

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Post by quaysider on Nov 4, 2016 19:12:12 GMT

Thanks for the replies gents - I asked as I was going out of the door and have only been able to check in on my (cracked) phone screen...

Just to clarify, the panels are 3 x 195 watts circa 40v each (household ones) in series at the front end of the boat using a run of 10mm2 wire the full length... the vdrop from one end of the cable to the other was something like 0.1 earlier... that could be down to my multi-metre not being TOO acurate anyway.

When I said "old" I meant, in a box in the garage that said 16mm2 that I've never needed to use - hence saving the hassle of looking for wire locally today.

I've done it today and the "run" ended up .75 metres as I put the controller on the engine bulkhead - the theory being that IF the thing gets too hot to work at it's best level, it'll be because the engine is running and the big alternator is chucking out far more power anyway.

I've put a 70amp fuse about 6 inchs from the battery.

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Deleted Deleted Member Posts: 0	What size fuse between mppt (40ah) and batteries? Nov 4, 2016 19:22:21 GMT Quote Select Post Deselect Post Link to Post Back to Top Post by Deleted on Nov 4, 2016 19:22:21 GMT Assuming your system is 12 V, isn't the controller a bit undersized? I understand that your 3 x 195W panels will never , in the uk, actually produce their rated output.

tonyqj
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What size fuse between mppt (40ah) and batteries? Nov 4, 2016 19:24:28 GMT via mobile

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Post by tonyqj on Nov 4, 2016 19:24:28 GMT

Nov 4, 2016 19:22:21 GMT @rusty69 said:

Assuming your system is 12 V, isn't the controller a bit undersized? I understand that your 3 x 195W panels will never , in the uk, actually produce their rated output.

You'd be surprised. On a cool bright day they could actually exceed their maximum. But that won't harm the controller of course, it will just limit at 40A.

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Deleted
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What size fuse between mppt (40ah) and batteries? Nov 4, 2016 19:27:24 GMT

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Post by Deleted on Nov 4, 2016 19:27:24 GMT

Nov 4, 2016 19:24:28 GMT tonyqj said:

Nov 4, 2016 19:22:21 GMT @rusty69 said:

Assuming your system is 12 V, isn't the controller a bit undersized? I understand that your 3 x 195W panels will never , in the uk, actually produce their rated output.

You'd be surprised. On a cool bright day they could actually exceed their maximum. But that won't harm the controller of course, it will just limit at 40A.

Phew, thats a relief, as I think mine is undersized for the amount of solar I have installed.

Last Edit: Nov 4, 2016 19:47:17 GMT by Deleted

Telemachus
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What size fuse between mppt (40ah) and batteries? Nov 4, 2016 19:44:09 GMT

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Post by Telemachus on Nov 4, 2016 19:44:09 GMT

Nov 4, 2016 19:12:12 GMT quaysider said:

Thanks for the replies gents - I asked as I was going out of the door and have only been able to check in on my (cracked) phone screen...

Just to clarify, the panels are 3 x 195 watts circa 40v each (household ones) in series at the front end of the boat using a run of 10mm2 wire the full length... the vdrop from one end of the cable to the other was something like 0.1 earlier... that could be down to my multi-metre not being TOO acurate anyway.

When I said "old" I meant, in a box in the garage that said 16mm2 that I've never needed to use - hence saving the hassle of looking for wire locally today.

I've done it today and the "run" ended up .75 metres as I put the controller on the engine bulkhead - the theory being that IF the thing gets too hot to work at it's best level, it'll be because the engine is running and the big alternator is chucking out far more power anyway.

I've put a 70amp fuse about 6 inchs from the battery.

70A sounds like a good compromise to me.