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Post by quaysider on Nov 4, 2016 7:54:06 GMT
Yesterday I fitted the solar panels to the roof of Ellis (1 week old now ) ( Ellis - not the solar panels)... and today I'm going to wire them up...
I've got a 50amp fuse which I think I'm supposed to fit as close to the battery as possible but I was thinking a) is this large enough? and b) if it DOES blow, then the mppt will be fooked given that the battery MUST be connected to the charge controller before the panels are connected.
Is it "allowed" NOT to have a fuse or would that trip me up at bss time?
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Post by Telemachus on Nov 4, 2016 8:07:15 GMT
You need to have a fuse. This is to protect against a wiring fault/short circuit that could see 1000s of amps flowing from the batteries. The fuse size should be rated according to the size of the cable so if you use thicker cable you can use a bigger fuse. Fuses can age and eventually fail due to operating close to the limit for very long periods. However you should consider what the actual likely maximum current will be which depends on the total panel wattage rather than the controller's rating.
tell us what the panel power is, and what cable size you'll be using. It may be possible to fit a larger fuse which will thus be less stressed in normal use.
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Post by geo on Nov 4, 2016 8:13:03 GMT
General rule is to protect the cable. So cable size etc is the important thing here.
How long is the run from the MPPT to the battery?
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Post by cuthound on Nov 4, 2016 8:17:49 GMT
As others have said, you need the fuse to protect the cable.
If you are worried about the fuse failing due to ageing, just change it every 5 years. That is what is done in the critical power industry to reduce the chance of random fuse failure.
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Post by quaysider on Nov 4, 2016 8:21:14 GMT
the cable is 16mm2 (old jump leads) and is about 1.5 m long.
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Post by Telemachus on Nov 4, 2016 8:27:19 GMT
Presuming the cable is not in ducting (which affects its ability to get rid of the heat) I'd say 100A fuse would be acceptable. The current rating of a cable depends not only on the conductor area, but also the nature of the insulation and how it is routed so it's hard to be exact.
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Post by cuthound on Nov 4, 2016 8:29:49 GMT
the cable is 16mm2 (old jump leads) and is about 1.5 m long. Assuming the cables are single pvc insulated, then the current carrying capacity is 57 amps, so fuse at 32 amps.
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Post by Telemachus on Nov 4, 2016 8:32:51 GMT
the cable is 16mm2 (old jump leads) and is about 1.5 m long. Assuming the cables are single pvc insulated, then the current carrying capacity is 57 amps, so fuse at 32 amps. 57A only if enclosed in an insulated wall. You need to be careful of the conditions surrounding cable ratings.
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Post by geo on Nov 4, 2016 8:37:20 GMT
Assuming the cables are single pvc insulated, then the current carrying capacity is 57 amps, so fuse at 32 amps. 57A only if enclosed in an insulated wall. You need to be careful of the conditions surrounding cable ratings. I would still be cautious and not go much above 60A. The cable is old and we don't know its real condition. Also it is probably twin not singles Also if the run is 1.5 metres I would suggest 25mm to get a loss of 1% or less
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Post by Telemachus on Nov 4, 2016 8:44:53 GMT
The only other thing to bear in mind is what are the likely or even feasible failure modes. The current rating for any cable can be substantially exceeded for a brief time without overheating, due to its thermal mass. So if we had a 16mm cable connected to a domestic battery bank, protected by a 200A fuse ,and a short circuit was created, although the cable's rated current would be exceeded the fuse would blow without the cable overheating. In order for this scenario to cause a problem one would have tomenvisage a prolonged fault that just happen to have the right resistance to create a current greater than the cable's rating and less than the fuse rating. Seems highly improbable.
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Post by Gone on Nov 4, 2016 8:48:07 GMT
57A only if enclosed in an insulated wall. You need to be careful of the conditions surrounding cable ratings. I would still be cautious and not go much above 60A. The cable is old and we don't know its real condition. Also it is probably twin not singles Also if the run is 1.5 metres I would suggest 25mm to get a loss of 1% or less Until we know the panel output in Watts we can not calculate the volt drop for a given cable. Likewise so long as the fuse is say 50% greater than the max output of his installation then the fuse is unlikely to suffer nuisance failure. Of course the fuse must not exceed the cable and installation condition requirements. So to give best advice, please tell us the panel output and if you have any plans to add more panels onto the same controller in the future.
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Post by geo on Nov 4, 2016 9:06:39 GMT
I would still be cautious and not go much above 60A. The cable is old and we don't know its real condition. Also it is probably twin not singles Also if the run is 1.5 metres I would suggest 25mm to get a loss of 1% or less Until we know the panel output in Watts we can not calculate the volt drop for a given cable. Likewise so long as the fuse is say 50% greater than the max output of his installation then the fuse is unlikely to suffer nuisance failure. Of course the fuse must not exceed the cable and installation condition requirements. So to give best advice, please tell us the panel output and if you have any plans to add more panels onto the same controller in the future. Max output of the unit 40A
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Post by smileypete on Nov 4, 2016 9:10:44 GMT
What does the MPPT manual say if anything about what value fuse to use?
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Post by Telemachus on Nov 4, 2016 9:11:21 GMT
Until we know the panel output in Watts we can not calculate the volt drop for a given cable. Likewise so long as the fuse is say 50% greater than the max output of his installation then the fuse is unlikely to suffer nuisance failure. Of course the fuse must not exceed the cable and installation condition requirements. So to give best advice, please tell us the panel output and if you have any plans to add more panels onto the same controller in the future. Max output of the unit 40A Not if there is one 100w panel
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Post by geo on Nov 4, 2016 9:18:12 GMT
Max output of the unit 40A 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.
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