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Robert
Robert

Posted: Wed Oct 03, 2012 5:31pm

Post Subject: Fuse Blowing.

I have a problem with a blowing fuse, I have 3 battery banks, a leisure bank directly charged from one alternator, and 2 other banks of batteries, the starter battery and the Vetus 75 kGf bow thruster battery charged by the other alternator. Between these two batteries is the Cyrix-I 120A battery combiner,  the Bow Thruster is connected via connection 30 on the Cyrix-I 120A, soon after this connection is a 30 amp midi fuse.I do not use the the Bow Thruster often, but when I do most of the time it for a short burst and I have no problem. However on two occasions when I have given 2 or 3 bursts of 5 second bursts the 30 amp fuse have blown. Why is this and what can I do about the fuse blowing. Thanks Robert Hilsdon

Fuse Blowing.
Tony-B
Tony-B

Posted: Wed Oct 03, 2012 6:58pm

Post Subject: Fuse Blowing.

If you want me to look at your diagram you will have to email it to Tony@TB-Training.co.uk. The Cyrix unit appears to be a volatge sensitive relay and it's installation diagram shows no 30 amp fuse but it does show a maxim,um 120 amp fuse. I think your 30 amp fuse is in place of this one and if so whenever the current flowing from the other bank to the bow thruster exceeds 30 (probably more like 50) amps it will blow. With a well discharged bow thruster battery plus the load of the bow thruster itself when it is in use could very well exceed 30 amps so it blows. The reason the bowthruster battery may be discharged is perhaps self discharge when the boat is not in use. A dirty/resistive connection on the bow thruster battery of internal interlink fault could also cause it, as could the propeller becoming jammed and stalling the motor. Personally I think a 30 amp fuse here is pushing ones luck. First of all find out the currant rating for the cable or find the CSA of the conductors. You can then look it its current rating. That will tell you the maximum size of fuse that you can fit. If the cable fitted is only 30 amp cable then you either have to rewire in heavier cable so you can fit a larger fuse or obtain a supply of 30 amp fuses and do quick fuse changes. Do NOT put a larger fuse in than the cable's current rating. Tony Brooks

Robert
Robert

Posted: Thu Oct 04, 2012 12:11pm

Post Subject: Fuse Blowing.

Thanks Tony for the reply. I have checked the battery connections and they look good. The wire connecting the battery to the Cyrix is 16mm2 and the length of the cable less than 50 feet. On checking this I believe that the 30 amp fuse could be changed to a 50 amp. Am I correct? Robert

Tony-B
Tony-B

Posted: Thu Oct 04, 2012 12:48pm

Post Subject: Fuse Blowing.

Cable with a conductor cross sectional area of 16 sq mm is rated at around the 110 amp mark (varying depending upon its insulation and installation) so you could use a 100 amp fuse. In this case the cable length is not relevant because we only need to ensure that we do not exceed the cable's current rating. The voltdrop along the cable is another matter and that will probably only be a major problem when the BT battery is well discharged so drawing a high charging current. As the battery charges and the charging current drops the voltdrop will also decrease. A small 250N bow thruster draws about 200 amps so with battery problems much of that will be supplied by the alternator and if your alternator is rated at more than 30 amps it is easy to see why the fuse blows. Tony Brooks

Robert
Robert

Posted: Sun Oct 07, 2012 3:57pm

Post Subject: Fuse Blowing.

Thanks Tony that make the situation clear. Robert.

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