disco_al Posted September 18, 2009 Share Posted September 18, 2009 Can anyone recommend what size fuse would be best to use with my x-charge? The relay has got 100 amp on the side of it. Now i'm not going to be running winches or anything seriously heavy off it (yet, anyway), although i may add a connector in the grille at some point to allow easy jump starting of cars if needed. So, in reality, all it will have running on the 2nd battery will be the supply for the spot bar, a 600w inverter, and some interior auxilliary sockets. I have a choice of mega fuses ranging from 100 amp to 200 amp in 25 amp steps, that will be put in line in the main battery cable from the x-charge to the 2nd battery, just a bit confused about which one to go for??? Quote Link to comment Share on other sites More sharing options...
Aragorn Posted September 18, 2009 Share Posted September 18, 2009 If the relay is rated to 100A then i'd suggest using a 100A fuse... Otherwise if you were to fit say a 150A fuse and draw 140A thru it, the relay is then overloaded...? Quote Link to comment Share on other sites More sharing options...
disco_al Posted September 18, 2009 Author Share Posted September 18, 2009 which is what i thought, although looking at the x-eng site, the relay is capable of handling highter ratings than that? i'll stick with the 100 amp for now then, if it blows too easily, then i'll go for the 125 amp. cheers Quote Link to comment Share on other sites More sharing options...
Bowie69 Posted September 18, 2009 Share Posted September 18, 2009 Pretty sure the X-Eng relay is designed to carry 200A for short periods quite happily, i.e. when winching, 100A is it's continuous rating. PM Simonr for a definitive answer Quote Link to comment Share on other sites More sharing options...
leeds Posted September 18, 2009 Share Posted September 18, 2009 Si should be able to give you as definitive answer as is possible. The 100 amp will be continuous rating and the higher rating will be for short periods of time. Ensure that all your auxiliaries are correctly and separately fused. I have found that the rating of cables/relay/connectors is confusing to put it mildly. There does seem to be a lack of consistent standards for electrical rating of cables/leads etc in the motoring market. i.e. have seen jump leads of 16 and 25mm2 cable rated at 600 amps. Yet 35mm2 cable is rated at 500 amps for three minutes out of 10 so how can 16mm2 leads be rated at 600 amps? 600 amps for a few milliseconds on 16mm2 maybe Brendan Quote Link to comment Share on other sites More sharing options...
FridgeFreezer Posted September 18, 2009 Share Posted September 18, 2009 Cable ratings come down to lots of factors so vary wildly, some manufacturers use more safety margin than others. Heat dissipation (directly related to the insulation) and the temperature the insulation will handle make a big difference. We've all used jump-leads that get warm after a prolonged period of cranking, but then the manufacturers probably expect that they will never be used for more than short bursts, so 600A jumpleads are spindly little things compared to 600A welding cable which will likely have 4-600A passed through it for prolonged periods of time with little chance to cool off. The same applies to relays etc. I believe TSD had some jumpleads made from ~1mmsq cable which was rated to some massively high temperature, just to prove the point - just don't grab them in use! Quote Link to comment Share on other sites More sharing options...
errol209 Posted September 18, 2009 Share Posted September 18, 2009 Si should be able to give you as definitive answer as is possible. The 100 amp will be continuous rating and the higher rating will be for short periods of time. Large fuses often have 10s overload ratings of over double the continuous rating ... The safest route is to match things by continuous ratings, I think. Quote Link to comment Share on other sites More sharing options...
ejparrott Posted September 18, 2009 Share Posted September 18, 2009 Tri-rated cable has a higher capacity than other cables of the same size, so if your jumpers are made of this, they will be small. Quote Link to comment Share on other sites More sharing options...
disco_al Posted September 18, 2009 Author Share Posted September 18, 2009 Emailed Si and got a response back (cheers for the speedy reply) the total load i will be drawing is going to be around the 60-80 amp range, so i will go with the 100 amp mega fuse. cheers all Quote Link to comment Share on other sites More sharing options...
leeds Posted September 18, 2009 Share Posted September 18, 2009 Tri-rated cable has a higher capacity than other cables of the same size, so if your jumpers are made of this, they will be small. As far as I can find out tri rated cable just means that the cable conforms to three standards and has nothing to do with current carrying capacity. According to Eland Cables 35mm2 cable is rated at 167 amps Current ratings are based on a conductor operating temperature of 85°C and an ambient air temperature of 45°C and assumes single cable isolated in free air. Hi Flex cable is rated byAerco at 250 amps at 40C Whereas Twinflex 2 x 35mm2 cable is rated at 500 amps for 3 minutes out of 10 and 171 Amps at 60C Three cables there, all nominal area of 35mm2 with there specifications given in different ways. I doubt whether tri rated cable has a greater current carrying capacity then Hi Flex or Twin Flex. I do not understand why they have to give the current carrying specifications in different ways (apart from trying to confuse the layperson) Surely it would be better if they stuck to a standard method of presenting the cable specifications? Brendan Quote Link to comment Share on other sites More sharing options...
Aragorn Posted September 19, 2009 Share Posted September 19, 2009 becuase cables can be used in different manners? Most manufacturers will state maximum current at the maximum operating temperature, which is exactly what you've posted above. The other issue is voltage drop, if you have two pieces of cable, one rated to 100A at 85C and the other rated at 200A at 85C, if you put a load of 100A across both cables, you'll get less voltage drop on the 200A cable, which can be desirable. This is most noticable in practice when trying to jump start a heavy diesel engine with a set of spindly cables. I recently jumpstarted a merc sprinter, and with a single pair of cheapo jump cables, the motor would barely turn, and the cables got toasty, i clipped a second set in parallel onto the clips from the first set, the motor spun over MUCH faster and fired right up. Clearly there was that much voltage drop over the single length that there wasnt enough voltage to crank the engine sucessfully. Quote Link to comment Share on other sites More sharing options...
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