I think I can answer my own questions after a bit of research.
First, yes I do need a fue rated for the correct voltage. When a fuse blows a plasma arc can form across the gap caused and if the voltage is high enough (i.e. the fuse is not rated correctly) it will maintain that plasma which will allow current to continue to flow. So I need a fuse rated for at least 144VDC - realistically 250V or higher.
Now as for the amp rating. Well the Kat's heater produces 1500W when running on 120V AC. Using P = V*I that means is draws 12.5A. Now P = I^2*R too, so that tells me that the internal resistance of the heating element is 9.6ohms (1500/(12.5*12.5)). My multi-meter confirmed that value by measuring directly.
But I'm running the heater on 144V DC. V=I*R says that I'll actually be drawing 15A. Which also means that my '1500W' heater will actually be producing 2160W. I think that means it's heat the water 44% faster! (I'm pretty comfortable that the heater element will be able to cope with the additional load - someone yell if you disagree!)
So lastly what make of fuse? Well I was planning on using some Ferraz Shawmut A30QS600 fuses between the elements of my pack - they are rated at 250V and 600A and it seems a popular option on many EV parts sites . That type of fuse comes in smaller amperage levels including 30A (A30QS030) which is what I think I need here.
So I think I'll call http://www.fusesunlimited.com/ on Monday and order those (together with the fuses and traction pack, charger and DC-DC converter) at the same time. Has anyone here used these guys? Any feedback or other suggestions for fuse suppliers.
Thanks
First, yes I do need a fue rated for the correct voltage. When a fuse blows a plasma arc can form across the gap caused and if the voltage is high enough (i.e. the fuse is not rated correctly) it will maintain that plasma which will allow current to continue to flow. So I need a fuse rated for at least 144VDC - realistically 250V or higher.
Now as for the amp rating. Well the Kat's heater produces 1500W when running on 120V AC. Using P = V*I that means is draws 12.5A. Now P = I^2*R too, so that tells me that the internal resistance of the heating element is 9.6ohms (1500/(12.5*12.5)). My multi-meter confirmed that value by measuring directly.
But I'm running the heater on 144V DC. V=I*R says that I'll actually be drawing 15A. Which also means that my '1500W' heater will actually be producing 2160W. I think that means it's heat the water 44% faster! (I'm pretty comfortable that the heater element will be able to cope with the additional load - someone yell if you disagree!)
So lastly what make of fuse? Well I was planning on using some Ferraz Shawmut A30QS600 fuses between the elements of my pack - they are rated at 250V and 600A and it seems a popular option on many EV parts sites . That type of fuse comes in smaller amperage levels including 30A (A30QS030) which is what I think I need here.
So I think I'll call http://www.fusesunlimited.com/ on Monday and order those (together with the fuses and traction pack, charger and DC-DC converter) at the same time. Has anyone here used these guys? Any feedback or other suggestions for fuse suppliers.
Thanks
