Ralph Whitaker Posted January 25, 2021 Report Share Posted January 25, 2021 As others have done, i decided to fit a main fuse to protect the non fused wiring behind the dash, ammeter etc, and ordered an inline fuse holder and some spare 40 amp fuses. I did not realise I was buying a Maxi fuse and holder. Pics below are of the fuse holder and fuses with a normal 40 amp blade fuse on the left. Both are 40 amp fuses, but I am assuming that the smaller one must blow at 40amp, whereas the Maxi fuse must be rated at 40amp continuous. What do you reckon the blow amperage will be on the Maxi fuse? Ralph Quote Link to post Share on other sites
trchris Posted January 25, 2021 Report Share Posted January 25, 2021 Hi Ralph just because they are different sizes they should both blow at 40amp there are different fuses that you can get which behave differently but these are both standard type blade fuses Chris Quote Link to post Share on other sites
RobH Posted January 25, 2021 Report Share Posted January 25, 2021 (edited) They are BOTH rated to carry 40A indefinitely Ralph. The time-to-blow depends on the degree of overload for both but the standard size fuse is fast acting whereas the maxi-fuse is a slow-blow type so will take longer . Littelfuse publishes curves if you are really interested. https://www.littelfuse.com/~/media/automotive/datasheets/misc/littelfuse_aftermarket_ato_mini_maxi.pdf characteristics here: https://www.littelfuse.com/~/media/automotive/datasheets/fuses/passenger-car-and-commercial-vehicle/blade-fuses/littelfuse_atof_datasheet.pdf https://www.littelfuse.com/~/media/automotive/datasheets/fuses/passenger-car-and-commercial-vehicle/blade-fuses/littelfuse_maxi_32v_datasheet.pdf You can see that the 40A standard fast fuse takes between 0.15 and 5 seconds to blow on a 200% load (80A) whereas the maxi fuse takes between 2 and 60 seconds for the same overload. Edited January 25, 2021 by RobH Quote Link to post Share on other sites
Ralph Whitaker Posted January 25, 2021 Author Report Share Posted January 25, 2021 3 minutes ago, trchris said: Hi Ralph just because they are different sizes they should both blow at 40amp there are different fuses that you can get which behave differently but these are both standard type blade fuses Chris I was concerned because they appear to have different sized fusible links giving me the impression that they were somehow different. Quote Link to post Share on other sites
RobH Posted January 25, 2021 Report Share Posted January 25, 2021 Sorry Chris but that is duff gen. Neither will blow at 40A and they do differ. See my post above. Quote Link to post Share on other sites
Lebro Posted January 25, 2021 Report Share Posted January 25, 2021 (edited) The maxi fuse has a longer, but fatter link, the resistance is probably the same as for the standard size fuse, so the watts generated but a certain current will be the same. watts = temperature, so both will blow at near the same current. Bob. I see Rob has just replied ! Edited January 25, 2021 by Lebro Quote Link to post Share on other sites
Ralph Whitaker Posted January 25, 2021 Author Report Share Posted January 25, 2021 So Rob an Bob, do you think the Maxi fuse is ok then to use as a main fuse between the battery and the loom. Ralph Quote Link to post Share on other sites
RobH Posted January 25, 2021 Report Share Posted January 25, 2021 (edited) Depends where you are connecting it Ralph. I have a standard size one fitted in the battery feed on my car but nothing in the alternator line. My thinking is that the battery can supply a hell of a lot more current than the alternator in the event of a short and it isn't going to want to stop, whereas the alternator diodes will soon give up. I have separately-fused the individual circuits anyway. The maxi-fuse will do the job, as the time-to-blow difference on a heavy short circuit is not going to matter much - at 240A it will blow within 1 second. It should prevent a fire even if it doesn't save the wires. Edited January 25, 2021 by RobH Quote Link to post Share on other sites
trchris Posted January 25, 2021 Report Share Posted January 25, 2021 Hi Rob/Bob agree with you both regarding the two fuses I was referring to a dead short on them only. Glad you both jumped in and gave Ralph the correct information Chris Quote Link to post Share on other sites
Ralph Whitaker Posted January 25, 2021 Author Report Share Posted January 25, 2021 1 hour ago, RobH said: Depends where you are connecting it Ralph. I have a standard size one fitted in the battery feed on my car but nothing in the alternator line. My thinking is that the battery can supply a hell of a lot more current than the alternator in the event of a short and it isn't going to want to stop, whereas the alternator diodes will soon give up. I have separately-fused the individual circuits anyway. The maxi-fuse will do the job, as the time-to-blow difference on a heavy short circuit is not going to matter much - at 240A it will blow within 1 second. It should prevent a fire even if it doesn't save the wires. Apart from the starter motor and a short section of wire from the solenoid to the non ign side of the fuse box Horns, auxilliary fuses for map lights etc which are protected anyway by the 35 amp fuse in the box} the Maxi fuse protects everything and the alternator charges through it too. However this may change when I fit the voltmeter as I will then run the alternator straight to the battery via the terminal on the solenoid . Ralph Quote Link to post Share on other sites
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