They are stating the derated capacity of the circuit. 12 amps is about 80% of a 15 amp protected circuit and even less of a 20 amp circuit.
ST1300P Need assistance identifying fork mounted fog lights
- Thread starter ST11Nut
- Start date
My bike came with Motolights,, mounted to the brake calipers. When one of the bulbs eventually popped, I replaced it with the higher wattage bulbs available from Motolight. Those bulbs had a very high current draw,,, and I would get a red light on my aftermarket voltage indicator when they were turned on. So I replaced those bulbs with LED bulbs (from Big Bike Parts,,, I believe). The LED's work great,,, provide a heat color that matches my LED headlights,,, and they illuminate as just as well as the H4's. Bonus is that they use less current,,, and create less heat. CAt'
The bulbs in your picture are LED's . An expensive upgrade.
The LED's that I purchased cost a bit less than the larger H4's from Motolight,,, at the time,,, CAt'
Motolight has crazy high prices on their optional bulbs. The bulb spec is MR16 and you can buy lots of different bulbs from lots of different suppliers that will work in the housings. I use an amber halogen MR16 bulb that I like because its color is very different and recognizable making it a good "conspicuity" bulb. I have only found them in the UK and buy them on amazon.uk
There are lots of MR16 bulbs in the big box stores that do not work well - especially some very weak LED alternatives.
There are lots of MR16 bulbs in the big box stores that do not work well - especially some very weak LED alternatives.
I don't find that either the H4's or LED bulbs add much to illumination of the roadway. Especially with the F2 headlights in place. They are purely for whatever conspicuousity value they can create. The Motolights are very expensive,,, and I would never purchase them myself. Mine came with the bike,, and the PO referred to them as creating the "triangle of life",,,, okay says I,,,, CAt'
I agree that they are better for conspicuity than illumination and all I try to do with them is triangle lighting. For that, though expensive, they are fantastic, good looking, and bullet-proof. This is the UK MR16 amber bulb that I favor.
https://www.amazon.co.uk/Casell-GU5-3-Halogen-Spot-Amber/dp/B00HWSJLCQ/ref=sr_1_2?keywords=mr16+amber&qid=1575223558&sr=8-2
When my stock is depleted, I'll need to find another way to get them here from the UK. The amber in this bulb is really more orange. There is a red hue to is that amber doesn't have. I got stopped for a license check once and the State Trooper asked me if the lights were red. I told him they said "amber" on the box they came in and he dropped the subject. But I get lots of comments that they are distinctive and attention-getting. But as floods in the Motolight enclosures they do not blind. I wish I could find a good LED equivalent because 100 watts is a lot to devote to the job.
https://www.amazon.co.uk/Casell-GU5-3-Halogen-Spot-Amber/dp/B00HWSJLCQ/ref=sr_1_2?keywords=mr16+amber&qid=1575223558&sr=8-2
When my stock is depleted, I'll need to find another way to get them here from the UK. The amber in this bulb is really more orange. There is a red hue to is that amber doesn't have. I got stopped for a license check once and the State Trooper asked me if the lights were red. I told him they said "amber" on the box they came in and he dropped the subject. But I get lots of comments that they are distinctive and attention-getting. But as floods in the Motolight enclosures they do not blind. I wish I could find a good LED equivalent because 100 watts is a lot to devote to the job.
Andrew Shadow
Site Supporter
Either I am more daft than I realized or you guys are having fun at my expense. Let me know which one it is because this is not making sense to me.
It is my understanding that the fuse in a circuit, regardless of the actual load in the circuit, should never exceed the maximum capacity of the wiring in that circuit. If the stated 75 watts per light, a total of 150 watts or 12.5 amps per pair, is the actual design limit of the wiring as stated on their website, I don't see how a 15 or 20 amp fuse can safely be used in this circuit. Given that the fuse should always be a value less than what the wiring can handle this limits this circuit to a 10 amp fuse.
If they do supply kits equipped with and intended to use 20 amp fuses the same rule of not having a fuse exceed the capacity of the wiring still applies. A 20 amp fuse means that a load in excess of 240 watts would be required before this 20 amp fuse would blow. This amount exceeds their stated wiring design limit by 60%. This seems far to excessive to be reasonable. Even if the stated wiring design limit of 150 watts is only 80% of the total as speculated, that means that the total (100%) would be 188 watts. This is still 52 watts less than the 240 watts needed to blow the 20 amp fuse. Does this not mean that if something were to go awry the wiring will burn up before the fuse blows?
My understanding is that either what is written on the website is incorrect or this circuit should not be exposed to a load exceeding 12.5 amps. I don't know which is correct. I would be tempted to not exceed a 10 amp fuse until the answer is determined. The highest wattage bulbs available from MotoLights is 50 watts. Two of these is an 8.3 amp load. A 10 amp fuse is sufficiently sized to handle this load with a reserve capacity of 1.7 amps safety margin available. I would think that would be sufficient to avoid nuisance failures.
I would hate to see the OP use an oversized fuse and risk damage until he knows for sure.
It is my understanding that the fuse in a circuit, regardless of the actual load in the circuit, should never exceed the maximum capacity of the wiring in that circuit. If the stated 75 watts per light, a total of 150 watts or 12.5 amps per pair, is the actual design limit of the wiring as stated on their website, I don't see how a 15 or 20 amp fuse can safely be used in this circuit. Given that the fuse should always be a value less than what the wiring can handle this limits this circuit to a 10 amp fuse.
They state on their website that a light bulb of maximum 72 watts can be used in these lights. This equates to 12 amps per pair of lights which would seem to be in support of the 12.5 amp limit they state that their wiring is designed for. They do not list different wire sizes based on light bulb selection that I saw. All of their wiring appears to have the same design limit of 12.5 amps.
If they do supply kits equipped with and intended to use 20 amp fuses the same rule of not having a fuse exceed the capacity of the wiring still applies. A 20 amp fuse means that a load in excess of 240 watts would be required before this 20 amp fuse would blow. This amount exceeds their stated wiring design limit by 60%. This seems far to excessive to be reasonable. Even if the stated wiring design limit of 150 watts is only 80% of the total as speculated, that means that the total (100%) would be 188 watts. This is still 52 watts less than the 240 watts needed to blow the 20 amp fuse. Does this not mean that if something were to go awry the wiring will burn up before the fuse blows?
My understanding is that either what is written on the website is incorrect or this circuit should not be exposed to a load exceeding 12.5 amps. I don't know which is correct. I would be tempted to not exceed a 10 amp fuse until the answer is determined. The highest wattage bulbs available from MotoLights is 50 watts. Two of these is an 8.3 amp load. A 10 amp fuse is sufficiently sized to handle this load with a reserve capacity of 1.7 amps safety margin available. I would think that would be sufficient to avoid nuisance failures.
I would hate to see the OP use an oversized fuse and risk damage until he knows for sure.
I found the motolite website to be hard to use. Since their lights use a standard MR16 lamp, I want to say a few things about these. MR16's are halogen lamps and come in various wattages - 20,35,50, 60 and I think, 75. They also came in several beam spreads. I think you could once get a 5, 10, 23, 35, and 45 deg beam, with some of those a special order from only one or two manufacturers. MR16's were rated at 12 volts. However, now that LED's are replacing the once common halogens, most of those wattages/light outputs have gone away. Philips - my brand of choice in no small part because my electrical wholesaler carried their complete line - was an excellent product but I think they have stopped making them. I fact, most of the manufacturers no longer make halogen lamps in the USA, and what we now have to choose from come mostly from China and neighboring countries. The early LED MR16's were not very good, later ones were/are much better. Again, progress rears its ugly head and most of the once MR16 using fixtures now have integral LED's. Since each MR16 LED incorporated a power supply, many of today's fixtures have done away with these separate lamp/power supplies in the name of cost savings and efficiency and use one central 'driver' and the small LED chips.
Motolite's design is interesting. Where Clearwater (and most everyone else) uses an integral LED chip and reflector, Moto uses replaceable lamps, and has an incredible markup on their lamps. I used to pay $5 to $7 for halogen MR16's, and the comparable LED-MR16 ran in the $20 range (my prices are approximate, its been a few years since I bought any and I'm going on memory). There is nothing wrong with Halogen lights, but LED's have largely replaced them. While Moto's product looks to be of very high quality, they are really a dinosaur looking for extinction. If you question that last comment, go read a few of the threads on replacing our headlight halogens with LED's. Why would anyone spend $500 for a pair of Moto's when Clearwater's offerings are the modern, low maintenance replacement? You can also get similar performance in cheaper brands (although Clearwater's are clearly a premium product). I will say that the Moto's machined brackets look to be outstanding, and I assume the rest of the product is of similar quality.
Motolite's design is interesting. Where Clearwater (and most everyone else) uses an integral LED chip and reflector, Moto uses replaceable lamps, and has an incredible markup on their lamps. I used to pay $5 to $7 for halogen MR16's, and the comparable LED-MR16 ran in the $20 range (my prices are approximate, its been a few years since I bought any and I'm going on memory). There is nothing wrong with Halogen lights, but LED's have largely replaced them. While Moto's product looks to be of very high quality, they are really a dinosaur looking for extinction. If you question that last comment, go read a few of the threads on replacing our headlight halogens with LED's. Why would anyone spend $500 for a pair of Moto's when Clearwater's offerings are the modern, low maintenance replacement? You can also get similar performance in cheaper brands (although Clearwater's are clearly a premium product). I will say that the Moto's machined brackets look to be outstanding, and I assume the rest of the product is of similar quality.
I'm honestly not. I'm Master Electrician and electrical contractor, also into electronics, especially audio/video, I have been installing car stereo and cruise controls since the days of 8-tracks. I realized back when I was an electrician's helper that I understood electrical theory much better than the guys I worked under, but I did learn the nuts and bolts of electrical work from them.
I started in electronics at age 5 when I built a foxhole radio from a book I got from the school library, I have scratch-built and kit-built many items over the years, modified equipment like adding a headphone jack to my brother's stereo record player, ran phone lines in my parents' house, and wired their shed. I also rebuilt a Corvair engine (my first car) when I was 18.
Sorry for giving you my resume, but I want to assure you my intentions are to educate, not poke fun. You have to keep in mind that theoretical discussions are based on nominal values, not necessarily actual, voltmeter-read voltages. Theory is a tool that must be applied correctly to real-world applications, so all of it is important to understand.
Added: I'm also the fifth-highest poster on the Mike Holt NEC forum.
Your understanding is correct; it's the application that needs more detail. You always start with the load to be served, and work backwards to design the power supply and its protection. They may be claiming that their wiring is designed to carry a maximum of 150 watts, but that may include a bit of headroom to avoid damaging the wiring, and not that 13 amps will melt the wire.
The whole purpose of circuit protection is to avoid heat damage to the insulation and terminations. In code-compliant wiring, a circuit should be designed to never to carry more than 80% of its capacity on a continuous (more than three hours) basis. That's the built-in headroom that takes variables into account, and helps keep from starting fires (the greatest risk of electricity).
The wire may be sized to safely carry 12.5 amps without damage, and not that it's on the verge of destruction, and any more will cause it to burst into flames. I would recommend at least a 14-gauge wire if I had a load of 12.5 amps; 12-gauge would be even better, because voltage drop (caused by current and resistance) is more detrimental (to load operation) at lower voltages.
A 20-amp fuse would be a good rating for a 12.5-amp continuous load, but the wiring must be sized to the fuse is the weakest link. None of our bikes have fuses that are loaded near their maximum capacity; that would be poor design. However, there have been plenty of reported issues with some of the factory terminations overheating not related to choice of fuse size.
It's easy to forget that current over time affects materials. All electrical wire and terminations get warm when carrying current. When heated well, metals lose their tempering and spring tension, and loosens connections that depend on springiness to remain tight. Loose connections get hotter, and the effects eventually snowball and open connections and/or melt plastic.
Possibly. Do we know what gauge wire they use? If you were to tell me the specs of a given load, I could design a safe and functional circuit to supply it. For a pair of 50-watt lights, I would use 12-gauge wire and a 15-amp fuse, even though 16-gauge wire is large enough for an 8.3-amp load. Again, it's poor design to use a circuit near its maximum capacity.
Without more info, one must default to manufacturers instructions and recommendations.
Last edited:
skidgillen
Site Supporter
Boy this turned into an oil thread!
Andrew Shadow
Site Supporter
Larry- thanks for taking the time to put together a detailed response.
I could not agree more that when designing an electrical circuit the first thing that needs to be determined is the load that will be on that circuit. Once that is known all the parts in the circuit are then chosen to safely supply that load in a protected manner.
Here we are dealing with a set up that already exists. The components are already in place so we can do none of that. We have to decide on a fuse rating that makes sense based on what is already there. I am sure that you have a deeper understanding of the intricacies than I do so please take a moment to read the below and let me know if my logic makes any sense.
I don't really see the load as relevant in this case however. The only safe choice is to select a fuse that will protect the wiring regardless of the load. If the load exceeds the capacity of the wiring, using a higher rated fuse is not a safe option so it shouldn't be allowed to change the fuse choice anyway.
MotoLights would have chosen a fuse rating based on the components in their circuit. Since they state that their wiring has a design limit of 12.5 amps the fuse needs to protect that wiring. Once or if the OP replaces his wiring he can select a fuse to meet this new criteria. Based on MotoLights wiring having a stated design limit of 12.5 amps I suggested that a 10 amp fuse would be the proper choice to ensure that this wiring harness will be protected and can not be overloaded.
Does this make sense?
I could not agree more that when designing an electrical circuit the first thing that needs to be determined is the load that will be on that circuit. Once that is known all the parts in the circuit are then chosen to safely supply that load in a protected manner.
Here we are dealing with a set up that already exists. The components are already in place so we can do none of that. We have to decide on a fuse rating that makes sense based on what is already there. I am sure that you have a deeper understanding of the intricacies than I do so please take a moment to read the below and let me know if my logic makes any sense.
From MotoLights the maximum wattage bulbs you can get is 50 watts. For two bulbs that is an 8.3 amp load. They do state that the maximum wattage bulbs that can be used in these lights is 72 watts. For two bulbs that is a 12 amp load.
I don't really see the load as relevant in this case however. The only safe choice is to select a fuse that will protect the wiring regardless of the load. If the load exceeds the capacity of the wiring, using a higher rated fuse is not a safe option so it shouldn't be allowed to change the fuse choice anyway.
They do not state what gauge wire they used. They do state that their wiring harness has a design limit of 12.5 amps.
ST11Nut was looking for what size fuse MotoLights specified for their set up but could not find it so he was asking what size fuse to use.
MotoLights would have chosen a fuse rating based on the components in their circuit. Since they state that their wiring has a design limit of 12.5 amps the fuse needs to protect that wiring. Once or if the OP replaces his wiring he can select a fuse to meet this new criteria. Based on MotoLights wiring having a stated design limit of 12.5 amps I suggested that a 10 amp fuse would be the proper choice to ensure that this wiring harness will be protected and can not be overloaded.
Does this make sense?
The fuse is to protect the wiring, not the load, in most cases. You could even use, say, a 30-amp fuse and 10-gauge wire for a load of 1 amp. This is unless a load requires limiting the current with a specific fuse size for some reason.
Here, we're talking about a wire size that has already been selected, so the fuse must protect the wire provided. However, once that has been accomplished, a 5-amp load does not require using a fuse smaller than a 10-amp load.
Here, we're talking about a wire size that has already been selected, so the fuse must protect the wire provided. However, once that has been accomplished, a 5-amp load does not require using a fuse smaller than a 10-amp load.
Since it is a safety issue (fusing) you have to account for worst case scenario. The lights could be potentially turned on when the engine is not running, then they would be drawing the max amperage.
This is true for incadescent lights/resitive loads. I was just loking at the face value of amperage for 50w at 12v vs 14v. Wiring and fuses need to be set for worst case scenario, max draw.
Last edited: