Help selecting correct fuse. - Page 1
Forum section: electronics / beginners

author: Terry01
author_rank: Frequent Contributor
timestamp: February 03, 2020, 11:53:11 am
content: I am going to wire a spot light up to my wheelchair for some extra light at night.It's a cheap 60w 9-32v LED light that I will run off my chairs 24v supply. I would like some help with what size of in line fuse to use and confirmation that I join it in the positive line before the on/off switch? I am only using 1 of the spot lights.Thanks in advance for the help.

author: Wimberleytech
author_rank: Super Contributor
timestamp: February 03, 2020, 02:33:40 pm
content: Quote from: Terry01 on February 03, 2020, 11:53:11 amYour pictures are not a lot of help, so I looked around on the internet to find similar. My guess is that these draw 5 amps at 12 volts (thus 60 W). Most likely LED constant current regulators on board so the 5 amps would be a little more at 24 volts due to efficiency.I would probably start with 10 amp fuses. If they blow under normal operation, try something bigger. You could just measure the current with a DMM and then size up the fuse a little bit.BTW, I 100% test any fuse I install in a system.I would put the switch in the positive line for no other reason than habit. There is unlikely a common ground in your chair, so it probably does not matter.Comments above are mostly guesses, but if I were doing this myself, what I have described is exactly what I would do.

author: LateLesley
author_rank: Frequent Contributor
timestamp: February 03, 2020, 03:23:47 pm
content: At 60W, 24V, its going to draw around 2.5A. That will increase a little as the voltage drops (since I think these use an internal converter for the wide voltage range input), So I personally think you'd be good with a 5A fuse. I think 3A would be a bit close to the wind, and 10A a bit much.Concerns I have - You say you are running these of your chair batteries. What's the capacity (AH) of the batteries? (I assume 2 x 12V in series? )Why such a high power light? 12000 Lumens is a LOT of light. I've seen these ones -http://www.ledworklight.net/20W-Cree-LED-Work-Lamp-Spot-Light-Bars-OffRoad-12V-24V-for-Car-Trailer-DRLthey are only 20W, 1500 Lumens, which while not as bright, is still a lot of light at a 1/3 of the power, which would mean less drain on precious battery life.Its just I'm thinking if this is running off the wheelchair's batteries, efficiency might be a concern.Edit, I forgot to say, as to where to put the fuse, try and fit it as close to the battery as possible, then run cable from there to the switch, then switch to light. The reason being, you want the fuse to protect the cabling, so if it gets damaged before the switch, and shorts to the frame, which I assume would be grounded, it would pop the fuse, and not cause a cable/battery fire. So always try and locate fuses as close to the source of power as possible.

author: Terry01
author_rank: Frequent Contributor
timestamp: February 03, 2020, 04:55:10 pm
content: Quote from: LateLesley on February 03, 2020, 03:23:47 pmAwesome, that's the info I was looking for! Thanks!My batteries are either 85 or 87Ah, I can't remember exactly but defo 1 or the other. They are also 2 x 12v in series to get the 24v like you guessed.I need the light mostly for walking the dog at night and the few times I get caught out in the dark. My chair has already got factory fitted lights and indicators which are fine for pavement use at night but the lights are just not strong enough for the park as there are no street lights or anything like that.I think the battery consumption will be fine as i'm not in the chair 24/7, I use it 4-10 hrs a day. I only have MS so just use the chair when I go out, I use rails, walking poles and the walls to help me get about in the house. If I find it is draining the battery too much I will buy a smaller light to adjust like you say.I am using the one have as it is what I have laying around.Thanks again i'll post a photo when i'm done

author: Terry01
author_rank: Frequent Contributor
timestamp: February 03, 2020, 04:56:56 pm
content: Quote from: Wimberleytech on February 03, 2020, 02:33:40 pmYour guesses are not a lot of help so I looked elsewhere

author: IDEngineer
author_rank: Super Contributor
timestamp: February 03, 2020, 06:43:30 pm
content: A couple of comments....* As mentioned by the other respondent, those LED lights do generally have an internal switcher so they can accommodate a wide input voltage range. However, the input current does NOT strictly follow Ohm's Law. I characterized a few of these a while back for a one-off project and the input current vs. voltage relationship is neither linear nor monotonic. The good news is it's not insane either, so you don't really need to worry too much. Just don't be surprised if you measure the current and the math doesn't seem to pencil out.* The input current on every one I tested was about half what would be expected from the wattage rating. I was so surprised that I double checked and repeated all of the measurements, but it was very consistent. The 60W units, when run on 12V, consumed about 2.5 amps instead of the ~5A one would expect. Almost makes me wonder if the "amperage" specs on these lights is their recommended fuse rating to allow for inrush startup current rather than sustained consumption. That one really had me scratching my head for a while until I finally realized that I trusted my bench equipment more than the chinglish "spec sheets" from some unknown source.* Remember that fuses exist toprotect the wiring, not the device. Fuses are there to prevent the wiring from catching fire. You can also derate the fuse in an attempt to protect the device, but in many cases a traditional fuse will be too slow to save the device itself.What I would do - and what I actually did in a very similar situation with nearly identical LED light modules - is choose a wire gauge large enough to carry the current load. Since these lights seem to spec themselves at about 2X their actual consumed wattage, let's presume that (60W / 24V =) 2.5A is their "rated" amperage (which probably means they'll consume a bit over one amp sustained). Even 18ga wire is more than sufficient for your proposed application, but I'd step up one size to 16ga and protect the wiring with a 5A fuse. If 3A is available in the fuse size you select, you could drop to that if you want to "protect" the light but as mentioned it's likely the light will be damaged faster than the fuse can blow.Yes, put the fuse in the positive side, ideally before the switch so more of the wiring is protected. The ground side can either run back to the battery, to a ground bus, or (if the chassis acts as ground) perhaps straight to the mounting bolt on the light itself. In this latter case, you'd then only have to a single wire to carry the positive side back to the switch. EDIT: This presumes that you mount the light's bolt into metal that ties back to the battery's negative terminal. Probably a better idea to just run the negative side yourself so there's no question of a solid, non-intermittent ground connection.The switch can be a simple SPST but it should be rated for DC, not just AC. The typical DC rating for panel switches is 32VDC. Do not just use any old AC switch that lacks a DC rating, again for safety (in this case, DC arc suppression).Those lights do put out a lot of light. I think you'll be very pleased. Do post photos of the finished project - we thrive on such things here!Hope this helps....

author: LateLesley
author_rank: Frequent Contributor
timestamp: February 03, 2020, 07:02:46 pm
content: Well, with 85Ah, you're good to run the lights only for 34 hours on a full charge.More realistic, an hour of running the light will take about 3% off your battery. So just factor that in when you are using the light, it will reduce your range slightly. (Were electric chair users the first to get "Range Anxiety"? )Anyway, best of luck with the project. Look forward to a pic of you lighting the place up like a small sun.

author: AVGresponding
author_rank: Super Contributor
timestamp: February 03, 2020, 08:10:34 pm
content: Quote from: LateLesley on February 03, 2020, 07:02:46 pmNothing I can add to the excellent advice and information given by LateLesley and IDEngineer here, except to say that "range anxiety" would have been felt by electric car users before internal combustion engined ones even existed, and that electric wheelchairs are a relatively new thing.https://web.archive.org/web/20101227132350/http://www.sciencetech.technomuses.ca/english/about/hallfame/u_i19_e.cfmhttps://en.wikipedia.org/wiki/George_Klein_(inventor)The lack of range is what allowed ICE vehicles to beat EVs when they arrived on the scene.There's a book called "The Complete Book of Electric Vehicles" by Sheldon R Shacket, I recommend it as a good read. It covers the history quite well, if not in exhaustive detail, and also covers things like motors and control methods.https://www.amazon.co.uk/Complete-Electric-Vehicles-Sheldon-Shacket/dp/0891960856In fact you've reminded me I need to replace my copy as I lent it out and ofc it never came back...