# Inline fuse



## gazza19 (8 Jun 2020)

Hi everyone I have a 36v 250 watt electric bike I was wondering if I could put a inline fuse holder in instead of the fuse holder it has in as when the fuse blows I have to get a new holder all the time I would appreciate any help and advice given thanks in advance


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## roadrash (9 Jun 2020)

I would be looking at why the fuse is blowing rather than just making it easier to replace.


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## the_mikey (9 Jun 2020)

Which fuse are you fitting as a replacement? Assuming the motor is drawing a maximum of 250Watt no matter what condition the battery is in, and ignoring potential overheads from the control circuit , the current draw could range from 6.3A to 8.4A (given the battery won't necessarily be 36V, assuming a bank of 10x lithium ion batteries in series, it could be anything between 40V when fully charged to 30v when they are near fully discharged) , this would mean you'll need at least a 10A fuse, maybe 15A.


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## raleighnut (9 Jun 2020)

the_mikey said:


> Which fuse are you fitting as a replacement? Assuming the motor is drawing a maximum of 250Watt no matter what condition the battery is in, and ignoring potential overheads from the control circuit The current draw could range from 6.3A to 8.4A (given the battery won't necessarily be 36V, assuming a bank of 10x lithium ion batteries in series, it could be anything between 40V when fully charged to 30v when they are near fully discharged) , this would mean you'll need at least a 10A fuse, maybe 15A.


Yep my 36v 250w kit has a 15 Amp fuse, never 'blown' it.


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## CXRAndy (9 Jun 2020)

If its blowing you need to monitor the current draw, ideally with a meter which has min max hold feature. Current clamp meter (read up to hundred of Amps) would be better because most digital meter have only a 10 Amp internal fuse for current protection. Ride the bike and see what the peak draw is to help locate fault.


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## numbnuts (9 Jun 2020)

raleighnut said:


> Yep my 36v 250w kit has a 15 Amp fuse, never 'blown' it.


Goes off to check...........36v 250w kit has a 30 amp fuse


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## ColinJ (9 Jun 2020)

numbnuts said:


> Goes off to check...........36v 250w kit has a 30 amp fuse


Hmm, sounds like your motor and/or wiring could 'blow' to protect the fuse!


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## Tenkaykev (9 Jun 2020)

It's worth looking for any other letters/numbers that might be on the fuse. 

When I was working in electrical engineering we'd see occasions where the correct amperage fuse had been fitted but with an incorrect rating. For example some fuses were " quick blow" some were " slow blow"
The quick blow fuses were usually used to protect electronics, slow blow would be used when there was a high inrush current such as switching on an electric motor. 
While some were dimensionaly different, some were physically alike but with ratings such as " T1", "T2", "T3" to reflect the time sensitivity.


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## Low Gear Guy (9 Jun 2020)

Have you fitted the correct replacement fuse? As well as current and voltage some fuses are designated as motor or time lag variants. They purpose of the motor fuse rating is that they do not blow with the motor start current.


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## numbnuts (9 Jun 2020)

ColinJ said:


> Hmm, sounds like your motor and/or wiring could 'blow' to protect the fuse!


Been OK for the last 3 years


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## ColinJ (9 Jun 2020)

numbnuts said:


> Been OK for the last 3 years


I knew someone once who used a metal nail as a fuse... seriously - he told me that he had run out of fuses!

It's OK until the moment when you actually NEED a fuse which is when it is NOT OK because the fuse (or nail!) doesn't blow...

I'm not saying that 30 A is _definitely _too high a rating but it does sound high by @the_mikey and my calculations.


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## the_mikey (9 Jun 2020)

ColinJ said:


> I knew someone once who used a metal nail as a fuse... seriously - he told me that he had run out of fuses!
> 
> It's OK until the moment when you actually NEED a fuse which is when it is NOT OK because the fuse (or nail!) doesn't blow...
> 
> I'm not saying that 30 A is _definitely _too high a rating but it does sound high by @the_mikey and my calculations.




15A seems about right, maybe the battery is running lights and other things, which would need to be taken into account although at 36v, we're talking maybe 500mA of extra current, and that's being very generous.


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## numbnuts (9 Jun 2020)

the_mikey said:


> 15A seems about right, maybe the battery is running lights and other things, which would need to be taken into account although at 36v, we're talking maybe 500mA of extra current, and that's being very generous.


No lights and the kit bought from cyclotricity in the UK


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## the_mikey (9 Jun 2020)

It's also worth bearing in mind that not every e-bike will have a 250watt motor, there will be some with much more powerful motors limited by a control circuit, and others with smaller motors offering a little bit of assistance, and many variations, and while there are legal limits on power and speed in the UK, these may not be absolutely respected, or will be different in other countries, and won't necessarily be achieved through good design but by simply limiting more capable equipment, what you have may be capable of delivering 500 watts or more.


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## gazza19 (9 Jun 2020)

i was using a ten amp fuse the wire on the fuse holder came off and touched the other wire that was connected to it i was thinking of an inline fuse holder to make it easier to change if it went again the fuse has been ok for a few years does anyone have a pic of the fuse they use does it have to be a glass one if anyone can recommend a fuse holder and fuse and have a pic or link to one would be very much appreciated


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## roadrash (9 Jun 2020)

gazza19 said:


> as when the fuse blows I have to get a new holder all the time



this sentance gave me the impression that it was happening on a regular basis, hence my earlier reply.


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## CXRAndy (9 Jun 2020)

What about one of these. 


View: https://www.amazon.co.uk/RKURCK-12V-24V-Circuit-Inverter-Protection/dp/B074RKP5F1


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## the_mikey (9 Jun 2020)

gazza19 said:


> i was using a ten amp fuse the wire on the fuse holder came off and touched the other wire that was connected to it i was thinking of an inline fuse holder to make it easier to change if it went again the fuse has been ok for a few years does anyone have a pic of the fuse they use does it have to be a glass one if anyone can recommend a fuse holder and fuse and have a pic or link to one would be very much appreciated




You can use whatever style of fuse holder you like, but be sure to ensure the fuse holder itself will handle the current, and maybe upgrade the 10A fuse to 15A as 10A may be too borderline.


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## gazza19 (9 Jun 2020)

would that work tho with it being a 36volt battery


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## gazza19 (9 Jun 2020)

the_mikey said:


> You can use whatever style of fuse holder you like, but be sure to ensure the fuse holder itself will handle the current, and maybe upgrade the 10A fuse to 15A as 10A may be too borderline.


thank you, you dont have a link to one do you and could you use a fuse that goes into a normal plug or does it have to be the glass type


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## the_mikey (9 Jun 2020)

gazza19 said:


> thank you, you dont have a link to one do you and could you use a fuse that goes into a normal plug or does it have to be the glass type




I don't know what would be practical in your case, if you are able to crimp cables you can purchase a moulded ready made automotive fuse holder complete with leads suitable for 30A or more and simply crimp the fuse holder in place of the old one.

https://www.ebay.co.uk/itm/Inline-A...030627?hash=item1f092e8823:g:uZYAAOSwUOJeFgjG

Or something similar to that.


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## CXRAndy (9 Jun 2020)

gazza19 said:


> would that work tho with it being a 36volt battery


The voltage could be an issue, I see its reset fuse


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## slowmotion (9 Jun 2020)

Here's a cheap gizmo.....







The W54 Series thermal circuit breakers come at different current ratings and cost about the same as half a pint of beer. Here's a link.

https://cpc.farnell.com/potter-brum...54-xb1a4a10-20/circuit-breaker-20a/dp/FF01648

OK, you'll have to keep the weather out but that's not too difficult. Stick it in a very small box with a cable gland.


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## raleighnut (9 Jun 2020)

I think the reason that Lithium Ion batteries use an internal fuse is if the wire leading to an external one shorted out the batteries tend to explode.


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## gazza19 (10 Jun 2020)

Still finding it a bit hard to work it out lol the fuse goes between the ignition and the battery the battery is 36v the motor is 250 watts so the amps are 6.9


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## numbnuts (10 Jun 2020)

gazza19 said:


> Still finding it a bit hard to work it out lol the fuse goes between the ignition and the battery the battery is 36v the motor is 250 watts so the amps are 6.9


My fuse is in the battery (see photo page one)


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## gazza19 (10 Jun 2020)

found this would this do https://www.ebay.co.uk/itm/Electric...rts/333316941028?_trksid=p2485497.m4902.l9144


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## the snail (10 Jun 2020)

gazza19 said:


> Still finding it a bit hard to work it out lol the fuse goes between the ignition and the battery the battery is 36v the motor is 250 watts so the amps are 6.9


The 250W rating is max continuous/sustained output, typically the peak output will be a lot higher


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## gazza19 (10 Jun 2020)

the snail said:


> The 250W rating is max continuous/sustained output, typically the peak output will be a lot higher


can you suggest anything


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## gazza19 (10 Jun 2020)

What about using this as a temporary measure until I find something


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## CXRAndy (12 Jun 2020)

A limited motor wont exceed 500W peak Lets say 750W absolute micro peak thats only 20 Amps at 36V

25 Amp fuse would be ample, protect against short circuit conditions

DC clamp meter would confirm, but its not necessary unless a fault occurs


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