How do I best fuse the wiring of battery box?

[S8961]

I have bought some heating sleeves to go over bare handlebars. I also have bought a battery box from China designed for 24v batteries on electric cycles. I will use a 12v battery as my bike is not electric. The purpose of all of this is to get heated handle bars.

The battery box has the following connections:
Socket for lead from heated handlebars
DC socket for charging
Ignition lock
Fuse (I do not recognise the fuse. It is glass with powder inside, but with no indication of type or amps. The connection points are small which makes me consider it is to fuse the dispay panel in the lid which I can not use because it is designed for 24v.)

The vendor told me that it is good practice to separate the charging point from the socket to the handlebars and I can see that if the socket is switched off by the ignition lock a separate charging point is sensible.

I am assuming that the first connection from the battery will be a connection strip so that the terminals can be split off to the DC charging point and the ignition lock. Next after the ignition lock would be the power out socket, but do I need to put the fuse somewhere? Where is the best place to break into the circuit? Immediately after the battery and before the connection strip. Is that the best place, if at all?

Robin

 

[paul04]

You could put 2 fuses in, one before and one after, that way your double protected
You can buy in line fuses from maplins (or look on google for cheaper price)
http://www.maplin.co.uk/black-in-line-blade-fuse-holder-444

 

[S8961]

You could put 2 fuses in, one before and one after, that way your double protected
You can buy in line fuses from maplins (or look on google for cheaper price)
http://www.maplin.co.uk/black-in-line-blade-fuse-holder-444

I have just checked the fuse supplied as part otf the battery box and it says it is F20/ 240v. Google has not been very successful with that code. Do you know if it is a standard 20mm fuse?
I did not find what amp it is rated.

Following your suggestion I think I have a clearer view of what is needed:

+ Battery, inline fuse, junction block, (a) to ignition switch and then to socket
(b) to dc charging point
- Battery to junction block (c) to socket
(d) to dc charging point

Thinking it over this should give me sufficient protection against shorting because the fuse is at the earliest point after the battery. What do you think?

Thanks for your hepfull repyly,

Robin

 

[Davidc]

I've used polyswitches in similar applications, though not on the bike. They have the advantage that to reset them all that's needed is to remove the current source and let them cool down.

This is a link to one of them, just put polyswitch in as a search term to see other values.

 

[Archie_tect]

Low tech solution would be to wear thicker gloves and cycle harder?

 

[BimblingBee]

I had heated grips on a motorbike, great but still led to cold hands/fingers. I'm sure there is an easier, lower tech, lighter, and cheaper solution to your problem!

 

[snailracer]

I agree that the best place to put a fuse is as close as practicable to the battery.

Average Current = Power/Voltage

e.g. if your grips use, say, 50W, then average current = 50/12 = 4 amps.

So, the fuse should be at least 2X the average current to avoid nuisance fuse blowing.
Your wires should be sized to carry at least the fuse rating.
Sand-filled fuses are normally used for circuits that connect to the mains, but for your application it is not important what sort of fuse you choose. I would suggest an anti-surge glass instrument fuse, as there is an outside chance that your grips might draw more power when they are first turned on, plus you can easily see when it's blown.

 

[Wobblers]

I have just checked the fuse supplied as part otf the battery box and it says it is F20/ 240v. Google has not been very successful with that code. Do you know if it is a standard 20mm fuse?
I did not find what amp it is rated.

Following your suggestion I think I have a clearer view of what is needed:

+ Battery, inline fuse, junction block, (a) to ignition switch and then to socket
(b) to dc charging point
- Battery to junction block (c) to socket
(d) to dc charging point

Thinking it over this should give me sufficient protection against shorting because the fuse is at the earliest point after the battery. What do you think?

Thanks for your hepfull repyly,

Robin

That's the fuse rating. The "F" indicates it's a fast blow fuse, the current rating is the number after, so it's 20 Amps. It's rated for 240 V so will be fine for 12 or 24 V DC operation. There are two standard cylindrical glass fuse sizes: 20 mm or 32 mm (1.25 inches). The simplest way to find out is just to measure it!

Where in the circuit is the fuse? Ideally, it should be as close to the battery as possible: an inline fuse on the positive lead as you've suggested is a very good solution. Selecting the right fuse rating is a bit of an art. The important thing to remember is that a fuse will only reliably blow at 150% of its rating - and even then may take several minutes to do so. I'd work out (or measure) the current draw of your heated grips then go up 50% in the fuse sizing. So if your grips draw 4 A I'd choose a 6.3 A fuse. A fast or quick blow fuse should be fine here, as the grips won't have much of a current surge when you switch them on. Lastly, make sure that the current rating of the wire you use is greater than the fuse rating, so if you're using a 6.3 A fuse as in my example, use wire rated at 8 A.

 

[Davidc]

I've got some heated gloves. Run for about 4 hours on rechargeable 4.5Ah D cells. Much easier way to avoid frozen fingers than heated bars and a battery box!.

Haven't used them yet this season but may have to soon.