Fuse for my trike

[oldbiker]

Hi Guys,
I have a 750W, 36V GM. I also have a 36V LiFeP04 20AHr battery connected to it on my 6 speed trike. At this point all seems to be fine but I am worried about a fast discharge that may ruin my setup.
I would like to know the proper size fuse that would give me some sort of protection; I have none at this time. Dumb, I know, but I had to get it going first.
The speed of the trike is so fast that at about half speed there is no need to pedal. My gears have no effect. I think I am getting about 25+ mph at full throttle, and 6 speeds is no big deal anyway. Well… it is when you have young legs.
I don’t have many hills to climb in El Paso, so I mostly just use the throttle to move me around. I use the pedals to get going from a dead start; thus saving some power, and avoiding a massive power surge.
At this time I cannot afford a Cycle Analyst. Riding the trike was supposed to be cheap.
I plan to hookup a DC-DC converter to handle some lower powered devices so I should protect what I have before I get started.
Thanks for any help you may provide.

[Bikemad]

To provide 750 Watts from a 36 Volt battery would require between 18 and 22 Amps depending upon the actual battery voltage.
I would therefore suggest a 35 or 40 Amp fuse, to ensure you don't unintentionally blow the fuse when the motor is working harder pulling away from a standstill.

Your Battery Management System (BMS) may well include some form of over-current protection, but you would need to check with the manufacturer to be certain.

If you want to restrict the maximum current to below the batteries maximum, you might be better off using a trip switch that can be easily reset when overloaded, then you can quickly continue on your way without having to stop and replace a fuse each time.

Alan
 

[MonkeyMagic]

Alan you should totally write a book man and amazon that shiz !

You would make a ton, call it 'Alan Answers' or something,... all you need to do is copy and paste all your posts, make a front cover, dedication (to me of course) then an intriguing blurb

ill be happy to peruse the draft, if I can get the privalidge

 

[TOM]

You have better to use a 30A reset table Fuse.It can't be blown.If overload,this fuse will stop motor working.Turn off/on switch can reset this fuse.

[oldbiker]

Thanks Guys,
My calcs show about 21A but that is too low, so I wanted to know the effective size that would keep me going without constant replacement. A 40A resettable sounds like the key.

[MonkeyMagic]

It says 12 but it's rated to 40v+/-%% so running a 36v liPo is no problemo.....

http://cgi.ebay.com/12V-DC-CAR-AUDIO-CIRCUIT-BREAKER-FUSE-40AMP-40-AMP-40A-/260664195079?pt=AU_Car_Parts_Accessories&hash=item3cb0cbf807


$10 w00t

[oldbiker]

Hi Guys,
When I started looking for the 40A CB I was surprised at how few stated they could handle 36V; that caused me great pause.
The only one I found on eBay is: http://cgi.ebay.com/Circuit-Breaker-40A-40-Amp-12-24-36-48-80-Volt-DC-161-/350390527947?pt=LH_DefaultDomain_0&hash=item5194e727cb , which can handle up to 80V.
And it’s about half the price w/sh of the item MonkeyMajic suggests. The only problem I foresee is in mounting it; as it is a bit larger.
I am using a mortar shell ammo box so it has plenty of room to fit bunches of stuff; the battery, BMS, Controller, Alarm, and even the charger if I wish. What I need to do now is drill some holes for ventilation.
I do appreciate all of your efforts.