I have had two throttles go bad on a 36v bike build. I have a question so here goes. I know that a 12v 30amp auto fuse is only 15amps on a 24v bike. so what are the amp on a 110v 20amp house switch on a 36v circuit. Is it about 60amps. I did melt a 15 amp house switch on a 36v bike pulling about 40amps of current. I am sick of controllers and throttles. My motors are just helper motors. They mostly run at wot anyway.
Please help me out here.
Hi Deacon,
a few things going on here.
a 30A fuse will always attempt to break the circuit if the current flowing is above 30A for long enough.
The voltage rating gives an indication of the area of voltage and current actually flowing where the fuse is actually capable of breaking the circuit.
This is called the breaking capacity.
A 30A autofuse that attempts to break a 24v circuit will arc and destroy the holder.
switches that are intended for use in AC lines have vastly inferior breaking capacity ratings than ones meant for DC circuits.
a switch rated to 110vac is only good for around 15vdc.
im actually impressed the AC rated switch was able to break the circuit at all.
i hope this helps in understanding what has been going on.
Matt
Daily Ride:
2007 Vectrix, modified with 42 x Thundersky 60Ah in July 2010. Done 194'000km
Thanks for the information.
I guess I just got lucky. I ran the bike on my one mile test ride that I always do and the 20 amp household wall switch worked just fine. That is not to say that I expect it to hold up. Most likely it will melt shut and leave running headlong down the road to my death... Life is like that you pays your 5 bucks and you takes your chances I guess.
I was under the impression that a dc fuse would take less amps to melt down at higher voltage. Thus actually reducing the amperage value of the fuse. I guess I had it wrong that there was some kind of formula for all things electric.
I suppose one can not relate AC to DC current. Thanks again for the information....
A quick google for "compare dc fuse & ac fuse" produced this link:
http://www.interfacebus.com/fuse-operation-ac-dc-voltages.html
Quote from the article:
"The difference between an applied AC voltage or is DC voltage to a fuse; The fuse-links are on principle suitable for use at alternating and direct voltage. The breaking capacity at direct-voltage is however considerably lower than the one at alternating voltage."
And to add to the confusion, from ElectricScooterParts.com:
Scooter Fuse Information
Electric scooter fuses should always be replaced with the same Amperage rating fuse. The Voltage rating is not quite as important though. Some scooter makers will use 250V fuses while others will use 32V fuses in their scooters. The reason for this is that 250V fuses are rated for AC power and 32V fuses are rated for DC power, and because AC power is more efficient to transmit than DC power is, it is much easier for fuses to handle. A 32V (DC) fuse is compatible with a 250V (AC) fuse and they are 100% interchangeable when used in electric scooter and electric bicycle applications.
Fuse Amp Rating (A)
Use the same Amp rating as fuse being replaced.
Fuse Volt Rating (V)
OK to use 250V or 32V fuses.
Do not use 125V fuses.
I think there is some confusion here.
The rated current of a fuse is always the RMS or DC rating. For 30A DC and 24V application you should use 30A and any voltage rating greater than 24V. So 125V or 250V all would work.
Now the AC current rating is the RMS value of the current. The difference in this value to the peak value is the square root of 2 or 1.41.
So the peak current is higher than the rated current by 40%. A 10A DC rated current may fuse at 7A AC RMS due to this factor.
First: Fuses and wires/switches can generally be used at voltages equal to, or lower than, their rating. The AMPERAGE rating of a fuse, switch, or wire does not change with voltage, a 20 amp 120 volt fuse is still a 20 amp fuse at 12 volts! (A motor, operating at the one horsepower level, might require 100 amps at 12 volts, but a similar motor would need only 10 amps at 120 volts-this is a different situation)Your breaker was too small! Buy a circuit breaker or fuse marked to handle more than the actual continuous current used, if you do not wish it to fail unexpectedly, and be sure that the associated wiring is big enough to handle this continuous amperage.-Bob (Be sure that devices used on D.C. circuits are rated for, or above, the D.C. voltage involved, or severe arcing may cause damage if overloaded!)
Robert M. Curry
I did some real time testing today and discovered that the 20amp 117v on/off switch works better than the same setup with a controller. I also found that this setup allows me to lower the voltage I had been using to power the Rhino friction drive motor. I think it is pretty safe. I also made an emergency pull wire for the power circuit, if the switch melts shut. I think I have all the bases covered now.
I am going to be running a 30amp dc fuse, Thanks for clearing up that fuse thing for me. I had been running a 40amp fuse and might still need it as this motor can pull 36 peak amps. It seldom has to since I always start it after pedaling. The only thing it is protecting is the switch hopefully it will blow before the switch melts closed. If not, I can always pull the 'oh crap' wire and open the circuit.
Most ordinary fuses, rated at 5 amperes and above, will allow double the rated current to flow for anywhere from 30 seconds to 2 minutes, before they blow, so the 30 amp fuse should easily handle your 36 to 40 amps, if it is not for too long a time period. Be SURE that you have a good means of retaining CONTROL of your vehicle! It is advisable to link the brakes, so that applying either brake will interrupt motor power. If you are inadvertently propelled out into traffic, you may not get a second chance!--Be SAFE!-Bob
Robert M. Curry
Just a note to add confusion, and maybe save a trip to the store, if you go to an "electronics" oriented store, there is also "fast acting" and "slo-blo" fuse types, so make sure to match apples to apples, even if "upgrading"
In the last chance saving grace I have a bit of wire gently wired into the power circuit with a loop I can grab and pull hard. That will interrupt the circuit. That's in case the switch melts.