Will a 36v LED throttle work at 48 volts?

[Larry]

I'd like to add a battery and give 48 volts a try. My motor and controller can handle 48v. I realize I could just cut the 36 volt throttle wire and do without the LED lights and the throttle should still function ok, but I hate to do that if I don't have to. That light is my reminder to be sure to turn the key switch off and if the throttle lights will work at 48v without damaging anything, I'd like to keep it. I realize the "low battery" light won't work at 48 volts, but I don't really care about that. Heck, with SLA batteries, you can definitely feel when you are about out of juice.

I found a few mentions in old threads that overvolting will damage the throttle and possibly other components, but it wasn't clear whether the posters who had experienced the problem had possibly overvolted all the way up to 72 volts rather than just to 48. Does anyone know whether these inexpensive 36 volt LED throttles can usually handle going to 48 volts without cutting the wires or adding other electrical parts?

 

[The7]

There are two simple ways:
1) Use a resistor R.
With 36 V battery, use an mA meter to measure the current I for the LED branch.
Then R=12/I
Suppose I = 10mA, then R = 12/10m = 1.2 k ohm.
2) Use an 12V zener diode (1/2 watt or 1 watt) as an 12V drop for the LED branch.
Both ways will give you the full functional LED status. Of course it may not be 100% accuracy.

I use method (1) when up-volting from 24V to 48V and it is fairy satisfactory.

 

[dogman dan]

Works fine at 48 v on wilderness energy ones.

 

[docnjoj]

Mine works good at 42 volts (35 cells) NiMh. Lights are a little brighter than 36 but no smoke!
otherDoc

 

[rkosiorek]

the point is that it will still work without the series resistor or zener diode. but it will no longer act as a battery gauge. it would just be an on/off indicator then.

if you add the series resistor or 12V zener diode the battery gauge will still work as before. since i am lazy and prefer not to measure and calculate resistors the 12V zener is the slightly more expensive but easier solution.

rick

 

[docnjoj]

Thanks Rick! I didnt think of that!
otherDoc

 

[solarbbq2003]

I was talking recently with someone about using a zener dioded to drop voltage by 12volts, he suggested that a zener diode doesn't drop voltage by 12v, but gives 12v output whatever goes into it, is this correct or he has his knickers in a knot?

 

[rkosiorek]

I was talking recently with someone about using a zener dioded to drop voltage by 12volts, he suggested that a zener diode doesn't drop voltage by 12v, but gives 12v output whatever goes into it, is this correct or he has his knickers in a knot?

i don't think that that person really understands how a zener works. a zener diode has a trip voltage. below the trip voltage it acts pretty much like a standard diode. exceed the trip voltage and it starts to conduct in the reverse direction. so yes a 12V zener will drop 12V across itself.

it also has a power limit as to how much power it can absorb. so a 12V 1W zener can handle a maximum of 1W/12V = 0.083A a maximum of 83mA but it would get pretty darn hot.

for the small amount of current (20mA or less) that the LED voltmeter in a throttle needs though, a 1W zener will work just fine. i use this all of the time.

rick

 

[solarbbq2003]

thanks rick will be extremely useful to use 12v or 24v zeners

 

[needWheels]

For the less skilled, is this a part I might be able to find in a dead PC power supply (I've got a few)
and where is the proper location to wire it in?

 

[Link]

Yeah, you can find them in power supplies. They're used to help keep a constant voltage.

You'd wire it reverse biased to the wire on the throttle that goes to the LED lights. Ex: If you had a throttle with red for +, black for -, green for signal, and something like a blue/purple wire, it would go on the fourth one.