# help with a 48v scooter



## mxmtech (Apr 21, 2009)

ICE motorcycles don't have a brake safety input


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## Amberwolf (May 29, 2009)

mill said:


> The new controller doesnt have a brake saftey input, so I want to add a relay to the motor output to open when the brake is depressed.


Just be careful what you give it, so it can't do anything rash in that state. (sorry, bad joke, couldn't help myself). 

You shouldn't interrupt the motor output, but rather the battery input to the controller. If you try cutting the motor current, you may just weld the relay shut instead. Battery current is likely to be lower than motor current at any particular instant. 




> I was thinking of using an automotive 12v relay since they are common


Measure what your actual max current draw is in the place you will put the relay, and get a relay that can handle that *DC* current and voltage. Otherwise it's likely to weld shut at an inopportune moment, and when you expect it to cut the motor off when you try to stop, it won't, and if you're still holding the throttle in position you're not going to stop as fast as you expect (if at all). 




> and I would also like to add some small 12v lights that come on with power on. should I get/make some sort of small dc-dc convertor or just hook up each one to a different battery which may get them out of balance?


Check out my project blog (in my signature) for some ways I've done it. The most recent is using CFLs for a headlight and taillight, and so far they work well. The headlight does not really focus well with my current ghetto method, but I am trying different things for fixing that. Taillight is at least as bright as some cars, and brighter than some older cars' taillight+brake.

They are run from the battery pack's full voltage, and take little power. No DC-DC converters needed.

That said, you can use laptop power supplies or celphone chargers, in many cases, as a DC-DC converter, and in certain cases even to boost your pack voltage to something higher to run brighter CFLs (or other low-current things). See the blog for more details, or this thread on Endless Sphere:
http://endless-sphere.com/forums/viewtopic.php?f=2&t=14193 .

I also have an Instructable on the basics of how to do both of the above:
http://www.instructables.com/id/CFL-Headlight-and-Taillight-for-Electric-Bicycle/



> which brings me to the next question, would it be worth it to make a set of mini battery balancers for this rig? The charger charges them in a string so I guess they will eventually will get out of balance.


They might. There are a number of ways to make a simple balancer circuit; you might look around for some old Volt Blochers for lead-acid batteries; there might be some used ones for sale (they're not made anymore).
________
Nataly


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## mill (Aug 22, 2008)

thanks for the very informative reply amberwolf, I solved the brake switch problem by using a different controller since the first controller was junk(caps blown). I think I will wait on the lights and balancers for now as I still need to finish the deck and wrap up some loose ends, and there is not much room left in the under deck area/battery box. I will probably just give it a one battery at a time charge with a 12v charger every once and a while. I took it on the maiden voyage last night for a few miles, now I have a new problem, this thing is way too fast to give to an 11 year old, I had to be doing 30+ mph and he is a 100lbs lighter than me. Plus the motor was getting very hot and starting to stink, Im pretty sure it was designed for 24 volts. So what I need to do now is limit the thottle voltage, I think it is a hall effect type, it has three wires, 5v ground and 0-5v signal. I was thinking about adding some resistors between ground and signal wire to try to pull it down some, I think I will need to limit it to 2.5 - 3 volts to have it safe for him and the motor. Does this method sound good or does any one have a better idea?


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## Amberwolf (May 29, 2009)

mill said:


> I solved the brake switch problem by using a different controller since the first controller was junk(caps blown).


What are you going to do with the blown controller? (I'm always looking for really cheap bits and pieces to improve CrazyBike2 or stock up to build CB3; blown up stuff seems to be the cheapest way to get them for those willing to part with them, as I can often fix stuff).




> I will probably just give it a one battery at a time charge with a 12v charger every once and a while.


If you have the willingness to DIY a bit more than you probably have had to so far on this, you can make a timer from a 555 chip and a CD4017 decade counter, some transistors and a set of relays that will connect the charger automatically to each battery in turn for a specified amount of time. If the charger has a "done" light on it, you can use a photodetector instead of the timer, which would increment the counter and continue to the next battery automatically. 

I plan to do something similar but less complex to switch a single 24V charger between two pairs of 12V SLAs to charge them unattended, where currently I have to manually switch things around. May be a while before I get to it, though.



> I took it on the maiden voyage last night for a few miles, now I have a new problem, this thing is way too fast to give to an 11 year old, I had to be doing 30+ mph and he is a 100lbs lighter than me. Plus the motor was getting very hot and starting to stink, Im pretty sure it was designed for 24 volts. So what I need to do now is limit the thottle voltage, I think it is a hall effect type, it has three wires, 5v ground and 0-5v signal.


If the motor is getting hot, it means it is having to dissipate too much total power. You either have to reduce the voltage going into it, or the current. 

Instead of limiting the throttle voltage, I would simply eliminate one of the batteries, bringing it down to 36V, which would reduce it's maximum speed by about 1/4. To cut it in half, bring it back to 24V by taking out two batteries. If you want to, you could even wire the four batteries as two parallel pairs wired as 24V, so that it has longer range but less speed.




> I was thinking about adding some resistors between ground and signal wire to try to pull it down some, I think I will need to limit it to 2.5 - 3 volts to have it safe for him and the motor. Does this method sound good or does any one have a better idea?


You can make a voltage divider for the throttle input into the controller, to limit it to some specific max speed.

Some controllers already have a way to limit current, via a shunt resistor or wire inside, and this limit can be used to limit total power to the motor, which can result in a speed limiting depending on load. It'll also help prevent burning out the motor by pouring too much power into it.

If you can find the shunt it can be made a higher resistance, either by replacing the shunt resistor with a larger value, or if it is a wire shunt by removing some of the wire strands or shaving off some of the metal if it is a solid wire shunt. If you're willing to open up the controller box and take good photos of both sides, then post them, I can try to find the shunt on it for you.

That effectively lies to the controller to tell it that more current is flowing thru it than it expects, so whatever limit it has built in to prevent damage will kick in sooner than usual, letting it limit the current output to the motor (by limiting it's voltage, which does essentially the same thing as limiting the throttle).
________
VAPORIZER EXTREME


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## mill (Aug 22, 2008)

I kept the case for the controller and tossed the rest, I wish I would have known or I would have saved it and mailed it to you. I want to keep the controller as I dont have time to wait for another, chistmas is next week. and I want to eventually upgrade the motor to take the 48v so I think Im going to give the resistor idea a go tonight and see how it turns out.


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## icec0o1 (Sep 3, 2009)

So did you finish the project in time?


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## mill (Aug 22, 2008)

yes it is ready, I cut the 5 volt line to the throttle and put a resistor in, after a little experimenting I found the one to give me the right amount of speed and not overheat the motor.


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