Search found 11609 matches

by fechter
Feb 05, 2007 10:07 pm
Forum: E-Bike Technical
Topic: Magnetic Breaking
Replies: 19
Views: 2967

If that's too scary for Xyster, I could use this one instead: On RC controllers, the brakes work by shorting out the motor. This is a bit rough on larger vehicles. Basically you need to short out the motor, but at a high frequency and with a limited duty cycle where it doesn't stay shorted for very ...
by fechter
Feb 05, 2007 10:01 pm
Forum: E-Bike Technical
Topic: Magnetic Breaking
Replies: 19
Views: 2967

SILENCE MORTALS!

You want to see something really scary, how about this one:
by fechter
Feb 05, 2007 5:28 pm
Forum: E-Bike Technical
Topic: Magnetic Breaking
Replies: 19
Views: 2967

Lock and Load, Baby!
by fechter
Feb 05, 2007 3:22 pm
Forum: E-Bike Technical
Topic: Magnetic Breaking
Replies: 19
Views: 2967

To get braking, you need to switch all the low side FETs on at the same time. This momentarily shorts the windings in the motor. When the switches open, the voltage kickback will circulate back to the batteries and charge them. Then you use a PWM to control the amount of braking. In order to do this...
by fechter
Feb 05, 2007 1:07 pm
Forum: E-Bike Technical
Topic: 2 Mode Controller
Replies: 26
Views: 4016

Well, if I would ever find time to build the "current mode" throttle adapter, it would be real easy to put a switch on it for two ranges. 1. legal (dork mode) 2. "off road use only", which gets used all the time unless you get pulled over by the cops. With a current mode throttle, it should make the...
by fechter
Feb 05, 2007 11:12 am
Forum: E-Bike Technical
Topic: 2 Mode Controller
Replies: 26
Views: 4016

Well, in theory, if you just stayed at the higher voltage all the time and just limited the throttle in one mode, it should perform almost exactly the same as running at a lower voltage. In fact, if you limited the throttle on a 72v pack so that the top speed was the same as a 36v pack, you would ha...
by fechter
Feb 05, 2007 9:54 am
Forum: Battery Technology
Topic: Backpack battery
Replies: 31
Views: 4067

From those fire reports, it sounds like you could scatter them on the ground and use them as mini-land mines.

And you can take them on an airplane with you, but not a bottle of water.
by fechter
Feb 05, 2007 9:39 am
Forum: Polls & Surveys
Topic: Colour poll
Replies: 13
Views: 2365

Other= one of my favorites: camoflage.

or how about completely plastered with bumper stickers.
by fechter
Feb 04, 2007 12:00 pm
Forum: E-Bike Technical
Topic: New approach to brushed motor controller
Replies: 55
Views: 6674

We're getting pretty far off Joe's original topic here,

but if the granularity is small enough, the current surges will be absorbed by the motor. You'd want to be able to use up the juice from all the sub-packs evenly, so I'm not sure exactly how you would that.
by fechter
Feb 04, 2007 11:55 am
Forum: E-Bike Technical
Topic: what do you guys do for lighting
Replies: 15
Views: 2577

I use a dc-dc converter, but they aren't cheap. On one of my led lights, I have a simple 78xx voltage regulator. It's limited to 35v input. LED lights are easier to deal with since the current draw is so low you don't need to worry about efficiency as much. For incandescent bulbs, you might be able ...
by fechter
Feb 04, 2007 11:45 am
Forum: E-Bike Technical
Topic: New approach to brushed motor controller
Replies: 55
Views: 6674

That's pretty much what they did back in the '20's before they had transistors. Resistors were also used to avoid a huge inrush current when you switch. Gives sort of a jerky ride, but it does work and it is efficient if you don't use the resistor much. Such a system would also be EMP resistant :wink:
by fechter
Feb 04, 2007 11:41 am
Forum: Battery Technology
Topic: Open Source Battery Equalizer
Replies: 77
Views: 12426

Has anyone ripped open a 12v dc-ac inverter? They might pump up the V to 120V before conversion to AC. Sure. I have a couple of them ripped apart. They bump up the voltage to 170v before chopping it. I suppose you could use one of those cheap 2hp treadmill motors with one. I don't think the overall...
by fechter
Feb 04, 2007 11:32 am
Forum: Battery Technology
Topic: Open Source Battery Equalizer
Replies: 77
Views: 12426

It's a good design. I like it. I STILL haven't made up my mind about my battery purchase yet and now that I understand this "grid" layout for series and parallel cells (rather than the series only way I was envisioning it) I see the benefits of the built in balancing. All you really need is to have...
by fechter
Feb 04, 2007 11:27 am
Forum: E-Bike Technical
Topic: New approach to brushed motor controller
Replies: 55
Views: 6674

Seems like it should work. I don't see why they don't do something like that anyway, it wouldn't add much to the cost. It could automatically compensate for different motor inductances too. I think I've seen some switching power supplies that work like that.
by fechter
Feb 04, 2007 11:13 am
Forum: E-Bike General Discussion
Topic: Milwaukee Electric battery pack for GoHub!
Replies: 20
Views: 5733

Nice report guys, The stock current limit on the Vego controller is around 50 amps. If you tweak the pot all the way, it will be around 60. To get a higher limit, you need to hang a resistor on the circuit board, but I wouldn't recommend it unless you upgrade the main cap and beef up a couple of the...
by fechter
Feb 04, 2007 12:48 am
Forum: Battery Technology
Topic: 'Exact Behavior' of Battery Chemistries?
Replies: 30
Views: 4421

Maybe Xyster ran the whole pack down so low that one of the sub-packs went into reversal. Bet lithiums aren't happy with that.

My experience is lithiums usually fail in the "paperweight" mode and go open. If you smash it, it could short.
by fechter
Feb 03, 2007 4:54 pm
Forum: Battery Technology
Topic: Open Source Battery Equalizer
Replies: 77
Views: 12426

Now back to the discussion, Hi Reid There's more than one failure mode for the cells, but generally the cells will stay happy if they never go outside their allowable voltage range and they never exceed a certain maximum charge / discharge current. Cells in parallel are forced to the same voltage, s...
by fechter
Feb 03, 2007 4:34 pm
Forum: Battery Technology
Topic: 'Exact Behavior' of Battery Chemistries?
Replies: 30
Views: 4421

If you had 10 cells in parallel, they would always have the same voltage because they're wired together. During discharge, if one cell is weak, its voltage will still be the same as the other cells, but it will stop contributing to the output. The opposite is true during charging. The weak cell will...
by fechter
Feb 03, 2007 4:20 pm
Forum: Battery Technology
Topic: Open Source Battery Equalizer
Replies: 77
Views: 12426

That's interesting. I posted that, but it looks like you posted it. Are you trying to steal my posts? I can moderate you for that. Seriously, I edited that post about 3 times and quoted your post. Somehow it did screw up, but I don't know if it was something I did wrong. I might have messed with som...
by fechter
Feb 03, 2007 11:27 am
Forum: Battery Technology
Topic: Backpack battery
Replies: 31
Views: 4067

If you could design a containment for the batteries that went in the backpack, it could have a nozzle to direct the flames to the rear.

That way, if the batteries decide to go exothermic on you, it will act like a rocket pack.

Got Nomex?
by fechter
Feb 03, 2007 11:19 am
Forum: Battery Technology
Topic: 'Exact Behavior' of Battery Chemistries?
Replies: 30
Views: 4421

Lithium and lead-acid: charge and discharge in parallel OK Nimh and NiCd, discharge in parallel OK charge NOT OK The wierd thing about Ni batteries is when they approach full charge, the cell voltage drops slightly. If you have a bunch of cells in parallel, the first one to hit full charge drops its...
by fechter
Feb 03, 2007 10:31 am
Forum: E-Bike Photos & Video
Topic: Voloci Project
Replies: 16
Views: 5691

I see you have a rotor. You just need a shaft and and a housing.
You might be able to adapt a housing from a car alternator or AC motor if you could find one the right size. The shaft might be more challenging, something a machinist could make fairly easily.
by fechter
Feb 03, 2007 12:04 am
Forum: E-Bike Photos & Video
Topic: Voloci Project
Replies: 16
Views: 5691

Yes, the streets of San Francisco. He doesn't have moped plates yet, but he's going to get them. He lives close enough to work to commute with it. Perhaps the cops that are tailing you are just interested in the bike and not out to bust you. A lot of cops ride bikes. The controller could take 48v (6...
by fechter
Feb 02, 2007 10:00 pm
Forum: E-Bike Reviews & Testing
Topic: Puma Motor in a 26 Inch Wheel at 37V
Replies: 34
Views: 7504

I think somebody finally got the torque arm right! That looks great. If you're worried about the thickness, you could stack a bunch of them. It looks like there's plenty of thread left on that axle. Imagine the hub locked to the axle and you started pulling the rear wheel backwards so the bike start...
by fechter
Feb 02, 2007 9:53 pm
Forum: Battery Technology
Topic: Open Source Battery Equalizer
Replies: 77
Views: 12426

By then, you would now need to make the circuit more complicated and you'd have to carry around a bunch of 'spare' weight. Back to my original idea, there's several possible ways to balance and monitor the pack. Everything is a trade-off when you design something. My approach is usually to get the m...