switch insted of controller???

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aljsk8   10 mW

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switch insted of controller???

Post by aljsk8 » Apr 14 2008 7:28am

Is there any reason (apart from its a bit crude) that you cant just switch a motor - as in on/off, instead of a controller?

you could just use a cable operated insulated switch (home made) to avoid electrocution

if hammering all that current in under load is a problem then maybe a 3 speed switch like the old tamiya radio controlled cars

obviously you don't get nice power delivery but you could make it ultra reliable and ultra low cost

let me know your thoughts

Alex

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Drunkskunk   100 GW

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Re: switch insted of controller???

Post by Drunkskunk » Apr 14 2008 8:52am

you can't use just a switch on a brushless motor, and most on this forum are using brushless motors.

A switch would work fine for running a brushed motor. I think Jay64 was doing this for a while on his bike. it worked fine for him untill he got his throttle repaired. but the current would be an issue. too much current could hurt the batteries pretty quickly, and Too much current is being pulled at too high a wattage for a tamya style speed controller, you would have to design your own. Plus a cheap controller is less than $40 from diffrent sources. Building your own would eat up most of that.
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aljsk8   10 mW

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Re: switch insted of controller???

Post by aljsk8 » Apr 14 2008 9:13am

Yeah i currently (no pun) have a brushed motor and want to go 36v but will need a controller and battery's £££

i know controllers can be had for low price but id be worried that low price = low quality and so will probably
break pretty fast

its nice to know that it could work if i needed it

i could build the switch for pretty much zero cost - just my time

thanks for the help

Alex

deardancer3   10 kW

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Re: switch insted of controller???

Post by deardancer3 » Apr 14 2008 9:14am

aljsk8 wrote:Is there any reason (apart from its a bit crude) that you cant just switch a motor - as in on/off, instead of a controller?
you could just use a cable operated insulated switch (home made) to avoid electrocution

let me know your thoughts

Alex
As mentioned earlier, this tactic is only for brushed motors un less you can switch windings REALLLY fast, like 10 times a second:)

all kidding aside, this is a technique people have used to make it home with brushed motors after a controller failure, the "2 cent" or 2 penny controler, wires soldered to two pennies as contacts then press and release for speed control. A switch rated long term for the massive inrush of initial DC current will cost about half of a controller. Once the motor is spinning its not tooo bad, but the first shot of current can be big.

this is very hard on your batteries as the initial current needs of the motor are normally moderated by the controller. the shortened life time of a set of decent batteries would easily pay for a minimal brushed PWM controller.

But this tactic will get you home.

my two watts worth.

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aljsk8   10 mW

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Re: switch insted of controller???

Post by aljsk8 » Apr 14 2008 9:19am

thanks for the reply

id probably ride to like 5mph before switching on

i would have thought for a single stage switch the cost would be very little

(look in my box of junk for some steel plate a spring some bolts an old sti or thumb shifter - a bit of imagination - there you have it)

it would be something to keep me going for a few weeks to test 36v

then funds permitting id get a controller

Alex

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TylerDurden   100 GW

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Re: switch insted of controller???

Post by TylerDurden » Apr 14 2008 10:44am

You might find an old starter relay (ford), like this:
http://www.autozone.com/R,APP209411/veh ... Detail.htm
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Dr. Shock   100 W

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Re: switch insted of controller???

Post by Dr. Shock » Apr 14 2008 1:06pm

Here's an article where they had two switches, one for 12v and one for 24v.

http://autospeed.com/cms/article.html?&A=2419

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fechter   100 GW

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Re: switch insted of controller???

Post by fechter » Apr 14 2008 8:54pm

The original Zappy just used a relay and it had a clever SCR circuit that prevented it from turning on unless the motor was moving at some minimum speed.
Old golf cars and mining equipment used a kind of 3 speed setup with giant resistors to get up to speed. Not efficient at low speeds, but very simple and robust.
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lazarus2405   10 kW

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Re: switch insted of controller???

Post by lazarus2405 » Apr 14 2008 9:19pm

You can pick up a relay with two sets of 20amp contacts and a momentary pushbutton from radioshack foor about $6. Drive the relay off a 12v tap into your pack, and use both contacts in parllel. As long as the motor is brushed, and can't draw more current than your batteries can safely provide, you'll be fine.

A momentary would be better than a switch, since if something happens the motor will cut out as soon as your hand leaves the button. Yoou don't want the thing zooming off without you!

It would be a cheap way to test a higher voltage, even compared to a $30 controller. If you're running SLAs, which it sounds like you are, they'll be fine with the current. Just pedal first and remember that any time your switch is closed, you'll be at "full throttle".

aljsk8   10 mW

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Re: switch insted of controller???

Post by aljsk8 » Apr 15 2008 3:40am

all very helpful info guys - thanks a lot for the replies

Alex

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Re: switch insted of controller???

Post by truckerzero » Apr 16 2008 8:15am

what about using a light dimmer thats for your house i know its ac but may work for systems up to 1500 watts thats the rating on them
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fechter   100 GW

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Re: switch insted of controller???

Post by fechter » Apr 16 2008 9:58am

truckerzero wrote:what about using a light dimmer thats for your house i know its ac but may work for systems up to 1500 watts thats the rating on them
Nope, those won't work. AC only.
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Link   100 MW

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Re: switch insted of controller???

Post by Link » Apr 16 2008 2:57pm

fechter wrote:
truckerzero wrote:what about using a light dimmer thats for your house i know its ac but may work for systems up to 1500 watts thats the rating on them
Nope, those won't work. AC only.
Yeah. If I remember correctly, they use a small capacitor that charges up before the waveform reaches its peak, cutting power for a fraction of a second. It's effectively a very simple PWM controller that only works with AC. The light filament's thermal inertia keeps it from flickering.
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fechter   100 GW

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Re: switch insted of controller???

Post by fechter » Apr 16 2008 3:18pm

Link wrote: Yeah. If I remember correctly, they use a small capacitor that charges up before the waveform reaches its peak, cutting power for a fraction of a second. It's effectively a very simple PWM controller that only works with AC. The light filament's thermal inertia keeps it from flickering.
Most of them use triacs or SCR's which cannot turn off unless the current reverses. In a DC circuit, it would turn on and get stuck on. In an AC circuit, the capacitor delays the point where the triac turns on, effectively making a PWM at 120hz.
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Link   100 MW

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Re: switch insted of controller???

Post by Link » Apr 16 2008 3:28pm

fechter wrote:
Link wrote: Yeah. If I remember correctly, they use a small capacitor that charges up before the waveform reaches its peak, cutting power for a fraction of a second. It's effectively a very simple PWM controller that only works with AC. The light filament's thermal inertia keeps it from flickering.
Most of them use triacs or SCR's which cannot turn off unless the current reverses. In a DC circuit, it would turn on and get stuck on. In an AC circuit, the capacitor delays the point where the triac turns on, effectively making a PWM at 120hz.
Was wondering if they would use those or a FET. Otherwise you wouldn't be able to change how long it stayed on.
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