soft start solution

[crazy dreamer]

Hi all, i have just been given an injusa 6 volt quad with a dead battery, i have fitted a 12 volt 7ah battery i had lying around and it works great but the start up on the motor is too aggressive, it spins up the wheel from a standing start and will eventually break something. any ideas on how to slow down the initial torque for a second or so (soft start) ?
C.D

[Lessss]

dimmer switch

[amberwolf]

If you mean a typical wall-mounted AC-powered dimmer switch, it will not work on DC--the SCR/triac will latch on and that's it, until you disconnect power. No dimming. They work by slicing up the gate signal on the triac to allow more or less of the AC waveform thru on each cycle, quite a lot like a brushless motor controller....but not on DC, only AC.

It's possible to make a dimmer that can run on AC or DC and dim either AC or DC lights, but the common ones don't do that, and I expect you'd burn up anything cheaply available that could do it with DC. Cheaper to buy an actual motor controller, I expect.

[crazy dreamer]

i was thinking along the lines of a resistor/capacitor/diode type solution? there is no point buying a controller, i could just fit a new 6 volt battery! (but the grandchildren like the extra speed 12 volt brings)
C.D

[amberwolf]

Depending on the current draw, it would have to be a HUGE resistor to dissipate the heat created. Yes, it could work, but the resistor might be bigger than the battery, and might require a fan and heatsink to keep it cool enough to not burn up.

Capacitors and diodes won't do what you want. (well, diodes could, but again, depending on the power consumption of the motor, they'd need to be large and have large heatsinks and possibly fans to carry off the heat).

[drewjet]

use 2 6 volt batteries and a switch to go from parallel (6v) to series (12v)

[Gregory]

I'd pick up a 12v dc brushed controller for well under $20, maybe $10. But you would need a throttle too.

Can't help on the soft start thing, but I'm sure such a thing could be made. Plenty of electrical geniuses on here.
Could you have a FET that you slowly opened the gate over a period of seconds?

[Lessss]

I'm sure you can find a DC dimmer switch at naval stores or off grid living stores.

Some people build tiny homes that are very neatly and efficiently designed to minimize wiring and plumbing so no need to go from dc(solar/batts) to ac(for distance) then DC again(at device).
http://www.reddit.com/r/TinyHouses/

If you need a DC controller search on a thread called the score. or pm user mcdesign memberlist.php?mode=viewprofile&u=16686

[crazy dreamer]

thanks for your efforts, still scratching my head. the motor is stamped as 75watts, not sure about the amp draw but it wont be very high.
C.D

[crazy dreamer]

thinking of adding a high wattage car bulb in parallel to absorb some of the surge?
C.D

[Gregory]

Hi C.D

I found this DC brushed motor soft start circuit, As I suggested it uses a FET to open after a short period.
[url]
http://www.electro-tech-online.com/elec ... start.html[/url]

Initially it passes a few amps thru the 0R5 resistor then as the cap charges and the gate on the FET allows the Fet to pass current, the electricity flows through the FET instead. So I think it's like a two stage on switch.

I built this up today out of curiosity, seemed to work but may need some tweeking. And I couldn't really put a consistent load on this crappy scooter without stalling the mortor.
Was a very simple circuit. I just used a FET I has out of an old upgraded controller.

Hope that helps.

Test on a 24V scooter using 3S LiPo

softstart2.jpg (158.98 KiB) Viewed 1538 times

my version bodged together

softstart1.jpg (164.83 KiB) Viewed 1538 times

[crazy dreamer]

this is just what i was looking for, will grab a few components and give it a try thanks,
C.D