7.2V Nicad + potentiometer with switch

Ian_S

Ian_S

Registered
I have a 7.2V Nicad battery pack and want to switch on a motor and vary the speed of the motor

I bought a Omeg 1k Ω Linear Single Gang Potentiometer with Switch from Maplins

http://www.maplin.co.uk/p/omeg-1k-andohm-linear-single-gang-potentiometer-with-switch-ku91y

omeg-1k-andohm-linear-single-gang-potentiometer-with-switch.jpg


I wired it up this morning and it sorta worked.............

Rotating the control turned on power to the motor and the motor speed increased as the control rotated - then the "magic smoke" began to emanate from the potentiometer.....

I guess I need the same type of product - but can cope with the 7.2V nicad - Anybody point me in the right direction please?

Thanks in advance

Ian S
 
Ian, as it's a Maplin product, why not use the question tab on that linky?

My guess though is that the pot is rated for 4A and the battery current will be much higher....
 
Try these

http://www.ipengineering.co.uk/page60.html

http://cambrianmodels.co.uk/speedc.html

http://www.brianjones.free-online.co.uk/page5.html

http://www.peterspoerermodelengineers.com/90275/info.php?p=3 - ER2

Rik
 
The current is the problem.

W=V x A

As V is 7.2 and for a typical G scale motor, A can be 0.5 - 1.0, which give a power value of 3.6 - 7.2 Watts

None of the Maplin ones get anywhere near that, as far as I can see. The one you've used was only 0.4.

Edit: I should add that all of the speed controllers above use semiconductors of one sort or another to achieve more efficient use of the power, rather than heating up a big resistor.
 
So I guess I need a "fully fledged" speed controller then - Like those used in R/C cars, boats, planes etc?

Or one of the ones that Rick kindly posted (Ta Rick)

Hmmmm - Given that this is a cheap project (I'll let you know what I'm building when I have the fundamentals sorted) - then it looks like I'll be ripping a toy R/C car to bits to get to the speed controller and see if I can get it to work.

Thanks all
 
Use a LM317 voltage reg and pot

http://www.circuitstoday.com/few-lm317-voltage-regulator-circuits

That should do a simple control
 
I use the IP type of speed controller for my trailer layout (12v track power) with a 3amp (car type) blade fuse. I can run up to four locos at once with it. Obviously twin motored locos count as two ;D
 
Or to be really way out there at the very cutting edge why not go Wireless? We have discussed these ad nauseum and for your application they would work a treat; http://www.ebay.com.au/itm/11-Keys-RF-Wireless-Remote-Mini-Controller-Dimmer-for-Led-Single-Colour-Strip-/350935699135?pt=AU_Lighting_Fans&hash=item51b565cebf&_uhb=1
5 - 24V these are pulse width modulated controllers, power goes in as indicated, motor connects across the end marked led....
or: http://www.ebay.com.au/itm/Wireless-Remote-LED-Light-Dimmer-Controller-Control-12V-24V-MR16-LED-spotlight-/161184882541?pt=AU_Lighting_Fans&hash=item25875e1f6d&_uhb=1
Take the board out of the box to save space will handle 8 amps....
 
Or if you insist on a wired connection try one of these; http://www.ebay.com.au/itm/12V-24V-3A-DC-Motor-Speed-Regulator-Controller-Switch-Control-PWM-HHO-RC-New-/271449461402?pt=LH_DefaultDomain_15&hash=item3f33a6129a&_uhb=1
 
tramcar trev said:
Or if you insist on a wired connection try one of these; http://www.ebay.com.au/itm/12V-24V-3A-DC-Motor-Speed-Regulator-Controller-Switch-Control-PWM-HHO-RC-New-/271449461402?pt=LH_DefaultDomain_15&hash=item3f33a6129a&_uhb=1
Click to expand...

Ha, pulse wave? Tried it once - made the motors whistle (or something did).
 
If you've got a duff cordless drill then the cheapo ones have a suitable pot connected to the trigger. If you're stuck Ian, let me know and I'll have a look for the smashed up one I rescued from a skip.
 
trammayo said:
Ha, pulse wave? Tried it once - made the motors whistle (or something did).
Click to expand...
Yes they can do that. ;D The advantage of them though is that they deliver full voltage to the motor thus the motor torque is available even at slow speeds.
If you insist on resistance control then a wire wound pot is the way to go, carbon film wont handle the current....
http://www.ebay.com.au/sch/i.html?_odkw=wire+wound+potentiometer&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0&_nkw=wire+wound+potentiometer&_sacat=0
 
sparky230 said:
Use a LM317 voltage reg and pot

http://www.circuitstoday.com/few-lm317-voltage-regulator-circuits

That should do a simple control
Click to expand...

Totally agree with using an LM 317 or for higher current an LM338.

I used LM338s for the controllers I built for my old HO layout.

The easiest way to calculate the value of the adjustable resistor is use this formula Rv = (96xVout)-120.

Alternatively as Trev has said the LED dimmer controllers work well.

I have one in a small gravel train that works well and it even has reverse via a picaxe and relay, I copied the article on "trainelectronics" by Dave Bodnar.

I bought the ones from "TMart" that he recommended.
 
tramcar trev said:
Yes they can do that. ;D The advantage of them though is that they deliver full voltage to the motor thus the motor torque is available even at slow speeds.
If you insist on resistance control then a wire wound pot is the way to go, carbon film wont handle the current....
http://www.ebay.com.au/sch/i.html?_odkw=wire+wound+potentiometer&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313.TR0.TRC0.H0&_nkw=wire+wound+potentiometer&_sacat=0
Click to expand...

which can make your motor very hot, especially simpler can motors.
 
Dtsteam said:
If you've got a duff cordless drill then the cheapo ones have a suitable pot connected to the trigger. If you're stuck Ian, let me know and I'll have a look for the smashed up one I rescued from a skip.
Click to expand...


Many thanks Dave for the offer - but I think you have enough on your plate with the MIL in hospital and your first "little un" imminent

Thanks to all others for their input / ideas also

Hopefully - in the next few days - I should have something to test / try out / play with

I'll let you all know in due course........... 8)

Thanks again

Ian S
 
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