a curious ignorant ask about small dc motor starting

Thread Starter

wbs

Joined Jul 29, 2020
31
Tanks a lot but this picure is very familiar to me. I understand very well the principle behind it go further with lever and cut resistance cutting down inrush current gradually.

But the techical construction of resistors? Ordinary resistors can handle even 4 watts of energy and there are commercial power resistors 1 ohm even to wattage 750. But big motors will need resistors which can handle tens of thousends watts I guess! And if we want to use this technique with 2-point starter will we need miles of resistive wire and move lever on it or something different technique ? Network of huge number smaller parallel and serial resistors arrangement or what?

Of course this it to any practical meaning with my case but it just bare interesting historical thing.
 

MaxHeadRoom

Joined Jul 18, 2013
28,768
But big motors will need resistors which can handle tens of thousends watts I guess!
If you have ever looked at the top of the cab of a modern locomotive you may have seen some vents running along the length of the cab, Under these vents are huge resistors about 6ft long with fans mounted below them. ! :eek:
A project I did a few years ago was converting some old retro loco motives to dynamic braking for running through the Canadian Rockies.
 

Thread Starter

wbs

Joined Jul 29, 2020
31
If you have ever looked at the top of the cab of a modern locomotive you may have seen some vents running along the length of the cab, Under these vents are huge resistors about 6ft long with fans mounted below them. ! A project I did a few years ago was converting some old retro loco motives to dynamic braking for running through the Canadian Rockies.
Unfortunaly I have not ever had opportunity to look at internals of locomotive. But I was thinking earlier to build black smith hardening owen using Kanthal wire when my hobby was blade smith work. I did give up this and used tradititional fire heating whole time. Now after 3 brain strokes ( I am 78 years old) I do more light hand work as motors . I am happy to find out that at early times they had not any better solution than this rough glass melting and hardening owen technique. I tried very thin Kanthal wire with my strong battery just for fun. It has resistance of 20 ohms/ yard. Of course it burned in very short time, I was expecting that.



Using a long thick wire (wrapper around a ceramic bar) would work but it would too much to expriment for me. What to do with soft starter then! I have working at software field but wanted some short time to get familiar to electronics so I did some exercise of electronics just for fun.

I designed a card working in old time computer ISA-bus, I programmed a fpga chip with hdl-language for fuctionality and tested finally with oscilloscope, worked fine also inside a computer.



Still I am reluctat to use electronics with my old time tiny motor.



However, there is always a solution to this level small problem, I will find it for sure (if I am not dying in a month).
 

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Thread Starter

wbs

Joined Jul 29, 2020
31
i disagree, 10 years old boy likes just some whatever moving thing like toy car, in addition to that there are lot of simple things involved easy to explain, for example electromagnet , battery can produce power to not only create light, it can be controlled to make mechanical work and if there is interest many other more detailed things and priciples.

Of course anybody can easily find why all somebody else does futile if he has will to do that and he seems it to be good in some sense.
 
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