Motor Circuit - Large 1ohm 10w resistor - Why?

[Szewczykm]

Hi,

There is a circuit that goes into pinball machines for those equipped with a "shaker motor".  I understand most of the circuit but I'm curious about a big resistor that's in there.

Here is the Schematic
http://www.ki4swy.org/images/pinball/lah/lah-shaker-board.png

Here is a picture of the board
https://ksarcade.net/media/catalog/product/cache/1/image/a449636a7e0327a12453e7ee4d97c439/5/0/502-5027-00.jpg

Basically A/C is coming off a transformer, there are a couple of Diodes that I'm assuming are acting as a rectifier (half wave I think), a couple of fuses and a big 10w 1ohm resistor.  The motor is being driven on a different board, and that part of the circuit is on the schematic.

I'm wondering if anyone knows what the purpose of the big resistor is?  I spoke to one of the electrical engineers at the iron foundry I work at (we use a lot of electricity melting iron!)  what his guess was and he said he thought that maybe it was a kind of protection against the motor seizing up.  He said that if the motor were to get jammed, stuck, seized, whatever, and it started to draw a lot of current then rather than burning up the circuit or motor, that resistor would just dissipate the draw as heat.

This seemed reasonable, but I wondered, wouldn't a fuse just blow?  Maybe there are instances where the fuse wouldn't blow but the motor would get hot if something jammed it, but the resistor helps dissipate some of that.  But really it's a guess.  I'm trying to get into the designer's head.  Any ideas?

Thanks!

Mike

[dannyf]

To limit the start-up current.

[SeanB]

It limits the start up current and also reduces the speed of the motor slightly so that it does not vibrate so vigorously. As the motor draws more current during lifting the shake mass the resistor lowers the voltage applied to the motor ( it is 100/120Hz full wave rectified DC, the lower link on the diagram shorting the one diode and fuse is incorrect) so it does not shake itself to bits.