Minit lathe - can you help ID my wiring?!

[HankMcSpank]

Ok, I'm on the home straight ...I just need a sanity check re the DC motor connections & the 'current sense' resistor.

Firstly, I reckon the DC motor connections are A1 & A2 on this diagram (there are spade connectors marked as such on the PCB)...



(John S, confirmed that on the original Sieg board that A1 & A2 are the DC Motor connections & I gather this must be a standard naming convention, but those F1 & F2 connectors are messing with my head!)

Ok, next challenge' ....current sense resistor! This board talks of having an external current sense resistor, but if you look at the chart, it seems ludicrously low...



my motor is 250W, which apparently is 1/3rd of a horsepower - therefore looking at that chart it needs a current sense resistor that is 0.027 Ohms - are they having a laugh?


Where on earth will I be able to source a resistor such as that? (Danfoss apparently don't make these driver boards any more ...not sure if Graham do) ...since the resistor is in series with the motor ...it's going to have to be able to handle a fair whack of current...therefore I'm figuring it'll need to be able to disappate a fair bit of power too?

Has anyone experience of such current sense resistors? Is there a 'frig' where I can do away with the darned thing?

Many thanks

[ptjw7uk]

No the resistor should only have to dissipate 0.5watt.
so at 4 amps and 0.027 ohms then 4 x4 x 0.027 =0.432 watts.
You may have to parallel some to get near the value. Just did a quick search so far nothing in uk.

Peter

just found http://cgi.ebay.co.uk/Vishay-LVR05R0...3286.m63.l1177

so should be available in UK

[Sparks]

Rob

Firstly you only need to use terminals marked F if you have a shunt wound motor, I am assuming that you only have two wires coming out of yours if so you just use the A marked terminals.

The sense resistor is used in some drives as part of a feedback circuit to limit the amount of current the motor can draw, and help prevent your motor from burning out, it can also help out with low speed torque issues, this subject can get quite complex so we'll leave it here!

Anyway this rs part number should help you: 199-6356 it is for a 0.03 ohm 6W resistor which is just about right for you. As peter correctly says your dissipation will only be about 0.3 - 0.4 w.

You posted while I was typing, glad you got it going Rob.

Dave