Hi from South Africa, a little help please

[irving2008]

Neale beat me to it, but he's said pretty much what I was going to say. Those NEMA 17 motors have precious little torque anyway so before buying anything you might want to do the calcs to see if they are suitable.

[JAZZCNC]

Dito Every thing Neale and Irving said but Also the L298 36V is Maximum and in reality if you push them much over 30V they don't like it and won't last very long, that's why most use 24V with these chips and play safe.! . . Even then they can go pop if you so much as look at them in a funny way.!!

[irving2008]

Dito Every thing Neale and Irving said but Also the L298 36V is Maximum and in reality if you push them much over 30V they don't like it and won't last very long, that's why most use 24V with these chips and play safe.! . . Even then they can go pop if you so much as look at them in a funny way.!!

Jazz is right; the early L298 were 36v and had a habit of going pop and were overtaken by better devices using MOSFETs, the L298 is a bipolar device. However the later ones were updated to 50v so were quite happy on 36v. In their day (mid 1990's) they were good little drivers, indeed I used to run them at 42v, but check the datasheet for your actual device/manufacturer and not a generic datasheet, not all manufacturers updated their devices as newer more integrated chips came along.

However Dan, without wanting to be overcritical, you need to learn how to read the nuances of a datasheet.

As already said, one of the main issues with the L298 is that it's bipolar; the sink and source saturation voltage of the output transistors totals 3.2v max @ 1A so on a 5v motor supply the steppers will be lucky to see 2v - you'll get no useful work out of them. You need at least 12 - 24v to be useful and then you need to limit the current using a sense resistor and chopper circuit (or use the L297 driver).

The other main issue is heatsinking. You get about 5v drop @ 2A on each bridge. For two windings that's 20W of heat generated in the chip to lose through a heatsink. Since the junction to case thermal resistance is 3℃/W you need a heatsink of better than 1.6℃/W to stop it frying. That's a fairly big heatsink, about 300mm square of 3mm alloy plate; I think the ones I used to use @ 1.4A were 120mm x 80mm with 20mm deep fins and they got pretty hot to touch, about 60℃.

Don't let this put you off Dan, I applaud your desire to experiment and try to achieve things with limited resources but you have a lot of learning to do before you're ready to spend money