look at my reply #8
and
Which scale did you use on your DMM? 10A or the mA one?
If you broke the load connection to insert the DMM, the driver output would have swung high and you would have offloaded all that energy into the LD.
Assuming you cut power before you inserted the DMM using the mA scale, you just inserted a couple of ohms of resistance in series with your load - what happens then? If your battery overhead is great enough the driver will stay in regulation, if not, it will drop out and the current will fall. The 10A scale will have the least (notice I did not say zero) effect on the circuit.
You mentioned that you pur the DMM (while on current mode) across (parallel to) the LD. If you were in 10A scale, you just shorted out the LD.
As you can see, there were lots of times the train could have left the tracks. Don't get too torqued over this - anyone who has experimented with electronics has "released the magic smoke". These are invaluable learning events.
and
Which scale did you use on your DMM? 10A or the mA one?
If you broke the load connection to insert the DMM, the driver output would have swung high and you would have offloaded all that energy into the LD.
Assuming you cut power before you inserted the DMM using the mA scale, you just inserted a couple of ohms of resistance in series with your load - what happens then? If your battery overhead is great enough the driver will stay in regulation, if not, it will drop out and the current will fall. The 10A scale will have the least (notice I did not say zero) effect on the circuit.
You mentioned that you pur the DMM (while on current mode) across (parallel to) the LD. If you were in 10A scale, you just shorted out the LD.
As you can see, there were lots of times the train could have left the tracks. Don't get too torqued over this - anyone who has experimented with electronics has "released the magic smoke". These are invaluable learning events.