unexpected negative voltage from JFETs

On Friday, 4 December 2020 at 03:30:53 UTC-8, Jasen Betts wrote: ...

You also needed to hold down the cut-out for a few seconds to polarize the field of the generator so the remanent magnetism matched the new battery polarity. ..

kw

On Thursday, 3 December 2020 at 12:20:50 UTC-8, John Larkin wrote: ...

That's what hybrids like the Prius or ones based on the same approach do.

However they can normally only use the battery for power when in reverse - any engine torque generated is still in the forward direction.

kw

There are two permanent-magnet electrical motor/generators in the Toyota (and Lexus) hybrid drive. They are connected with the engine and drive train with a planetary drive functioning as a differential.

The effective gear ratios between the engine and the road are made moving the electricity between the two electric machines and the battery in a way the control electronics thinks best. The gearing ratio range extends also to reverse, so both forward and reverse can be driven by electricity only or combined engine and electricity. The battery power is used when deemed suitable.

Slight braking is made by the electric drive, feeding the extra energy into the battery. The disk brakes are used only to augment the electrical braking.

A friend once wondered if an old Saab had positive ground. But no, some true genius had charged and connected the battery wrong way.

But more on topic, I once saw old 7400 chips which had negative voltages on their inputs if they were floating. Those chips were old, old fashioned and from probably Soviet Union, so it is of no wonder. I thought the chips were oscillating.

On Saturday, 5 December 2020 at 01:10:53 UTC-8, Tauno Voipio wrote: ...

..

I'm not sure what point you are making.

In reverse the torque from MG2 can propel the car backwards -- however any torque from the engine will be in the opposite direction attempting to make the car go forward thus reducing the combined tractive effort.

In my Prius (gen4) reverse usually seems to be accompanied by the engine st opping, so MG2 with just battery power is doing the propulsion - so no torq ue from the engine/PSD.

If the battery had too low an SOC to provide the required power to MG2 the engine could be started so MG1 could generate power to feed MG2. In that ca se however the balancing torque through the PSD would tend to drive the car forwards - the available traction force would be less than if the engine w as not running (of course there is potentially more torque available from M G2 because of the power generated by MG1).

When the engine is running I haven't noticed whether it is accompanied by using a high-rpm low torque operation to minimize the reverse torque.

kw

Prius and Tesla M3 owner.