Why my multimeter and charger reading on generator are not functioning? DC Motor reverse polarity part 2: Residual or Remnant Magnetism

with reversed polarity the voltage will not increase because the remnant magnetism in the field core is opposite to that required at start-up. The voltage regulator relay will never close to strengthen the field. All else being equal, a momentary closure of the output relay will reverse the remanant magnetism in the generator field.

 https://www.quora.com/What-are-the-two-ways-by-which-the-polarity-of-the-output-voltage-of-a-separately-excited-DC-generator-can-be-changed

Fascinating! So will this destroy the new DC-DC Buck converter? I am getting charge... I think.

I better go switch the direction of the motor around....

OK I just flipped the DC motor around - but one of my screws is stripped. So I have a board at an angle - and hopefully the V-belt is tight enough to try get a volt reading now.

OK so I tore out the multimeter connection that I had wired in with my charging wire connection to the generator. So then I tested the multimeter with a new AAA battery - sure enough I got 1590 millivolts!

So I now the multimeter is working. So I cut longer wire for a better connection from the DC motor. So then I hand spun the motor and I got a couple volts. So now I AM getting a volt reading!! So then I tried on the bicycle and I didn't even get up to 4 volts!! Terrible! Why? Because the belt is slipping.

So now I need to tighten up the belt - but switching the motor direction did fix the reverse polarity problem.

I just need to cut up some lumber for a better connection - and maybe get more screws. I keep stripping out the screws - cheap metal.

The readings become erroneous once the battery is low on the multimeter

I thought it had a low battery indicator? Maybe they mean it will indict if batteries are low...

So I was getting amp charge reading (with the wires switched) but I couldn't get any volt reading. Then I noticed the charge percentage on the generator wasn't working right. So I looked it up - and turns out that the permanent magnet has a remnant polarity - so just switching the wires will not allow the voltage circuit to close off. So then I did physically remove and switch around the DC Motor. So now I am getting a voltage reading! The V-belt is too loose though - I have to reconfigure the whole mounting bracket set up. At least I'm "going in the right direction" now! haha. So I figured I better fix that since I ordered a higher power DC-DC buck converter.

DC Voltage Regulator, DROK DC-DC Buck Converter Module 10V-75V to 0-60V 12A Adjustable Power Supply Step Down Transformer Board -

it has a voltage display on it. So I can now pedal up to 75 volts (I think it can go a bit higher) - and maybe get 6 amps charging hopefully.

Yes was I definitely getting charge with the reverse polarity - but the Charge percentage reading was not working! Only when I turned off the generator and then later turned it on  did the increase in charge then register.

Residual magnetism is utilized in case of DC generators. In a DC generator, the initial emf is developed due to residual magnetism of field poles. As the generator voltage feeds the field winding also, field gets gradually strengthened till the generator full voltage is developed.

 https://www.quora.com/What-is-residual-magnetism-and-how-does-it-help-to-build-up-output-current-in-an-alternator

 It is the generator effect within the motor that produces the back emf, that limits the current flow into the motor, so if the magnetic field is somehow kept alive through remnant magnetism, permanent magnetism or separately excitation methods, then one cannot have a rotating unit that can act as a motor without acting as a generator at the same time.

https://www.quora.com/Can-a-DC-motor-be-converted-into-a-DC-generator

In fact, in a brushed permanent magnet motor, no conversion needs to be done. Just spin the shaft and it generates DC voltage/current.

 Now start your prime mover and with leftover residual magnetism in the pole cores, the generator will have sufficient field strength to develop voltage almost immediately.

.for a same dc gen converted in dc motor the direction of rotation of motor will be same if u give dc supply or connect the + terminal of dc supply to that brush which was initially + that is current was flowing out of that brush into load in case of dc gen and in case of motor if u connect the external dc supply = to that brush only from which current was coming out

Oh - I forgot to REVERSE the WIRES back - in connecting to the DC-DC Buck Converter!! Oops. Hilarious.

However, you need to be aware that the DC voltage that the motor will produce, if you spin the rotor externally, will likely be very dirty and spiky, and you will need capacitors to smooth it out into usable DC. Spinning in one direction will produce positive DC voltage, and the other direction will produce negative voltage, assuming you stay consistent with which wire you label as neutral.

However,because of the constant switching action of the commutator, the current produced is constantly interrupted, although all in one direction. Also, the carbon brushes bridge between the commutator segments; good for a motor as it stops sparking but wasting power from a generator. Not good. It's much better to generate AC, using an alternator (which has no commutator) and then rectify if you want DC output. I hope it helps.

In case of generator the shaft is rotated by some external force due to presence of residual magnetism in the field winding the electrical power we received from the brush rings..

  An alternator uses mechanical energy to spin the rotor, to electrically excite the windings.

  But make sure about field current direction. If you make a connection that makes field current flow in reverse direction to that during generating mode, motor tends to reach dangerously high speeds and may damage.