Bench testing Dynamo

[Drew Back]

Would I be able to test a dynamo with a drill and voltmeter on the bench? connect the 2 leads together with one lead of multimeter and the other lead to the dynamo case?Which direction would I run the drill?
The reason I ask this is I dont want to go through the trouble of mounting it on bike and it does not work>>I already have one bad one mounted dont want to do that again..Or could they test it at the auto store?

[duTch]

 Yep, spin it in the direction of the arrow, that's the direction it spins on the bike. ...meter red(+ve) to D+F, and meter black(-ve) to body... fairly sure that's right, sounds too easy, Hey?

[beezermacc]

That will work. Not trying to tread on toes of previous post or cause confusion but be aware of the following.... some dynamos have been moved from one bike to another and some have been built from parts so, whichever way the arrow points, you need to spin the drive anticlockwise because that's the direction it spins on the bike. Multimeters can be very confusing and you need to be sure the output (+ or neg earth) from the dynamo matches the battery and regulator wiring. Most A10's from about 1951 were +ve earth. I would do the test as you describe and see whether you have a charge (+ve or -ve doesn't matter). It would help if you know how fast your drill is turning. 1000 r.p.m. should give you about 6v output from an E3L dynamo. If you get a decent charge you can then 'flash' the dynamo to make sure it is charging the correct way. Do this by connecting the +ve side of a 6v battery to the dynamo body and tickling the 'F' terminal with a lead from the negative side of the battery. You will see a few faint sparks as the field coil connects. Once you've done that you know your dynamo is delivering in the right direction.

[wilko]

Just put a charge across the bridged terminals and that will show you which way it spins. Some drills won't spin fast enough to get decent voltage as I found out the hard way. Scratching my head all day why I was only getting a few volts until I tried another drill.

[KiwiGF]

I tested mine before fitting it, if you want to be really certain it works then connect up the battery and regulator and headlight bulb as well, get the battery powering the bulb and then spin the Dynamo with a drill. You should be able to see the voltage rise on the battery to circa 7 volts, or 13.5 volts for 12 volt systems.

You can also check charging current as well. I was surprised by how much the battery discharges through the Dynamo at low revs when doing this sort of testing with a mechanical regulator, and bought a Dvr2 as a result.

It's a lot easier fault finding this way than having to run the engine etc, once it's on the bike.

[Drew Back]

I got it all clean and it is putting out about 4 volts with a drill spinning at 800 rpm max so I think it should do great at 2000rpms on the bike..Now I have to swap the bad one and see whats going on with it..

[beezermacc]

That sounds OK. Dynamo speed on an A10 is about 110% of engine speed. You need over 7v to charge the battery due to 'dropout' current absorbed by the regulator, so you should achieve a charge by about 1400 r.p.m.

[Dynamo Regulators Mike]

Yes, you need just over 7V at the battery terminals to fully charge it. That is dictated by chemistry, not any aspect of electronics. The voltage drop, or lost volts between the D output and the battery depends on the type of regulator. Not all regulators are the same 

I had a customer this week who returned a DVR2 which was not giving a charge on his bike. The Lucas dynamo passed the usual motoring test and with D& F connected lit up a bulb fine. It turned out, after a fair amount of time wasted, that the internal wiring to the D & F terminals on the dynamo were reversed. Live brush to F, and Field coil to D. Another thing to check if not seeing a charge on a dynamo you have never seen working correctly on a bike.

[duTch]

That will work. Not trying to tread on toes of previous post or cause confusion but be aware of the following...

 No offense taken Beezermacc, I have steel-toed thongs (flip-flaps) and thick feathers, and did that in a short bit of downtime- had a bigger week than usual, but just wanted to get Drewbacca encouraged...and I figured that there'd be variables, and whatever I get out of whack will maybe end up as some kind of a learning curve
                       

[nimrod650]

if you wire dynamo direct to battery and it runs like a motor does this mean its ok

[beezermacc]

if you wire dynamo direct to battery and it runs like a motor does this mean its ok

..... not necessarily, unfortunately. What you are describing is the motor test. i.e. bridge the D  and F terminals then connect a battery to the bridge and the other battery post to the dynamo body. In this configuration the dynamo should spin like a motor. If the dynamo spins really quickly you've a good chance it is OK but this is still only a crude test. The ultimate test is to spin the dynamo at various speeds and test the output voltage against the manufacturer's spec or against familiar information based on experience.

[trevinoz]

If you can get it to spin at 2 to 4 volts it is likely to be good.
However, beezermacc is giving you good advice.

[andy]

Just bench tested my dynamo with the electric drill attached on maximum revs(about 500 rpm I think) and meter was reading 9.50 with readings up to 10.03 so I think it's good enough for 12v. Interesting point is that at first it was reading 3.7 but the longer I ran it the more it crept up so I was thinking if it's going to be a while before it's used is it a good idea to spin it up on a regular basis to stop it from deteriorating????