How Do You ID a Johnson Motor?

[Stu :)]

Today in my Mother's kitchen I spied an old Remmington mini-vac in the trash, Mum said it only worked for about 20 seconds after charging and was useless. Far as I was concerned 'There's a motor in that'. So I've taken it home pulled it apart, discovered the NiCad pack was leaking all of it's life-juice and found a nice 540 looking and WORKING motor. There was no obvious ID sticker like on the Mabuchi motors, the only details on the Johnson sticker are:
63280 on the top line and 361924 on the bottom. Tried using Google but it was only returning gobbley-gook regarding Johnson outboard dealer phone numbers and such like.
So I checked the Johnson website (http://johnson.manowar.e-pro.de/index.php?brandID=49&plugin=search_results&search=PMDC), measured up my motor and found listings for three motors that are used in hand-held vacuums.
http://johnson.manowar.e-pro.de/index.php?IdTreeGroup=49&IdProduct=464
http://johnson.manowar.e-pro.de/index.php?IdTreeGroup=49&IdProduct=466
http://johnson.manowar.e-pro.de/index.php?IdTreeGroup=49&IdProduct=468

Now I'm lost, how do I work out if it is the 9.6V, 4.8V or the 7.2V?

Many thanks,

Stu :)

[patmat2350]

Chuck the shaft in a drill press, or even a hand held drill if you know its approximate speed.
While running the motor, measure the voltage at the terminals- it's a generator!

Now divide rpm by measured volts... this is the "Kv" value, rpm per volt.

Multiply this characteric value by any applied voltage to get the expected no load running speed. See if that no load speed comes close to any of the specs listed.

Vac applications tend to pull a lot of amps iirc, which means these motors may be pretty "hot" for a scale application, unless run on lower voltages than rated.

Pat M

[patmat2350]

Actually, these might not be so "hot". Looking at the 9.6v spec, it only pulls about 7 amps when loaded down to 75% of no load speed- which is about as far as you want to go in a non-cooled scale application.

Pat


oops... the 7.2v unit pulls 25A at 75% ! hot hot hot...

[rlboats2003]

Cut open the pack covering and count the cells. Use plastic gloves and an a sharp knife. If you identify the cell size through the pack covering you could almost guess how many cells. What was the charger output volatge for the unit? If it is 6volts output the motor is either 6 or 4.8 volts.

Just some thoughts,
Rich

[der kapitan]

I totally agree with Rich, why haul out the calculator and electrical handbooks? ;)

You can check how much voltage ran it by looking at the battery packs and/or charger. :p

This isn't exactly rocket science, y'know---. :D

[Stu :)]

...Oh yeah I forgot to mention the battery pack was puny a 2.4v 1300mAh (two C cells stuck together). So at first I thought it was the 4.8v version.

Stu :)

[rlboats2003]

Well if there wasn't a large gear on the out put of the motor and a small one on the input of the sucker fan and it picked up dirt I would have to beleive that you have a unit that you could pump 6 -7.2 volts into and have a max of 7,800 -8,500 rpms. Now the important thing is does it have 3 poles or 5 poles? 5 will draw a little more current but give you greater torque. If you have a 5 pole there is a good posibility it is the same motor that Phil sell on the vac-u-boat web site. Take a look at his johnson motor information. What diameter is the output shaft 2.4mm (.125) Can't remember what you measure in down there. What type of boat were you planning to put it in. Rule of thumb if direct drive the Prop should be no greater than the diameter of the motor. The is true as long as you don't go crazy on the pitch.


By the way, My wife was on company business down your way about 9 years ago. Just loves the NZ country side, loved the harbors full of sailboats. Based of their love of Sail, I can't think of any country that deserves to hold the America's Cup more, other than the US. I hear they just settled on the AC boat design for the next challange.

Have Fun,
Rich

[Stu :)]

No gears, directly connected to the fan-disc that creates the vacuum.
3 Poles, sings along quite happily on a 6v SLA. The shaft would fit inside a 3.2mm bore coupling insert, if it wasn't for the three very small fins on the shaft, obviously there for grip.

Thanks, in my neck of the woods sailing is part of the school curriculum and a few of the 'Cup sailors come from the suburbs around here. Besides, at least it was a team of Kiwi's that won the Auld Mug, using Swiss money ;)

Stu :)
P.S. Still reckon they should have had the regatta on Lake Geneva.