How To : Determine polarity with a Voltmeter !

[Ypedal]

This comes up regularly, i get emails asking for help etc.. so i had to do this tonight and took a few pictures to illustrate.

Say you get a new charger, and the connector that comes with it does not match the one on your battery pack !

Ok, "no worries" you say to yourself.. you dig in your pile of parts and find the right connector you need to use.. or better yet, you switch to Anderson Powerpoles ! :wink:

Grab the wire cutters and cut the wire off the charger near the end.. slice the wire jacket and find non-standard colors !!!! or all black !!!! :x

For example, below we have Blue and Brown !

Since i'm using powepoles and they are unisex, i crimped a tip on each wire as i can pluck a red or black housing on either one.

Then set the meter to " DC V " . if you have a " - " and a " ~" symbol on your meter:

- = DC
~ = AC

Make sure each wire is seperate, very important that they do not touch, sparks will follow ! I assure you ! Sometimes followed by smoke(cheap chargers), sometimes not(better chargers)..

Don't worry about using the wrong probe on the wrong color.. just touch one voltmeter wire with one charger wire, the other with the other.. :

 

[Ypedal]

So above, Red on Brown and Blue on Black from the meter, tells me that :

BLUE charger wire is negative

BROWN charger wire is positive

If you flip the meter wires around you get a negative reading on the display !, and no harm done.

 

[Ypedal]

A few more things to point out.

There are alot of different meters out there, this one for example has the + and - wires permamently attached, 10$ at Radio Shack before they shut down ..

When you look at the DCV section of the dial, you have 500v, 200v, 20v and 2v. Always select the higher number on the meter.. For example, i'm testing a 36v Lithium charger, so i set the dial to 200v.

Edit : this comment --" If i set the meter to 20v and tested a higher voltage it would pop the fuse inside the battery compartment."-- is false.. see posts below.. so if you get this wrong the fuse will NOT blow !! .. ( keepin it honest, forums rule !)

 

[Ypedal]

Another thing to note.. Some chargers have removable wires..like the better/more expensive one's that you plan to own for a lifetime. Inevitabely you will screw up at some point and fry the probes in a spectacular heart wrenching fashion !!! so you can replace them as required ! ( Yeah.. i'm on my 3rd set )

The meter will be labeled + for the Red wire, but there are 2 spots for the negative wire to go.. one " - Com " and the other " 10A " . Use the " -Com " .

The 10A side is used when you want to measure " Amps " and it requires the meter wires to be inline with the circuit, that's another chapter better left to someone more qualified to explain properly..

But either wire can fit into either hole.. pay attention to this so you don't get a wrong color combination !

 

[dogman dan]

Good thread! I went through some stuff the hard way, even after getting a voltmeter. I did stupid stuff like putting the red wire from the voltmeter into the black wires socket, etc. Fortunatley mostly I just melted connectors to sla wiring and got it together better by the time I started fooling with expensive lithium.

Now I check polarity, put on connectors and check again. Many times I've still mixed up the colors. ( By now ya'all know I'm a doofus) nice thing about andersons is you can just switch the covers when you screw it up.

 

[monster]

If i set the meter to 20v and tested a higher voltage it would pop the fuse inside the battery compartment.

not true

 

[Ypedal]

Hmm... i will try that tonight.. i'm used to my auto-range DVM but i could have sworn my cheapy one blew a fuse last time i did that.. then again.. the display might go to overload or " --- " ... what does yours do ?

 

[tostino]

Hmm... i will try that tonight.. i'm used to my auto-range DVM but i could have sworn my cheapy one blew a fuse last time i did that.. then again.. the display might go to overload or " --- " ... what does yours do ?

Even my cheapy just displays "-e" when measuring a voltage higher than what it's set to. Only time i've popped a fuse, is going over the amp limit when trying to measure current.

 

[dnmun]

i think the voltmeter section of the DVM has high enuff impedance that it will take higher voltage. i suspect the little fuse is inline with the ammeter scale, and the 10A is unfused. jmho.

 

[Ypedal]

You guys are correct !.. i tried my 72v pack on the 20v setting and got " O.L " on the display ! flipped the dial to 200v and tried again.. 79.8v ! 8)

 

[spinningmagnets]

This thread should be stickied. Also in the same thread should be as much info as possible on positively identifying the pos/neg leads on controllers. I would gladly pay extra to have a pigtail with diodes on the controller leads so If I plug in the power wrong, nothing is hurt.

There are so many different controllers, and it seems the black/red wire thing is ignored by most of the Inscrutible Society of Chinese Engineers. Once the proper leads are ID'ed I can make up plugs that can only be plugged in correctly (I desperately need idiot-proofing where-ever its possible)

If the motor leads are "somehow" plugged in backwards, does it fry the hall-sensors?

 

[biohazardman]

I know many don't understand how to use the multi-meters. So your tutorial is a good thing. A couple weeks back I heard a tech I werq with talking to another on the Nextel near me so grabbed the phone to stop the sillyness I was hearing. I told the tech to check for continuity between a DC ground and an AC ground there should have been none. He told me there were zero ohms so everything was OK. ;^) Gotta love this stuff.

 

[Ypedal]

Split the off-topic to OTD :
http://www.endless-sphere.com/forums/viewtopic.php?f=26&t=11882

i have never, i repeat, never ever, seen a controller where the normal red for positive and black for negative rule was violated ....(edit cause of off-topic )

i only know of one person who said they actually had wired their controller up with reversed polarity.
.

I have a picture of a controller to add here.. have to dig thru " the box that smells like burning plastic "

 

[rkosiorek]

well maybe not black and red together. but...

i have 4X BMC 2A controllers that i got together with a few BMC motors the power wires were BLACK and a REDISH-BROWN. the BLACK was the positive and the brown was the negative. these were assembled in India.

also seen a couple of examples of Black for positive and Blue for ground (Sanyo/Rabbitool) and a couple with Brown for positive and Blue for ground from CT's Strong E-Bike. then again i have seen a a lot more using the regular RED/Black. Blue is commonly used as the neutral/ground wire in European/Asian household wiring. and here in North America RED and Black are BOTH "HOT" wires for 220V wiring.

the only place that red and black being positive and negative are sort of a standard is in the Automotive Industry and small portable devices. most others also follow it but it is no guaranty.

a common practice in many industrial apps is the wire color defines the voltage. for example looking into the back of a process controll panel you will often see a legend that will tell you that all 12V wiring is YELLOW, 5V wiring is RED, 110AC will be BLACK etc.

so i really hate to say it but even though RED is usually positive and Black is usually gnd, i would never accept it as an article of faith. i have smelt the magic smoke and released the powerful genies too often by taking things for granted. when in doubt RTFM!!. if still in doubt open it up and check which wire the (-) end of all of the big capacitors is attached too. that is usually a good clue.

rick

PS. just think of another "STANDARD" everyone knows that rule is ALWAYS "Righty-Tighty, Lefty- Loosey" to tighten and loosen nuts and bolts, that is unless you have a left hand thread.

 

[rkosiorek]

Gaston,

you being the owner of this thread.. you think it may be worth while for you to move it to the "Technical Reference" Forum. in future it could be a lot easier to find it there.

rick.

 

[Ypedal]

Yes, i plan to copy it there and trim the fat a bit.. since not everyone can reply in the tech section i figured i'd proof post it here 1st.. if anyone wants to add usefull stuff . please go ahead !! :wink:

 

[spinningmagnets]

Thanks rkosiorek, I didn't want to reply and sound uppity or mouthy (I'm nowhere near as experienced as others here), but some controllers/motors have been "repaired" with whatever wire scraps were nearby on the warrantee shop floor.

Also, When there is a very competitive business environment (China/India) and they run out of red wire a half-day before the next shipment arrives, I imagine there will be a few new units made with whatever wire is handy and then hopefully labelled correctly in engrish.

 

[John in CR]

2 pages of thread for determining polarity using a voltmeter! unbelievable!

John

 

[TPA]

John

I just want to kindly point out that you are sounding a bit uptight the last week or so.

I hope everything is ok your way! Seems a shame not to be relaxed when you live in paradise!

 

[liveforphysics]

2 pages of thread for determining polarity using a voltmeter! unbelievable!

John

I have to agree with you John. This does seem like hitting the bottom of the barrel, and scratching down through it.

 

[John in CR]

John

I just want to kindly point out that you are sounding a bit uptight the last week or so.

I hope everything is ok your way! Seems a shame not to be relaxed when you live in paradise!

TPA,
I probably haven't been biting my tongue as much as usual. I'm relaxing in paradise like always, and thanks to my ebikes the one remaining item that occasionally caused me stress, traffic, is all but eliminated. Thanks for the concern though, but I'm the last person in the world to worry about. I may not be rich in terms of money, but life is otherwise near perfect.
John