Hi, I’m replacing a switch in an ac electric chainsaw and seek help. Is there a way to know which brush should ultimately receive the hot wire through the switch?
Thanks

 

Normally we switch the Hot side of the AC mains. In the US this is normally the Black wire and AC neutral the white wire. 120 VAC A picture of what you have and where you are would help.

Ron

 

Did you already disconnect all of the wires? If yes, then there may be a problem. There are several wrong ways to wire a motor..
Does the motor have a field coil, or or does it have a permanent magnet field?

If there is a wire directly from the switch to one brush, then that is the one. How many terminals did the old switch have?

 

Usually the standard for mains fed hand tools is the Universal motor.
It will work either way, but as already mentioned, the switch should be in the live conductor.
The connections should already be obvious if replacing an already existing switch?

 

Here's the general schematic of a universal motor.



Nandu.

 

Thank you all, I’m in the US. I should flesh this out more- Poulan AC 2.5 horse motor
Single speed trigger switch was becoming less and less willing to turn on consistently. I was given, what appears to be, a pretty good used replacement (however amps rating is 12 vs original 16.)
So I took apart the saw and the switch. Carbon build up, mostly on one side of switch, appears the cause.
So I put in the new switch, reconnected to my best recollection and notes. Feeling a little concerned, I opened a friend’s poulan which is similar but a 3 horse. I saw that the hot and neutral wires coming from the plug end were opposite what I had done. So I swapped mine in the new switch, plugged it in, pulled the trigger and heard a small pop and blew my breaker at the panel.
Next, I consulted a friend and we considered to our best ability, swapped the plug end wires at the switch and plugged it in, pulled the trigger and heard a bigger pop probably from the motor. ( didn’t blow his breaker.)
So I wanted to wire the motor directly with 110 to see if it still works.
There are two black wires coming off the motor and each goes to a brush.
So that’s where my original inquiry came in; how to know which black wire would get the hot wire from the 110. Is there a better way to see if the motor still works? If it does, I have doubts about the switch now and may try to clean and reassemble-looks challenging.
Thanks Very much for any consideration
Good day

 

If both incoming AC conductors went to the Commutator it is no wonder it blew, see the diagram by @vu2nan both fields and the armature all have to be in series. (In whatever order)
Per the diagram, the incoming AC lines can be reversed and it should still work, just that it is normal to switch the live conductor.

 

This looks like a series wound (Universal.) motor. On this type of motor each brush connects to one end of one of the field coils. The other end of that field coil is one leg of the supply. When the breaker tripped I think you must have connected neutral and hot to the connections to one pole of the switch so that when the switch closed it shorted out the supply. The picture would be more helpful if all the sawdust was blown off with an airline.
Test the switch with a meter to identify the connections of the two poles of the switch. (I am assuming it is a two pole switch which will have four connections.)

Les.

 

Some are connected as per @vu2nan diagram, other method is both field in series together then fed in series with the Commutator with one lead to the com and the other to the first field connection.
So doesn't matter as long as all in series, However the polarity of the fields have to be correct.

 

Thanks; Okay this is all helping.
The new switch seems different.
When new switch is pushed in (on)—
There is continuity inthe top section, and separately, in the bottom section.
When it’s let out (off)— continuity remains in the top but not in the bottom.
I assume I will insert the black/hot wire from the plug into the bottom section and white in the upper section. Does anyone think it’s important which side of the switch I plug the hot into? Any clues from the picture? Then I imagine I would insert the white neutral into slot straight up from the hot.
The old switch was such that the plug wires were both on the bottom. So it makes sense from what you are saying that in applying the old wire pattern to the new switch I blew the breaker

 

The first thing I would do is a thorough clean of the motor and get rid of all the sawdust so you can see what goes where. the original connections should be fairly clear as long as nothing has been disturbed that much.
You only use both supply conductors on the switch if it double pole, otherwise it should just switch ONE conductor,=

 

Cleaned what I could - looks okay
Both sides look identical so I am guessing polarity may not matter for moter side????
I am wondering now if this new switch is appropriate, as the old switch broke continuity on both the hot and neutral sides???? Old switch pictured
Showing hot and neutral and motor

 

Its apparently a double pole switch, operates on both L & N.
Two in, two out.
If using a single pole, one conductor (N) would go direct to the motor, the other through the switch.

 

Thank you
so I guessing the replacement is single pole and may not be a good swap???

 

SP is often used with no problem, as long as you switch the Live conductor, DP is more often seen on 240v appliances where it is necessary to switch both L1 & L2.

 

Thanks , I hope so but Could the amperage of the 2.5 horse motor require it?

 

The switch must carry the same current whether SP or DP. the 2.5hp is not really a deciding factor.
e.g. T.M.'s are 2hp to 3.5hp and generally are switched with a SP sw etc.

 

Just as a side note. As long as you have the motor taken down this far, having looked at the images, you may want to clean the commutator. Depending on brush wear you may also want to replace the brushes. Not saying this is a must but wouldn't hurt and this way it's done.

Ron

 

Thank you both
600 emery paper to clean it?
And back to thread #10, any thoughts on where I plug the hot wire from the plug end into the switch ( bottom right or bottom left?)
And Is it pretty safe to assume the motor wires are okay hooked up either way?

 

Just check continuity when the switch is operated.