AC to charge Nicads? wtf?

[joecool85]

Like I said, get a scope on it, you're wasting your time with a meter - particularly a digital one!.

Alright. First, what is a scope? Do you mean an oscilloscope? And second, why is it a waste using a DMM? In virtually everything else I've done with electronics the DMM is the tool everyone recommends using.

 

[bananasiong]

Nothing is bad for trying to use oscilloscope. Since you can't find the solution, just do what ever you can.

 

[Nigel Goodwin]

Alright. First, what is a scope? Do you mean an oscilloscope? And second, why is it a waste using a DMM? In virtually everything else I've done with electronics the DMM is the tool everyone recommends using.

Yes, a scope is short for oscilloscope.

A DMM has many limitations which preclude it's use for certain things - and measuring a high ripple DC voltage is certainly one of them!. A scope will let you see exactly what's happening.

 

[Hero999]

Does your drill have a charging stand?

Perhaps the rectifier is in the stand and it's knacked so you're getting AC on the battery which will bugger it up for sure!

 

[joecool85]

No charging stand, all there is is this:

The drill (built in battery pack)
Charger (this is just a power supply that plugs into the wall)

Thats it.

 

[fingaz]

Ok, to check if the power supply has a rectifier built in all you have to do is. . . with the unit unplugged, check for continuity on the secondary winding of the transformer, now swap the test probes of your DMM round and see if you still get continuity.

If you only get a circuit one way, and open circuit the other, then your power supply is rectified. (and likely not filtered, which would explain why it's confusing your multimeter)

If you get continuity both ways, then your power supply is either a)NOT rectified or b)the rectifier is shorted

 

[Nigel Goodwin]

Ok, to check if the power supply has a rectifier built in all you have to do is. . . with the unit unplugged, check for continuity on the secondary winding of the transformer, now swap the test probes of your DMM round and see if you still get continuity.

If you only get a circuit one way, and open circuit the other, then your power supply is rectified. (and likely not filtered, which would explain why it's confusing your multimeter)

If you get continuity both ways, then your power supply is either a)NOT rectified or b)the rectifier is shorted

We don't want any incredibly simple, amazingly effective, suggestions here!

 

[fingaz]

Sorry, I tried to word it to sound as complicated as possible. . . I even used more than 30 words!

 

[Sceadwian]

A meter in diode test mode will quickly find out where the diode is in the drill.
By the way, even if you have to throw this thing out, the motors are quite useful =) Cheapest way I know to get good mid power DC motors without paying the 500% markup the R/C hobby imparts. They're so cheap just gutting it for the battery pack and the motor recoup it's cost.

 

[joecool85]

Well, there was definetly no rectification in the power supply. I took it apart, all it had in there was a small transformer, thats it. I took the drill all apart too, when I disconnected the wires from the drill's switching mechanism, the output went from the changing 6.6v DC/8.2v AC to a straight 15.1v AC. So the diode/resistors must be in the switch. This is retarded because that means that there was AC getting to the battery.

It was wired like this:

................Switch -> motor
15.1v AC -{
................Battery

Regardless I found a 9v DC 150ma power supply I had sitting around, put on the appropriate plug and just charged my drill overnight, did the job perfect. It held the cells at 8.64v all night. This is perfect because you need a minimum of 1.41v per cell @ 20C (8.46v for a 6 cell) to charge a nicad (max is something like 1.6v or 9.6v for 6 cell). And when disconnected from the battery it didn't have any of this crazy AC/DC going on. Just straight up DC.

 

[john1]

Maybe you have the wrong supply block.
Some of them are an AC output.
Maybe it just looks like the one for the drill,
and has the right plug on it.

John

 

[mneary]

I have a similar unit (a power screwdriver). One of the "wires" is a diode in shrink tubing.

 

[joecool85]

Maybe you have the wrong supply block.
Some of them are an AC output.
Maybe it just looks like the one for the drill,
and has the right plug on it.

John

Nope, it's definetly the supply that came with the drill, it stays in the drill case at all times.

Regardless I got it figured out with a proper power supply have have charged the drill 2-3 times so far using the new one and it works awesome.

 

[Ambient]

I have seen the same thing as mneary with some equipment I have had. I guess it saves the manufacturer wire and solves the problem of mounting the diode somewhere. I would put money on it that that is where the diode is hiding.