BF20LV problem

I have a lightly used BF20LV about 5 years old. Today whilst milling some aluminium, the motor stopped,( it had been running for about 5 minutes) the speed control read zero, turning the speed knob made no difference to the readout, the motor stayed stopped. Powered it off for a couple of minutes, turned it back on, and everything worked as normal for a couple of minutes when the same thing happened. Can repeat this cycle.

Any ideas as to probable issue, or fault finding procedure?
TIA
Gary
Geelong Australia

Welcome to Gary and bump - this question seems to have dropped off the front page without getting a response.

I suggest having a look at the speed control pot.

• Check the wires from the pot are firmly connected. They're probably soldered at the pot but plugged into the board at the other end and one may have come loose.
• Being mechanical and on the inexpensive side, the pots are prone to wear out. Turning the knob moves a wiper over a track, thus altering the output voltage. Put a multimeter from either side of the pot to the centre connector and check the voltage goes up and down when the knob is turned.

Just a guess. I hope by posting to attract one of the forum's motor/control experts.

Dave

The drill mill at the museum started doing that a few years ago, it has a 1 1/2hp single phase motor. There was a thermal cutout on the motor which was failing. Since replacing it there has been no more trouble. I'm sure somebody can point you in the right direction for getting one of these, I can't remember the details.

A very common issue with these motors is the brush tails go high resistance and then the springs have to carry all the motor current this can cause stopping and starting at random.

Another problem is soldered joints carrying high currents go bad, particularly with the advent of lead free solder. Three to five years is about the right time frame.

Hi gary,

Some time ago I had a problem similar to yours and the cause could be the same.
Using the browser, please, search for the following, full, string:
site: https: //www.model-engineer.co.uk/ dcosta bf20
Perhaps you will find useful information ...

best regards
Dias Costa

Edited By dcosta on 11/04/2020 16:25:24

Hi all,

Thank you so much for the suggestions. I will firstly see if I can get a replacement pot. If that doesn't fix it, I will pull the boards and check the solder joints. My shed is prone to a bit of condensation, so perhaps some joints have gone bad.....didn't know about lead free solder issues. Ill check all the things you all have suggested progressively. The mill was getting a bit of use for the first time in quite a while due to boredom from being in virus lockdown. 😏

Cheers

Gary

Geelong, Australia

Hi Gary,

Condensation is bad for electronics, if you pull the boards check carefully for corrosion or tracking (power flowing between tracks.)

As the mill fires up and works briefly, I suspect an intermittent fault. These can be caused by contacts moving as the board warms up, or by motor vibration. Poor contacts are likely if condensation has got into the works but it can often be fixed simply by working switches and pots to and fro, ideally with a squirt of switch cleaner. At the board, wires are more likely to be plugged and socketed or screw-terminaled than soldered. It's worth making sure these are correctly seated. Also, try unplugging and reconnecting to wipe clean the pins. If these are visibly corroded, clean what you can off first but don't be too aggressive (pins are often plated).

Bad solder joints often look grey and crystalline rather than shiny silver. These can often be fixed by remelting the solder with a dab of fresh. If that doesn't work, remove the solder with a sucker and clean the metal underneath : corrosion or dirt will stop the joint forming properly.

I used to enjoy diagnosing faulty electronics. Now I'm older I lack the patience! If the fault isn't obvious I've decided there's no shame in replacing the whole board. Shameful but true.

Good luck,

Dave