Biax Speed Controller

[JohnAU]

I’m in Australia on 240v (50Hz) and I have a 110v Biax Scraper with no speed control. I currently run a 240v to 110v transformer and I run a inline 120v speed controller between the Biax and transformer that I purchased off Amazon

https://www.amazon.com/gp/product/B07PYGCHXY/ref=ppx_yo_dt_b_asin_title_o00_s00?ie=UTF8&psc=1

This setup works however, at the slowest speed on the controller, the Biax still runs a bit fast. Does anyone have suggestions on how I can slow it down further?

 

[Richard King]

try one of these https://www.amazon.com/dp/B07Y2MRQ79/ref=emc_b_5_i

 

[JohnAU]

try one of these https://www.amazon.com/dp/B07Y2MRQ79/ref=emc_b_5_i

Thanks Richard, I’ll try and find one that will ship to Australia

 

[M.B. Naegle]

That's what I use with my old blue Biax. It's one more clunky piece to tote around, but it does the job. Most of the time I use it at 30%, 60%, or 100% voltage.

 

[nt1953]

I had been intending to post about my experience with a green (7ELM) Biax scraper with a failed speed control, so I guess I will go ahead now.

My Biax speed control failed and not being an electrical engineer, I could not figure out how the board worked or what some of the components were, so I looked for another option.

eBay has several vendors selling angle grinder speed controls like eBay number 385632706067. They are cheap.

I bought several of these and tested them by hooking them inline with a cheap Harbor Freight drill that had about the same power requirements as the Biax. It was not perfect, but it worked.

I stripped off all the components, cut out a hobby board matching the configuration of the original Biax board, mounted all the components on the new board and used tinned AWG 23 wire to wire everything. I also potted everything so that I could prevent possible shorts.

Before you can wire the new board into the Biax, you have to note that the original Biax control board is three wire and the new board is 2 wire. What that means is that you need to trace out the wiring on the Biax and do a very minor bit of rewiring so that you can hook the board in series with the Biax. You may want to test your new rewired board on something you don't care about before putting it in the Biax (like a cheap Harbor Freight drill).

I have installed the new board and it works fine so far.

 

[Bakafish]

Thanks Richard, I’ll try and find one that will ship to Australia

If you are going to use a Variac then you don't need the step down transformer you are using as it will essentially do the same thing, just make sure you don't set it to more voltage than it can handle. A native AU Variac will likely go from 0-250v. Lowering the voltage of a 'universal motor' affects its efficiency, so heat, loss of power and excessive current draw are all factors you should plan for. The amperage rating of the Biax is at the voltage specified (120v in your case I believe) but it may well draw more if you are feeding it lower voltages, so you should measure it with an amp meter to make sure you are not exceeding the current capacity of your Variac.

As far as the semi-conductor based (Triac) speed controllers, they are far more efficient but (especially with cheap aftermarket units) create a noisy waveform which makes these motors sound like they are chewing a box of rocks when slowed down. In either solution this type of motor will hit a wall at a certain speed where the torque generated can't overcome the internal friction and it will stall. Stalling these motors is bad. I suspect that you will not get lower speeds with the Variac, although it may be quieter at those speeds.

The hard truth is that you probably need to practice with the machine and learn how to use it at higher speeds than you may be initially comfortable with. These motors don't like to be choked down a lot, you are throwing away most of their power which is required for a clean scrape. Short of reengineering the motor side (something you may face if you fry the motor running it too slowly) there's not a lot that can be done.

 

[Richard King]

Thanks for the info nt1953 and Myles, Ed Dyjak who repairs BIAX scrapers told me he pry's off the rotating cover of the green scraper and uses a ladies emery board to clean the rheostat contacts. one of our members Peter in the UK installed a variable speed switch inside the case of his old blue model. hopefully he will tell us how.

 

[nt1953]

Most of the components on the controller board that I bought were the same as those on a Bosch board that is also being sold by many on eBay (I bought several of each board). The amperage on the Triac was different, but otherwise the boards were almost identical.
If the motor stalls with either a Variac or a Triac based board, just turn it up until it is operating like you want it to.

 

[JohnAU]

Just an update on this. Inside the cheap Amazon speed controller, the circuit board had a small pot on board. I was able to adjust that slightly which enabled the main control to slow the biax down to a useable speed.

 

[Bakafish]

My advisories are still worth paying attention to. Pay close attention to the heat and give it time to cool down as often as you can. Not only is the motor less efficient when run at lower speeds creating more heat, but the cooling fan is also running slower and aerodynamically designed for a higher operating speed.