how to wire the "soft start" of a Bosch GWS8-125 angle grinder

[larrywalker]

Hi all,
Does anyone know how to wire the "soft start" of a Bosch GWS8-125 angle grinder.
There are 3 connectors : blue wire, white wire and a plug-in connector near the blue wire (see pictures).


Thank you in advance.
B.R.
Larry.

 

[marconi]

View: https://www.youtube.com/watch?v=973M_Tsy_Pk


Take a look at this youtube clip at 4mins 27secs onwards and you can make out where the wires of the soft start controller attach to inside the grinder.

 

[larrywalker]

Take a look at this youtube clip at 4mins 27secs onwards and you can make out where the wires of the soft start controller attach to inside the grinder.

Thank you Marconi. After watching (several times) the clip, I think that:
the scheme is like this:

Anyways, I go for it as soon as I have the time.
If it works, we win.
If it blows, I'll post a warning for everyone not to try this scheme.

 

[marconi]

Please don't try it before I have another look to check your diagram. Can you not see in the Youtube clip how the blue, white and black have been connected? I had to pause and inch through the filming to follow the wires.
[automerge]1587908093[/automerge]
The best view is at 5min 51secs.

Blue wire of soft start goes to white wire from suppressor.

White wire of soft start goes to motor brush.

Black wire from field coil goes to bare terminal on soft start.

If you send me some photos I will check for you.

 

[larrywalker]

If you send me some photos I will check for you.

The problem is that I had kept only the bare motor from the grinder.
I also have a capacitor and the soft start.
With those 3 (electric) parts, I try to make a grain mill.
All works well, but it needs to soft start, otherwise, the grains are thrown out before they have a chance to get between the blades.

 

[marconi]

Could you take a picture of or draw and label a diagram of the filter in your grinder please?

There are two types so I need to know which one you have. Then I can draw you a diagram of how to connect everything together.

If you draw a diagram be careful to show me the physical layout of the wires. I'd prefer some pictures though if you can do them.

 

[larrywalker]

Hi Marconi,

Thanks a lot for your time and patience.
Not to mention your helpful hand - my knowledge about electric motors is improving after the videoclip you sent (and I've watched more related videos).

As I said, I have no more the filter (only the bare motor) but I have 5 capacitors of 4.7 µF, which I bought from Aliexpress (see picture).

The motor is recovered from a (mechanically) broken grinder and I placed it in a mill.
I wired it according to a scheme I've found on Wikipedia (see diagram).

For the moment, it is connected directly, with no filter (I know this is stupid, but I assure you, I was VERY happy when it started).
I welded the frame of the motor to the frame of the mill; thus, I prefer not to cut it to take pictures.
I try to add the "soft start" (and the filter) from the exterior, to the power cord, if possible.
But, if necessary, I can cut and weld it again (welding is not an issue).

What do you think, could you draw a schema with a motor, 1-2 capacitors and a soft start?
Thank you again.

 

[marconi]

I will reply later today after I have done some thinking.

 

[marconi]

I have attached a sketch of the grinder at the brushes end. Note the orientation of the grinder to identify top/bottom/left and right as viewed in the sketch. Using this sketch I hope you can follow what wire is connected where. The sketch includes the original 5 wire BOSCH filter. If you still have this filter then use it. Otherwise you will need to buy this component:

2609120008 Genuine Bosch Suppression Filter | Bosch - https://www.gardenhirespares.co.uk/2609120008-genuine-bosch-suppression-filter.html

2609120008 Suppression Filter - Filter Antiparasitic: Genuine Bosch Spare | eBay - https://www.ebay.co.uk/itm/293530769361

To run the soft-start motor without the suppression filter will cause unacceptable electromagentic interference to you and your neighbours. The yellow capacitors you bought are not going to be sufficient.

Contact me again if this is not clear or if you want me to check your wiring before you power up.

 

[marconi]

With my serious hat on - before I had my interested hat on - you are making a machine using the motor from an old BOSCH grinder. When I first got involved I thought you had taken apart a grinder and lost track of what wire went where. Later you mentioned a milling machine for grain which is when I start to be nervous - designing and making a machine requires careful analysis about hazards and measures to then address them so a safe machine is produced.

What then is your project ? Pictures are always good.

 

[larrywalker]

Thank you very much Marconi.
I checked with the videoclip you sent and it looks like you are right.
I ordered the filter and I'll post pictures with all the assembly when it is finished.
Cheers.