servo control vs stepper control

[Peter.]

So from that I gather that whatever voltage I use to power the BOB, that's the signal voltage sent to the drive? Will that BOB linked in post 3 definately run safely off 24v?

[irving2008]

So from that I gather that whatever voltage I use to power the BOB, that's the signal voltage sent to the drive? Will that BOB linked in post 3 definately run safely off 24v?

The problem I have with running this BOB at 24v is this:




The output circuit has a pull up to 'Isolating + supply'. Without knowing the value of that resistor you can't be 100% sure its not going to fry. In the manual it shows 'Isolating Supply +5v'so I would assume they are sized for 5v and not 24v supply...

[boldford]

The problem I have with running this BOB at 24v is this:




The output circuit has a pull up to 'Isolating + supply'. Without knowing the value of that resistor you can't be 100% sure its not going to fry. In the manual it shows 'Isolating Supply +5v'so I would assume they are sized for 5v and not 24v supply...

They are 1K.

[irving2008]

They are 1K.

Ok, so 5mA collector current on 5v, 24mA on 24v.. so it wont fry :)

EL817 optos are rated 35v, 50mA so should be ok.

However, as I recall the diode has a 330R series resistor so forward current is about 10mA and those devices have a transfer ratio of about 1.1. So with 10mA in the diode the collector current is going to struggle to be more than 11-12mA which means the output volts wont drop below about 12 - 13v, so though it won't fry its not going to work. No good on 24v :(

[JAZZCNC]

So from that I gather that whatever voltage I use to power the BOB, that's the signal voltage sent to the drive? Will that BOB linked in post 3 definately run safely off 24v?

I wasn't referring to that particular Bob or any Bob really and so obviously it would need to support 24V but most decent Bob's feature a range of input voltages.

I wouldn't use a cheap BOB with quality Servo's and to me this BOB isn't really a quality Item, it doesn't have a Charge pump for one which is nice feature and it looks a bit small and cramped.
Cheap nasty BOB's are a pain in the arse and a large source of problems and they don't always show has plain "works or doesn't" so can cause any thing from weak signals to dropped signals to slow acting Opto's etc all of which if your unlucky to drop for it will drive you crazy. .