Harprit's 18200 H-bridge amplifier saves the day!
Mickster
Posts: 2,693
Retrofitting a CNC tube bender that can only be out of production for a few days. This involves 2 axes of closed loop brushless servo motors and 2 axes of closed loop servo hydraulics.
Come to connect to the hydraulic axes to find the servo amplifiers had disappeared and nobody knows how/where. Replacements are close to $1,000 each and have a 2-week lead time....not an option.
I just happened to have one of Harprit's (haven't seen him here lately) H-bridge amplifier boards laying around....hmmmm.
The servo valve only requires a max of 20mA so, to give some DAC range, I dropped the current gain via a 680 ohm, 2W resistor in series with the valve's coil. This works out to 20mA @ 64% PWM duty (about 12bits in this case).
Tested late last night...beautiful! Holding position to +/- one quadrature count (0.025 degrees).
A dual amp board for $50 substituting for two $1000 amplifiers? I'll take that!
Just thinking; I need to drive lots of "bang-bang" directional valves where I typically drive solenoid A or B via SSRs. Rectifying the outputs of the 18200, I could use one direction to drive solenoid A and the other direction to drive solenoid B. This would result in two SSRs in one package and provide the option of PWM-ing them to provide a variable fluid flow. I need to try this.
Come to connect to the hydraulic axes to find the servo amplifiers had disappeared and nobody knows how/where. Replacements are close to $1,000 each and have a 2-week lead time....not an option.
I just happened to have one of Harprit's (haven't seen him here lately) H-bridge amplifier boards laying around....hmmmm.
The servo valve only requires a max of 20mA so, to give some DAC range, I dropped the current gain via a 680 ohm, 2W resistor in series with the valve's coil. This works out to 20mA @ 64% PWM duty (about 12bits in this case).
Tested late last night...beautiful! Holding position to +/- one quadrature count (0.025 degrees).
A dual amp board for $50 substituting for two $1000 amplifiers? I'll take that!
Just thinking; I need to drive lots of "bang-bang" directional valves where I typically drive solenoid A or B via SSRs. Rectifying the outputs of the 18200, I could use one direction to drive solenoid A and the other direction to drive solenoid B. This would result in two SSRs in one package and provide the option of PWM-ing them to provide a variable fluid flow. I need to try this.
Comments