2019-07-23, 04:25 PM
Nothing wrong with your design, just wanted to point out to rastam4n that it's not for hydraulic.
Did you manage to heatsink the h bridge to the metal enclosure?
My mosfets are 2-3 milliohms so I did count all channels. Also using 500 micro ohm shunt (needs amplifier) uses little power. Also there are some losses during switching and the pcb traces themselves become significant.
The 0.05 ohm shunt plus 0.15 ohm resistance of h-bridge you used equals 0.2 ohm
So at 12 volts with a tiller pilot drawing 3 amps
3*3*.2 = 1.8 watts, 95% efficient. In reality there are other losses so its closer to 90% which is not bad, and not too much heat to dissipate either. This also means .2*3 = .6 volts drop.
So motor only sees 11.4 volts. This means the motor turns slower and operates in a range it may (or may not) be less efficient. Usually tiller pilots are more efficient with more voltage. This allows for more short faster corrections, but it also really depends, and if it has a ball screw rather than a lead screw then slower speeds are not as inefficient.
In my case, the total resistance of the basic controller 40 milliohms drops only 0.12 volts, so 98-99% efficient (arduino and drivers taking it down to 97%) hydraulic controller has 20 milliohms resistance, so half the losses and it uses a metal enclosure so it can also dissipate many times more. The efficiency varies depending on the current for each controller.
This is just an example at 3 amps. If your motor draws less power, say 1.5 amps, then on resistance is less important, and the higher resistance controller approaches better efficiency, but it's already ok even at 3 amps.
Did you manage to heatsink the h bridge to the metal enclosure?
My mosfets are 2-3 milliohms so I did count all channels. Also using 500 micro ohm shunt (needs amplifier) uses little power. Also there are some losses during switching and the pcb traces themselves become significant.
The 0.05 ohm shunt plus 0.15 ohm resistance of h-bridge you used equals 0.2 ohm
So at 12 volts with a tiller pilot drawing 3 amps
3*3*.2 = 1.8 watts, 95% efficient. In reality there are other losses so its closer to 90% which is not bad, and not too much heat to dissipate either. This also means .2*3 = .6 volts drop.
So motor only sees 11.4 volts. This means the motor turns slower and operates in a range it may (or may not) be less efficient. Usually tiller pilots are more efficient with more voltage. This allows for more short faster corrections, but it also really depends, and if it has a ball screw rather than a lead screw then slower speeds are not as inefficient.
In my case, the total resistance of the basic controller 40 milliohms drops only 0.12 volts, so 98-99% efficient (arduino and drivers taking it down to 97%) hydraulic controller has 20 milliohms resistance, so half the losses and it uses a metal enclosure so it can also dissipate many times more. The efficiency varies depending on the current for each controller.
This is just an example at 3 amps. If your motor draws less power, say 1.5 amps, then on resistance is less important, and the higher resistance controller approaches better efficiency, but it's already ok even at 3 amps.