kinarfi said:
I did read most of the thread and toward the end I only read every other page or so, but it sort of appears that we're attempting to fix poor design problems.
alec coined a couple of terms and I think PDM is a Pump Drive Module.
We think we are. In fact we thin that the pump uses a Melexis DLDC motor IC and some of us think that it's not designed to operate at 24 V. If you look at the datasheet available on this page: **broken link removed** there is a diagram showing a +12, +24 schematic. From reverse engineering, that's essentially what I found. We don;t know the IC or FET part numbers or whether or not they are N or P, but Melexis has a patented property that the circuit has.
It seems strange that the above page mentions +5,+12 operation and the Max Vcc is 18V, but the datasheet has a pic about +12, +24 VDC operation. We're guessing.
The OEM controller uses a LM2576 switching regulator which does allow a brief surge of 6Amps, but it's a 3A regulator. The OEM controller runs the motor at three different speeds for adjustable times. It does not run the motor for very long at full voltage hence supporting the 18 V limit.
The first PDM that Joe tested was integrated into a sequencer and it had virtually unlimited power available. Something like 10A at 24V and (I think) there was a 6A fuse or so. The internal BLDC controller board that is potted within the motor self-destructed. The motor windings also shorted and so did what we assume were FETS.
So, the question is:
What can we assume and what can we do to protect the pump while running it at nearly full speed?
As the pump runs, it will develop more friction and a unprotected stalled pump isn't good for the pump.
Joe wants two different kind of controllers.
One is a tide controller. It operates two pairs of pumps for a long time (12 hr or so) and while the other pumps are off, they are constantly "flicking" or turning on briefly every once and a while to keep the fish away from the propeller. With two pumps on each end of the aquarium, you simulate a tide.
The other controller is a wave controller and it uses a pair of pumps. When one is on, the other is off. These pumps provide motion for the coral reef which needs motion to survive.
Not included yet, is the ability to create a "feed mode" which turns off the pumps or slows them down for a time such as 10 minutes so the fish can eat.
The PDM currently incorporates an alarm to detect a stall and attempted restarts every 30 seconds or so.
The pumps Joe is using are cheap, otherwise he could be looking at $6000 for 6 pumps and he still would not know if he could get the sequencing he wants.
It seems that all of the pump manufacturer's consider their pump technology proprietary.
Yes, a PLC or micro controller option did come up, but Joe's motto is simple and cheap and DIY and who knows what would be required to do it if the budget was $10,000 USD.
And, I did suggest that a new BLDC driver be designed from scratch. That would require removing epoxy potting non-destructively from inside the OEM pumps and repotting.
Both options are currently not being considered, but the latter is possible if all else fails.
We have not addressed speed control except for changing the power supply voltages for each pump. It's not known if it's needed.
Some BLDC motor IC's have a tachometer and or a fault output which "COULD" be utilized in a total redesign of the internal BLDC controller. We really don't want to go there.