Building controller for slow brushless hydraulic pump? - Page 1
Forum section: electronics / projects

author: rhodges
author_rank: Frequent Contributor
timestamp: August 20, 2020, 08:49:30 pm
content: Last year, I tried using cheap peristaltic pumps for feeding waste oil into my burner (in a wood stove). The pump housings would fail pretty quickly, say in only 15 or 20 hours. So I gave up for a while.What I want is a pump that I can use to feed oil at the rate I want. That probably means that a positive displacement pump is best. And I want to control the motor speed.I am looking at a hydraulic pump with a brushless DC motor. I don't have experience with stepper motors, or H-bridge controllers, but the principle seems straightforward. Here is the cheapest one I found on ebay:https://www.ebay.com/itm/193506959618I want a feed rate of probably 10 to 50 grams per minute, and this pump claims 1 liter per minute at 3.6 amps and up, depending on pressure. I won't have any pressure here. So I might expect (naively?) that I want 30 to 150 RPM.I expect that I would make a bridge of 3 N and 3 P MOSFETs and maybe buy a driver chip. At these slow speeds, I hope I could drive it blindly, and change the speed slowly.Does this sound as simple as I think? For reference, here is my project with the peristaltic pump:https://github.com/unfrozen/pwm_pump/wikiThanks!

author: thm_w
author_rank: Super Contributor
timestamp: August 20, 2020, 09:21:05 pm
content: Simplest is to use an off the shelf hobby ESC, but it may not run at these low RPMs.You might want a dedicated BLDC driver chip, with or without external FETs.Some info here on low RPM:https://hackaday.com/2015/04/20/driving-a-brushless-dc-motor-sloooooooowly/

author: Cerebus
author_rank: Super Contributor
timestamp: August 20, 2020, 09:28:57 pm
content: It's possible to drive a (3 phase) BLDC motor as slowly as you like, they are used industrially as servo motors with tiny angular resolutions. The key to doing it easily is to have rotor position feedback available, ideally from something like a shaft encoder. There's way too much to know about the subject to pack into a post on here - I suggest you do some searches for "Field Oriented Control". There's a few videos on You Tube by Dave Wilson of Texas Instruments on the subject that form a good overview.Your basic assumption is correct, you'll want 3 half bridges and a way of measuring the phase current being produced in 2 or 3 phases (2 plus Kirchoff to derive the third, or just measure all three). You'll probably want to use a gate driver chip that's dedicated to the task, that'll let you use just N-channel FETs and give you current sensing too - TI's DRV8302 is one such dedicated driver. For a small motor you might only need something like TI's DRV8312 which can drive a motor directly from on-board FETs (up to 50V 3.5A). You can guesstimate the rotor position in software if you can also measure the phase voltages, or you can use a motor with either hall effect rotor position sensing or shaft encoder rotor position sensing.I'm guessing that with a peristaltic pump you probably need to go pretty slowly. The slower you plan on running the motor the more important it is that you know the current rotor position accurately to get the maximum torque. It's possible to get full rated torque from a BLDC at zero speed. If you can find a suitable motor with a shaft encoder (or that can be used with one) it will be a lot easier to get the software right for low speed than with electrical feedback sensing methods.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: August 22, 2020, 03:27:08 am
content: The hackaday article from 2015 mentiones the L6234 which is a quite easy to use driver chip for (small) BLDC motors.You can also have a look into "SimonK".It's firmware for an ATMEGA8 and is used in some "ESC" (Electronic Speed Controllers).These ESC's are standard building blocks in remote controlled gadgets, so the only soldering you'll have to do is to add a programming connector for the on-board microcontroller.Normally an ESC won't run so slow, but you can of course use the hardware of one, and re program the uC.These things start at around EUR10 or so on Aliexpress, but it's difficult to predict which uC will be on it.Ali also has BLDC controllers with discrete TO220 mosfets, and no onboard controller, but some 0.1" header pins to control the bridge, so add a uC.Also, Youtuber "GreatScot" has some very simple BLDC controllers build and documented, complete with "arduino" code that may be worth watching. Just close your eyes when he starts soldering, or smile loudly if you think your own soldering skills are better than hisAlso: lots of pumps are made from plastic, which may react badly to your fuel.

author: NiHaoMike
author_rank: Super Contributor
timestamp: August 22, 2020, 05:01:57 am
content: Have you considered using a replacement fuel pump for a diesel or kerosene heater? The kind that's common nowadays pumps a fixed amount per pulse so adjusting the flow is more or less adjusting the timing of the pulses.

author: Renate
author_rank: Super Contributor
timestamp: August 22, 2020, 02:15:14 pm
content: Have you considered still using the BLDC and peristaltic but adding worm gear reduction?I wouldn't like a stepper for reasons of noise even with microstepping.There's no reason to bother with angle feedback.This one is kinda pricy, but I didn't look long:https://www.ebay.com/itm/Machifit-GM4058-BLDC3650-DC-24V-Rated-Speed-30RPM-Brushless-Worm-Geared-Reducer/392771650003

author: rhodges
author_rank: Frequent Contributor
timestamp: August 22, 2020, 03:16:51 pm
content: Quote from: NiHaoMike on August 22, 2020, 05:01:57 amThat is exactly what I want. I will start looking for that item. Thanks!

author: ahbushnell
author_rank: Frequent Contributor
timestamp: August 22, 2020, 03:52:55 pm
content: Quote from: rhodges on August 20, 2020, 08:49:30 pmThe driver would need 6 N type MOSFET's Or IGBT's. Probably MOSFET's would be fine at this power.This show a schematichttps://www.google.com/url?sa=i&url=https%3A%2F%2Fwww.researchgate.net%2Ffigure%2FCircuit-diagram-of-a-three-phase-inverter-with-an-LC-output-filter-for-stand-alone-DGSs_fig2_260541922&psig=AOvVaw0p2ZsJ4UzZo9yXdLOWdRam&ust=1598197869325000&source=images&cd=vfe&ved=0CAIQjRxqFwoTCIj7s5SVr-sCFQAAAAAdAAAAABAL

author: Renate
author_rank: Super Contributor
timestamp: August 22, 2020, 06:57:09 pm
content: The solenoid pump might not work so hot, oil is more viscous than diesel or gasoline.,Here you go, reservoir, pump, driver, controller, front panel.Just replace the controller if you don't like stock.https://www.ebay.com/itm/1-8L-Digital-Automatic-Electric-Lubrication-Pump-Oil-Pump-Oiler-NC-Pump-110V-USA/264271505500Heck, it even has a level sensor.

author: rhodges
author_rank: Frequent Contributor
timestamp: August 22, 2020, 09:10:17 pm
content: @RenateThanks! The feed is stated at 50cc per minute, which is probably much higher than what I want. But as you wrote, I can replace the controller.Does anyone have any idea what viscosity of "30-68cts" means?

author: Renate
author_rank: Super Contributor
timestamp: August 22, 2020, 10:38:15 pm
content: Quote from: rhodges on August 20, 2020, 08:49:30 pmQuote from: rhodges on August 22, 2020, 09:10:17 pmThe density of used motor oil is 0.93 gm/cc.50 gm / (0.93 gm/cc) = 53.8 cc.Still, I take back this suggestion.This is a piston pump and I don't think that it will really be what you want.And it's probably fed by an AC motor.You want continuous delivery.Or how about using the cheapest (automotive) oil pump that you can find on ebay?https://www.ebay.com/itm/GM-Oil-Pump-1965-1990-260-307-350-400-425-455-NEW/122292535644