Step up Dc-DC and inductive load pump

Thread Starter

DJ_AA

Joined Aug 6, 2021
308
Hi All

This is my Step-up DCDC design. It is capable of powering 12V 1A. I am trying to control a water pump that is 10W and rated 12V 0.8A.
But when I connect my motor/pump to this device, I see a voltage drop and current consumption of about 564mA. Do I need to do something in particular for inductance load?
1710265105623.png
 

LowQCab

Joined Nov 6, 2012
4,217
Your "nondescript" "Motor-and-Load" probably draws close to ~3-Amps at start-up,
especially if it is controlling a Load with a lot of built-in inertia.

Even if the Output-Capacitors were allowed to fully charge before connecting the Motor
it is still unlikely that the Circuit would maintain stability of it's Output-Power.

There is definitely not enough "over-head" in this design in any case.

"12V 1-Amp" is a "possible under ideal conditions" "peak" rating.
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Papabravo

Joined Feb 24, 2006
21,264
Did you read the datasheet carefully as you determined the component values?
You really can't just slap components onto a schematic and expect it to work.

Looks like you copied the LTspice test jig with some minor modifications. Your input voltage is 4.2V and not 5V. When you overload the output you cannot reach the design boost level.
1710271990890.png
I can try to make the test jig replicate your schematic, but I don't think it will make much difference.
 
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Thread Starter

DJ_AA

Joined Aug 6, 2021
308

LowQCab

Joined Nov 6, 2012
4,217
It would be much simpler to use a 12-Volt, Deep-Cycle, Lead-Acid Battery for Power.
And, it can run the Pump for a full ~24-hours, if necessary, without any stress.

The above Circuit will ultimately waste ~20% or more of you Li-Ion-Cell's capacity.
And, unless it's a very expensive, and large, Cell, it won't last very long before requiring a Re-Charge.
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Thread Starter

DJ_AA

Joined Aug 6, 2021
308
Well, the battery we are going to use is 8000mAh or 12000mAh @ 4.2V.

There will be a solar charger for these batteries, so I do not have to worry.
 

LowQCab

Joined Nov 6, 2012
4,217
So You will have roughly ~3-hours of run-time on a complete charge, of the larger sized Cell.

If the Pump must run everyday during the Daylight-Hours, how will the Battery be charged ?
Is your Solar-Charger capable of producing roughly ~4-Amps at ~5-Volts,
so that You can run the Pump and charge the Battery at the same time ?
What will happen on a Cloudy-Day ?
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Thread Starter

DJ_AA

Joined Aug 6, 2021
308
The pump will be active a few times a day for a maximum of 5 minutes only. So the duration will be very low.

Yes, we have a solar panel, which is 30W, with a Li-ion MPPT charger.
 

LowQCab

Joined Nov 6, 2012
4,217
Use a "3S" ~12-Volt Battery.
The Cells that You have suggested are way past over-kill in Amp/Hour capacity.

It's much easier to make a "Boost-Converter" Battery Charger,
that charges at maybe ~100mA, or even less,
than it is to Boost ~4-Volts to ~12-Volts, at ~12-Watts, ( plus Motor start-up Current-Spike ).

It might even be worth while to use 3-smaller-Solar-Panels to charge the 3 Li-Po Cells,
using 3 completely independent Cell-Charging-Circuits,
this would certainly be more efficient, and much simpler.
This would also eliminate having to implement proper Cell-Balancing-Circuitry.

Only 3 standard Linear-Voltage-Regulators would be required,
as the Current would be automatically limited by the
maximum Current output of the small Solar-Panels.

Then the only other Electronics that You will need is
a simple FET Switch to run the Motor when needed.
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Thread Starter

DJ_AA

Joined Aug 6, 2021
308
Thanks
I could use a Li-ion battery rated to 12V and then my existing MPPT charger(LTC4162) to charge the battery that is not a problem.

My Solar panel will be 30W, so I guess there would be an adequate charge.

I would then need to reduce the 12V to 4.2V for my GSM module/Electronics, but I guess a simple Step-down would be sufficient.

In order to run the motor, i could then use something such as
drv8837c.pdf (ti.com)
 

ronsimpson

Joined Oct 7, 2019
3,147
What 4.7uH inductors are you using? They may have gone into saturation. It is common for people to pick a low current device. I think the inductor current is much higher than you think during startup.
 

LowQCab

Joined Nov 6, 2012
4,217
"" In order to run the motor, i could then use something such as drv8837c.pdf (ti.com) ""
You don't need an "H-Bridge", or anything even remotely similar, just to run a simple Pump-Motor.

A single MOSFET, plus a "Freewheeling-Diode" across the Motor-Terminals, is all that is required.

Better-yet, just use a heavy-duty MOSFET-Gate-Driver to directly drive the Motor,
instead of an actual MOSFET Transistor.

This will provide You with a Logic-Level-Input with hysteresis,
and, an automatic 9-Volt UVLO ( Under-Voltage-Lock-Out ) to protect the Battery from over-discharge,
and, there will be no complications with properly switching
a MOSFET-Gate completely-on, and completely-off reliably.

Why are You using a Cell-Phone-Connection, plus a Micro-Controller, to control a simple Water-Pump ?????
Why not automatically control the Pump with local Sensors ?

It seems like this project is probably being made much more complicated than it needs to be.

Having fewer "Potential-Points-of-Failure" is always a better plan.
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Thread Starter

DJ_AA

Joined Aug 6, 2021
308
Do you mean a load switch? Do you have a reference design?

My device has GSM, so I can see other sensor data remotely.
The pump is something i am trying to integrate into existing unit, so its new element.

The existing design works of 4.2V, so that is the reason for using a 4.2 to 12V step-up,
 

LowQCab

Joined Nov 6, 2012
4,217
Here is a Spec-Sheet for a very heavy-duty Gate-Driver.
It is rated for a continuous 8-Amp DC Load, so it can easily handle the "start-up" Current of your Pump,
and, it does not require a Freewheeling-Diode across the Motor-Terminals like a single FET does.

It requires a ~3-Volt Input to turn-on, and has a 0.2-Volt Hysteresis to reduce sensitivity to Noise.
A 10K Resistor in series with the Input will provide protection from any type of accidental Input-Spikes.
Other than a ~100nF Capacitor on the Power-Input-Pin, it requires no other Components.
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Thread Starter

DJ_AA

Joined Aug 6, 2021
308
So, with the device,

Pin IN will be 12V with 100nF
Pin Out will connect to the Pump + wire.
Vcc will connect to the PCBs 3.3V
Enb goes to the uC via a 10K resistor.
 
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LowQCab

Joined Nov 6, 2012
4,217
Incorrect .........

Vcc is the ~12-Volt Motor-Supply-Input, and requires a ~100nF to ~1uF Ceramic-Capacitor to Ground.

Pin-IN determines the Voltage at the Output-Pin, which will always be either Ground, or Vcc.
Pin-IN will require more than ~3.1-Volts for "On",
or less than ~2.9-Volts for "Off",
( with 0.2-Volts of Hysteresis ).

Pin-IN will vary it's Voltage-Sensitivity very slightly with large Temperature-variations.

Pin-IN has built-in Spike-Protection that will not work unless a ~10K Resistor is placed before the Input.

If You NEED to get one of the part-numbers that has an ENABLE-Pin-Option,
it can be directly connected to Vcc for always-Enabled operation,
or, it can be used as a "Standby-Function" which causes extremely low Quesent-Current-Consumption.
It basically turns-off the Power to the whole Chip, which is generally not necessary,
as the Quesent-Current is very low under normal operating circumstances.
This EN-Pin should NOT be used as an "on-off" switch because doing so will not provide
protection against Flyback-Spikes created when the Motor is turned-off.
Properly using the IN-Pin to turn-off the Motor
will short the Motor to Ground when turned-off,
eliminating the normal Flyback-Spikes created by the Motor's Inductance.

If You have a definite need for a "Low-Power-Standby-Mode",
the EN-Pin should only be brought to Ground
AFTER THE MOTOR HAS COMPLETELY STOPPED TURNING.

Adding a Freewheeling-Diode across the Motor will insure against expensive dumb-mistakes,
and may be added in any configuration.

The Output-Pin can continually Source or Sink ~8-Amps of Current equally well.
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