Need Assistance to prevent voltage drop from Battery

Hi to all,

I am running the DC brushéd motor (max 7.2v without load 2A and with peak load current 12A). I am using PWM Arduino to control dc Motor using 5 MOSFET parallelly with the power supply NiMH battery 6v 1200mah.

Every time I am running the dc motor using pwm integer , the voltage drops from the battery. Since I am new in electronics. IS there any way to prevent the voltage drop from battery or make a constant voltage up to particular level of voltage

Need assistance!

Thanks.

How are your you measuring the voltage?
Yes the whole point about PWM is that the average voltage drops but the peak voltage remains the same.
What makes you think that their is anything wrong in this?

Is the measurement being taken on the battery terminals?
If so it could be an artefact from you measurement or you battery can't supply the current.

Grumpy_Mike:
How are your you measuring the voltage?
Yes the whole point about PWM is that the average voltage drops but the peak voltage remains the same.
What makes you think that their is anything wrong in this?

Is the measurement being taken on the battery terminals?
If so it could be an artefact from you measurement or you battery can't supply the current.

Thanks for the reply. I am using a PWM with the integer value of 60 with my fully recharged battery 6v 1200mah running with the time period of 5min continuously. off course, after a while due to the voltage drop from the battery it can not achieve the same 60pwm. might it reduce to 59 or 58? For this reason, I need a solution to prevent the voltage drop from the battery. Is there any other way to consider voltage regulator or capacitor. how to overcome this situation. Any idea

Up to now, I am using digital PWM pin as an input from Arduino to a resistor (10ohm) and parallel with five MOSFET and directly connected from mosfet to dc motor. With help of a battery of 6v 1200mah

after a while due to the voltage drop from the battery it can not achieve the same 60pwm.

Sorry this does not make sense. By 60pwm do you mean a PWM signal that has been set with an analog write value of 60? If so then how can you possibly know it does not achieve a duty cycle of 60 to 255 without measuring it on an oscilloscope. Even if you do it still makes no sense.

You have not answered any of the questions I have asked.

I am using digital PWM pin as an input from Arduino to a resistor

A PWM pin is an output not an input.

to a resistor (10ohm)

Why, it is too small to limit any gate current to below the point where damage starts to happen to the Arduino pin.

parallel with five MOSFET and directly connected from mosfet to dc motor.

What is the part number of these FETs?

It is normal for the battery voltage to drop while current is being drawn from the battery - the more current, the bigger the drop. The actual amount of voltage drop for any given current depends on the battery capacity, the battery chemistry and the amount of charge remaining in the battery.

You need to choose a motor/battery combination that provides the necessary performance when the motor is operating.

...R

A 1.2 AH NIMH battery has no hope of powering a motor with a peak current of 12 A.
You need a far bigger battery, and for that sort of current either a lead acid or lipo.
Even with no load, drawing 2A from a 1.2 AH NIMH battery will make the battery voltage sag.

Hi,
Please can you post a copy of your circuit, in CAD or a picture of a hand drawn circuit in jpg, png?

Thanks.. Tom.... :slight_smile:

mauried:
A 1.2 AH NIMH battery has no hope of powering a motor with a peak current of 12 A.
You need a far bigger battery, and for that sort of current either a lead acid or lipo.

Quite right. I missed the fact that the OP is using a 1.2Ah NiMhbattery. I have a 230Ah lead-acid battery and it will show a voltage drop when I draw 12 amps from it.

Even with no load, drawing 2A from a 1.2 AH NIMH battery will make the battery voltage sag.

Something mixed up here :slight_smile: If there was no load there would be no current or (conversely) the 2A current IS the load (as far as the battery is concerned).

...R

Actually a 1200mAh NiMH battery might deliver 12A or more if it contains the correct sort of cells. Consumer AA or AAA won't hack it but there are some 2/3A cells that will. Obviously you won't get a lot of run time but currents like that are quite common in the RC world (along with 5 minute run times).

But lipos are generally better and I'm having trouble imagining why you'd need 5 MOSFETs in parallel to control that sort of current.

I guess the "no-load" refers to the motor. A motor still draws some current even with no external load, though 2A sounds a bit high for what otherwise seems like a smallish motor, something like a Mabuchi 380 perhaps.

Way too much missing information to give any real help though.

Steve

A 1.2Ah NiMH running at 10C will suffer voltage depression (unless it happens to be an aircraft battery by design… I’ve heard of some good performers on the RC forums). A Panasonic Ni-Cd of the same capacity will run like a champ however, regardless of form factor.

Switch to Lead-Acid, LiPo or Ni-Cd, or if you’re dead set on using this battery, you could use a DC-DC boost converter to maintain a stable voltage but you’ll just kill the battery faster and when the voltage falls below 1V/cell you risk reversing the cells and having the voltage fall off a cliff, at which point even the chopper won’t save you. It’s a trade-off.