# DC-DC boost converters in parallel to run DC motor

Our aim was to power the motors of our bot (which were selected according to the torque requirement of our bot) using a single AAA Battery but due to limited time and and the difficulties in international shipment we are stuck with boosters only available in our country.

The boost converter cannot provided the required current to our motor at it's boosted state even though we are pretty sure that our battery can provide more current, as a result the output voltage of the convertor across the motor drops from 5v to about 0.8v. So we though of using a bunch of them in parallel to solve the issue. Using 5 such boost convertors we saw that this drops from 5v to about 3.8v. So naturally adding more of thes in parallel should be sufficenint to spin the motor at out desired rate. But this seems very sketchy. We tested all this only a single motor and connecting two across the whole configuration will obviously result in a larger drop. So even if we increse the number of boosters from 5 to say 10 there should be a limit where adding more of them stops giving us results. We are reallly hoping it is not the case.

What can we expect going forward or is there something that we are missing from this equation. This is pretty much our last hope

Battery : 1.2 volt 800mah

Boost Convertors : 0.9V ~ 5V to 5V 600MA

NOTE : I should have mentioned it from the start but using a single AAA is a rule in our problem statement that we have to follow. Also the motors are fixed according to our torque requiements

• Are you using just one AAA as power supply? How much current does the motor use? (measure its resistance) Mar 15, 2021 at 18:15
• What current do your motors require? Bear in mind that when you step the voltage up from 1.2 V to 12 V, the current drawn from the battery will be over 10 times the current consumed by the motor - if the motor wants 200 mA, the battery will have to deliver a little over 2 Amp. Mar 15, 2021 at 18:16
• These boosts have a diode so they're not synchronous, which means current can only flow from input to output, so putting more in parallel should not cause any problems, if the battery can deliver enough current. But if you use that many boost converters, that will take more space than a second AAA battery, which would solve the problem... Mar 15, 2021 at 18:28
• we have to use just 1 AAA battery for the whole process. Are there other problems we caould face like the one i mentioned about hitting a maximum limit when we start to power two motors instead of one Mar 15, 2021 at 18:33
• When the battery is delivering 4 Amp into a short circuit, remember that the voltage across the battery is approximately Zero. Measure the actual battery voltage with your normal load - it may be below the boost converter's minimum input voltage. Changing from an AAA cell to an AA cell may improve things... Mar 15, 2021 at 18:46

When powering circuits from low voltages you have to be very aware of voltage drops that may occur.

The leads from the battery to the circuit should be of heavy gauge, if you use a battery holder it can drop significant voltage (any springs used to contact the battery may be made of steel that has much higher resistivity than copper, I had to add additional wires across the sping on one design I did to minimize the voltage drop).

It is also difficult to measure the current on the low voltage side - a typical DVM may drop up to 200mV on the current range and the meter leads can drop hundreds of millivolts so the combination can lose up to half a volt.

Single-phase boost converters can take much higher peak currents than their average - the peak current can cause the supply voltage to drop below the cutoff limit and prematurely restrict the output current. Good low ESR capacitors close to the boost converter can help. You may need several thousand microfarads of tantalum or polymer capacitors - aluminium electrolytics may not have low enough ESR to help.

Why are you restricting yourself to a single AAA cell? The space taken up by the circuitry may end up as much as an additional cell or maybe use a Li-Ion cell. Its 3.6V terminal voltage will avoid these low voltage issues.

• It's also worth mentioning that the capacity performance of most batteries, most AAAs included, greatly decreases with current draw, so if you use 2 in parallel, cutting the current through each in half, you more than double your capacity. If you extended that to 4 to 6 batteries and wire them in series, the option of a buck converter opens up, which can often outperform a boost converter at similar or smaller size and cost. Even with just 2 or 3 in series, boost converters often get much closer to their ratings with a smaller step up.
– K H
Mar 16, 2021 at 2:46
• @KH sorry for not clearly stating this but using a single AAA is a rule in our problem statement that we have to follow. Also the motors are fixed according to our torque requiements Mar 16, 2021 at 16:21
• @Kevin White how exactly do you propose we add the ESR capacitors to the boost convertors, provided we are using several of them in parallel Mar 16, 2021 at 16:27
• @Shubhamsharma - You just put them in parallel with the power input, close to the converters. It is to reduce the effect of the resistance and inductance of the wiring. Mar 16, 2021 at 16:33
• @KevinWhite your suggestion to remove the battery holder worked wonders!!! The springs were a significant loss in the circuit. Thanks everybody for the help. And Kevin if you ever visit India, remember you have friends here :D Mar 16, 2021 at 19:08