I want to parallel connect 4 x AA NiMH batteries rated each at 1.2V, along with 4 x 1N4001 simple diodes to prevent unwanted current flow (recharging) between batteries. The electric circuit is:


simulate this circuit – Schematic created using CircuitLab

I get an estimated output voltage of 0.7V (because of 0.5V voltage drop for the diode).

How can I rise up the voltage from 0.7V to 5V and also have the possibility of a minimum current of 1A for the load resistance? If wiring restructuring is needed, then please offer parallel design solutions, because I need as much as possible amp capacity (2700 mAh * 4).

I tried this U1V10F5 step-up voltage regulator from Pololu (https://www.pololu.com/product/2564) and it gives me 5V, but somewhere in this circuit I think there is a high resistance (possible some current blocking from the diodes?), because the output current can't power up even a regular LED, when it's put in place of a resistance load (with some adequate resistance for the LED of course).

Thank you so much!

  • 2
    \$\begingroup\$ Why? Also, at that voltage level a diode drop is significant. Shottky is better but still, why? If one battery voltage is higher than the others, they will equalize. \$\endgroup\$
    – winny
    Mar 29 '17 at 12:12
  • 5
    \$\begingroup\$ Why not put them in series and have a regulator do the rest, or even put more in series so it only needs to buck down? The diodes are throwing away a major portion of your energy \$\endgroup\$
    – PlasmaHH
    Mar 29 '17 at 12:15
  • \$\begingroup\$ I thought in parallel because more amp capacity would benefit a robot car with many passive components such as a 1x microcontroller, 4x DC motors and other stuff. It's kinda difficult to achieve this parallelism and I should stick with the series version as you said. \$\endgroup\$
    – Daniel C
    Mar 29 '17 at 12:31
  • 1
    \$\begingroup\$ If you're going into a step-up, follow @PlasmaHH's good point. It's the right way to do it \$\endgroup\$
    – TonyM
    Mar 29 '17 at 12:44
  • 1
    \$\begingroup\$ Unless there's some specific reason you've chosen NiMH you'd be much, much better off with Li-ion in pretty much every way. \$\endgroup\$
    – Finbarr
    Mar 29 '17 at 12:51

First of all, PlasmaHH in the comments gives a good idea on how to do this better...... However if you REALLY want to do it this way (to answer this particular question)

First of all, use schottky diodes (less Vf and at these voltages, that drop can be significant especially with the input voltage on these boost regulators). Second, may want to consider using something different. Looking at the specs (which it doesn't give much info on) it says INPUT current is 1.2A. Please correct me if I am wrong people, but that is not the same as output current!

The thing it does say about output current is: "The maximum achievable output current is approximately proportional to the ratio of the input voltage to the output voltage." And it sounds like you are wanting 1A output current from this, which I don't think is achievable by looking at this graph: enter image description here

If you look at the BLUE line (1V input even though yours will be less because of the diode drop) the efficiency is awful, even at less than 200mA. This wil probably explain why it struggled to light an LED.....

Anyway, the short answer is, either rethink your input or use a different IC to boost the voltage.

(feel free to critique my answer if I have missed something or got something wrong as I am still learning electronics myself and am always happy to learn! I can edit the answer if I have accidently given any false information)


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