Voltage from battery dropping

[Pheetuz]

Im currently doing a project that involves me running two 12V motors and several IC's off of one 12V drill battery, there is no current limiter on the battery itself.

What i was wondering is, will the voltage from the battery drop when the motor draws current from it? As that is what seems to be happening when i use a normal power supply, although i know the current from these is limited. - the voltage seems to fluctuate from between 12V and about 5V.

Basically, if the voltage starts to drop then its going to cause mayhem around the rest of the circuit, although the IC's are on the other side of a regulator with 2x decoupling caps, it wont really help if the voltage drops by a lot.

Someone on here suggested using a bulking capacitor in parrallel with my normal decoupling capacitors next to the IC's to help them stay powered when the motors draw current but thats not going to help my transistors that are activating my relay coils etc.

Basically just wondering if the voltage will drop??

Many thanks folks

/Pete

 

[kabiru]

Hi, what you should do is to know the power you consume and what type of battery do you use how many Ah is your battery

 

[fg]

Im currently doing a project that involves me running two 12V motors and several IC's off of one 12V drill battery, there is no current limiter on the battery itself.

What i was wondering is, will the voltage from the battery drop when the motor draws current from it? As that is what seems to be happening when i use a normal power supply, although i know the current from these is limited. - the voltage seems to fluctuate from between 12V and about 5V.

Basically, if the voltage starts to drop then its going to cause mayhem around the rest of the circuit, although the IC's are on the other side of a regulator with 2x decoupling caps, it wont really help if the voltage drops by a lot.

Someone on here suggested using a bulking capacitor in parrallel with my normal decoupling capacitors next to the IC's to help them stay powered when the motors draw current but thats not going to help my transistors that are activating my relay coils etc.

Basically just wondering if the voltage will drop??

Many thanks folks

/Pete

A bulking capacitor will probably help. Also couple the capacitor from the motors with a diode so the motors won't draw current from it. In this design, the transistors driving the relay coils will also use the (large) capacitor as their power supply when the battery voltage drops.

A silicon diode such as 1N4001 will cause a voltage drop of some 0.7 V or more (depending on current) but the relays should work anyway.

The battery voltage will drop more or less when the current drawn from it rises. The drop will typically be greater for a discharged battery than for a full charged one.

Regards,
fg

 

[IanP]

In applications where voltage may drop you should consider low dropout voltage regulator that provides stable output even if the voltage drops down to, say, Vcc+0.5V = 5.5V
Such a regulator is, for example, the LM2940 ..
In addition, it is a very good idea to separate both sections of the circuit by a diode .. see attached picture .. and add reasonable size caps ..

Rgds,
IanP

 

[Past751]

i think 7805 ic 5vdc voltage regulator is easily available anywhere and it is cheap
same circuit as bro IanP posted.

 

[Tahmid]

Hi pheetuz,

If voltage drops from 12v to 5v, I think that's a sign that the power supply can not provide enough power required to run the motor. You might look for a power supply that can supply greater currents.

It shouldn't be happening with a battery though, as the battery isn't as limited in current but will run out quicker.

Hope this helps.
Tahmid.