Voltage drop question - will capacitor help?

[robotnut]

Voltage drop question

Hi All;

Total noob, first post

I'm working on a small robotics project. I have an embedded computer (5V) and 2 motors with a controller. It's all powered from a 4.8V NIMH battery.
The problem I'm having;

As the battery gets somewhat tired and I load the motors for starting or climbing a steep obstacle, the voltage drops a little from 5V to about 4.5 momentarily but it's just enough to restart the computer :idea:

What I'm thinking of to solve this problem is adding a capacitor to the power cable of the computer. Would that help the problem? Like I said the drop only happens for a fraction of a second.

I know I could use a bigger battery but I have a room issue already as it is.

Thanx in advance.

 

[mandar_mahajan]

Re: Voltage drop question

[

b]What I'm thinking of to solve this problem is adding a capacitor to the power cable of the computer[/b]

This may solve ur problem as it seems to be a glitch while ur systems start. Also check the current consumption of ur circuit.

 

[betwixt]

Re: Voltage drop question

The trouble with simply adding a capacitor is it also discharges into the motor. What you need is a way to allow the battery to power your computer and also charge a reservoir in such a way that it doesn't empty back to the motor circuit. The classic way of doing this is to add a diode in line with the computer supply and add a capacitor after it (on the computer side) but the penalty for doing this is a small voltage drop. In view of being so close to resetting anyway, the drop may actually make matters worse.

Motors draw most current when stalled or when powered but not yet in motion. As the current drops rapidly as they start to move, you may have a slightly different problem than you imagine. It is possible the computer will still function at 4.5V but just for an instant as the motors start, it may be dropping much lower. A voltmeter will not show this, you need to monitor the supply with an oscilloscope to see such a rapid glitch. If you assume for now that the computer resets because of a very short drop in supply, try connecting a capacitor across it's supply (suggest 1000µF) and in series with the power wire to both, connect an inductor of a few mH. DC will still flow through it as though it wasn't there but it will hold back sudden spikes and dips in the battery voltage. No guarantee it will work but for the sake of two components it is worth a try.

Brian.

 

[hameeds01]

Re: Voltage drop question

but the voltage drop across the diode would be round about 0.7,
4.8 - 0.7 = 4.1 ????

the most better & clean solutions are
1) use high current same size lithium ion battery.
2) use 5v dc/dc coverter for computer.

 

[karesz]

Voltage drop question

Hi hameeds01,

Take please a Schottky for separating diode_ than is the drop max. 0.3V, may be only at 0.2V (depends of exact type)...
Than, is my be (for that application) better to apply two capacitors(1 on the Motor+1 on the Up) + an separating schottky(or eventuell germanium?)- diode...
A smal DC/DC Conv. is surly good Idea-only one quischen is price, if it will be produced in serie?
K.

 

[Rasika0612]

Re: Voltage drop question

Hi
**broken link removed**

it is long. but explains lot