Backup Power Source Options

[nxtech]

Here is a question that was recently discussed here at work and I thought I would ask this same question to the members of this board.

If given the choice of using only one, what would you use for a back up power source and why? Battery, Capacitor, or Inductor?

E

 

[A.Anand Srinivasan]

battery is the best option... the other two would be troublesome while switching off or on due to their inherent behaviour of kickback....

 

[nxtech]

That was one of the replies from an engineer here in the office. A follow up question was then presented.

Take into consideration the useful lifespan of the back up source. What would then would you use and why?

 

[A.Anand Srinivasan]

still i would go for a battery...
because capacitor and inductor with long lifespan storage would become bulky and also not that stable.....also you would surely need protection circuit to make them useable...

 

[nxtech]

Even for a battery or batteries you will still need protection circuitry in case the battery is connected in a reverse polarity manner.

In regards to the size issue think bigger than portable devices. As you scale up your power system, your storage element will get larger anyway. So if you were using a battery or batteries for say a UPS, those do tend to get heavier as the number or size of the batteries are increased.

Anyone else have any input?

This question has generated some pretty interesting conversations here at work.

E

 

[A.Anand Srinivasan]

in case of battery if you connect in the correct polarity you would surely not need a protection circuitry but it is not the case with reactive component supplies....

 

[nxtech]

but with the battery you will need to have the circuitry to control the recharge of the battery or batteries.

A capacitor or magnetic does not need that recharge circuitry where as a battery will. All you need with the capacitor or magnetic is the reverse polarity circuitry to force the current to flow in the direction needed.

Try looking at this as if you could have a battery, capacitor, or magnetic, each that had the same energy storage potential and similar size.

 

[A.Anand Srinivasan]

the recharging of battery doesnt need special circuitry... it just needs a diode.... inductor needs the same diode to protect the load from it.... also to charge a inductor you need special circuitry because it has to be charged using a varying current source....

 

[nxtech]

actually batteries do need a recharge circuit or you run the risk of overcharging and damaging the batterie(s).

as for charging an inductor the only special circuitry you need as a bare minimum is an RC circuit.

E

 

[A.Anand Srinivasan]

no way..... i visited a telephone system and learnt that once the battery gets fully charged its impedance would be very high and hence it would take current only to equalise for the power it has lost due to leakage...... unless you use a very high voltage source.... that would be a problem for all three sources...

one important thing is when you use reactive component as source then there is a possibility that the stray capacitance/inductance would introduce oscillations in the output.....

look!!! this would go on because each source has its own merits and demerits.... and you surely know everything in electronics involves trade off......

 

[nxtech]

That battery system you are speaking of is a lead acid type. Just like the one in your car. This does not apply to other battery types and if you look at the phone system in the states you will find that every battery system has some sort of charge control circuit, even for lead acid. This allows for monitoring of the batteries useful life.

You are correct that oscillations can and do exist with reactive type components and any engineer who is half way decent will make sure there is some sort of filter mechanism if the peak to peak oscillations are greater than needed.

Again, you are right, there are always going to be trade offs in electronic design. That is why this topic of discussion was stated here at work. We design back up power systems and were asked to consider other options for back up power other than the industry standard of batteries.

I just thought that this would make a good topic of discussion for the EDA board beacause what we end up doing here at work will make its way into the rest of the back up power supply community.

E