What is the effect of an input ripple current on batteries? (example car batteries)

[Maloth Ramesh]

effect of input ripple curret on battery (example car battery )

i would like design sepic dc dc converter, input is (100-150)V supplied from battery (example car batteries, which are connected in series), maximum input current 10A.
what is the effect on battery life, due to the input current ripple, what is the maximum acceptable ripple current. if some one knows any related formula please send me ....

 

[chuckey]

Re: effect of input ripple curret on battery (example car battery )

" due to the input current ripple, " Do you mean the ripple from the charger or the ripple due to the discharge current being pulsed.
If you consider the plates in the battery as series inductance and parallel capacitance, for high frequency its the part that is closest to the terminals that is doing all the work, supplying the high frequency currents and accepting them if its high frequency charger. After some finite time, the rest of the battery "appears", So the first part of the battery wears out first then the next nearest part. For the charging part of the cycle its called "microcharging".
Frank

 

[KlausST]

Re: effect of input ripple curret on battery (example car battery )

Hi

A modern SEPIC controller works with more than 100kHz.
A battery is not suitable to handle current pulses with that high frequency.
You need capacitors for the SEPIC input side.
I recommend at least a low ESR high frequency electrolytic bulk capacitor and a ceramics capacitor in parallel.

Klaus

 

[Warpspeed]

Re: effect of input ripple curret on battery (example car battery )

Even with short interconnecting cables, the battery and cables will create enough inductance that will be a problem at 100 Khz.
The battery will be fine, but the inverter will suffer.
It definitely needs some low ESR capacitance with efficient high frequency bypassing right at (or within) the inverter.

 

[D.A.(Tony)Stewart]

Re: effect of input ripple curret on battery (example car battery )

A car battery with say 800A rating for CCA is defined by current dropped from 12.5 to 7.5V. This also defines the ESR but not the ESL ( inductance) ESR in this case is 5V/800A=6.25 mΩ in theory per battery or for a string of 10 = 62.5 mΩ in theory.
As other have stated microcharging with HF pulses may not distribute well so a Film cap with low ESR (~10mOhm ) is advised , placed very close to pulse load. IN this case additional inductance guarantees attenuation of ripple current , making the cable inductance negligible.

(details)
OF course this CCA rating is done at cold temperatures such as 0'C and ESR drops at higher temperatures along with more rapid aging and more sulfation, if left undercharged for long periods, which in turn increases ESR rapidly.

 

[BradtheRad]

Re: effect of input ripple curret on battery (example car battery )

Besides the above recommendations to install an input capacitor...

It also helps to add an inductive choke, to smooth current draw from a supply, when the load is commutating.



Values must be custom selected, to suit the operating frequency and Ampere draw.