Boost converter

[Harald Kapp]

Have you considered teh resistive part of your inductance? Rwal inductances have a resistance that will help to limit the current. Otherwise add a series resistor between your circuit and the battery to limit current.

 

[duke37]

The amount of charge transferred is dependant on the charge supplied to L1.
To reduce this, the signal could be modulated so thet the fet is turned on for a shorter time.(PWM).

 

[Graeme Kelly]

It seem to have reduced after i re simulated it . as seen in the picture attached
Thanks for your help

 

[Graeme Kelly]

It has arisen again, so are you suggesting decrease the switching frequency ?

 

[BobK]

hello bob thanks for your reply . see if i was to build this circuit would i put the 12.8 volt resistor in series with the battery to keep the voltage to 12.8 v ?

No, in a real circuit you would need to cotrol the charging current. That cannot be done with a voltage source, as you see in your similation.

Bob

I am interested in the simulation in #12 by BobK.
The output overshoots on switch on and eventually settles down. Since a certain level of charge is transferred each time, I would expect the voltage to rise gradually to its final value.

What is the origin of this apparent oscillation?

Ringing of the LC circuit.

Bob

 

[Graeme Kelly]

Thanks bob any suggestions on how i can reduce the current at the battery end to under 1.5 amps as 1.5 amps is the maximum charging current my battery in real life can take. i have attached a picture of my simulation

 

[BobK]

You can’t. If you need 1.5A at something over 12V, you will need about 4 times that at 3.7V. And that is average, the peak current will be higher since it must supply all the power in 73% of the time.

Bob

 

[Graeme Kelly]

Thanks . So do you have any idea what wpuld happen if i connected this circuit to a battery that the maximum charging current is 1.5 A ?

 

[Harald Kapp]

The ssafe method is to use your circuit to provide a stable power supply at e.g. 15 V, buffered by a large electrolytic capacitor. Then use a charger circuit suitable for your battery. Thus you decouple the generation of the higher voltage from the regulation (and control) of the charging process.

 

[BobK]

You do not have a design for a battery charger, as I have stated before an Harald just stated.

As an alternative to Harald’s suggestion, you could implement a battery charger by controlling the boost converter via both current and voltage feedback processed by a mocrocontroller. A practical charger fo SLA batteries needs, at a minimum, current control for the fast charging stage, then voltage control for the float stage. A better charger will also have a pre-condtioning stage and top-off stage.

Bob

 

[WHONOES]

I am interested in the simulation in #12 by BobK.
The output overshoots on switch on and eventually settles down. Since a certain level of charge is transferred each time, I would expect the voltage to rise gradually to its final value.

What is the origin of this apparent oscillation?

Overshoot in the simulation could be caused by the lack of dc resistance in the inductor. A spice simulator will treat L1 as a perfect inductor with a correspondingly high Q.

 

[WHONOES]

You do not have a design for a battery charger, as I have stated before an Harald just stated.

As an alternative to Harald’s suggestion, you could implement a battery charger by controlling the boost converter via both current and voltage feedback processed by a mocrocontroller. A practical charger fo SLA batteries needs, at a minimum, current control for the fast charging stage, then voltage control for the float stage. A better charger will also have a pre-condtioning stage and top-off stage.

Bob

You don't need to resort to a microcontroller, it can all be achieved with a suitable PWM controller (even a 555) and some opamps.