battery preload / power limit

battery load design with ptc resistor

Hi,

I'd like to create a preload system to load battery which restricts the boot power.

Indeed, it must charge a battery pack at 90% of its capacity in a few seconds with 600V. It represents a power of 1000W. But I'd like to avoid the peak power when I connect the battery.

First, I thought of a thermistor NTC (resistor decrease when temperature increase) but it can't support so many watt.


Is anybody have a solution?


Thanks a lot... (and sorry for my bad english)

Your question is missing almost all important information, particularly characteristic of the power supply and battery, intended charge current. No chance for a meaningful answer. Generally, a fixed resistor can do, possibly better an electronic converter.

Please see the schematic in attached file.

I'd like to use the preload to increase the power little by little during 2 sec and then close the relay.

is it more clear?

Yes, very clear now. I didn't expect a capacitor, as you have been talking of a battery. However, the resistor (either if it's a fixed value or a NTC) must be able to handle a pulse energy of about 1200 Ws, which involves a certain body size. The resistance should be e.g. 100 ohm for complete charge within 2 secs. There are power NTC available for this kind of application, they have the form of a low block respectively a thick plate. Also high power fixed resistors could be used, but NTC has the advantage of fail safe behaviour if the contactor doesn't close.

Ok thanks. but it's really a battery, it can be simplified by a capacitor of 6600µF.

And do you know how to choose correctly the ntc? I want to charge the capacity of 90% of the supply in 2 sec, but in the ntc's datasheet, it's impossible to know how the temperature will evolve depend of the power, so I don't know which resistor's value to choose at 25°C.

Do you have any idea?

Thanks a lot...

What kind of battery is that? Is it a bunch of series connected batteries?

What is your power supply? Any change you can use a current-limited supply? Then, you don't need the resistor.

I'm not aware of a battery that can stand a 1800C (2 sec) charge current, but doesn't matter regarding your specific question. As I previously mentioned, the preload resistor has to absorb 1200 Ws pulse energy.

Regarding availability of suitable NTC, my previous statement is most likely wrong. I have been thinking of self protecting PTC power resistors, but I see now, that you are trying to replace the contactor with an NTC. The problem is, that if an NTC has once reached it's high temperature, e.g. cause it hasn't yet recovered from a previous load pulse, there's no current limit any more. At this high power levels, immediate damage of the NTC would occur. For this reason, current limiting circuits for a higher power level, e.g. in motor drives, always use contactors and fixed resistors (or possibly self protecting PTC).