I have to start a motor by energising a Contactor, and I have only positive 24 volts dc,but the connection needs positive as well as negative 24 vots dc. How can I get Positive,negative 24 volts dc from only positive 24 vols dc..

manzoorulhassan

Do you mean that you require in total two 24 V DC supplies, one of which is permanent and the other temporal?
Often with "negative" in DC equipment is meant the common 0 V line.
I suggest you investigate the possibility that the + 24 V DC is connected to the motor by an On-Off switch, with a press-button switch from the On-Off switch to the energiser.
In that case the - 24V DC supply is considered the common 0 V line.